J therm BIol Vol 16, No 5, pp 277-279, 1991 0306-4565/91 $3 00 + 0 00 Pnnted m Great Bntam Pergamon Press pie

THERMAL PARAMETERS OF SERVAL FELIS SERVAL (FELIDAE) AND BLACKBACKED JACKAL CANIS

MESOMELAS (CANIDAE)

COLLEEN T DOWNS, JANE M BOWLAND, A E BOWLAND and M R PElutrN*

Department of Zoology and Entomology, University of Natal, Box 375, Pleterrnantzburg 3200, Republic of South Africa

(Recewed 1 December 1990, accepted m revised form 11 May 1991)

Absa'act--1 Oxygen consumption (Vo2) and body temperature (Tb) of servals Felts serval and black- backed jackals Cams mesomelas were measured at ambient temperatures between 10 and 35°C

2 F serval has a broad thermoneutral zone, exhibits thermolabfllty and relies on decreasing conductance to retain heat at low temperatures

3 It Is hypothesized that F serval allows thermolablhty to conserve energy 4 C mesomelas has a definite thermoneutral zone and exlubRs less thermolabdRy than F serval 5 F serval has a lower, and C mesomelas a lugher, than prechcted basal metabolic rate based on body

mass

Key Word Index Cants mesomelas, Felts serval, thermoregulatlon, basal metabolic rate, oxygen consumptmn, body temperature, conductance

INTRODUCTION

The blackbacked jackal Cants mesomelas has a wide habitat tolerance, Rs &stnbut~on m southern Africa ranges from montane areas to sea level and includes meslc to xeric condmons (Skinner and Snuthers, 1990) The serval Fehs serval occurs only m meslc areas and is often assooated wRh wetland (Skinner and Snuthers, 1990, Bowland, 1990), ~t is usually strictly carnivorous (Bowland, 1990) whde C mesomelas can be ommvorous (Rowe-Rowe, 1983)

Generally, httle is known of the basal metabohsm and thermoregulataon of fehds, whde knowledge of cared metabolism is sparse (McNab, 1989) Basal metabohc rate, determined from oxygen consump- Uon, Is useful as an index of energy expendRure m endotherms (McNab, 1989)

The objectives of this study were to investigate temperature regulaUon and basal metabohsm of F servai and C mesomelas

MATERIALS AND METHODS

Ammals were housed outdoors m enclosures (25 x 35 m) wRh natural vegetation for a nummum of 6 months before being transferred to constant en- vironment rooms at 20°C ( + 2°C) w~th a photo- penod of 12L 12D Here individuals were kept m small enclosures (2 x 3 m) carpeted m woodshawngs with a wooden kennel for refuge Ammals were fed chicken or red meat daily and water was avadable ad hb~tum

Oxygen consumpUon (Vo2) of the ammals under a range of ambient temperatures (TD) was quantified using an open-clrcmt a~rflow system (Depocas and

*To whom correspondence should be addressed

Hart, 1957) connected to an oxygen analyser (Ametek S-3A/I) Since both speoes were nocturnal m the laboratory, all measurements were made dunng day- hght hours when the ammals were at rest Postab- sorpt~ve mdw~duals were placed into a resp~rometry chamber (volume 16 31) for a m~mmum of 4h Thorough a~r c~rculauon w~tlun the chamber was maintained w~th a budt-ln fan A~r, dried over a column of sd~ca gel, was pumped through the chamber at flow rates of 7 0-7 5 l/nun A sample (300 ml/mm) of excurrent air was diverted to the oxygen analyser after passing through sdlca gel and soda hme to remove water and carbon d~oxade, respectively A data logger (Chart recorder, Model RYT), runnmg at 2 mm/rmn recorded Vo2 contmu- ously Influx and efflux percentage oxygen were corrected to STP and used to calculate specific Vo2 (Hdl, 1972)

Behawoural thermoregulauon, particularly pos- ture, sahvataon and sluvenng were noted Data from mdlwduals that had shown any s~gn of activity or agRat~on were excluded, On removal from the resplrometry chamber, subjects had body tempera- tures (Tb) measured rectally wtth a copper-constan- tan thermocouple connected to a digital d~splay thermometer (DigRron 1408) cahbrated to + 0 01°C Thermal conductance (C~o) was calculated according to Scholander et al (1950)

RESULTS

Imtlally both species were agitated when placed m the respiratory chamber, however ammals settled and usually rested m their natural resting postures wRhm 30 mm F serval (2 males, 2 females) had a mean mass of l0 12kg ( + 1 14), while C mesomelas (2 males, 2 females) had a mean mass of 7 72kg

277

278 COLLEEN" T DowNs et al

. ~ 1 0

0~0 9

~ o ~

_~o7

~o~

~o. d o a

O2

0 I 10 Arnbm~t temperature (*C)

t 30

Fig 1 Vo: (mean + 2SE) of F serval and C mesomelas in relation to T~

( + 0 30) The response of Vo2 to changes in T~s experienced by F serval and C mesomelas is shown m Fig 1 Simdarly, the responses of Tb and Cm~ to T.s are shown in Figs 2 and 3, respectively

There was no statistical difference (P < 0 05) m Vo2 for F serval over the T. range 10-35°C, although mean values were elevated below 15°C The lowest, average resting metabolic rate (RMR) (0 2553ml OJg/h) occurred at 22 5°C, and is equivalent to 73% of predicted basal metabohc rate (BMR) [Hayssen and Lacy (1985), polynomial equation for Car- mvora] F serval have a broad thermoneutral zone, w~th tolerance of a small range of thermolabdlty as T b decreased until T~ = 15°C, below which T b was maintained ( y = 3 3 4 6 + 0 1 7 1 x , r 2=0762) De- creased C~. (Fig 3), < 27 5°C, was essential to mare- tam msulaUon at low temperatures, and to prevent further oxygen consumption

C mesomelas have a narrower thermoneutral zone (22 5-27 5°C) than F serval Lowest mean RMR was 134% of predicted BMR [Hayssen and Lacy (1985), polynomial equation for Carnivora] Tb (Fig 2) de- creased untd T. = 12 5°C, however the gradient of this regression approximated that for F serval, but possibly suggesting greater thermoregulatory control (_v = 35 46 + 0 085x, r 2 = 0 779) Below 25°C, the C~. of C mesomelas (Fig 3) was minimal to reduce heat loss, but resulted in increased Vo~ Above 27 5°C, C~,o increased sharply to prevent hyperther- mla Avoidance of T.s > 25°C would be expected, to negate the need for increased C ~ and to prevent increases in T b

4O ~ 5

- 39 °LJ 38. 5

38 37 5

o 37 38.5

_~ 36 3 8 S

"~ 35 o

34

ttt t t t tt It 10 1:~5 15 1~'5 20 22.5 2.5 275 30

Ambient ternl~rature (°C)

Fig 2 The response of Tb (mean ± 2SE) of F serval and C mesomelas m relation to T,

6.

e E

U

Fig

014

012

010

0.08

006

0 04

002

0

0.02

ltttt t 10 125 l~ 1;5 2b 2~5 2~ ~ 5 ab 33

Ambient temperature (*C)

3 Cm, . (mean ± 2SE) of F serval and C mesomelas m relation to T~

t t

C~. was reduced at low T.s by F serval and C mesomelas curhng up and reducing surface area At high T.s F serval lay outstretched to increase Cm~., whale C mesomelas panted to increase evaporative cooling

The limited nature of the data base, particularly at low temperatures, is recognized This is unfortunate but was unavoidable CauUon is therefore exercised m interpretation

DISCUSSION

Thermoregulatton

F serval show little change in Vo2 for changes in T. of 10-35°C, but rather minimized C~. Tlus allowed Tb to decline at low T.s (eg Tb=352°C at T. = 15°C) before Iio2 was increased to regulate Tb Such thermolablhty may reduce energy expenditure when F serval are unable to hunt F serval are pnmanly nocturnal and spend long penods inactive (J M Bowland, personal observation) or lying-up (48%) (Geertsema, 1985) In mountainous regions servals are often exposed to snow, making hunting condllaons difficult at low T.s Energy conservation would be a significant advantage in such situations

In F serval and C mesomelas, fur thickness, pos- ture and pdo-erectlon must be important parameters controlling C~. At low T~s, increased Vo2s indicate that Tbs are actwely maintained Selection of ade- quate shelter to reduce heat loss would be expected when animals are inactive

Above T.--25°C, the Tbs of F serval and C mesomelas increased rapidly Despite the Increased C~. and To of animals at T. > 25°C, there is little value in avoiding high temperatures to prevent heat gain, increased energy expenditure or evaporative water loss, unlal the upper cntlcal temperature is approached Indeed, thermolabdlty typifies the ther- mal charactensucs of many and zone mammals (Flelden et al, 1990, Downs and Pernn, 1990; Taylor, 1969), and greater vanablhty might have been antici- pated for C mesomelas

BMR

The thermoneutral zone is defined as the range of T. within which the metabolic rate is at a minimum, and within which, temperature regulauon is aclueved by non-evaporative processes It would appear that a fehd and a cared both respond to low T.s by sup- pressing any increase in Vo2, maintaining low Cm~.

Thermal parameters of F serval and C mesomelas 279

and perrmttang some thermolablhty, which results m broad thermoneutral zones Broad thermoneutral zones charactenze many camds (Gohghtly and Ohmart, 1983, Henneman et al, 1983), C lupus shows no consment relatmnslup between T. and RMR (Okarma and Koteja, 1987)

The use of pred~ctwe equations is often cntmzed because diet, behawour, phylogenehc relahonsh~ps and habitat are known to affect basal metabohsm and thermoregulat~on The study of a generahst cared and a specaahst fehd, provided an opportumty for com- parison of certain metabohc and thermal parameters Carmvores, which are pnnc~pally or excluswely ver- tebrate eating, have BMRs that are close to or greater than the values predicted for their body mass regard- less of habitat (McNab, 1989) A decrease in the vertebrate content of the d~et lS generally assocmted vath a lower BMR than predicted by body mass (McNab, 1989)

The crab-eating fox Cerdocyon thous and the Cape hunting dog Lycaon pzctus inhabit s~mllar savanna grassland habitats but have BMRs that d~ffer greatly (Taylor et al, 1971, Hennemann et al, 1983) How- ever, when the composmon of d~et was examined, the strict carmvore, L pwtus, had an elevated BMR while the ommvore C thous had a lower BMR than predicted by body mass (Taylor et al, 1971, Hen- nemann et al, 1983, McNab, 1989) Yet there are exceptions to th~s trend, C lupus, a strict carmvore, has a BMR 15% lower than that predicted by body mass, possibly for econormc use of energy dunng periods of low prey avadabdlty (Okarma and Koteja, 1987) Fehds, usually stnct carnivores, have been found to have BMRs approximating predicted values derived from body mass (Taylor and Rowntree, 1973) In this study, F serval had a lower than predicted BMR although It is a strict carmvore

Camds exhlbR great differences m BMR, even within a genus, as a consequence of vanous ecological parameters (McNab, 1989, Gohghtly and Ohmart, 1983, Hennemann et al, 1983) In this study, C mesomelas had a higher than predicted metabohc rate, however, geographical vanatmn is hkely be- cause of Rs broad and dwerse habitat tolerance

SUMMARY

Vo2s and TbS of servals F serval and blackbacked jackals C mesomelas were measured at T,s between 10 and 35°C Over this range F serval did not mcrease Vo2 in response to cold, but mlmmlzed Cao and allowed Tb tO dechne, before increasing Vo2 to regulate Tb Tb and Ca, were less labile m C mesomelas At low Tls increased Vo2 indicates that Tb IS actively maintained Above 25°C, the T b of both specaes increased, which is a widespread phenomenon

m terrestrial mammals, particularly common m and zone species

F serval, a strict carmvore, had a lower than predicted BMR, while C mesomelas, a more general- 1st feeder, had a lugber than predicted BMR, contrary to expectation

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