feathered reptiles of ths el;a,such as

strueturn a d ~ u r e ' ~ rapid rates of locorm tion, which in modern animals requires high met.- bolic nrtes that 6 m b n v i n warn-bodlsd an- imals, JM tis in mM.m .ndqMmn.'many ditmstkn had rdstiwly h& br~ns with suplerlor mnsory w a g . S i m bdn Mum h.B a high rmrgydemand, a l&gd bdn k n bveah irh- portant ~~~luenca on the whola b d y wbtabolk ram. Other thQo~*m haw, bewr n M to suppmtargu- ments thrt dinosauewera a thwer, no argumeint is full~'mnvindn~ bdarrse of hm #mi- tations in using the r n o d w n ' m of snlmds as guideiinw in predicting tko p h ~ i d o g b l h w a s of these tonwxtinct animals..

Protarchampteryx robusfa and C a e m w . ,

hod symmdrical feathers. sines th&- " .

featham would be uaeloss in must* ari-n tirtcrydlnwnur k r othrr m i d m i n r u i a t i o i ~ ~ ~ ,- . . .red n p t i l n ~ , ~ ~ ~ ; : r:h, <<,:.. . - . ,.. ..- v ,

y m e r m i c , m .:-<A : ,::' . , . S . I

nation ~ t h - animals had & high metabolic r a w for an #ndotharmic animal. Bone

W PART TWO Intagrating Physiological S y r t m s

R a d h m & n p W r 2 t b t h r m d c ~ i r i u - eaces chemical irntorrctioas in ways that affect m a c m ~ ~ l e ~ s $ u m md hiochsmical mu- tiom. Comoque~tly, temperature has pemasive ef- facts on dl physielgical processes. As 1 result of thesr bmporature mffocts, every animal displays a thermal strategy: a cgmbiaatisn of behavioral, Mo- chemical. and physielegical raspomsea that ensure b d y temperature (Ta) is within am acmptable limit. The mest important environmental duencat on tha thermal strategy (though net the o~dy one) is amlai- e d tmnpsraturs (TA). Anhals must survive the m e s t and lewest TA in their niche (thema1 ex- tremes), as w h as t$a change in TA (the& dmga).

Animals izrhabit m ~ s t thermal niches on tha planet (Figure 14.1). The hottest environments exploited by animals are the regions near thor- ma1 vents, such as the hydrothermal vemts ef the deep sea, velcrlaoes, and geysers. The caldest places inhabited by animals are the alpine and polar regions. The animals that survive in the ex- f e m s of heat and cold are impressive, but the ability to tolerate changing tempratme is @very bit as challenging physiologically. Environmental temperatures are most variable in terrer~al ecosystems; air temperatures change more rap-

(high TA)- Hot *rt

idly a d ma& seater aXlc'&ms ttu do wekr t a r p a t u r n . .

h i P P y - e a v r r i r * ~ m temperatun. Undeqpmnd rsfqps are $&ered b m t h e d m m e s on the &. The TA in alpine re@em vuiw u r r m d mf ~ ~ r l m- rnls arisihg B V I ~ only a few hilomators. h q a ksli.s ef~ctsr, s u c h a s h k r c u d ~ , ~ v u y i r TAwith depth. Beepooban hathyp4c) ma s h n clase ts 4"C, w h e w mid-* 'ph&l and rrurfu, water Iepipow) krpur)rrr ma k much wamm a d 111era varhbh. l a k e s m a y ~ m m d y u u l f ~ i r ~ ~ ~ ~ e ~ d e ~ l i m m s ( I ) i . r r r y . r ) Y l u * l r d b m l ~ e r r w a m , ~ d m n g ~ ~ m k lm t h a n a m m k r d ~ .

E c n m r u r t r , - * - a m k m ~ . T e m s W a l a m d ~ ~ b * * ~ p i m t u l d t e b . w o * ~ ~ T . L l & p e k a d k m p ~ a k 1+mw -- and daily cyclas af ceU & W. Air k- ura ~ m r e r . F i y y y u I ~ ~ & ) u n r , serneba mre tLu ;n"C 5 a 4ay. Iltkr- *dal+ m y r- tb W J a m e r dry m - d s kfm Ell+ WWW- mver m. m y * iatmpu* M hta tkdr t k e d -, h m m h a k m u aW cape with thm mffmm mP kmpraWo ea b c h a i - ism a d pkyri*l*s*

~ A l p i r t e (@&erne cold)

IniMidd (rapid wiiYsn in TA)

CHAPTER t4 ibumat Pkysi* W

.- .:,;- " L;*; c , d . . .- i rdnmmlJ11- -$ ,2 : ..' I --

> - A / ' " - ^ . I

h r m t * ~ l n * . t p h p h ~ * ~ . t n r m w h d ' n t h m d pW8- b b d y tpper8- ~ . A U ~ s ~ s m ~ ~ t 0 toad t b ~ . f ~ ~ ~ m i m a t ~ t h r n m-t. h e *blamWwide I I F B 8 d ~ ~ l t a e ? d ¶ ~ ~ ~ l a a a r a y p l r y r - i ~ p ~ . ~ ~ ~ ~ w 8 l l . ~ r b l i . a of phy#iebgtd 4 MavierJ meam te ansum U t 7''~- W W ~ m-t. ~hyria- t@edsyswm#, W * ~ ~ c 8 a R r l r e g - uWm41~yb mbb md kragdlbb. Thm phyiolqpd

h t impart a -hat T, us8 emqy. W $, % dmd ht vary, bpo- phyiielogical premm SU& as &elupmeat bbaeme d o i r e to envir~nmambl w. Ahhm T, hu tlae flp-

obvious hapact om l i t d Biew, e h r reum &hat e m h a p aw a h hportrat ia mamy mbxb.

Ananidk~isambch~efthetbermalenmgy held with 1Le nmlmuk ofthe M y . Thermal en- - un mew &em the animal t9 the envjmment, w &om the ef~vkommt te the-auimal, alepen- on temperature *. M W h ~ ~ + t h e sum ef oU bidmmrticrl rncticms o m m h g whbh he Wy-b wm&mw:~d 9 f W d anem fn the heat laJuw quahim d moat ar'-rPnls. Rowwsr,

* C & U i p t k e + u c k r m f t l t r r n r l e a e ~ kern om of u . b j d mr iuid te wtLer.

.k h i m l s c a a b a m ~ m d n ; i u Y o r r u l e r ~ i r mnductd away h m t k ~ M y , er can b6 6 m m d u thy rbwrb Lmt h m mmdukcva oejectc.

~ i s t k e ~ o f t h a r m a l ~ b s - tkr#11Ul8b@Ct(fJBIah&hm)@w' ~ l h l i d t h a t b m e ~ . Fer-,- ~ h r l s ~ k w h m n i t i g w s o w r y e ~ ~ ~ ~ whm the air is siilL Mert ebn, mn- a- 8 hi bf b ~ d - m w h d d S .

~ i s r g ~ a m r ~ t a r r t u n * n t o Y . emisshla ef dactramrpm~c ens- &om 'U ~bjmct. An amimd w abwrb rqrliutAm emitksl h m tlts surreumdhgs, hut car,rk emit mdiamt heat frmm it# 8- d a c e , 8

jex farm ef hss. The Wamd r a d k h d m d =-.*as ib - , . temps-

t h e w . mu, ~ Y F ! lmala!p@ -.-dmy$,iYrrw*-

I& haat among axtimahi and can the anhid, i a t a phydcd -@n md cak, h r en the relath impor-& of &eat@ ex&ahges.

&W -t SOW- d Sbk# %r &WlTd en- a h rffsct am d m a r c t l 4 e d budget (Fqgure- . Water has a higher thermal cbnductivity

1 4 2 ) . T h e t h ~ ~ b Q r t L i s r ~ i n t o mm- than air

If *% &b@v8-5- b 29re = 011 &ere will h no 3Ht c u e in e m of the animal and 7''' will remaim m~slm~t. If the flcw of thermal emrgy in& the aniBaal exceeds the heat less. TB will increase. Each ~ l f these mutes of thermal energy e x c b g a depends en the thermal prepdies of ths environment as well as th f i y ~ i n d proporkies r s l p-kw J the W r L

G m n B w L i r r i e ~ 8 + . ~ ~ - b a ~ e l t h a ~ a n ~ ~ ~ d ~ ~ ~ ~ . b t ' ~ ~

e l r r d i l ~ L y a e e i ~ . h ~ s n i r k v e l v s e l i m l b ~ o f ~ ~ ~ ~ a ~ e ~ ~ ~ a ~ ~ ~ u a t ~ n e a n b m e ~ o f b a t ~ h E m h w ~ d b bkr c l o n l . u d B e r t : k & k m , @ Fmrrierla bm d tb fhIhjm@-

A A T +

Q*-. L

where heat flux EQ) dapeudsw the pa^ gadht4AT)d t h ~ m WW~M km

+.

k

fer in o -wmXCIIJrithrrwe

1 heat uaifomi s ~ & i S t k t ? m w P ~ material. '~hsss some @ W q pa-

:\ r ~ r l ] & A r ; a a L l * b i e * - 2 d - 1 W!~mE-ur;B

twmpMqMww. -Gmwider&e .MWG@ ,PL 1 c-dwwx.

~ ' W i a . c s ~ ~ 4 ~ ~ ~ jP,tom tissues, threw 8th~ tiOPUls U1$

f l w d s * ~ to* -1sJWm€w- W * ~ q b [MtB a +W-C '44m- d wmiwii*.fldm 141). w b d ~ l m - l r C l y ~ -8 p e s s j,n- dati%.LtlrC , r & w s oandWve heek&w&. h*&uc8 As fur d f ~ * ~ * ~ f h 8 as- trracG WWeentBr bo$kstpjl&tmar theflriamdtht @des4@utd$h

r&@&fiw,%of .hrrt,:W complicated by the geomelq ,@ ,$ha environment a d the animal. Heat

thro* a ~ ~ m * d ~ of air extending &om your s h , but rather ia c o n d ~ ia m-b dt- mmsimns h tku a s m m a Anlrturl gmmew U e p b p atwb.. A long,

Hlnul.lI2 SmrmsradriIk,irrmwm , thh a- pradutrr && mu* b a t T h a ~ ~ q m f ~ J ~ m d i s i ~ m ~ k W * ~ n g e w i t h ~ s n v F asadmrt,FbWdmhWlef~mnia rmnmnt.Thismaks i s w r r m d $ 5 ( n d i a n t 8 ~ ~ , f r q m t b ~ ~ & w s ~ to tb rmh glw aai-m a energy r 4 . t . d from its surroundings. The animal mxch8nar thermal n o q y mmm hdmk. Siacs -- thr~ugh objacts and fluids in contact with its sxtornml surfmcm (conduction). Move- murt ofthe air nnhmcas the efficiency of thermal exchrngm bv convaction. ma dUdv* hu* IWm"- -"&*

extends (L), and the thermal conduetih& (A) s loasdis watts pm mm per kelvi. (wfaper Kj- m o d and- k a spec& p e d a mat.- Thosr sbjecb mm.l$ial; af as k t gnks hwa .- ducli*. Fm am*, an a b u h u r p ~ ~ t i W d d te tktachbwru--Pitb~ a-& t h e d w ~ v i w 1 2 1 0 ~/a.#ei.~) and m y draws kert h m hand, dmddy, 5% water feels whr -8 5°C a t bcaxw,mtm has a thermal conductivity that is 2 5-fold higher than air 10.58 vsrsus 0.024 W/m per K). Because water has

mbmd stw&es, an animal can 81- / tar upndume heat axchaage by en-

ga& in a&vhB tk&t d* I * . M V & , s&e arsk.~For =am** a pmjgub rskicss W k w f iQlas . th f e ~ t by r u m backen * hedWuhg ito tail feathers for balance. Because its tail feathers are 1 a e wnductive U its feot. law b a t is W. Figure 14.2 shews a -am& simtltaneously ex- changing heat with multiple surfac~s. It loses heat via cond-ea amam 4W up#er strdbtb while dsu exchmgkg b a t *ugh IU low* M a m h wtl- W&withthwroeki. > . '!,

1 '

more m o l d e s per ufrlt'volurpe, there is a greater likeliheod of a molecylm mllision that results in a convectiv6 heat kxchawa I . I d a b & . - . on

transfer of energy. fluid ,~QW.B@S The Feu* dmmribesLhew hm1 Ima@aydwselfhemd h1apmdafwaterthdtia

d ~ " m o v & % a: wry ~rhplsl ~ t t r t l : ~ h e 1 ~ a s - 18°C colder than your body. Almost b e 1 a t p 5 ,

-. . . . - . . . . . - - . . - . . .

14.1 Thermal conductivity of materials. :5,> 7 *3>r< 1 - 7 7 , l f . 3 ' , '

, ..: ,. ". , " ' " ; ; , ! ! i ' , , <, f

. ; ;r - - : P W ,!' . *- \: - . >

, , , ,-,;, , : ,: ,; ,<; > :*;, , * j am:: - , " ,-,,' , < J ' ?

1 1 :

, . j >

.'! ' ,

~ L * l y ~ . k . b ~ ~ # i t r r ~ ~ t L r w r k r h t b ~ ~ L ) . ~ t l ~ C . *crtirkiuluyLywLw8rmd,tbmdlrt- e r y t r l m ~ ~ ~ t h e W k p k m * f t h a wr- * - W b a ~ ~ ~ m ~ ~ 8 i d y s k k , Iln M y h a s m a l enew at thm rrk r q w d ~ t b b ~ h y w W s l r m l y & a s it J v r i c J r r U r ~ m ~ r ~ l t w t w a d M & b u l k p h . M u J , h n r r ; y h ~ t . r r r v v r r t l n L e u n r l v y l a y ~ r ~ ~ y r W , ~ ~ u t8anwasrvrlwrrrJ~hthbeunhrylaprkILG jirst @we. Nmw W hm t h m prJlrWlr change whmm IltddishwhgrrwtLe W y . TbMympidly 1- errrywamhgr beunhykylrtiat L -4 Lly ->c*lrlw b u d - my:@. W W l r . a w h A & W e t & mt!

~ i , ~ b S k w r a ~ n h r f m r v d m M b - r h M m t b m m skmm%-dtb I tu i r l , I k rakdf lm~ . f tb ,M a w & o r h , dilr wmMvi@,

Radiant energy warms same animals

Ln b i m l e ~ d syskrns, radiant heat exchange occurs through rleckenapeti!: rabtien in the bng wavelength, Mared range. Thus, if a red hght (long wavelength) and a hiue hght (skart wave- length) ef equal intensities are shene en your skin, the red light will nore effedvmly warm the surface.

In the natural world, the mest impartant source rf radiant heat is the sun. Photons kern the am excik the mylecules in the &Wasphere, the sril. and tke watmx, warmimg them by radiamt heat. Thus, when animals u e warmed by canduclian from air, water, or soil, thg ultimate source of the

1 l r i f r m ~ p m a $ J r ~ & . k m d w ~ ~ 8salgsratRlrdWddllFlk. hthihage,~ammmks~s -m t h m , r n ~ ~ , p k O v d m b m r ~ abrbirrg &nt energy. The stad% with kgmter surfam a m , &y also baffected mws by warn+ clw~lhsg.+adurts$y*.l3fim~,** J ~ ~ . ) 8 .

2 - 1 , )

heat is radiant energy. BU~, can' also be warmed di&tlY hy solar, +&ion, which many species accentuab the-dor known as bask- ing. WMe hlody cobkiod reffec$s Psptons in the visible raige, and darl'co~aijogi aby& *@o- tons within this range of %vebqgthg. m b t bask to warm the- ofaen p&sess high levels of black or brown- $@& to help absorb thermal esergy. As,a result of div&ity in color, an- ~ i n t h i s ~ a r e a c a n h a ~ , ~ d l y d i & ~ n t . , temperatures F i e 14.31. h te* ptems: @ B : ~ M & wq& &-

ing the day and then bemhes mi irhpb&i&ms of t h e d energy in the forrn of mrrduction and m- "diant' b a t W h f l tHe surr *. A&& 'ds,Pk thermal energy when they w i t radiant heat. ' huh :

~CL@~~WW+F~ a W t g ~ , U r ~ ~ ~ , f r s m mtrla, The mIrS- @+ >&* r** f m m ~ ~ w a r m n n i n ; b i l l i s d e g ~ ~ t h e S t e E a n - ~fdtmann m-

, . sweaw,jc& p *Maw#& - ~uWV~. w&& w ? h@pp@h-

mus dht i r~&* d ef r etirwbmk, *a 4 mud WW4eat h m Ibl ~ r ~ W d u c t i ~ n ) . TUB is aw-6 cooling s e ehh n the mdki wG;'ib&i% enew iqabyxbmi Ltom the M y as the mud dries. Other m h d ~ cover heir b d y surfaces with water, such as an ehphant that spays water onto its back or birds that splash im a pool ~f water. Wet feathers rIso have a . v F e d insul+tary capacity,) do- more metkboli<b'b'at t6b:kd: Bircrs th.tlive in hot environmsd &aY kkk ale belly b~fore returning to the nest, &whg *e eggs to benefit Born evaporative COP* b n - garoor, .which & not produce swwf, lckIr vaisc~$&&d skin iurfaces, which &hi h o o l b the @#Gi i'&"ibr: : '

' fitit P &[~ora#ve c o o w i g positive. When &miagua8"c a n i A ~ s leave be iiiter, ttiey are typi- cally left with wet body s d k s , c&u,t.pAbody brn: prature to dmmp~k ~ U E I tQ ~+oBQs~'#~? . I > . tlrf!r ~vliag, ,

The ~ b t 1 aTkWhes mrteuBhme (see PIgurs I~.%I can MliiedlllltWpetAs of the heat ex- m- Pw: d a d k d n , d h ~ d m , radiation, b d evaio- ration. Variation in the ratio b ftgpdth several contexts. A given -1 may alhr its expsed sur- face area to change h&t ~tlx. h& h t c h eut when hot to rnaxisnize conductive heat loss te the peund, hut mB up when cold, &'%h&nb &dU~tib'Ituf ftimdotlae&.b*~of~smatb~e&(l ch. i d b p i y ~ S O ~ ~ Y I *- I

d ~ d ~ d & n & & ' o r b d m. W SI&U&*; of &dy s h , W&&'prsl

son$ caekicr d f i u i r e c h w ~ & j ~ ~ & ~ ~ t *

--aris*iB:M* k l T m i f l l C & h d e a & z & ~ w ~ r r dh rz* 6fi$--ICB1ume8 Although they five in s d ~ & ~ ' f h s arctic N ~ Y U ~ X & t * & ~ - memguhbry costs hcauso of itr slzr. S-, whan om a@d"grohlrr, fb ffsw m u d Irtcmxrpe * t b n 0 ~ ~ - h # ~ p 1 F 4 ~ d low heat him slew& and m h h a t bmmr Ihh do small &&. TBs eff- of M y sizetad shape &a mgnifest tbemdvB~ h daml m l U - tior psrdplcuuk& st.s~~~tht..iulsil&ii cold enviremmnb bnd to h larger thm d in warmer mdreamm0s. ~ i i e n f nrle states tkt aaimnln in ml8er q r n tend k, h m shortsr a- *amities than a & d a h warmer &mates. Thus, mammals or birds living h phr Wmii or h@ aMmh clydt *-h-<d&-Ew* i r m d i v i d # 1 9 . f ~ ~ ~ P r e r . w u ~ ~ s k r & # m ~ . I b m W &mw.app&* m t e f t h b ~ u d ~ w ~ a h * have Umb m-*ki- U ~ ~ ? T . B ~ U hw, I I

) . I , . .

An amimd rd-h-rrrcialr, by d m the posture ef && bo8y-4U * rrjritP th exposed sut#t m. mm -4 brll b o e n m hut!-1-l When the pythw; ap-irj- -k sbpe, mh ~ a W , W e m s - S W

~ e m r ~ ~ ~ ~ 5 % ~ r u l ~ h#&thss. * a

,t.> . ' , : .

Anb& caaf* -'.-."a- Ly huddhq - mhmls:.llW d raw

14.4) IiW M h m ~ . w M W W & . ~ M t e m p s r m m t m l ~ ~ a ~ ~ ~ b D ~ r ~ matabtjliwl ttJ m-1 -cbYJyr.-. If h o w d im groupk whUd--

CHAPTER 14 , T k m a I Physiolagy ibl

b h ~ &rt- BEmC.. k .,. ,:

trin + . m l . l i ~ ~ m-t 'I; r+u 22.C. H m w i r , i " m.mkd mh ,rat iE UJ)b-b Mend its T, at lmw FA. When f.r-Luyli4, iLE T1 clw~ly rrlkctf Th bma&mg k as 1mw ~ t b 2 . C . From the p r s p d v e mf the Wvilul mhd, kudiluy ra- duwshtbyinlc~uimg T* mp- w1d airwith a 8 wul-b thr mf thm wlwy, 3 Mdkg mrLE as a tbmmragdabry skatey by .: d u d q rag= .f& m a k valume. LL

Insulrtian reiws thermal exchange

I a b s d wad Qxteimaf insuhtie~i &o reduct heat l o r s e $ . , ~ d mammmh have a thick layer of ad& p&m h u e under the skin in the fam of blubber. ~urchickness lhis lipid layer dirrupts the Bat bf them1 energy

HIYn huW.r %om the core 0 the Wrnal surface of the aninul. is Ck,thlckn,sr of fur More COUM~~OQ, animd~ Wl9 B X ~ H I A ~ iasulation ,,d it, to r * ~ ~ ~ ~ . hm: ~odi f id frorn

reduce heat lms. Fur and feathars rrswct the ~1rnereta1.,2002.) , ,

movement of molecules between the surfirce of 4im animal a d the bulk phase of the envhmtnt. Heat ir lest f sla the mkd in proporkion ta the themud gradient (AT) at the surface of the animal. Mole- marma, 8trrt.gier m h of air ar water in the insulation layer are warmtd by the mhd end then trapped within the insulation. The overall temperature @ant kom the skin to the bulk phase is the same, but the dis- tance is greatsr and the animal loses Lss heat to conduction. The fur dsr impedes the flaw ef fluids over the surface of the skim, so thwa is less csnvec- tive heat loss.

' ' h e W v a n e s a gf insulation depends on its thichwr. Wen iamd with cold temperatures. birds (or rrmmaIs) can change *e orimtalion of the feat?ms (or furl t~ &t the volume ofah trapped within the coat. S i d k l y , animals k t live in colder enwanments have thicker coats with greater insu- law capad@ 14.5). Semb s p a = change the ~ ~ I I S S af the e~~ insulotian seasonally.

, Thlck mats are r thsrmeregulatoq b d ~ r i in the warm season. so it is benefiad ta s h d fur in spring.

Invertebrates are the most themotolerant in each thermal niche. !I%& hotbat de~erh are pop- ulabd by m@s of ihsi%ts, but d y r few wxcte- bra%. Invertebrates can also taletab the coldest temperatures, o h n by I&- m inactive, 4er- mant state. &Ice sta6ilizd in &is state &%us- pended animation," they can s-e Umperatures far colder than even the coldeat natural emiron- mnts. In con-, only a h w vctrtebrates, such as the wood hog, can s u m i v ~ subzero body teanpgre- tures, kozen in mdergmund mfugos.

The lay terns c o l d - b l d d md mm-bl& fail to reflect tha cdmpletf of &ernid skatqies. which are properly described by two alternate srk of terms: poikilothumy mrsw homeothermy, or ectotherrmy verrms endethermy.

Slncemuchofh.irismm~sedofdeadcells*the Poiki/othermsondhmmoothermsdjffmr @st of rehdding the mat when rmperatures cool is the str bil ity ef T. minw in cornparhen ts the metabogc ask the ani- d would in& to cool LtMlfushg physielog- The terns pottilethermy and hpmeethcmy distin- id ~~~. Mammals alter the miwe of their guish animals oa h hais ef the stability of T* h fur coat serswmlly, prsdudng a greater density of peildletbrm ia am anirnrl wish ov-le T ~ n m hairs. Some bids; sUCfi as the ptamigan, produce that variea in response to envirsme~trl con&- spcialjzed feathers g t h an additic~aal shaft n in- tions. A homdhmm, in contrast, is an - mase the father density. with a relatively mn-t T, Mwt Lornegd~ems

r I *.-C'JL---- w -\i i -. iula I&

,- . :.Ir---

' hu-m?-'wmd O I : .Pert%i-cr4-'Tb;,&*

d o W - ' I $ I k h W m w - h i 4 m-hr-. +, I :,

*..". dm-* @OR ~uQ&< . % t h m & i ~ ~ . M i x i t ~ r a n d ~ c a n be clueihd as h ~ ~ t t p e m s , be- d~~ b uw&;kiad did as e n ~

,*my lfl* h * t -wusr; wwv$mb

, m b$aP@bd %,WVb.insti~~ of b w &$@r Fy m h

3: G?Fl,.jl 1:54jr"L!. th+hmw ~ , w w 4

I I ,- w , m -m #q- Thwd- . : 7

I . - &thwmsi Tg 5& -.J%:.&

Mert animakcnt $I cd#.iiiad u h o d r r n or -, or rWrmtrly, temh%d:& -4. MQJwmIrr,@s, ##Q

wtothsrm or ~&AIw#I. Thii figura illustram thl many wiaa wh* thamwl ~thfz pWW!4?t pl rlr-kmmbiw .*n*n* of rnukiplm str- For.ounC*, m o n n r s m ~ .n bawqRmI &= h hormeohwmic d k# endothermic thrn mthw mamlluh. e'p ( t - varidlh. Rwpr'A#q; d4beae tams

. _ 1 rmpims M II&&B- of tb8 !i . ' ~ Y U W m w i p = o f , f *

rc$ieve&& T. us in^ FJ4Yf&l#@km m l a s w d ~ ~ ~ w B w B ~ ~ ~ ~ R W - t s e Pa rates ef heat ~redww W4 fie6 ofib en-. . , . , , a , , ;(

Tbp .wtipWp, ,brn~~ m w a d ‘ 1 I t , L b

hornea-*pm# both rlw g $ m d ~ n a b r u a f + e ~ v Q m m e n t . A r s M t i - s ~ ~ 4 ~ a ~ u i n t . i s r .mmw lpy in p J ; < ~ i -macsncl(sstG- F o r e l goLr wkm h w - * $ ~ ~ o ~ , * > o q M S rsrl by M t i a a am lam*. However, the@>- relatives live In - * m r w Mtvary -*w * * ~ ~ ] P ~ W ~ ~ I F - ~ S y , r ~ - W w , @ ~ m 4 4 t w m ape- fi w p ia,Tm hut if it was wovd rut- side to a.&~t~syould kyy. Tbe gsldhsb wpld arguably be d e d , ~ hw*erm or)# p w - thdrm, depending im the situation. Shce thgse b m s d m mcm on the turn of the environ- ment ttuh h M s p-, tbibhhs are not %hays wefd in d e s m M g % d w e s .

Heterotherm mMUt t q e n l . r 1 . , or regimal M d a w ~ ,

Just how cow@nt #oer T. b v r l ~ m a l to ba cqnsidered a hm? @,@w&w, most - w p ~ ~ v ~ ! either S W ~ Y or m'. ,- a - fig-@* m,**=: tain aMtoraicJ *.'mm veq ihw- rnalmw.mHI-*et4@ central servous ,-. jmkryl at a

h g the rep- -ma rim swwhl d e ~ a o o ~ o f + k * ~ ~ ~ ~ * ~ , ~ m ~ , m h r ~ m d t e q n ~ o n l ~ L L T ~ ~ a ~ 1 0 0 ~ H - rirlrnjr- ;, - a l .<

In ---whW U i l Y C ~ ~ f e c o ~ ~ t t i m 3 .nd-%

t e m p e d . T m - & d v (Figure- M.7). d. wch as g r ~ u n d r v r E p r i r t r L ~ k t r , ~ T ~ l i ~ d r a p f o r t h e w h b r man*. W amimrlr Jl+w their bedibs to coot Gd& still considemd ~ndotherms because they md ratah mehbolic heat to m a h e T1a@,;Ft*pw&v8f; these entkyb@@c aak& are mom precisely described -to the uariabiliw % TB over tim. Some aekPtwmic amhals a b 4t & de- scriptien ~f h~tero&erms. M a q w snakes, such q ' w p n s , wind their b&dq into a b d a b r *ey&ie izqest& their prey; Thip Wps t l i m ~ h m t t a b o l i c h a a t p ~ I r y d i - -i I&&- hotemthemy is a -.#at hu z. l,. b l ~ ' ~ W t s lF,, ' - for endothela. : 'vd ec-

~t .an endothem to. w e en- e r ~ h d&-- by red*& - of thmm~reguhtian. It prgvidas an e c b t k m with a period of acceleratcrd metabolism b spd Ws- tion, nutrient assimilation, a d biosynthesh.

T m of d a y

-143 W W + # q B b i r J I . ~ ~ W a H a w t h r i r b o d y ~ m p r t m m t a -- n i g h t t i m u c m p n w u m ' ~ Thi* ~ d ~ d ~ h . r m y - + k c - 4 n m r g y . I- ModW from R d m a d HafWrn, 1088.)

4

.k.

M )CktkFU r w 1- d b c Lmt*--&8d-q?ur.t -TamIHL.-TA. H m m M - ~ a r r W r k U 4 ~ ~ e w o f t h G ~ ~ , . u . ~ ~ ~ u d s w m ~ u ~

*~t m J.. . 3 Y ~ j r r s w c rm- a.u @f Y+@. TL& L.Lln. yu m u m am@ bat gw am u d a* mamma b k- p r w . ~ ~ ~ t l u y & ~ d m ~ h b ~ wahrs (we Ckapkr &W!@ ph#c i3L pmssoss c r u m k ~ t haat ox- k m e the hart ef dig-n w i t b tL/ -re EM C5rpter 12). mmu md lammid sharks &h ?. rmhh mymwd haat rytLu tha muscle. W w g mf t k m d mU&# h-~ m a h h k @@Aw m8y hpre~m ~1k8& 4- SWh-

rairy (sw C-r 13). T k m -tr cur with the bdiw of many e, but these re- @ e d hahrmtherms we s-? @gnhl@ccl m.chuqR, u p d y m imd+iih"+irm*&+

151-4 we* imew+m -6,- SPWA~S m -d k b - r -.- r d het-m, a d WW- r, lrCTr,'.& pendmgmmtb w r f y & ? h & q w w h - sects, such as b u m b l a h . h q m mmths. and eicdcs, 4 v a L very -4iC ~ite ia the

megmlaicpthways ta wwm the Wm-wn fkght coucne . , Ley cu &r IWtcJ*y. t. main- taim n a y - d t tkr* $&ntms

a. *vinm by h w ~ W M CIW- ten. Aa t r&v i I Id bw tr the w h y is wif- warm mr lu~irrly WM. u-ir &- Me. in tk w o r e q e * * .Flu9 YI HE bf. r e @ d heterethm*~: &ad. "wd W y heat d l ~ ~ drry ir kr-d ~y-$? her h t w @a@ meu h r &tar if,h c w r - TJqrnp.r- z q

m a d f m r ( ~ r u ~ h s l r c t ~ ~ ~ ~ n . ~ *. ,-

P ~ ~ d @*9,fw with m*- turs &F 4 qtqheqpa (Ulr! qg#othem. For sc- tothems, a change & T, a k s '5' and directly

k.

.81 PART TWO Intmgrating PhysieIogical Systrms

Figm 14J Imrcl M a r m s . Many Imlye ins- ar+ ablm to oonsmrve metabolic heat thmt mriwr wh.n *eir ffight mu.cln .re mivMed during fliwht. +hk wrrms thm thorax while tha rrrt of th. body n r n a i ~ near ambient temperuturo, mn mxmmple ~f ngional heterothermy. {Smurcm: k s J en Harriron etal., 1M.I

changes the rates of many bislo@cal processes. In contrast. an endotlaem responds to a change in TA by indudng r compensatory regulctory response. Despite the Msrances, both endothems and sc- tathem irmcur physicrb@al costs and come- quences when environmental conditions change.

The effects sf temperature can be dehed in t e r n of its impact on mhd function. An &al typ idy spends most of its life h a m g e of temper- atures that is o p b a l for physiolegical processes. The, the-td zemm of a resting horneother- Hlic eadethtrm is the range of ambient tempera- tures where metabolic rate is minirtcl, which is considmred the Basal metabolic rate, or BMR (Figure 14.91. Iftemperatures rise to a point called thauppr crldhl tampratme (UCT), the meta- bolic rate rises as the animal induces r physiola- cd response ts prevent overheating. If the temper- ature falls below a kwer critical tempratare (LCT), the meubslic rate rises te increue heat pro- ductian. For many animals, the TB can Be predicted £re= the sxlrapohtiem d t h e lina that damrks the matshelic rate at tmperakrrs below LCT. Wan faced with a hypathemic challenge, animals may reduce Tg te maintain hameastasis at metabolic rate. In general, these compensatsry rergoases at

LCT UCT M p n t Tempnare

Figurol4.9 Z o w s o f 1 L r r m t ~ c k d a ~ y M m r m . Hmwthmrmic mnd&ierms maintain nsrr-cemrclnt body tamparaturn over a wide range of r m # m t m v r m r a s ( r d line}. Once ambient tsmprrrturu m a n b l e w the lower critical ternpantun (LCTI. thm animal must inerama ita metabolic rat. (MRI to generata heat to M p maimin m mnstant Tg. By axtending tht linr axpirining t h m m- belic r e klnw LCTW thaXurir , t tr ,bodytlm~ure (T,) can be e b t a i d u t h s intwwpt, kkw cwtain mint, the animrl can ne longer maintain a constant oen Ilrnp.r- ature and hypothermia resutts. Whm rmlsimnt temptra- tures increase pad the upper critical lemmaturm (UCT), the animal incramm mrtrbolic rrto to ~Mtwt kt Itill highar temperrtulw, Ihe rnimrl un nm d h n d it. bodytemparatura and hypwthrrrni. m w h .

hqgh TA or low TA allow the animal ta maintain a c e m t T, but beyond a point, thg anhad -net suatah a constant Tg.

The concept af a themo~~eutrl zenm dres not apply to m i n d s that dbr T, but rum -them have r q e s ef TA (and Tg) valuma whom growth and repreduction ars apthad. At law tempenhs , all develmpmentrl precesses slaw bom& ef the re- duced rate ~f metrbolic mdmms (- 14.1 0). Higkar temperatures aeldms, oslls, and tissues, jrepmlhhg am d m d s ktdtk. himah actively mek eut their prefernd tcmpmatum, a TA h t is withim its rmge for ~ p b d fmclion.

h i m a h Mmr im thgir dility teakrate chang- ing ambient temperature. 1- a a l s ~ S S Q S S a wid@ themaneukal zone, amel can Mar- at@ a broad range @f temperatures. The -on carp, for example, cm survive summer water temperatures as high as M ' C , and winter temper- atures close to 0°C. S - tb rdc aim& are re- stricted to a narrow raga of m b i o r a t temperatures. Sema st%nahms telerate enly cold tmprrhms. h W c fish thrive at --I.%*C. Mt die of heat

Z

C,HAPTER ,I4 Thermal P h y s i o l ~ .II

Film 1C10 Tmmpwrtrn r*l Jlvekpmrt Tmpsrature alters the nl#Mfkmyph@ielo#ich pees- h - i e m W a w r I h r M d tent- wrmture, d-ktMjlawto a l h t h , mimal to grow. GrowY14W- oxponsntirYy with wrnpra- tureto a pairl-mrr i n e m in trm)mtura ace dnbr i . l l r

s h w at ternperatwas oralgfrh b g m e o above 0°C. Other sbmebrm mnly M m W h&jh temperatanrss. NotethatitistheratigeMT, nottherangeofT, that is used to classify an animal as eurythermic or stenothermic. Endothermic homeotherms maintain body tempemtures within narrow ranges, but they can be either eurytherms or stenothernu dependq upon their ability to tolerate different TA levels.

Differenms In thennotolerance can be ob- served in cb&Wsoas of populations or species that ham evolved in regihns separated by latitude or dtttuda. Tbb ability of an animal t6 tole~ate a lower TA than its competibr allows the tolerant an- Imal to expand into a colder environmental niche. Many closelyrelated animals havd disdnct differ- enms in thema1 preferences 'that c o n ~ u t e to tbir geographical distributions. Latttudind pat- terns are common in Bsh spedes in both marine

, md freshwater. Clbsely related species ef bar- racuda, for example, litre at apedc latitudes along the Pacific mast wifi a charactewc bverage TA. From north to south, one spedes gradually re- places another once the average watgr tempera- hue changes by ody 3-8'C. There are also altitudi- nd patterns Men with t e r n i d anhah. Many bird 'species exisbin f&h-altitude and low-altitude population&, each with physiaTogical spacWa- tions and msrphologicd di%mncbs. The thermal environment resulting Born the combination of al-

ritudm u d Mtudm dsa datardms the rang* of WY LIY)~~.II. h h W e kegs CHyh- aluliw) cw br f ~ m d at lw bhvafion frr &am the eqwteE, h t d w t e h q u a k r timy -live at h i g h aMrndO#;

Tha enme hasif af a Weronce im tbmehl- rraacr is n& always ~laat. Wa a eftem determime why levela ar propertits d a ingh)Tokin U e r in two amhaah in ndatirr k temperatwe. Hmavor, the mdarlymg hasir fer camplsx Ummm in thermal physiolew is is aamph. Fmr example, two species of Siberian hamsters. Bhdapus camp- belIi and P szmgorru, W e r in thermal tsiolow in terms of morpQlogy, imlllatien, behavior, and physiology. Athaugh these &re very closely related spdes, thq last shared a om- amcestsr more than 2 milliem yeam age. A comphx trait ruch as fu r damity dmpmds en muttiple ganes. many cell types, u d mtwelJEP efgonetic rrguhbrs. Further- mem, tkm twe sped- may hawe many g e W &€- fwsmms, hut edy wmm ef t h s e say idu- thlir tLmd bialegy.

Although many ecbthmns a d p i W m m live in themally onrirBmn+undergr~und burrows. kepi& mimfuwts, the deep sea, or a h a m e s ~ ~ ~ l a ' s ~ e - r ~ m m i l s t w p w i t h be- w n t and drmac h T* ~ U M of the ef- fects of temperature on -mdacdw M a n ma mmhbdhm, ~ i k ~ and pubYrru must dtlUr Igbrab or gompmk kr the eempk, ehn d&krious, decOs eft-tempuakm.

Of the four classes of m a c r m m o l ~ . only p&teins and Hpids am substantidly afected by temperature over the n o d range mmceugtersd by animals. Weak bahds (van der Wads forces, hydrogen bonds, amel hyhphebic inkrqctions) govern h e interactions w i t h a d between &as& maerokuoie- d e s . Each t y p of bond has a clmacteris~c re- spense to temperature. Whereas hydrogen bonds and vam der Wads forcas are tbrnpted at high tem- perature, hylrsphobic i u t t r a c t i ~ ~ ~ are s t a h h d at . -

kr~&lm- lh@-the&&r -YIL-Lt"a&WTbuprtraaeae dl-r hid- @ . ~ m h r W s - hrld -&@,* Iryiwswhinh-- ~ i n ~ , a L s ~ w m h r o I l u t u l # ~ h i d m a q & t e ~ p m t h s t w b d w ~ m d d i E t w Irkrdy within tlae m e ~ r a n s . lurr* h m m m cause rnembrme liw to soh&@, which impah pmtek mvmoat. Cenvemly, hi#h t m m p m h p f y the &rant, which caa -proBLil8 h in---*---- i@ brrrier. CCaL Mlm-m solid gelstate an8 the k p d sd mb.

Ta~sywaturo. sYwbr - m a e - M tkr* =btbt--&mtion a d phesphdpd

Tlaa~em-.i#198ranepmhin r r ~ - & m g M -k. F e r ~ l l l ~ t e, as Ha?&+ ATPnrs- mkh me- lipids d m tb kanq&t-m~. n~ ~ m s f * * m r arr k- at a aerissd- p r a t u w , h p W * n b h n h.kmlplarrrLuw, Aelurrgr-*@yim@d&a breakpkt in the Arrhius plot of m e d r a m pro- bhfuaEtiea. u shown in Bex 14.1.

M e m b m e c ~ " h w ~ ; ~ membmec using r dye ( d i p h e - h t -9s in QIQWRW~@BS iS,nIrgwr t ~ i ~ ~ w - #em to move a~ih 41 d r * (wm j4.111. Wtp~pwr* fom mereat rpeciw up cola- WL t.*.$*i* . dm+$ iL f@dip @(.- s d 9,: +aqq ia ~4 mprrti.r) whG>*e m~mhapd is mula$. T h iub csllfidemgqk;t)~m *@paw b th-d Wysk sh- Urt ywwk.pr&upoiypbnnea$at &if he sur#W@ ww$,tgmp~rlb: Q%pb- WP-?, @ .d@~ ,t?:~?,~M~i+!f Kq, k n in enqmaa h m aaima~~ ir'&mwat niches

I

., Bird

L - Tropical fish;

> ,*.;;{y'yyY!(:!!,<: . ,

FigmrmUIl > r . . <;,., c , j , n ; J :>

M m b r m m * l u - a w ~ ~ ~ i l h ~ p r r r p a & # 4 l W ~ I h ' l ~ O ~ brm*flu#i. @cat- ~ t h r a b i ~ a f ~ l v a l t e r the b e l r r v l l i c w palarizmd IIQht Ankotnpy is Inwmly rm atwarmar wm-, r w i n m i s o t r o ~ m increlnr in fluidity. A n i d Ihrt Ikn in different d- renwwnta p r d w - U k & b # & i d @ a t ~ ~ k r m m r d n n e + e f ~ ~ ~ Dhl . th iakrnd~pdahrl iuys~-

(see chapter 2). I% me@ when la snimal is am- ta wkmh%>- ~ c - to&@rmic w w r+w *--*< ~f tenaperatwe by C- @e mmmqdfidr mamhrmes. Im p-, ulW bl)m*

wVS re,=dmL qm- t. p . w w fl~idiw- Three ,-& *&mPpids (Figurs 14.12X m m p - > , _ d m cho- lramml content.

+ s o ~ r ~ ~ i ' d u y e ~ ~ + 3 ~ k i a ~ i a t4q f+tty add &h. tb t b r W e h d

CHAPTER 14 Tharrnal Physiology I11

F i m l4.P Pkmqhlipii a d m m h m fheQ. Cdkehmge the fluidity et h r m u a by a b i n g the composition of merrkana phorphelipids.

whereas oleic asid (C10:l) is liquid at 12°C. The po- sition of the double Lend is also c r i t i d A douhle bond near the midpoint of the fatty acid chain (as with oleic acid) is mmre effective thm a double bond near the end of the fatty acid chain.

3. Phosphelipid classes. The difference in the shape of the polar head groups alters the ability of the phospholipids to interact at the s&e of the membraae. Phosphatidylcholine 0 is more corn- man in membranes of wm-acchated mh, whereas phosphatidylethanobmine WE) is more common in sold-acclimahd calls. The ratie of PC te PE decreases in the cold awlhation and adaptation.

4. Cholesterol content. A pure phospholipid hilayer is mostly fluid at high temperature and mostly solid at low temparatura. Cholesterol added

' to fluid phospholipid bilayer has little effect on Bu- idity. If the same membrane is cooled, cholesterel tends to prevent it kern solidifymg. Put another way, cholesterol tends to make a membrane more fluid whem ehrnal csnditionr otherwise encour- age a tansition to a gel phase.

Cells we two general pathways to medm membrane cornposition in response to tempera- ture: in s@ moacation and de naus synthesis. Both pathways re* cells to modify the proper- ties of the fatty acids within the fatty acid pool using

I

CeaH

i Fay, acid

Phospholipid Lywphosphelipid

Figrn 14.13 Pbqkdipid mmkliq. Ce8scan remodel the phospholipid6 dirmtly within mom- branee by removing a ht ty aid. A phwpha l i is rebuib by lwophoapholipid acyttran&rmm, w h i i madm a n ~ r ~ a c i d p m d d & t h . c e B . T l r r f r t t y M m u r t first Iw activaW the eiF.mtign ef-zymr A

suites of enzymes that elengate, shorten, saturate, and desaturate fatty acids. 41nce these enzymes be- gin with fatty acids derived from hi diet, the na- ture of the diet also affects the pro& of htty acids within the membrane.

Enzymes alter the structure of individual phos- pholipids dhctly withh the memhrane (Figure 14.13). First, phosphoipw A rmow m acyl chain kom m d r m e phwphopids to f a a lysophosphotipid. Next, lysopbspholipid acyhms- ferase uses a mere appropriate fatty acid (in the form of fatty acyl CQA) to rebuild dae f io~hoQh4.

More commonly, membranes me remodeled by endocytosis and exscytosis {see Figure 14-14). Tbo OH memhrsme is removed us* enelemis. Phesphalipids are synthesized de neus within the endoplasmic reticuhun, packaged i~ta vesi- cles that fuse with cellular m d r m m s .

Temperature changes enzyme kinetics Temperature sects protein stnicture and fun&on in complex ways. Changes in tempmapure dter the number of h d s that form wit$in and W e e n mobcdes. Even minor in protein skudme can have important effects on-protein function. In e ~ q r ~ e s . for example, these slmt$wal effects

\

I Box 14.1 M1*thematlcal UnderpCnrrlngs

\ E-lumtin~ Thermal Effects on Physiolo meassas Using Q,9 amd Arrhenius Plots -

For many physiologicat processes, a 90°C energy of the readon. The purple lines show another p e ase in temperature typically doubles or tential outcome of an Arrhenius analysis, where the rela- of the process. We can describe these ef- tionship between temperature and the reaction rate can- rature on reaction velocity rnathernaticalty not be described by a single tine. Instead one lime fits the

using Q,, value. The 4, value is essentialty the ratio be- data at low temperatures, but a different line fits the rele twmn reaction rates at two temperatwes, ad tionship at high temperatures. The point where the two

ure difference. It is calculated a lines cross is calted the breakpint. Since the slope differs

K2 10 between the two lines, we can infer that different act*

U - - x l 0 - K 1 ( T 2 - T I )

tion energies govern the reaction wer each temperature range, In many cases thls is due to a mechanistic transi-

s of a reaction (f l are m ~ r d at tion from one state to another state. If the process under temperatures (1 and 2). Thus, if a rate of 10 unitdmin IKJ considemtion is membrve fluidity, for instance, the wasobservedat20"C anda ~ t e o f 2 0 u n i ~ ~ (6) breakpoint might reflect the transition from a sol to a gel at W C U&.W - . . , phase. If the process is an enzymatic reaction, the break-

> A

I zu ..EQ\. point might occur at a temperature where a critical bond is Q,,=--X-;.~ . . on< + ,

broken, converting the enzyme from an efficient catalyst l o U02' ,$ $; < g4.@wd, 2 b a less efficient catalyst or denatured enzyme.

T h e ~ ~ v s l u e $ r a ~ r o c e s s i s t h e b e n ~ t o e x & s s ~ ~~eve tsa t i~ i tyo f t~e~r~en iusp~o~a~~owsresearchen influence of on but a better to describe the thermal behavior of any simple or complex a ~ ~ m a c h to the mechanism of action is through pimess, However, the reasons for pshcular relajonships an Awh.niur In me late 18Ws# the Chemist Svante are more difficult to asceltain in complex systems. Ther- Arrheniusdescribeda mathematical approach to exploring mal eff em cm membranes are -,, difficult to the impanof temperature on macromolecular processes. the considerable of the mem We now use his approach study processes such as bmne. Lipid rafts, for example, are cholesterol-rich re- enzymat~c reactions, diffusion of molecules, and lipid

@,, of membrane that often accumulate distinct membrane phase transitions. The sensitivity of a reaction phospho,ipids, Temperature has a difPerent on the to temperature reflects the activation enemy (Ed of the Ruidrtydhese regions in comparison to&le bdkphase of process. The Arrhenius equation describes the relation- *e membrane. Similarly, many membrane pr+ ship between the activation ener

, Bins accumulate dierent types of tipids. For example, rate of the process under study: pe mitochondrjai enzyme cytochromicoxidose binds car-

diolipin molecules within the inner mitochondria1 mem- ? L*<&<" o <,

ften, the Arrhenius equation is shol &yF"'Ag I I brane. Changes in the bulk phase of the membrane do not

, "ecessarily reflect changes in the lipid membrane in direct In(H =In(& - EAMRTf'- - ""

+ contact with the proteins of interest. Even more complex

&& k is a rate coefficient, R is the gas '&stant @mcesses, such as metabolic rate, are really the sum of 7 "

'18,31447 x 1 o - ~ W/K per moll, T is temperature (in many simple processes, each Wvind, A is called the pre-exponential factor, and EA is irnd unique Arrhenius equatio , .. . the activation energy (Wlmol).

Let's say that a researcher was interested in how ,

temperature influenced the rate of an enzymatic reac tion. She would vary temperature over a range of inter-

E E

*st and me6ure enzymatic rates. The data she csol- $ 4 0

lected could be plotted on. a graph with axes chosen 7 from a rearrangement of the Arrhenius equatlon that 5 generates a linear equation ( y = mx + bl:

InM = -EA/Rx ( I I T ) + in(&

Plo€tmg InIld versus IJTgiWs 9 slope of - EAIR and intercept af hf4. ,

CHAPTER 14 Thermal Physiologv I 1 S

protein in a way h t forms the site. W n d , bmperatupe dpr I the ionization Scab of critical amho auds within the active site. For in- stance, the amino acid histidine is important in many active sites, and

~ u r ~ h ~ p * erties. First, changes in weak boa& can dter the three-dimensional stmc- t w e of the enzyme. For instma. wmn t e r n p m s cwld b~& bonds that we nscesoary tO fdd the

b e s in bigtidine protonation state can alter enzyme substrate a5i ty .

during catalysis. Thus, temperature cw sect enzyme kinetics through effects on rn&- rnalvelocity ( V . or for substrates 0, al- losteric activators KJ, and inhibitors IK,). When an- imals experienm a change in Tg they may either tolerate the effects on enzyme hetics or alter meta- bolic regdation to compensate.

Biochemical reactions are accelerated by W e r temperature and rgdumd at lower temperature. Re- caU b r n Chapter 2 that the rate of a chemical reac- tion depends on the proportion of molecules within the system that possess energy equal to or greater than the activation energy 0. As tempenture in- creases, the average kinetic energy of the substcatas increases and a greater proportion of molecules has m c i e n t energy to be converted to products, caus- ing the enzyme velocity to increase (see Figure 2.42b). For most enzymes workmg ovar a biologi- W y relevant range of temper-, an inwease of ' 10°C results in a two- to threefold hcrease in reac- tion velocity. Recall from Bog 24.1 that tbis implies a Qlo value of 2-3. Qlo can be calculated for simple re- actions such' as an e m t i ? step, or complex processes such as lnetabolic rote.

Consider how temperature affects the V,, of lactate dehydrogenase (LDH) in the muscle of a desert lizard as it experiences daily transitions in Tg. Over the course of a single day, fie total number of LDH enzyme mol&des does not change appre-

membrane Any haease or decrease in K, could Iw disruptive. Third. temperature can - alter the ability of the enzyme to un- I+14 Mrk.n rmWLI, deao the chances neces- M I membranes sra cmnmntly rmnrohid byundwybsis .nd*xocyta&r. When sary for ca@~*. Enzymes be hmratura docre-, t b wll prod- vwiclm -ng phospholipids with rigid enough to maintain the proper faWacids that &re shorterand more unmturatbd than thow in the a l l membmnm. c o ~ m ~ 0 4 but fle&e enowh to Ov.r time, the cycles af mdocytosis and sxocytocis remov, unb i rabk phospho-

und8rtake conformational changes lipids, raplacing them wtth mbn dmrlrabk pho*phelipidr.

ciably, but their catsslytac activity changes with tem- perature. LDH muhml activiw V& typically doubles when temperature is inmased by 10°C (that is, its Qlo is 2). Let's hgin at a TB of M°C, and assume that the muscle of tha lizard has 4QO units of LDH per gram of tissue: enough catalyiic activity to convert a maximum of 800 pmol of pyruvab to lachte each minute. With Qlo = 2, a decrease in temperature £rom 40°C to 30°C muses the LDH en- zymes to operate at only one-half the velocity (V- = 200 U/g). Similarly, at 20°C the LDH V- is 100 U/g, and at 10aC only 50 U/g. Over the course of a single day, from the midday heat td the cosl evening, a desert lizard m y have to cop0 with an eightfold change in its LDH V- activity as a result of changes in T*

It is easy to imagine how an eqhtfold reduction in LDW capacity might sevarely impair the capacity to produce ATP by glycolysds. How does an animal cope with such dramatic reductions in the rates of enzymatic reactions? The simple answer is that the rates of ATP synthesis decline in parallel with the rates of ATP utilization, with each step exhibiting a Q,, ranging from 2 to 3. Put anofher way, the animal can tolerate lower rates of muck ATP production because it slows down and needs less ATP for mus- cle activity. However, it is imporht to r e c o w that QIQ = 2 is quite Merent than Qlo = 3. If a 10°C

LC

Evolution may lead t9 chsn#es i h enzyme kinltiw

W l n t n ~ u 8 ~ t O s ~ m p ~ ' - . i k - , h k H e m e f ~ ~ -

' ~ c ~ ~ . % l g m e s e n ~ ~ ~ # . We draw again on re=@ wit$ LPIN fer exam& of evolutioauy that Merencea & e w y m ~ h e k s as -11 as enzyme synthesis.

Hut,tir,nq may lead to s b m t u r d changes ia &'&i tli.t idput a Iavordh &arena i. i i e kinetics. As we h e e l in Chapter 2, I&- ering bmptwatim increases tlps <*@ of L ~ H f*r its substrate pyruvate (see Fim 2.43). Evolutioa hss led to r h - b m b g of s d b i ~ p r t i a s such Wt' s ~ d dig.mnms .Uon each n* &s a d h r K. at its respective nbr- md This mtm$gr , .Wed cowemtien of Kh, is colparody seen whpn'we co~pare ti^^ effects af wperature in he eqzyme' kimucs' if Merent

I < I . . ,

mbals. Alternatdy, mvolulCen m y lead b mutations ia

the promehr for uaenzyae,, c@ng a change in the level i f g q e srareqsirn;'df 4 ethmmise lu- ch~hged , m e . WMSP ~vi"al&g the erstam coast mf N e d < America .kom Nmfeudhnd to Flerida. With &e'populaa~n a~ a whole, there arq differsnt Ales :if the ~ k - & #G. ma dele predsnrinatk h nd?@aen papdpM8lis, while'le- ether aUeIe p&d&bi in smuthmn :pi@- ti* litswedi.* ~ U M Q ~ S Lit* * hdats. Tkese @deb luva Wokances ,@ biuy*. pmper- tin aid Wer in (be levrl'dgd$* *&-ion. Ths northern allele m x p n r d at tcre f i ; ld '~ar 'k- I > ,

eh than the s u h n h f i l e , due to aub~& b thc' pruoter. I h 6 aO&h Bsh w u e < k e r e LpH- ~*zyhre' i~~h$deS , p k h ~oai~.ii.tii; for the dePiEhhg &&I& of k k p e r l ~ t k eh'bazp

,. . . M;.r -*Ak rnirsrlj r***i *ir I U *

to miwte the'm~ecW d f y a f h ~ k i in T,,* M & ~ r a t e r y , whttra the & ' h b $ e ~ + s

WS ~ d e h p r o a ~ ' & & W-. la thtmtunl kifi, '&;qsrmd ww- garr h-r'atm are acmi&dlay etkdmmi- ~ & ~ w ~ t t . e c p e & e f t h r W t ~ r#plrr#mas@l&l~kcPiled~Whtieri. h rrinw, pa&piiea gei'iaorzlbt, my be less dub*, uul exygen i t ~ l r iW dhp i T i i B C~IRI-

p h i @ d these ~ a a I an-mi c h p s &e i tdmc&k fink n r r e d e h g w i ~ , ~ ~ ~ - ature. On one knd, them t * ~ ~ t y -r frr the remodeling 6-z is champ 17, : " , initiateti by champ in t&-d, & by Eome other factor, subl as p h ~ & d ? #k tbs ether hand, it is net clear *.I (k i * d ~ serves to c o r n b ~ shb- ktimpratuqe.

Tempenma-dependeat rkd~v-''hwku combinations d -t.*e' pd &litat& strategies. In #Srp%r 13, *e''&msml hi?;'&: tothems remeC1 their rrue*. b I Y V ~ . ' ~ temperatun. L.\* teap&&* iryuu th. number of r n i ~ u n d k i a hi k&ii"er the hypertrophic wwth of the h k . l+ii ir ah m u m - ple ef r quuntitatfue *a*; *bra $ ply more of the same macbjaety. M d s tm + alter the types of pretsiaE they us6. @ U t i e - 1 1 a 4 machery. Fer m c e . d h a k e r ~ h t myosin isofom in wintk w d d r - k &-

I > . , ple of a qualiWtiut skabw,

~urprisi& li* is knam abut did Behoaas d n d ~ ~ ~ ~ ~ m w a n ~ ~ t a mnidel its ~ 6 s - d w i q -a WWba- tizagoh (sah k x 14.2, G H I ~ a&-: T.p- pentvs %aUy u d Aly*vr h@4?elhl).'W: ssnslng knd wh-semhg lke- VI id- for tiatacting ~ p e r a G 6 , hrt Y e I*L~ Y &i(ex- p-ion are m.t wbH ,b a- as&.' sea- sonal changes jlP p w l b dm e h ef t e m p g m ~ ' irb' hy &.the pha- @pod&. lriChip*r 7 m *. Importwm of tea varisu ph~Md *yllnl pathways tlut r c t h w t h r ] i ~ m ~ ~ i i P ~ * & ,

t

---.--, ~ImJird-~wa#=-- w L y w r - . - - ~ b t b r r a a r l c h a h g a s ~ u r t ~ s s ~ - IP' ta mitigab the mf tampratwa on m l e c u k r s e u c t u i and are*lhm. In con- IruC, mnd~ttlomic e s h v m thermal ex- - using m p b x rqdatory pathways to

a e t T, Tlaeir existence at exkemes is a t 9 s m e ~ t b thir physiolegicil @ty to re- k t h dTA.

,Same enzymes display celd adaptation '

Bsrkier in this cbptm wm d k w s e d h ~ w relatively d e Me- in TA can lead to mvelutionary b q e s ha e m and gene qression. Hswwer, th m m d for enzymatic s- mods- Wea is much more pronounced at thermal ex- -. +i&ly at the subzero - raws w o u n b r d im plar s i w . Psgchrstmphs are or- - W M v e in OhC -erne dl, ir contrast t e - - - c w h * m e m ~ ~ m -

Ind* p&r ~ Q T -

~ ~ ~ ~ a c r i ~ e a t b d y ~ ~ I ~ ~ @ O ~ ~ ~ J ~ O ~ - ~ ~ d - a l l q M p r o t e i w ~ * m -dwb-.-*= ~ ~ ~ s t a M e i & e ~ l d , ~ e y c r s m p i t U y ~ ; a t d i @ l y ~ ~ ~ .

*-and-d-hm- ~ @ E ~ ~ r r m d m e m ~ ~ i n t n o e d b t g , W L - - h t ~ e q m t&ucture. Enqmes undergo pronounmi changes in k h d i m d e l a a l &ape during the crtdyric cy- cle. k a o n as p t e i n b w h i n g . mmg these Sean- W m k foIdiug, - L m k and ferna. W $ a ~ ~ ~ s r a l u r , m ~ o f ~ w u & k -8m-r-h-ina B K m t b t ~ a r r a r Z b r v ~ a . L g t h L ~ 8 ~ - . ~ , a i a r a ~ ~ k r k b ~ ~ k 4 m t $ e , r l u a & ~ 4 i y ~ @ # h d m ~ ~ u y h a f r l - d m i T Z 1 e p @ r a k e p h ~ b h w u r m a k ~ ~ 4 b ~ i t k m p h a W g e r v o h m e d b u r a m u i e r ~ ~ d u r h g t = W y d s . I k d ~ ~ ~ i t t r F I l g ~ n

In h, mid, #W lark& it vmhrabie b tmpm-d~mt mhwng. IrP c m w

tS-m,-w-.m=-- w e n t - a -.hut iu-

*!ywktd#N- ..';p .- --&la

~ ~ ~ ~ , ~ w ~ # l p r a a ~ e g l o h i & T l s # b r b ~ m w ~ m p - ~ ~ u w t k e y b h ~ n k s ~ the " *pdrr-ue*h-.

, T P I r # r r u y l t v r P c a ~ d o b e m & l &apb*am ef htliMar3 gmm in * w h d s . Hormsr, mars b tha w- tionmf*rL&mrwmtpgkr m i m a k b ~ a f m d a - mem* t~rdks- efw- u r mult of -1ution h~ tab artrmpr d d . Bmiy W- i e s s u ~ p r t e d t s r t ~ r r t i l n r h h d ~ l i c rabs taif were mwh h i g h #am ttid meWmlic m t o r e f h m p r r b * ~ m & r W C . T h m ~ ~ ~ ~ d * n g ) r c t a ~ r y thrt~-rlrr!bwa~-w-* I t ~ r s p p p a d k t ~ d ~ k ~ m x - t a m B ~ ~ t e ~ v ~ ~ t l u t p r 0 - v i d d t h m pkr ra'--rL M mh&@y te eslevate their metabolic rab . w&hm&dDTdy it re- m a i n s u a c i e & r w t t s t t r e r ~ ~ ~ ~ i s a d C e m m m . T b m r l & & & w h m based ern m m w d m mi m*. ~ a w ~ m m m e o s i # ~ ' ~ ~ u h g mom 8qlkWtel X seem less

general e L e m . ,- -8s havm i b M & w- --'- 0 l ~ ~ ~ W ~ ~ . l - . - - 1 - - -

Stress pmteins arm induced at thermal extremes

Many proteins am best srrSbd b fundm over nrr- r e w r ~ e f ~ t h t s p a ~ ~ r a n g e e f ~ e ~ ~ ~ t b n # l l u t 1 S r w Q r r r t ~ ~ t e c u m w h n a r ~ ~ , t h e pntehk-hbfurCter-iu-. O c c a c i o l u y s t h e ~ ~ u P f B y a r m i d d d i a k a n e n f u m m d o r u " - - . IW d m p- teinaavrtla~r&d~r&~&thmdhh itdWup&etaw.cdlulrhwWds.Ebmatutr~~r n u m d i m m ~ m d a J b s m a h h b 9 ~ ~ r e - mow h h w d )ntsias -mthwaya dpmtda

mW1. T b m pakkwap &mc&m tiwe* eut t$l liferimm mf a cek hM b m r wmri mnre

*r

Box 14.2 aeneti- and OmomLcs - All organisms, from simple prokaryotes to complex eukawotes, have a need to sense

and respond to temperature, which can induce changes in behavior, enzyme activity, membrane composition, and gene expression. Molecular thermometers are mol- ecules that change in structure in response to ternpera- ture, triggering signaling cascades that affect many tar- gets, including regulators of gene expression. Since temperature affects macromolecular structure, and most organisms have similar macromolecules, it is likely that many of the principles of temperature sensing in other model organisms also apply to animals.

The simplest thermatsensing signal transduction pathway occurs in bacteria. Like an ectothermic animal, free-living bacteria must be able to suMve short periods of near-lethal temperatures. Temperature is also the cue 1 to pathqenfc barnria that they haw found a warm- bodied host. One important mechanism by which bacte- ria detect and respond to temperature is through effects on RNAsecondary structure. The rnRNAfor.the transcrip tion factor # occurs in two temperaturedependent forms. At low temmrature 130°C1 the mRNA folds into a structure that masks a critical regulatory region encoding both the ribosome-binding site and translation start codon desaturases of many dlff~rent qpes intrduce double 7eeu, (see the figure). In this folded configuration, the mRNA bnds into fatty acids. Temperampendent activation cannot be translated. An increase in temperature to 42OC of desaturases has been investwed in several model breaks hydrogen bonds, causing the mRNA to unfold to a systems in an attempt to identify the links between tem- single strand and became available for translation. Upon perature and cell signaling. In most cases, the tempera- translation, the protein activatesa series of genes that en- ture sensor for desatumse activation is the lipid mem c&e other proteins critical to suNiving high temperature. bnne. In the protist Tetrahymena, fatty acid desaturase is %'%

As part of homeovismus adaptation, many ectoiher- associated with the cell membrane. At high temperatures 3 7 mic organisms increase the level of unsaturated fatty the enzyme sinks into the fluid Ipid bifayer, masking th acids in thes cells and me

1

h m h t d m - 8f thtWId W h I b- r m p d ~ c m a m u l a t e & W h c J E . -

~ ~ r n G ~ 2 t h a t h a t ~ ~ IWsp'sl oas & p r o m WJue the mn- wpfm tm eadyw pmbh fdbJj abbt tnapla- h(smngme2.31). C k r p e m r a r a u ~ r e - ~ ~ ~ ~ h ~ m e . ~ s o s ~ ~

8s. the membrane becomes less fluid and

rated fatty acids ~n the cytoplasm. Unsaturated fatty acids ptionai regulators that control gene expression. Many aspects of the response to temperature are

genes in response to cold, but the effects involve a trap ma1 acclimation. tl~vvever, it is not dear if organisms scriptional activation of h t u r a s e synthesis rather than achieve these physiological responses using the same

. an activation of existing desaturase enzymes. These sig- regulatory pathways. Simple wganisms, such as prokary- '

nating pathways involve a bvmomponent system. One otes end protists, rely on simple signaling systems to re- protein d a t m changes m membrane fluidity. and then al- spond to temperature. Although such systems may also ters the activity of another protein that acts as transcrip play roles in animals, much of the control of thermf re- tional actwator for the desaturase gene. sponses likely falls upon hormones and nourotransmit- ,

Membrane changes are also part of the temperature- ters. As in ptants, temperaturgsensitive channels are i n '

"mmg s g e m for plants. 14raMopsis 1s a temperate portant molecular thermometers in animals. This has zone plant that exhibits a cold acclimation response. After been most clearly shown in thermosensing neurons but : as Ilttle as 15 minutes of cold exposure, a series of may be important in other tissues. Animals also have the I

changes occur that alter many aspects of the piant's phys luxury of hormones that can mrd~nate responses tn dk iology. frrst, there are rapid changes in the cytoskeleton, verse tissues. However, it ts not yet known if the st~mula- ,

+ * including a disruption o# microtubule structure and a re- tion of desaturases in cold animals is in response to theef- i

' ductlon in cybplasmtc streaming. Next there is a change fects of temperature on the mllidirmly, as wrth bacteria : in the paltern of variatm in cytoplasmic C$+ levels, afip yeast, or ted secondarily by hormones. These patterns, or Cd+ signatures, are characterized by the amplitude of Ca2+ peaks and the frequency of ca2' os-

+R~eTCIRCBS .:+*: cillations. The reasons for the change in Ca2+ levels are

.' Knight, M. R. 2002. Signal transdumon l d ~ n g to lw -ex. Cold-hduced changes in membrane can tpmperature tolerance in AraMdopsjs *,hm, ~ ~ s ~ p h ; ~ ~ , alter the passive pemeabilm to ions. Because the m e n Tmmm&s ot fie nofit sonew of ~anlon~enar & B ~ ~ I C B I 1

, , + Orane is anchored to the cytosketeton, membrane &&J Xbncss357: 871-875.

GX?I~;:;F%% A r mngss - can cause mechanical stress that can be inter-"" . st,,>^. I=. a, w WW. Genes snd~ew~opmr~r i %& - "nreted by mechanasepsmg Ca<c&nnsk Thesn an- 12.~2- , ' - 4 I - - + " ,:<l,?; ... ". > . .

dye mu-em. Whem tern dl iw-Bd, the chap ~ a r e l d a w a y , ~ ~ h y ~ p m - w. TtPn ~ ~ ~ ~ ~ t h s p ~ , ~ ,

whichin m b a h e r p ~ a t d ~ ~ ~ ~ r n ~ ~ p e % , a d b d m g thtm hai p k i m ! 3 am- H s p 7 0 i s h P B M H 5 P m o ~ md.rwew th-M181 m.

T b 3 b p r e s ~ g g ~ i s ~ ~ ~ t h e a b ~ d a c - ~ ~ ~ i l s t e ~ ~ ~ f p & & ~ f a x - - 4 ~ r n p ~ & ~ ttant ehm 8a tx within thair =turd -m4? Fer most qaeCirr, ~f ej Hap ruporise is inhd at tm-a e ~ d y ~ a f m d a -

I

alaove t h a ~ l ~ ~ r ~ a . T U pwnr- fd p r e m w proass h anW W W tion of Qermal sensitivities anal t h d (sma Box 14.3. Wth& WdliyM'wmi Haat Sheck b i n s im BmsupMk). IrtmWm& S ~ U ~ S ~ V B ~ O S ~ ~ ~ S ~ ~ ~ ~ ~ & ~ ~ & B C &

r ~ p l t . ~ f i d l h r v s ~ e d f o r . t t i ~ af -at - 1 . % x . ~ t ~ ~ ~ ' t 8 s * c i e s ~ e n d @n&ie cbrnger ~~~ tha apkdty t a i r r d c t a ~ ~ h 8 c k ~ ~ . % u c @ t $ g ~ ~

I -

-- - --- -- - -

I The best-studied Hsp's are from the These studies also s h w d that flies with a robust I Hsp70 family. Each subcellular compartment heat shock response aiso had lower fecundity. In other

has Hsp70 proteins that help fold proteins into the words, superior thermtokrance comes with an evolu- proper conformation and target misfolded proteins for tionary cost. In a thermostable environment, flies with degradation. Mitochondria have Grp75, the cytopiasm lower levels of lisp70 could outcompete flies with has Hsc70, and the endoplasmic reticulum has Bip. The higher Hsp70 levels because of their greater fecundity. namesake of the family, Hsp70, is produced by cells However, at more thermally challenging conditions, the mainly under stressful conditions. When temperatures lower fecundrty is offset by the greater therrnotoler- rise to dangerous levels, cels dramaticalb induce syn- ance. These laboratory studies also reflected the nature thesis of Hsp70. It is produced in the cytoplasm, where of the evolution of Q&rmotolerance in the natural world. refolds proteinsthat have been denatured in response Wild populations of Drosophila from around the gbbe

to elevated temperatures. The ability to mount a heat exhibit a wide range in thermotolerance. In most popula- shock response is central to the thermotolerance of ani- tions the natural ability to survive thermal stress corre- mals. Genetically modified cells that lack an ability to in- lates with the levels of Hsp70 gene expression. For ex- duce Hsp70 are very sensitive to thermal stress. Since ample, flies in Evolution Canyon in Israel occur in his gene is essential for thermotoleranm, many re- separate populations that occupy the north- and south

searchers have studied whether variation in Hsp70 gene facing slopes. The flies that live on the swth-facing expression is central to the differences in thermotoler- slopes, which are hotter and drier, have a stronger heat ance among animals. shock response. The flies on the north-facing slope have

Many studies of thermotolerance and Hsp70 have a weaker heat shock response due to a disruption of the been performed on the fruit fly, Drosophila. If Hsp70 promoter of one of the Hsp70 genes. Since these two helps an animal survive heat stress, then it might be rea- slopes are only hundreds of meters apart, individual f lies sonable to hypothesize that an animal could benefit from probably move between the two populations. Thus, nat-

, greater expression of Hsp70. Laboratory studies have ural selection acts to ensure th'at the aiielic differences '

provided important insight into the links between Hsp70 between populations are retained. Similar studies on : gene expression, thermotolerance, and evolution. In other Drosophila populations showed that flies with

me study, lines of flies were manipulated to possess ex- lower thermotolemnce usually possessed mutations

I ~ r a copies of Hsp70 genes. Larvae from these flies had that disrupted their abitity to express one or more copies gmaterthermotolerance, demonstrating the importance of Hsp70 genes. In most of these cases, the animals of Hsp7O to thermotolerance. In other experiments, with higher Hsp70 inducibilityand therrnotolerance also lines of flies were exposed to high temperatures for gek showed reductions in fecundity. erations to see if natural variations in the Hsp70 genes These studies show that, though critical for thermm within a population muld be subject to natural selection, tolerance, Hsp70 can have deleterrous effects. Further- Within only a few generations the average therrnotoler- more, they itiustrate why genetic variations in popula- tnce of the flies increased. These thermotoierant flies tions are essential for the survival of a species, were able to induce Hsp70 to higher Ievels than the^ mosensitive flies. Surprisingly, the difference in Hsp7C gene expression between thermotolemnt and ther. mosensitive flies was never more than 15%. These dat; lrgue that Hsp7O may be important in thermotolerance but that other physiological factors may also play roles.

", 7

k.p"dG Feder, M. E., . E. Hofrnann. 1999. Heat-shock proleins,

@ rnolec~lar chaperones, and the stress response: Evalufionaryand ewlog~csl physioiogy. Annuel Review of P h y s i d q y F l : 243-282.

~33%

d tsss: The bow &re kghs'to b e z e sham forms lndide cells, so lk~eza-tqbrant se- therehr. '^ crbte nuaeators out of he &I. This restricts 'ice

Frmtte-tolarant a m & &y piodude ice formatibn to the extra~dflular fluids, such as he- nncleatdrs to ~oafrol the &ation mf&uTd&cs din, mowph, ahd allows the io~acelldar space to re- crystal growth. Ice is the most damaging when it main liquid. Many different typw of molecules am

82. PART TWO Integrating Physirlogicrl Systems

act as nuclraters in animals: calcium salts, mom- brme phosphslipids, end 1mg chain alcohols. However, it is met always clear that these ice mucle- rtors are actually necessary or helpful ta keeze- tolerance skategies. Fer example, the weed frog has aa ice nucleatgr that triggers ice famaaiola at ahgut -7'C. The s m e ice nuclaater is alse fmmd in the tifsues ef f mgs that cannet survive freezing. It m y induce the formation sf ice, but it does not necessarily provide the wwd frsg with its freeze- tolerance. Some nucleators may simply Be preseat for other furnctiens and have no adaptive role in freeze-Wbrance.

Because ice formation draws water from the cells, freeze-tolerant animals also produce intra- cellular solutes to counter the movement of water. Urge glycogen reserves of the liver are broken down and colavorted te compatible solutes consist- ing of organic pelyels, such as trehalese and glyc- erol. As we discussed in Chapter 11 : Ien and Water Balance, mmpaPibla solutes have two main benefi- cial effech. First, by increasing the esmotic pres- sure within the calls, they reduce the movement of water and cell shrinkage. Secend, the solutes help stabilize macromolecular smcture.

Antifreeze proteins can prevent intracellular ice formation

Freeze-avsidance is the secomd skategy animals use te survive extreme celd. In a car, antifreeze ele- vabs the esmelic cencentratien of the radiator fluid. Solutes in general depress tha hezing point of a solution. preventing ice famation at subzero temperatures. Freezing point depression is one of the cohga~ve properties of solutes (see Chapter 2). The solutas in animal &sues reduce the freezing point of water, but generally not lower than about - 2'C. Some animals possess antifreeze macrornol- ecules-typically proteins or glycoproteins--that reduce the freezing point of body fluids by noncol- ligative actions. They disrupt ice crystal formation by binding to the sur f&~& of small ice crystals t s pre- vent their grciwth (Figure 14.16).

The first anmeeze prom, or AFP, was dis- covered in an Antarctic fish about 30 years ago by Dr. Art DeVries. Since then, AFPs have been found in many distantly related tam of fisb, as well as in- sects and plants. Four -classes of AFPs are distin- guished by their structure: types I, 11, and 111, as

I v- - Water molecules

Figun 14-16 Antifnmzm p t r i n s . Antifreera protains bind to the surface of ice crystals to prevent thmir growth. They bind alrrng the face of the ice cryltal, whors the pretein forms wark bends with water melreules immsbilizad iwha ice crystal. h u s e ice growth is very orderly, the presance of the bound protain prev6nk iee crystal growth. (Sourer: Modillad b r n Davier. ot al. 2002)

well as antifreeze glycogreteins, er AFGPs. Inter- estingly, each of the classes ofAFPs has arisen mul- tiple timas in evolu8ien. In fish, AFPs arese less than 20 million years age. This ceincides with re- cent (in geological terns) sea level glaciation, which probably represented a strong selective pressure on the local marine species. The phyloge- netic distribution of AFPs suggests an intriguing evolutionary history.

AFPs provide geod examples sf parallel evolu- tion. For example, AFP I1 appears in herring, salmon, and sea ravema. fish f r m three separate orders. This suggests that AFPs arose multiple times in these lineages but well after the madern species diverged. These AFF 11 genes may have arisen from similar genes independently ia each lineage. The structure ofAFB 11 suggesb the ances- tral gene was a CaZ'-d~psndent leetin, a, protein that binds sugars. In aQuctura1 models, the inter- action of a lectin with the hydrexyl groups of sugars is similar to the interaction of AFP with the hy- droxyl group of a water molecule.

The evolutionary origins of AFGP are also un- usual in terms ef probin eveluhn. The ancestral gene was prohably a gene for panareatic trypsino- gen, a digestive prstease we introduced in Chapter 12. A region between the Grst intron and second exon was duplicated not just once but more than 40 times. The resulhg gene possessed inultiple, tan- dem sequences that resulted in a rebeating Thr- Ala-Ala motif necessary to prevent ice crystal growth. In most cases of gene duplication and di-

CHAPTER 14 Thormat Physiology -1

vergencm, thsr rwulhg genl brr rirrilrr proparties to the mcostr~$ene. with W v e $ mtle Mar- earns in fundam, h the cus ef AFGP, * rembnt g a . has a te tdy Wet b-. AFCFs have no protease activity a n 4 m - n hw aeamtikeeze activity.

hdathemy L sa h x t r i d l y i n m a d with a h @ ~ metabolic rate that it is not howm whi& trait arose ht. High T, daws metabolic prwwms such as pwth, develapmeat, digestion, and biosynthe- sis to operate at fwbr rates, and the higher meta- bolic rate in turn produces more he& The ability to become warm bodied requires metabolic pathways to produce h a t (-1 as wd as physi- 01& I I W & ~ & ~ S to retain heat Most en- dothems are also homeotherms and bammitted to maintaining a constant Tg. TO do SO, they must con- trol both thennogenesis and heat exchange. In cold emhelamezlts, emdethtfm stimulate themqgene- ah and redurn hart lass. In hot environments they increase heat lm, but m y also reduce thamogen- esis. To control TB mimds must ha able te sense both environmental bmperatwe and BsQy corn temperature.

Hmat predutCioa is ara inevitable conwquenm of be- ing alive. An emdothem warms its b d y using heat that arises as a by-product of o t k metabkc precesses. primarily energy m e t a h h , digestion, a d &wde activity. All mimWnd&-wms and ~ ~ ~ a e r a t t heat durleg llresa processes, but only &8 emdothems paws the physblegmd

' adaptatians that enable &em ts retain emugh mebbolic heat to elevate TB abow TA.

In addieion to the pathways that prodwa heat as s by-product, d h m pswsa apedic hame gmic pathwys with the main pwpw & ksat pro- duction. ne- pa-ys rely BB wl~ cy- &g, in which &emid poBBntial emrgyb spemt t& generalre hmt. Most futile c y h Involve cycling of ATP hydrolysis and ATP ~theuia..Hert is relewd

iT1 KIP hyblysPs MTP -t AlBF + phmsphate), but a gmat d d more haat is p r d ~ d when the cell usas ~~ m&h&sm ta migaterate the AT?. Hn- dothem can e h c u heat p r d a m either by in- maw the rab of ATF turnever M byt ducing the escieacy of ATF prodwti6n. In be* m a , most sf tbe rnetablic heat wises dimdy Or kplfra* tom r n i t e c h o ~ oxidative pkosph0qhtion, &sussad at length in Chapter 3.

Shivering t harme%enesia results from unsynchrsnizad n?uscla centractions

Muscle @lays a Wrl role in the thermal budget nf endothem. B e c u e mus& is tba most abudmt tissue in birds agQl mmmah. it produces consider- able heat, even at rest. h m o t i s n enhances the rate of muscle heat pmducti9n. However, mimy birds and mammals can also use skrletal mush generate haat by Mvedmg As in normal cernaaction, motar nrursas &om tho qbm release neumtansmitten rt the meter mad plate, but d w i q shiveriag the pattarn of adtation is dif- ferent. The smallest neurons-thw ianervahg the slow i9be-e recruited &-st, felowed by the larger neurons that innamat8 fbt mwle . As a re- sult, individual rnyo&iers teatract but t8r mator units are mcoordhatd amel th whdo much ua- d e w s no gross movement. Sbivmriag thermogen- esis is a strategy that works br dmrt periods of cold exposure, but it is net useful for pmlemgd cold stress. The mechanics sf shivering p ~ v e n t am ani- mal from ushg Its locsmetery mus&~ te h u t p e y or escape prdabrs. Fwthembre, if sbiverfy gar- sim, or repa& hqu~ntly, the d e s are rapidly depleted of nutrients and they becgme exhaustad. just as they would aRer hgh-btansi@ exembe.

Heat is produced in metabolic futile cycles Shivering t h e n w g e ~ ~ s i s is &@I ta birds rad mammals; hewever, ether m h a h a h #e muscle ta gemrate heat. ajtiag hmcb. su& as bum- blebees a d seme meths, can wrab emeugh heit te warm the thoxadc mt muscles, which hm- pmvirb &ght aetde pedmrmance in terms ef em- - produden, excitrtimn-cumUmn ceupling, and aws-bridge cycling. Thm hgh matrBelic rata

d m g mbt gerat8s abundant heat, to w m the fight rmwdes by several degmes. Re m~rk&ly, h s hec ts are even able to wann their fllghtmmtyreprior to takw£F.

Throe distinct mechanisms allow insects to warm the thorax prior to fhght. These s a w ther- rnlogenit: pathways also allow social insects to wark c&&vgP to warm tlm hive. The first mechanism is a metabolic futile cycle in carbohydrate metabo- lism. Within the flight muscle, two opposing en- zymes are activated simultaneously: the glycolytic enzyme phosphobctokiaase and the glum- neogenic @myme fructose-1 ,a-bisphosphahse. The metabolic cycle causes ATP hydrolysis and heat production, but without changes in the levels of the other substrates and products. A second warming mechanism relies on muscle contraction. W o sets of antagonistic flight muscles power wing movements during flight. Bumblebees can induce both sets of muscles to contract simultaneously prior to flight, so that energy is expended without productive movement. The third mechanism for heat generation is actual wing movement. The in- sect moves its wings fast enough to buzz, but con- kols the kequency and orientation of the wings to avoid generating lift. Collectively, these thermo- genic pathways allow the Q h t muscle to warm up prior to takeoff. There appears to be a critical tho- racic temperature that must be achieved before the insect will attempt to fly (Figure 14.17). At high Th less of a preflight warm-up is necessary to reach the threshold.

Most QE)U& m-ss mh@n an e W - c h e W - a i i s b g B d t W b ~ n W dsttih- *e @f bns t h m meadmino. Cells w e *mi- calenorw, madly in the form ofATP, te weals these grwkts . C o w q m a ~ , any pmea t$rt d i d - p a w ha mbnbr will muse tlae ssl W use -- mlawts-**&eBt.

I 9 P p a & n b ~ k F S n n ~ n ) ~ e 1 1 ~ . W t , a o a y ~ ~ r p g p ~ , w . h c -

e h m y d * m & - d - a d 8 btB .* 4 wha H & + 7 4 r m J - mm.yr.--isl.*~#U k wo NL+#K+ masn k

I

Time (min)

Figure 74.17 Thrnnogenmsis in insect flight muscls. Many large flying insects can undertake a preflight werm- up, using metabolic futile cycles and muscte activity to elevate thoracic temperatures ta a th-Id temperaturn required for flight.

pmg ttPe Na+,back wtef tka PIJl, T h mi-a- $rid FIFo ATP- i~ ~ ~ t h e r -&A- pates im g r d h % , k this =.* em O ~ g e . H e a t i s p ~ n + o a ~ ~ ~ ~ t r ~ p o p t s p t m d a m @ # d ~ ~ y - dents to regwrarta the p r a h g h t .

TBe second pathway taf im g d h n t W p a - tion is ion leak, in wM& ion ~ lg~vmwnb am not coupled to any 0th bmpert pmms. Shm no biol~bgical ntedwme is cgm~pla&ty bpmmt. ~ m i e ~ L i l r , W x ~ ~ ~ ~ ~ ~

g r e t e i l a r d l w J a a - ~ e ~ ~ p r e d u c s k t a w h y w m k u & m d ~ a U g h ~ * d h l ~ W w e h e h n , q s m d ~ 5 @ % h s m ~ * ~ , t j r r s t o t h e ~Cld1IB.iptBipiBy.iqn *-. b y pmoemz t h u t h u e w m Q e g o . d k @ ! ~ W i l X a h itymwe twmepnsriw. WC m e r n h s a resting @ebb& r W LZLqt h m m d ~ 143- W~brod4mW@$m ef113g -0

*.md Tp R d -r8@ id $W h M Se mmk- I-m; ad.t41011D1-a m 1 8 ~ 1 s a d -. 8M

mdy W r thra &BBB ef scl.*. Ea- d ~ t b ~ m t r m e ~ e kwt te m - k m Fa- diea*U=uale u w ~ Y Y

CHAPTER 14 Thermal P h y s i d m It(L

Arteriole

Fiure l4 . lO Brown adipose tissue in hamstom. Hamsters posses thick pads of BATbehind the shouldm.

pky). UndSerentiated -sex cells are in- duced to praIiferaM and then later difFer.nhta into BAT. T'glyceride is sylpthesiz@d and ]nib- chondria proliferate. At this same time, the ceUs begin to express thermageniln, whkh causes the tissue bo increme the rata of mihchondrial respi- r a h n and csnmquently b a t production. BAT heat production is eften called aarshfveriag khetrmqenwis INSTI; while the other pathways we have &cussed alse differ from shivering, NST is a term usually resewed far BAT-mediated thermogonesis.

In the absence of thermogenin, the processes of oxidation of reducing equivalents and phospho- rylation of ATF &e coupled by their shard de- pendence en ihe pmten moave farce. W n t h r - m o g e h is inserted into the inner mitochondrid membrane, it accentuates mitochondrid proton leak and dissipates the proton motive force. Since oxidati~a is no longer coupled to ptrosphorylation, themagenin is said to cause uncoz&ing. In the presence of thermogenin, oxidation awl proton pumping continue at high rates but with low rates of ATP synthesis.

The way in which themugenin induces uncou- pling is not yet certain. One theory suggests that themogenin acts as a proton ionophore. It picks up protons kom the cytoplasm and &es them into the mitochondria, dissipating the proton gradient. An &mative theory sqgwts that thermogenin dissipates the proton gradient by musing the futile cycling of fatty acids. Thermogenia carries an ion- ized fatty acid @-COO-) kern the mitochondrial side Thermogeni n enhances mitochendrial of the inner msmbrane and flips it the hilayer preten leak to face the @@lam. Because of the lugher proQon

Mammals possess a unique way of generating conwnlra& b w e r pH), the. ioniz J fatty acid is heat in specialized deposits of brown adipose tis- rapidly p w t d 03-CBOHI. In this neutral farnit sue (BAT), typicaHy located near the back and readily h p s back intD the inner leaflet of the bilapr, shoulder region (Figure 14.181. The brown where it ionizes again. The complete 'fip-flop" cy- rrdipocytes differ from white adipocytes in impor- tant r e s w . They have much higher lavals of

' mitoch~prdsin d exprbss &e gtt~se encoding tlw protein -emh. BAT'is particularly impor- tant far themgenesis in small mammals and newborns of larger animals, particularly those that live in cold environments, BAT growth and thermogemesis is under the control of the sympa- thetic nervous system. Norepinephrine released from these nerves causes BAT to grow in cell number (hyperplasial and cell size fiypertro-

cle causes a proton to be tamlocated across the in- ner mitochondria1 membrane. Still ether explana- tions for UCP function exist and a khitive model awniOs further experimentation.

The thermogenic capacity of BAT has been h o r n for decades. and the protein themogenin was first characterized in the wly 1980s. It appears only in nmmmds, and is expressed only in BAT. However, in m n t yem it has become clear that thermogenin is only one member of a large gene h d y of uncoupling proteins WCFs). In addition to

t&- *-1m+1,-- ~ t r m ~ - U C h i L E R - 2 d U f J 8 4 j . ~ l u r -u Mhdtwqb

t W + ~ ~ ~ U a n * ~ t e ~ t # r e d U & U t l r ~ d ~ a * . i a , ~ d r , . W ~ a ~ k ~ c ~ d d a l i w r C l a w ~ p ~ r m t .

BE-- JBSt E L i k b m -

d r i h T b W ? ~ b d y L & e ~ ~ t , w & t h ~ im n y 4 r r i e < * , , s u a s . ~ ~ ~ a m ~ ~ U a8

-m d -. It is hMyl.Yat h --u

4 a d then mutcM version mf ohor E F c .

-1 d k&p&atm h' dndotherrnic d- W&w --of'&dtip1e physiolqji- dl-. m & h khdh t0 ~ 8 d b r TB c h r ~ a n a ~ o d d m#&: ~ m h l t o r i n g internal core TB m h d s cllln W h h overall th&mal WCC. Feripheral*more&ers allow anhi& to d a m T,. The inBehm*n h m thermal sensing

> - < .., ' \ k . - 8 -

; < : . . - > <%&- : . Endotherms possWs a deWM thermostat that integrates cenml and peripheral ther~seqJnfmmst ion . . vA< -

As we discrvvd *- I.alljmIs pqueur dif- ferent types of n b (I;- and r b n d to ternperatum. Te re monitor$periph- e r e md a n t r ~ ~ t u m - s e ve neu- rons, both cold Birds and ammds me-.& s b i k neurons, although Jly k g $ h '&-jlrntral her-

,:' mostatdiirersinthetyyt~, ,> '

Mammals menitor ~ ~ ' g h r i ~ w r i d sea- ssry neurons located im ttra skim & tke viscera. When TA decreaser. mhqrrl &EM re J sig- n& to the h y p o t h - m ~ y.191. The pre- optic area of the -*$$&lkm has both cold-sensing and w*WL&* rne&&~~ that man- . L k "+?

,,.--

V m s t n c t i o n of , L a (Y - ' ' ? skin blood vessels

' I r

:M&ves&lr ,

frqm p@hesiqd mt@m~mp..n- , , I '

CHAPTER 14 Thermal Physiolgy

ihr COB^ M y *mpsrstum, J a f o H e ~ h m the peyhrdanr ikbdthsnra l~mmis ia te - graW in ths hypotWpmu, I*hich wndj ~tethebdytoabrthr~alherrtpdue b n sad &spatien. TheA h y p ~ u s is much more ruspVSr~o b isfariaatiea b m the c~nval tharmommptem tlarn born the p r i p h d thar- mmemptors. Chaages ef has taaa 1°C can smite cenwd tlaarmowptors, m g a rapid hypo- h h m i e response. Conversely, pdpbgral ther- rnormptors may recsrd and rimpond to r change of several degrees without invoking a bypothrb- mic response. Surface temperatures cam w e by m t d d v without Bsrming tbs animal, whmm the tempratwe of the central nervous

must be more -. Brd TB regdati.an ir Lss understood Ltlt is

dearly different b m h t of m d . Heating or mobg the hypothalamus has little e&ct on tha thermomgulatoty response of birds. The central thermostat k birds rppearo to be the spinal cord. not the kypthalrunus. Bowever, the thermostat is dl rmpadbh far intggrathg Wormation &om ceaeal and peripheral ~rmownsors. When the central thermostat detects changes in tempera- ture, it responds by k-hg neurons that lead to a compensatory response. Both birds and mammals alter TB by changing rates of heat production and heat dissipation.

Piloerection reduces heat losses

E d r in this chaptar we dimused how body osv- e x k p , such as hair and hthers , act as ipsulatlan for endathelms. Since t?m efficiency of the ins&- tory layer depends on its thickness, animals can regdab k i t loss by changing the orientrhn ofthe hair ll-mmah) sr hathm (ih birdsj. mds (and m u m & ) get f l a w in the &I by forcing their feathers land hair) to arient perpen&& to the . b d y surface. The zn- by which this mien- tatiom is mlmbd is k t wderstmd with mam- malian hair, but the p~silion ef bird feathers is mn- trolled in a s h n b way.

flair imlf is a coMecd~n of m k that ppssssss &undmt keratin. an interraedista fkment of the cytsskehton. The distal end of a hair is p m a i l y dead tissua. But the proximal md is &emposed of living cells embedded within tha hair follicle. Pe- pen- en khe spedes, a hair follicle can produce

either a m e hair shaft or complex ~~aabbmtions of hairs of m r h s lengths and slmdwes. Whereas human hair f a d e s produce singh hairs, dog hair PgUTck p d w ~ r primary guard W d muWple ~ ~ f t . h e ~ ~ t f & m ~ e ~ - b r a a t of the fur (Figure 14.20). The pit of the kak follicle is cempamd of e p i d e d &. Inmbtly assdated with each hair foU& hc s mbacwm gland. which relames complex mer- of &@d ( s q u h e , wures8ers, trqlyceri*, adds1 tbt form a protective coating on the hair and pMVih m o i s ~ o n .

Tiny smm& muscles, m b d eractor m u s c l ~ , corn&$ each ha@ faMc1e to the u p h m r f m ~ el& &piden&. Whm%e %rector muPcle m1krwk, tb hair is pulled perpendicular, a process termed pi- leamdh, so that the fur OW better hsulatiotl. The erector m w l e contractility is regdated by nu- merous factors, both bloodborne and neural in ori- gin. The situation is siglilar ie W, where srrector muschs rrlso conk01 the orimOrtion efthe feathers.

Figure l 4 J Hair fslCicl#. A hair is produced by cells in the hairfollick. Erector mus- cles attached to the bass of the hair contract in response to neural stimulation, -using eh. hairto become upright. S e w - glands lip& h t h e follielr d-.

*la.\- I * f 7 1

~ W t m h d U a ~ W Y Y n r n a n v i m . r m n t ~ ~ . ~ ~ 8 n a l ~ r n o v m s t h r ~ h h s e l m te th &in sum mhmncing hamt I-.

L_ t k

Chanses in blood. flew ., , rflm thermal exchange

&-at- B h & W n t b e veiaa d m r - ies throw comecihm ,*ed urtwj~uenotq anststomeses. At a ~ r m & l ' ~ d # ~ & ~ h d % ~ ' ~ ~

m - 1 - 3 - b . . . "'"'

- - A h € i m i * Y r . ~ r # * -*itb&hd*db ~ ~ ~ ~ b l $ ; d I m ~ L L ) - ~ ~ s m ~ ~ ~ ~ w w a & + ~ b u f * a ~ b y r l 3 n ~ ~ h ~ *wmuy ~~~~*~ 8&elb,r*

e t t h m t e q - t ai:*&&* &mr&wf,bsrF bmc m a h -& sRmUmWh~~!rn -''*&a,- *---. , + :, < ;' 4

@ d g m k ~ j l m ~ ~ ~ b.drdow u-*&dh#+41.

m - a m @ * - ~ i p f C w ~ a r f r a h-, whom rapid -IWrwh- ~ m m L ~ i ~ ~ 1 . h e a m h d core

0 . - , ' \ r , % . ' ; , 3 ,:It1

Ccuntercurreng ixchww~in, th, ; . I ' . -;A

vasculature help retain heat.. . , .,,,,, ,:.

In dditien te BstticBing b l e d dew te ths perigh- ery, some animals are &b ta slr$ract peat warmed blood ctad ttirns'krit tb c w r "Bitaed. This b ac##&sbd hy m e $be Y&-

M m#Mt?~cwh8Hrh#rr lr -~ The - 4 a w m g m e J ~ d * ~ &*&and asw. 2 . a t l P I ' 1 21

k r n ~ ~ W W m Y k * k r r r ~ b t - e ~ ~ ~ ~ i x f ~ ~ u m ~ Y B wrmlm -*t(in t h d r ~ m ~ ~ b ~ ~ ~ ~ ~ * m l W e t f ~ * r n ~ ~ i t b s m l ~ , d b w & l * ~ @ ~ ~ thev&kcktohrrtrrIee-HZhWd- b- leed -*~tw4-~ntm+hAm lWC o-nrr t tbaR!*hE:m w m -.-bwmbugm-m bat*- r m AS.w ~ b G b ~ k % d m h ~ - ~ ~ wclrwwkIes-lmter-W v w

CHAPTER .l4'+ Thermal P h y s i o t m

eye and e~,Ud--. Ce-. lrat h#t.-&lp wit in the optical system. Many large hh, EM& as w e tom- rant heat ex-= in &&-- testind *act W retain &e heat d digatitan. -

-heat exdangers mel w d by e m d d w m s ta *duce heat lwl at thm p r i * ~ . Birds s m g on cekl dams. sub M iee, c;an lose r **at of haat -ugh the fwtltFm 14.28). Thay rn redux hart loas by ~tr ic t ing Lkd bw to tht periphery, but ever long prieds this would cause the pe- ripheral tissues to starve. Counter- current heat exchangers m f e r heat from arteries e m e m from the body core to veins retaming &om the cold periphery. W- d the vmew blood lessens the impact of the peripheral coohg. Also, cooling the arterial blood demeasms the ther- mal gradfemt across ths skin and therefore reduces heat bs.

Sweating reduces body temperature by evaporative cooling S d anjmals have a f;svorable ratio of fllrfrcs arm to volume fer heat bss. se evaporative cssling is used prima- rily by large aakak. Mamy larger ad- r d s use spechhed skh fluid - tioms (sweat) te o h m evapraMve mhg. Humans are prohably the

minds that effectively um sw-to me1 their M m . S W is a mkkm af waiter, W. a d urn eils. The salt in sweat m h s tW bail- izlg point ofwakr, making svilpera*vt mohg more eEcient. kss of water and salts can a c t ion and osmeregu- lalien, but m i i d s exposed to hot weather for long prriads can change thn chemical cempasitim Qf their: sweat ts mini& ianic -4 @-tic prsbbm. Thmy praduce r1 larger

Wothermc nsh

Ventral aorta .

I Lateral cutaneous artery'

(b) MeWwmic tuna

[a) In rnomtfmh, the dorsal aorta and p o m r c M b l i n 4 h h m t h m md murelr directly. Any rnyegenic h u t is wried away from Wlmu@a in- p e m r r l i n r l vein. {bl In tuna, vmsselr am omanired to r . t b i m W within thm myrcl+ b #me species, hnchlo of the dmml aorta and poet cardinal vain form a v t r a l net- work, or am, within the hmd arch of tha apine. MOM tuna rpecilri m i c e the rod m u s k via I m n l vssnls that run underthmrkln. Rm lmrh n M e s run clere to t h m -1 vmh,wilh branchas that form plripkml rOH. This f ~ u n is a stylized diagram. Each hst.mthrrmjctunr 8p1cjsc r.li4~gn diffrr*nt cr0mbin&ons end nurnhnmfmbs.

f i n 1- PmripkdwmecmsWict~ in MY m4rYurm. .#idsmnding un eoY surF#norn rltbr th flay ctf b l e d irtW thq f..t, roducing MW. T h m L I d v w r h mf thr kg and fomt a n a r r m # d in parrllml, allowing

' * th&Win&en &a cowmrcumm hrat mchrngmr.

hmt a&ws bemuse of their lurgm sim Panting incream heat loss across the 3wef Eff f& iasuhtlak&:sldl&,-pera- respiratsry r u d m tunan (IWC), &xaindm b - m ~ b nese

The properties sap&lkr4mdCee-.W b#pintina

. . , j > ' 1 $ I [ , >

hwagp&mabacceaturG

rapid brea- is a sign that aa d n d auy Be overheated. G * W G * a mh be- b) w ~,,praiure bvior -am m birds, charwbr-

&A , I& # rapid contraction md mhMbn of the throat mm- -

dm. Mammals pant. Each sf ---the* o,, d qrdw ways. First, rafl ven-g ,igrnures t h ~ ~ loss - the respirawry &- ilee +~VWIP. ~..and, 4 p h l ) r more kqwrtantly, th rapill htllotion uws w*? & w '-kern surfs- , * . inu r**~u l sa~? .* , ,

*fa- la, &$&& - :~i$T$~* ; ;$,& J & , , . r1 1 1 - ~ ' 1 ',*::< -: * h r

*.t $>@*, .*tov bbg-" ,+ HLOh < , $: '!1,. ,: ' + r ; !,9

e ~ m i s m h ' well-vasmhized I ,' , ~ r r t : , respiratory s w that are Fi~mla Hemtlo#dwrilg Wfl* +; , . , < ,

kapt wef:rIMrd((V ~ ~ U ~ 4 l k e a U & w m m W @ & r ~ n)"aw&wbrenhing ul insryw &'& ~&ndur ,p-, * - * *w, 8*,p&+: .,-~u* st^ mmperatum. h e h M l r l c b o ~ k t w MOM eft;

+~~/a~-w &gsw, : &: ! p W i s MwughUls raslst tr t#btha nssd Vmsntempwatulsr

& c j k * m ~ b ~ ~ ~ ~ ~ n r f i u * n . ~ . , h l d gaS pram, imp- 811 b r m h minut?). {Sourn Au-Hamn .t 11. rn

*,

Time

CHAPTER 14 Thermal Pbysialogy UI

thm@ this chmgo in breathuy ma# re- duce direct cooling of the brain, it reduces b d y care Urnperahxu mare efiientLy.

Relaxed endothermy results in hypometrholic states

h p v i m u s chapters, we have tmmuntbd varim~s farms of h y p n m m ~ ~ used by sadelhmrms to survive adverse caadiuens. Hmmhghirds. far ex- ample, undergo a nightly r e d d e n in mtabslic rates. HiLarmahg mamnzals rho undergm a mta- Lolic suppression during th8 long, -Id winter mths when fmd is swcr. Whether a daily dor- mancy (tgqmr) or a mere prelangeel s e r d dor- m c y (hiberna*~), the hprnetahelic phasm is accompanied by a damease in Tg a phemmcaon called relrxddb1Lermy. The W e m m and magnitude of radudon in TB differ meng animals and typs of dermancy (Figure 14.25). An uct ic qukrd, for smmpla, can allow TB tB fall close to the kaatiag point. Hewaver, even rrriner redudens in Tn c i a effer hipertant *mergetic savings fer a dor- mmt animal.

Under normal (euthermic) csndiliens, ram- mds and birds main- TB within s narrew range. A euthermic animal induces a compensatery re- sponse when its csnkd thermestat-the hypthal- amus in m a m m l ~ e n s e s a decrease in Tg. h- iq periods of relaxed endothermy, the animal recabrates its central thermostat to recepize and dsfmd a difisraat TB set-paint. The endothermic animal may d e w T, te fall clwe te T,. wall belarw the euthermic set-point.

The lhks between metabolism and Tg re@- tian make it dficult to establish which parameter causes hypemetdmlic cooling. For mest animals embring domacy, TB and metabolic rate decline in pardel, and it is net clear 8th colder TB slows metabolism, or alternately if the slower metahalic heat productien causes mmhg. In some studies, animals show a reducfien in'mmtabehc rat6 before TB declines, suggeshg that hypometalelism initi- ates the reducien in T, Hmwevsr, in hrger animals a dohy in mding upgr entering demmcy is due in part ta thermal inertia; the large &ass and law ra- tie ef swfam areq te rolume delays the impact of rducod themoge~esis, allowing the amimd te re- main lmuch warmer than TA even with a reduced metabolic rate.

(a) Hibernahn

Time (hwrs)

(b) Torpor

Figurm 14.25 ~y~mmmt~bdic shtn. Many endethsrms rmopond to cold temperrturns by entering mmo form sf dormancy. Body tmmparrture gmnerally declines in parrllml with metabolic rats. The dormancy is callad (a) hihmatimn whrnthr matmbolic daprwion Im?s for m k s to manth or tW t-r when the animal mntmn a hypommtablic state in drily cycles.

Hypertherrnia is induced by pyrogens baviations kern eplimum T, usually impsir m o d physiels~, but in some cases mndothems can in- duce local hyperkermia as part ef the immune re- spense. Regional cell and tissue damage leads to a ha1 h e a m d e d inhmaaliam. Mora savtrre con- ditions result in whele body hyperherria. A fever, hducd by chmmical messengem cded pyrmg4~. helps cambat invasions by hchria and viruses. Or- ganisms rocegahe the presence of bacteria when cells ef the immune system detect specific badrial pr~teins, such as mdotoxia, sr other bacterial macrmmolecules such as lipopslysaccharides and preteeglycans. There cheBaicals, called exege- nous pyrogens, are detected by the blood cells of

th.iu&mrJlrCli.whm erl- deb&.* a-. *--Lug

m& u - 4 W :k. T h mwopltrfrr ivkur Warhuh r.into re$m~ aumumw tL-- mrtag t h c n k r v . f d c h N b d , d y . m y m m * ha a t h h y d . t y p &-kt, pm+

&WLh mrnW.mf ,&a -- aw* a q m m p u w ' rnpr- tlut leads tg t h m -. h- & . wmns r e d m &hg frqwncy md c m i l d t i v e neurons hew &hg fqumcy. ?%m my shivers b in- t : ~ metasolic heat prwhdien in muscles. Car- diac output increaws d peripheral vessels &lab to inmaw b h d h w in w& b &tribute cere b d y heat -out * uiard.

Sin- tkII immw rampma werks by ir- ing T& it& dt. )r praclicd~dy ha m h d ~ t h & c a n r m k i a ~ t . h d d , ~ s a s p t t & ~ f b a - muaiwir Lme M p u d in sip-c uierrlllr, p w M& and i d . awwor, eather- mic ra"irh also induce ly)rrllnrrsii ia m p s e te -ao. Shca they v t use phyg idq id mechanisms to increase Td, W e an&& induce a behavioral fever. Warn a M w bad is hhcbd with bacteria, it shows an in- In the pr&rmd T, moving hto r wg~riwr gqvirpnraaent.

Integrating System

I Lion Manes Are Hot Lions live in prides, with one mature male and a harem of females. The lionesses do the parentat care and a l ef the &inQ, Mile t b mile guaids over the m, his p m i f h ~ n l t t any mlrh &I- h g e r . ~ h m W fmab Hvill dmse a mole thlt ahe,psrceiwb la have W M "qwli, " in t a m af repdictive PgtmW Tb-cencept J mate W Zion is oftm dffkuit tb &arpr&.in tsm ~f anjmj physiokgy. H w W s a f s m a ! a h r a m - the rp

dw l * ~ ~ m m ~ h r l d W ~ 1 *k ' I

Most AfricmkarV h i n b k k a m x m m , . .

1 where dayLima ternpratures a n r u d greater than i 1 45'C. For them animals, the chllengm is to keep ml, so the thick mnrd males would seem to k

I counterproductive in relation to mermaf mi. I Studis using i n f w d meras suppsrt'thb presump I tbnttretmiieswithdaik, t h i c k m . W , a m x e

difficult time a-s bat. Sir#, the mane r ~ a + ~ a u k t s r y b u r d b n , HlljW Wt it k te SSKL~~I Um17:Rwwrchms im umstigatd m v d , mwtid eqhwiens for W seemi* rmb&w w&,

Tlrere is#ttk doubt lh~t C W s w mane ap- paarwx in maw c h k , but it is) I- 4 w r why the thkkw, d a r b mmi are m~ m. T h fi pl.ltWetyistbtthe thickwnmhbCaopfqtwth vulnereble-nqk s ~ i g n - f i * h W d M * vidmt f i t r fer cJsmllcnar. Fw . t b f-,, q ,<mlk protwted maim is b#@rpMq)e preSact tha(pcdm frsm invaders. F r ~ m the Ws- the lagnafits sf additimal protactien e d W Witbwl a t s associated with thermrqubtb, ttiE difktltt to m- tablish if long manes prbvide significant*- in a f i h t . An alternate explmien fqf the m i n g reason for mnes is Ih, --. Much like the mil of a i m r p m a advertise to fern& that1h-.~w- i d q y eo- mf Hnlh lfl~.m pbysb logical burden.

lndmpmndent of tho W r w i M why a mane is a Wt undw sexual sdmmn, s My-t might ask how Shwpwtb d thanma efadomk nant male are altered and k & i s F ~ W N ~ &mi- name. The l o n s w ~ , b - i n n m w v + f the wIWWgfW#W. H a k ~ i s ~ d M lay AS af h k f@@h W d * i a b w c h a m in relolien .$a emir- , . : fast hthe su#lmer and Mwlin ths wi-. M i r i d ~ I hirs in humans w w f g r . a W fh m s , thn m w i n -tic fw, snather 12 wmks,.At M a I h i r frwn the s ~ n e fdliile is m, m t h e m 4 i b i r wt In.prirw+, liens wldgrw,mr lwk @ haw

3 mg hair m htwwdw h g w psrWlef.tiaPI). Tha w w h W k *WinliJ by tha w d r m Mereid

, hm: .ws?=tmom a d dihyhtmteeterolul , . (E4il-l. m 0nm -.anysyte test*

ts~lno t o i t s w ~ P G t i ~ DM-. ThkWs~f* I &me@ d w ~ h l ~ h is p w d i r w tiy w

+

k

-- ,.&A. ..:i;: .qrn:,r ?<:: m.+c ikiiiq - i & m f r ~ ~ ~ ~ h ~

. - m f r w n 1Jui-m-Trn1r- dMtirrismuchhrrtuthwdwrlii h&ihts, such r ~ S s r s n # m t i . A M m m m w o u l d k w l . v s n ~ h i d r ~ t . m l . T s r w l i . T l w T s r w lions - ~ 5 W t m W R maid tm k mere messivo mn m + m h,

spotW in Shm Tsava. Researchers lured t&ns 'from thr W d - r a ~ 1 M t & &M w i n the Jwnirwnt mmies k k d hmi. Psr tt~sss &#IS,

i - ~ w i h m m ~ h n , d d t e * 1 ~ ~ WH & % ' d m -on.

Thus, in t h m ~ - ' M u t h i has r&Yd k ' k b s of the-, t ' f t ) ' ' ? \ ' ;~ t f r ' ; " . I J L ~ , ~ > 4 A

Tho mlaght' rirwt h k how thsk liaris be- 'BIM~~J-~. M m s O M 8 - . 2 ~ @ . 4 s W fer hair m, @Mi testderone

b -- h i r tam4t:il.rrot y& k w n if -.irlrles how higher t m s t e s ~ ~ s . h t h M m g a t i W m r i H ~ m ~ r c h m l ) e h h U i r W r m of p r i h thmt impticates testwergne. In Ihr Wonpti lms, a pride pesssses as m y as bur matwe mrbs, but mest Tsavg p i i s hrw enly a . single matun male. tareno both cause .:h - w , e m n ( ~ r t h s W a t Struotun of the pr-. : : , I ~ ;~ I~~; I ; . , . ,

P a - ---"--*- * " - - ' - ! M $ l r z y L ~ rti- '-PY**- ----- k t f w & - h d l # ; l r a 4

a I b ~ , l L I ~ r f : : &

msls CaH 8 h r b t h o d - h w * Yllt~ @ - e W L 3 y r l d r L - e n . mu-- *--: l ~ ~ l ' h ' ' ~ ~ ( ~ i ~ ~ ~ 4 f !:* +?) ' ' < : ' t-+ ):m-l-**-k*

-'@rll#Im' & r _ J I ,Mw*Ihs *h@-,--* h e- - W ' & ~ ~ * - m w - ~ T, > . - t , . r V r l a x ,-

d w m w h m d & e - ~ ~ 4 ~ * a m a m d ~ m m d ~ ~ errlveafam@--~?m14

dadt-$m- d* Y - * that exhibit ceslrsinrtierr ~f m y d - - tmhmy; mwal-mw en- d&hdc#w mmf.-Itr&/w___,,pri- &b*d hyphAL/l , j~YdL u I j U . ~ k h ~ i * r w r - - ~ ~ & & U e t * v v n ~ m - ~ r f l Y m W i y & e v a - ~ W ' &

- <-?&-.

Their th-*trRLriiw- twnvsilt---.

.,.JltYPw'm!- Arinrkm-**qfwb * r h g * m d ~ ~ h # r m s i d * & i d l i i r ~ ! , ~ & ' ~ p i d

rua * * l - m u t n a f f - ~ d s e m*--'--kdp-, k-& U b M m r d - m -m ~ M ~ b ~ r k ~

rr0 cw -=h@ v I w r b i a C d - - w d - pr%ki.ls ,Xkr~-~i, 4-1-b :;sk -&mm a f q - - - , d - - r m a ~ l i ~ I 5 r +

E&dmt.r~r. Uvb& htreYh-* often d m l * * y s b ~ ~ m a r a g e Z r a M for the effects af tcmpmrature. ~ , a m b & arm Pbb W s r v i l k ~ ~ ~ ~ T L s wt9st *.*I- fsmiim sf ica -, -makduca o s m & c ~ s & + r a p ~ d l y

mUu4r ina&rmes. F-Merant rai- JMIS d v e the -0 wid by~pduciag corn- p o d s that prmna9Peeziqg. -am im mude- atora a n d w @ @ h a way6- p r w n u d a m p r k m h a L 4 M ~ p r o - ~ a n s b e z e ~ t m p v ~ i 8 ~ ~ i a f e J -dlq that have lived kr hng pc- rinds ;ir cmkt.loikn passear culd-adapbd m-,

ri3: -rmic mkids pradummehkk bat ~ r e t a i n & t o ~ L ~ B l a y t e ~ ~ ~ ~ W e a t tempentun. Heat ir r ~ u m ~ e - queacs Bf d h ; h&l~rnmkwWs b e h@mr r n m W l i r + * tlzarr e e k t b m s bfsiallrr size, A &e-m l e ~ e s ~ is orra m s n d d k m haw h&bmeWrates.

E & h m w r > m m s tadehat a- hmal dhttmal wn-. Ii'bmmmkn h- htu- mnkd d pwq&eml t b r a d z ~ ~ q w - - w w al s y l l r r r l , ~ r W ~ & I l i l g d r ~ ~ e n ~ Pariphand cbld-e-raw hitha arhtaliom d hkirC er pilearegden, t, d u m hast l e ~ . and - 6 , d s o bsnW1 the blood flow to the skim mwfw4q-sak d WkJa#i,mr- hl fbn into -at mt-4m t o l p 4 l A , W * &&be* #Um;>-Ilread mu,- wa s w a b, e h m wapemklmd GO-,

w maiim- r n ~ t t b y eating, - h w m m w h ~ k w t ~ J m d

Rwiew 43umMbns ::+, -'

> , I r < - *J., . "I I > .. . <,,

- .&~p~p41 .o ;*& 9h$c~t: dW f~llMdpp W m S :

+omrot)lpyp$gaik~J@bww; e a d a ~ m y , and e c t o t B r q ; ,regiopCI1 ,heS9.ro@qmy, and

tamporal h@roth.ermy:, 2. .water at IUOC fit&, cswer 44s &, ,ah (1 O'C.

.why? n why ww p w i p f . faugd ip *e

fish but not freshwater-w? I . .

4. Qmpwe melw~ksstW.fl~&&sms ef h r - m ~ ~ e s i E , W k h bb&BaicJ ara re- spossible for hmt pqdwtim? . ,

5. Discuss the different sources ef e s i ~ m w - tgthemcauusgter;liraT,,, ,

6. What hehavirtrs .r&m b a t - b m s due b (a] canduction; &3~43nvWan? ..

7. How do we kmmv t L u k a m m p - m e , sevwd<-inwd-? - .

8, Hew do mmtwmmntbat work?

4. ,WhyYis,high hqmrahmrmore bgaa low temperature?

2. How could you cerwert a themosensitive armi- ma1 into a themotelerant mind?

3. Summarhe the physblgical changer that w- cempaay them1 acclimation. Q . :. ~ $ 3 E n ar

4. Why do endothermic h a i s need bth pe- ripheral laad ~aiaird ~ & a l & ~ b x & i ~ meu-

', m? P I . L : . .. ,' I