Life History

Life History

Photo of size variation in seeds from Panama from http://www.tc.umn.edu/~hmuller/

Major events related to an organism’s growth, development, reproduction & survival

Life History

Photos from: http://westboroughlandtrust.org/nn/nn54.php; http://portlandbirds.blogspot.com/2010_05_01_archive.html;http://www.rampantscotland.com/colour/supplement070519.htm

Life-history strategy is a population-level representation

Wood duck w/ 5 Wood duck w/ 7 Mallard w/ 11

Timing, duration, phenology, rate, allocation, allometry, etc. shaped by natural selection

Life-history traits vary among individuals & populations

Binary fission produces genetically identical clones

Asexual vs. sexual reproduction

Image from http://biodidac.bio.uottawa.ca/thumbnails/filedet.htm?File_name=OLIH023P&File_type=GIF

Paramecium


Cain, Bowman & Hacker (2014), Fig. 7.7

Isogamous gametes



Anisogamousgametes

Sexual reproduction produces genetically variable offspring

Chlamydomonas

Homo sapiens

A “cost of sex” / “cost of males”



Assume each adult female in a population produces 4

offspring, either asexually or

sexually

Benefit of sex: Genetic variation E.g., Red Queen Hypothesis (coping with ever-evolving enemies)


From a statement the Red Queen makes to Alice in

Lewis Carroll’s “Through the Looking Glass”

(“Alice in Wonderland”):

“Now, here, you see, it takes all the running you can do, to keep

in the same place”

Photo of harvestman with parasitic mites from Wikimedia Commons

Complex life cycle – 2 or more distinct stages that differ in habitat, physiology, or morphology

Simple vs. complex life cycles

E.g., Alternation of Generations in plants

E.g., Holometabolous insects

E.g., Anadromous & catadromous fishes

E.g., Metamorphic amphibians

Larval, pupal & adult wasps

Anadromous salmon adults live at sea, but spawn

in freshwater

Herbivorous, aquatic tadpole will become

carnivorous, terrestrial adult

Photos from Wikimedia Commons

The Life Cycle of Animals – Illustrated for Humans

Generation 1

Multicellular individuals;Diploid (2n) cells

Unicellular gametes;

Haploid (1n) cells

Generation 2

Specialized cells undergo meiosis

to produce gametes

Gametes fuse during fertilization

to become a zygote

AY

aX

AaXY

From the single-celled zygote stage onward, cells undergo mitosis to increase

the number of cells in the maturing individual.

Unicellularzygote;

Diploid (2n)cell

Muticellular individuals;Diploid (2n) cells

AX

aX

AAXY

AaXX

AAXX

AaXY

Gen. 3

AaXX

The Life Cycle of Fungi – Illustrated for Bread Mold

Several generations

Diploid (2n) zygote

Several generations

Haploid (1n) cells of hyphae

Multiple rounds of asexual reproduction

possible; all cell divisions occur by

mitosis.

Brief inter-generationalzygote stage

Haploid (1n) cells of hyphae

Zygotic meiosis



mitosis.



mitosis.



mitosis.

Fusion of compatible hyphae (plasmogamy and

karyogamy) to form a zygote-like

structure

Aa

+-a

-

Haploid (1n) spore

A+

a-

a-

a+

The Life Cycle of Plants (Alternation of Generations) – Illustrated for a Dioecious Flower

Generation 1

Multicellular sporophyte

Unicellular spores

Generation 2

Specialized cells undergo meiosis to produce spores

Gametes fuse during fertilization

to become a zygote

aB

AaBb

Single-celled spores undergo mitosis to increase the number of cells in the

maturing gametophyte. Mature gametophyte produces gametes

by mitosis

Multicellular gametophyte

Ab

Haploid (1n) cells

Ab

aB

Unicellulargametes

Generation 3

Diploid (2n) cells

Multicellular sporophyte

Diploid (2n) cells

Unicellular spores of

gametophyte

Haploid (1n) cells

Pollengrain

Embryo sac

Gen. 4

AAbb

AaBb

AaBb

Unicellularzygote

aaBB

Specialized cells undergo meiosis to produce spores

Ab

aB

Allocation Trade-offs, Costs & Benefits, Constraints


vs.

Resources

There is no free lunchA jack of all trades is master of none

E.g., offspring or propagule size-number tradeoff


Size

Number

Each dot represents the life-history strategy of a given species in a given clade

Constraint lines and wedge-shaped distributions


Size

Number

Each dot represents the life-history strategy of a given species in a given clade

Design Trade-offs, Costs & Benefits, Constraints


vs.

Design: shape, function, etc.

A jack of all trades is master of none

Design Trade-offs, Costs & Benefits, Constraints

E.g., consider pond-breeding salamander speciesin ephemeral pools vs. stable ponds

What life-history strategy would perform best in each habitat?

Is there a “one size fits all” solution?

Often entails a reproduction – survival tradeoff

Semelparous vs. Iteroparous(Monocarpic vs. Polycarpic)

Photo of monocarpic talipot palm from http://www.etawau.com/Agriculture/IndexTrees.htm; photo of polycarpic coconut palm from http://www.hawaii.edu/cpis/MI/plants/ni.html

Monocarpic talipot palm Polycarpic coconut palm

r-selected vs. K-selected

The concepts of r-selection & K-selection originated with MacArthur & Wilson (1967)

General environmental or population-level correlates

Correlated organismal traits

DisturbancePopulation growth rate

K-selected r-selected

Body sizeLife spanParental investment in offspring

Developmental rateRate of maturationReproductive rate

Stability

CompetitiveRuderal (“weedy”)

Stress-tolerant

Grime’s Triangular Model

Image from http://hosho.ees.hokudai.ac.jp/~tsuyu/top/dct/lc.html;original concept from Grime (1977) American Naturalist

Competition = “tendency of neighboring plants to utilize the same quantum of light, ion of a mineral nutrient, molecule of water, or volume of space”

Disturbance = “process that destroys plant biomass”

Stress = “abiotic factor that limits vegetative growth”

Competition – Colonization Tradeoff

The concept was elaborated by Rees & Westoby (1997) Oikos

Competitive Ability

Colonization Ability

Tolerance – Fecundity Tradeoff

Original concept from Muller-Landau (2010) Proceedings of the National Academy of Sciences

Stress Tolerance

Fecundity

Ontogenetic niche shifts

Photo of hellgrammite (larva) and adult Dobson flies (Order Megaloptera) from Wikimedia Commons

Occur routinely in organisms with complex life cycles, but occur in other organisms as well

Aquatic larva Winged adult

David Lack

“Lack Clutch Size” = clutch size that maximizes the number of offspring that a parent can rear to maturity, given the tradeoff between

investment per offspring vs. number of offspring

A Classic Example: Clutch Size

Original concept from Lack (1947) Ibis

Experimental evidence through clutch-size manipulation experiments

Documents

Life History