Evolution of Reproductive rates

Lecture 1

Behaviour

• descidion makinng

  • whre to live, what to eat, who to mate with , many offsrping, how much time to spend on caring for offsrping

• Natueral selsection should favour these things

• BUT

• depends on ecological stage on which individuals play their behaviout

  • physical environemnt

  • biotic environment

Proximate vs Ultimate questions

Lion prides: tkae over males kill the cubs

Proximate cause

• hormones

Ultimate cause

• So females get back into oestrus sooner

Group selection theory

• Indivudals restrain their reproduction for the good of the group

Why group over individual selection?

Selfish individuals with die out

• over exploit their resources

Testing altruism: Optimal clutch size (Great tits)

Experiement

• swapped eggs among nests to create different brood sixes

Results:

• larger brooder= survival per young declined

• each chick got less food

• reaches an OPTIMUM: balance between benefit of more kids to the chances they will not survive

Conclusion:

• results matched the prediction

Problem witht he experiement

Optimum clutch size calculated observed to be smaller in the real world

2 Hypotheses to why clutch size smaller than optimum

1. Ignored costs of egg production

2. Ignored trade off of increased parental care and parental mortality

Testing hypothesis 1

Costs of forming and incubating extra eggs= reduces success?

Experiment: increased brood size by 2 in three different ways

• adding 2 chicks

• adding 2 eggs (so incubate two more)

• Forcing parents to have 2 more (take them away then replace etc)

Results of testing hypothesis 1

Costs of forming and incubating an extra 2 eggs did not reduce success

Testing Hypothesis 2

Optimal clutch size to maximise lifetime reproduction is less b*

• Compare the adult mortality to optimum brood size

• Find where the gap between mortality and brood size is the greatest

  • minimum adult death to max brood

Hypothesis 2 results

Results:

• extra mortality is why females lay fewer eggs than predicted

  • Maximises lifetime reproductive success

• Female fitness= (female survival to next breeding season) + (0.5 x no.offspring surviving to next season)

  • only 0.5 relatedness to offspring

Overall conclusions of optimum clutch size

• Females made to pay full costs did less well than controls with their natural clutch size

• Only extra chicks given for free did better

Trade-offs involved in maximising Lifetime Reproductive Success

1. numbers v quality of offspring

2. reproductive effort v parental survival

Variation between species in these two trade-offs

May explain why different species have different life histories

Example of differing trade-offs in different species: Song birds in temperate vs tropics

Temperate:

• larger clutches

  • seasonal flush of food (not all year round)

• Future chances of reproduction are lower

  • Pays to put more effort into breeding

• Fast life history

Tropics

• resources all year round

• Slow life history

Factors that can cause differences in life histories of different species

• Food availability/ climate (when food come in)

• extra-pair paternity?

• Predation

• Cooperation?

When chances of future reproduction are very slim

Semelparous

• put all resources into one big bang reproductive effort

  • Pacific salmon

Extra pair mating

• The parents of the offspring are not always the same

  • no. offspring not always a good measure of reproductive success

• e.g Red-winged blackbirds in N.America

  • 20% of male’s reproducive success is from extra-pair mating

• What this means??

  • Measuring indiidual reproductive success is harder to look at

Influence of predation of life history evolution: guppies

High predation = fast life history

• quicker, larger broods at earlier age

Low predation= slow life history

• older age, less offspring

Guppies continued: when high pred put in low pred

• took 11 generations to shift life history

• breed later and smaller broods

Reproductive effort per brood varies with future chances of reproduction

Cooperation among male lions to take-over a pride

Reproductive success per coalition increases

and

so does average success per male

However: DNA profiles show…

Strong reproductive skew

• Subordinate males have little or no success

Why do subordinate males cooperate then?

To do with relation:

• Related males

  • Join larger groups with brothers

  • Gain no paternity… BUT

  • gain indirect fitness

• Unrelated males

  • only join small teams

  • make sure they will have some paternity