Sex allocation

What is sex allocation?

Allocation of resources to male vs female reproduction in sexual species

What does dioecious mean?

Describes organisms that have separate male and female individuals.

What different types of sex determination systems are there?

• GSD - genetic sex deterimaiton

  • chromosomal

• ESD - Environmental sex determination

  • (Temperature dependent)

  • Snapping turtles - extreme temps (F)

    • Chelydra Serpentina

  • Sea turtles, green or hawksbill, high temps (F)

    • global warming.

What did bull 1980 find ?

Temperature dependent sex determination in lizards, turtles, c. snapping turtle.

Lizards - Low temps (F)

Turtles - High temps (F)

C. snapping turtle (chelydra serpentina) - extreme temps (F)

Is there a huge diversity in sex determination?

Yes

What is the Dusing-Fisher theory of equal investment?

• Consider excess of males, each would obtain less than one mate,

• Value of females greater, favouring increased production of females

• Natural selection favours equal investment.

What are the implications of Dusing-Fisher theory of equal investment?

• If F and M are equally costly, all individuals should invest equally in both sexes

• If costs are unequal, selection favours cheaper sex.

  • Costs in broader terms

What are implicit assumptions of Dusing-Fisher (1880s/1930) theory?

• No differential effects of environmental conditions on M or F resulting in differential survival

• No interactions (cooperative and competitive) between relatives

When these are not → variation predicted from Fisher ratio.

What are the 4 instances of selection for biased Sex ratios?

• Local resource competition (LRC)

• Local mate competition (LMC)

• Local resource enhancement (LRE)

• Maternal condtion

What kind of Sex ratio does Local Resource Competition cause and why?

Male biased

• Male dispersal, matrilocal females

• Daughters compete with mothers over limited resources

• LRC reduces daughters value

• Silk + Brown (2008) → significant but weak effects of 102 primate species

What kind of Sex ratio does Local Mate Competition produce and why?

Female biased

• Strong mate competition between siblings, only one of 2 sons to mate with female

• Females assess LMC and adjust Sex ratio depending on number of eggs laod by other females

What kind of Sex ratio does Local Resource Enhancement produce and why?

Depends on environmental macros

• In some coop breeders, offspring of one sex more likely to be helpers

• Komdeur et al 1997 - high quality territories have female biased ratios (90%) and poor territories male biased (80%) → LRE and LRC occur

  • high quality territory maximise reproductive success of offspring.

How does maternal condition influence Sex ratio?

• Trivers and willard 1973 - adjust ratio depending on conditions

• Mothers in good condition produce more costly offspring

  • Sons gain higher fitness from being higher quality

    • bigger sons beneficial for reproducing mates

      • greater size = greater reproduction success

    • Smaller females - doesn’t make too much difference.

Can GDS systems have female Sex ratio adjustment?

Yes

What do charnel and bull 1997 say?

Differential fitness consequences for males an females in different environments

• matters more for males to develop in optimal conditions

  • e.g. they could be Smaller in colder environments

• poor conditions price average females but poor males.

What did McCabe et al 1997 find in water shrimp?

Males production early, so bigger than females at breeding

• size at breeding determined by time to grow before breeding season

• the earlier born, the bigger

• larger females produce more eggs.

• larger males more successful at finding mates

• but size dependency of fitness greater in males.

Give an example of social sex determination q

Sex change

• Changes sex during life if fitness for one sex changes with age

• Bluehead Wrasse, from F→ M

• Males set up territory, females choose mates with largest territory.

• Removing super males means the next largest females turn into males and become colourful.