Parental Care and Family Conflicts

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

Animal Families

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

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

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?

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

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

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

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

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

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

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

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

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

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

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

Parental Investment Females may also invest more when they are paired with an attractive male Common in zebra finches and mallards

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

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

Parent Offspring Conflict ADD DESCRIPTION HERE

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

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

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

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

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

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

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

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

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

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.

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

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

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