Parental Care Patterns Who should provide care? How much care should be provided? When should care be terminated? Who should receive care?

Insect parental care

Distribution of parental care in vertebrates Teleost fishes = 21% of families show PC –61% have male parental care Amphibians = 71% show PC –50:50 maternal:paternal Birds = 100% show PC –Usually biparental, sometimes one sex Mammals = 100% show PC –Usually maternal, sometimes biparental

Alternative hypotheses for providing care Confidence of paternity –Expect parent with highest certainty to be parental Order of gamete release –First to deposit gametes can desert Association –Sex nearest to offspring when care is needed

Parental care in fishes and frogs

Alternative hypotheses for providing care: evidence Confidence of paternity (fish and herps) –Internal fertilization - 86% maternal care –External fertilization - 70% paternal care Order of gamete release –Simultaneous fertilization (most species) - 78% paternal –Other species - male deposits first, but doesn’t leave Association (fits data the best) –Territorial males have external fertilization

Two or one parents? Birds and mammals are more likely to exhibit biparental care because parents feed young and two are often better than one Fishes and amphibians typically only guard eggs and don’t feed young. One parent usually can do this as well as two. –Exceptions include some cichlids that show biparental care

Why male only parental care? Randall’s jawfish Mallee fowl Stickleback Seahorse

Parental care can cost females more than males Mouthbrooding results in weight loss due to reduction in feeding, and the cost of brood care is higher in females than males

Growth, fecundity and paternal care

How much care to provide? Parental investment: “any investment by the parent in an individual offspring that increases the offspring’s chance of surviving at the cost of the parent’s ability to invest in other offspring (Trivers 1972) Costs of parental care include –Reduced future survival –Reduced mating opportunities

Parental care can decrease adult survival

Parental care decreases mating opportunities A female-biased sex ratio increases the cost of brood care for males because parental care detracts from mating

Parental investment changes over time

Parent-offspring conflict

Assume fixed total resource that can be used to feed offspring Parents want to distribute resource equitably to all n offspring Offspring want more than 1/n but not all since they are related to siblings Difference between parent and offspring optimum increases as relatedness decreases Wallaby conflict

Parent-offspring conflict: how much care to provide Parent is equally related to all offspring, but offspring are less related to sibs than themselves. Assuming full siblings, i.e. r = 1/2 Level of parental investment Benefit or cost to parent B C Max. inclusive fitness for parent C/2 Max. inclusive fitness for offspring B - measured in +units of RS of current offspring C - measured in - units of RS of future offspring

Begging loudness increases as relatedness within nest decreases Brown-headed cowbird

Parent-offspring conflict: time of weaning (Full-sibs) (Half-sibs)

Parental investment and maternal age If reproductive value declines with maternal age, then older females should be willing to expend more on parental care

Who should receive care? Concorde fallacy: past investment should not determine future investment - only prospects for future success Expect parents to use honest indicators of offspring quality to allocate care

Chick color affects parental care in mixed broods of coots Control broods were unaltered (orange) or had orange feathers trimmed (black) Experimental broods had 1/2 orange, 1/2 black chicks Chick color likely indicates offspring health

Sibling competition

Sibling conflict