How Long do You Care?

· Besides identity of carer, also have selection on type of care and length of time of care

· Both parents and offspring are essentially selfish

· Parents care only until benefit to survivorship is overtaken by costs to future reproduction

· Young want care until benefit is maximized

Hamilton’s Rule

· Kin selection – because parents and offspring share genes, selection may favor things that benefit one at a cost to the other

· A trait will be favored if:

(relatedness to recipient) x (benefit to recipient) – cost to donor > 0

Parent – Offspring Conflict

· Each parent shares half of its genes with each offspring

· Siblings share (on average) half of their genes

· Multiple matings may reduce these numbers on average

Siblicide

· Minor aggression and competition between siblings is fairly common

· In extreme cases, offspring will kill their siblings

· Not uncommon in birds:

- Large raptors, gannets, boobies, herons, egrets, skuas

- Also found in hyenas

Why Siblicide?

· Do parents benefit or are they just powerless to stop it

· “Obligate siblicide”

· In large raptors

· Lay two eggs, but can only raise one

· “Facultative siblicide”

· Response to variable environment

Parental Favoritism

· Parents may treat young differently

· First eggs may have more androgens and testosterone (cattle egrets)

· Loud beggers may get more food (songbirds)

· Visual signals may cue parental care (coots)

· Sex of offspring may also factor in

Parental Discrimination

· Some parents may care for young that are not their own

· Kin recognition

o Parents in colonial populations will invest more in kin recognition than those that nest singly

Brood Parasitism

· May be intra-specific or inter-specific

· Benefit to parasite, but cost to adopter

· Why don’t adopters kick out the parasite?

· Costs of discrimination

· Costs of mistakes

· “Mafia” hypothesis

Adoption

· Sometimes it may benefit parents to take in “genetic strangers”

o Fathead minnows

§ Males will take over nests of other males, but adopt the eggs

§ Females are attracted to parental males

o Choughs

§ Groups may kidnap young from other flocks

§ Kidnapped one may become helper at nest

o Mouth-brooding cichlids

§ Females of three species may mouth-brood young of a fourth species

§ Cost is low and it may reduce predation risk to her young