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
Taxon
Parental Care
Invertebrates
Uncommon in general, but female care mostly when present.
Fish
Ratio of genera with male only;biparental; female only care is 9:3:1
Amphibians
Female only and male only care equally common; low frequency bi-parental care
Reptiles
Either female alone or both parents
Birds
90% bi-parental care, but females invest more. Male only care very rare
Mammals
Females are in all species. 95% female care only. No cases of male only care

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
When sex ratios were female biased, males increased their likelihood of desertion, when the sex ratio was male biased, female desertion increased

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
Common in zebra finches and mallards

19. Sibling Rivalry and the Parent-Offspring Conflict
Intrabrood Conflict
Parent
0.5
0.5
Each offspring are more related to themselves than each other or their parents
There is no genetic reason for a parent to favor either offspring, but offspring are interested in their own welfare more than its sibling
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
There may be a time when a parent will want to terminate care to offspring 1 and put care into future offspring, but current offspring will want to maximize its benefits from the parent
0.5
Future Offspring
1.0

21. Parent Offspring Conflict
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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?
Insurance

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
Brood Hierarchy
Mean number of young surviving to two weeks
Good Food Supply
Poor Food Supply
Synchronous Hatching
2.9
1.3
Asynchronous hatching
2.3
2.1
Asynchronous broods have a size heirarchy that allows some chicks to pic on the others

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
They found that mothers 'set' the level they are prepared to work at before egg laying, depending on environmental conditions. 'Above this predetermined level, mothers are unresponsive to extra begging,' says Hinde, who reported the findings in Science.

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