Parental Care and Family Conflicts

1. Parental Care and Family Conflicts

2. Animal Families • Families are not collective units helping each other • Instead interacting organisms are aligned insofar as this reflects their degree of relatedness • Mothers are equally related to all their offspring • But each sibling is more closely related to itself than either its siblings or parents • Offspring can compete with both present and future siblings

3. Animal Families

4. Parent-Offspring Conflict • Parental care differs amongst many species in the animal kingdom

5. Parental Care and Animal Kingdoms

6. Parental Care • Female care is the most common with internal fertilization and male care with external fertilization • Why does fertilization mode influence which sex cares?

7. Parental Care and Fertilization • 3 hypothesis • 1) External fertilizers are more likely to be certain they are the fathers at the time of oviposition • They avoid all the sexual conflict between internal fertilizers • But it is not yet known whether paternity certainty is greater with external fertilization • And knowledge of fatherhood is likey species or mating system specific

8. Parental Care and Fertilization • 3 hypothesis • 2) Internal fertilization gives the chance for males to desert females • Male fish who externally fertilize must wait on females to lay eggs • Rejected based on data • Most external fertilizers simultaneously release-so both have equal opportunities to desert

9. Parental Care and Fertilization • 3 hypothesis • 3) Association with the embryos preadapts a sex for parental care • Internal fertilization, females are closely associated with the embryo • But in external fertilizers, eggs are laid in the males territory, and thus males are associated • Further, males will continue to defend territories to maximize further matings • BEST EXPLANATION

10. Parental Investment • Any investment by the parent in an individual offspring that increases the offspring's chance of surviving at the cost of the parents ability to invest in other offspring • Includes • Guarding Fish guarding and mouth brooding • Feeding

11. Parental Investment • What is the optimum parental investment per offspring? • Trade-off between offspring quantity and quality within a brood • More very tiny offspring • Less larger offspring

12. Parental Investment • This is a common trade-off theme amongst broadcast spawning invertebrates • Many small offspring may overwhelm planktivorous predators allowing more to make it to larval stage- but few will survive because they are allocated to few resources • Fewer larger offspring chances them all getting eaten but those that make it have a higher chance of making it to adulthood

13. Parental Investment • Wild vs Hatchery Reared Salmon • Salmon taken from the wild increase the mass of their eggs in hatcheries

14. Parental Investment • But parents must also optimize their total reproductive output • Too large a brood can • Increase a parents chance of mortality • Reduce their future fecundity

15. Parental Investment • When male gobies have to spend more time fanning their eggs by decreasing oxygen levels, they are more likely to abandon their next clutch

16. Parental Investment • Opportunities of further matings can also influence parental investment • St Peter’s fish, mouth breeding cichlid

17. Filial Cannabalism • It may also be beneficial to consume one’s own young to improve care for the others • Sergeant fish alternate between a mating phase and a parental phase • If male clutches are reduced by 75% on the first day of their parental phase, they are likely to cannibalize the rest of the brood and revert to mating phase

18. Parental Investment • Females may also invest more when they are paired with an attractive male

19. Sibling Rivalry and the Parent-Offspring Conflict • Intrabrood Conflict Parent 0.5 0.5 Offspring 1 1.0 Offspring 2 1.0 0.5

20. Sibling Rivalry and the Parent-Offspring Conflict • Interbrood Conflict Parent 0.5 Current Offspring 1.0 0.5 0.5 Future Offspring 1.0

21. Parent Offspring Conflict

23. Evidence of Sibling Rivalry • Facultative Siblicide • Interbrood conflict and fur seals • In years of poor condition, 23% of pups are born while their older siblings are still being nursed • Many of these new pups either die of starvation or are killed when they are attacked by their sibling • Seal pups

24. Evidence of Sibling Rivalry • Facultative siblicide • Intrabrood conflict and the blue-footed booby • Lay 2 eggs four days apart, so there is always an older sibling • The older chick has a size advantage • When food is rare, the younger chick rarely gets fed • When the older chick is 20-25% below its expected weight it attacks and pecks at its younger sibling causing them to be reluctant to beg for food

25. Evidence of Sibling Rivalry • Sibling rivalry in osprey • Obligate siblicide • In some birds of prey, the older sibling always kills the younger sibling • So why do the parents lay two eggs at all?

26. Sibling Relatedness Affects the Rivalry • As relatedness to other offspring declines, less related siblings become less genetically valuable, so the cost of depriving them of food decreases

27. Sibling Relatedness Affects the Rivalry • Increased offspring selfishness when broodmates are of lower relatedness • Nestlings red mouth is a hunger signal • Birds with high rates of extra pair paternity have redder mouths • Nestlings also beg more vigorously in species with extra pair paternity

28. Parent Offspring Conflict • Sibling Rivalry might sometimes benefit parents even if they are equally related to all offspring • Arms race between parents and siblings can be an extreme result of parent offspring conflict

29. Parent Offspring Conflict • Brood hierarchies produced by asynchronous hatching result in higher fitness in lean periods

30. Parent Offspring Conflict • Conflicts during pregnancy • Genomic imprinting- imprinted genes behave differently depending on which parent they come from • When females mate with many males, a male gene may act to sequester resources for the offspring in utero • Genes typically encode insulin like growth factors and their receptors

31. Parent Offspring Conflict • Can this conflict be resolved? Or is an arms race and battleground necessary? • A resolution can occur when offspring demand and parental provisioning become co-adapted, and each develops honest signaling • A stable strategy involves offspring only increasing its demand with need, and parents requiring an honest signal for that need

32. Parent Offspring Conflict • Example with Canaries • Nestling beg more vigorously when hungry and parents provide more food as begging signals increased • Nestlings didn’t beg extra because extra begging was shown to be costly • Siblings that begged for longer in an experiment has a lower mass gain

33. Parent Offspring Conflict • Begging is also genetically encoded- so parent feeding and offspring begging are related • Chicks from more generous mothers tend to beg more than chicks from less generous mothers

34. Brood Parasites • Brood parasites lay their eggs in the nest of others (hosts) and trick the hosts into providing all the parental care • Cuckoos • Parasitic offspring should behave exceptionally selfishly because they are unrelated to the host and the host offspring

35. Brood Parasites • Sometimes these ‘parasites’ are tolerated • Cowbirds are also brood parasites • But they don’t expel the hosts young • The collective begging of the brood evokes a higher level of provisioning by host parents which cowbird chicks exploit by grabbing more food than the host’s young