Parental Care and Parental Care and InvestmentInvestment

Psychology 3107Psychology 3107

IntroductionIntroduction

In many species, eggs are lad after In many species, eggs are lad after reproduction and the young are left to fend reproduction and the young are left to fend for themselvesfor themselves

Parents can go make more…Parents can go make more…

However, parents do care for young in However, parents do care for young in varying degrees and ways in a number of varying degrees and ways in a number of speciesspecies

A DefinitionA Definition

Parental Investment:Parental Investment:

Anything done for the offspring that increases Anything done for the offspring that increases offspring survival, while decreasing the offspring survival, while decreasing the parents’ ability to produce additional offspringparents’ ability to produce additional offspring

So there is a cost!So there is a cost!

Sex DifferencesSex Differences

So, why is it then that, as a rule, females So, why is it then that, as a rule, females give more investment than males?give more investment than males? Reliability of paternityReliability of paternity

Pretty obviousPretty obvious Gamete releaseGamete release

‘‘my work here is done’my work here is done’ Association with youngAssociation with young

The females are there at birthThe females are there at birth

Parent Offspring ConflictParent Offspring Conflict

If there is investment, the offspring would If there is investment, the offspring would like it to go on forever, the parents, like it to go on forever, the parents, eventually want to have more babieseventually want to have more babies

OK, look at this genetically, the mother OK, look at this genetically, the mother and daughter/son share .5 of their genesand daughter/son share .5 of their genes

At some point, the mother would be better At some point, the mother would be better served by having another child.served by having another child.

Parent offspring conflictParent offspring conflict

The conflict continues The conflict continues until the parental cost = 2 until the parental cost = 2 x the benefits to the x the benefits to the offspringoffspringThen, it is in the best Then, it is in the best interests of the parent interests of the parent and the kid to have and the kid to have another kid show upanother kid show upNot just the continuation Not just the continuation of investment, but also of investment, but also the amount can be a the amount can be a bone of contentionbone of contention

Sex AllocationSex Allocation

‘‘Shall we have girls or boys dear?’Shall we have girls or boys dear?’

Not as odd a question as it seemsNot as odd a question as it seems

Think evolutionarilyThink evolutionarily

Proximate mechanisms?Proximate mechanisms? StressStress X v y spermX v y sperm TemperatureTemperature

Parent Offspring ConflictParent Offspring Conflict

The second kid would be The second kid would be related to the mom by .5, related to the mom by .5, to the other kid by .5to the other kid by .5

This is NOT in the best This is NOT in the best interests of kid no.1interests of kid no.1

It shares 1.0 of its genes It shares 1.0 of its genes with itself, only .5 with with itself, only .5 with new kidnew kid

The offspring are only ½ The offspring are only ½ as interested in parental as interested in parental costs as the parent iscosts as the parent is

More sex allocationMore sex allocation

Low Ranking pairs may have more Low Ranking pairs may have more females, high ranking pairs have more females, high ranking pairs have more malesmales ExampleExample

Zebra finchesZebra finches

More attractive males have more malesMore attractive males have more males

(Burley, 1981)(Burley, 1981)

ConclusionsConclusions

Trivers (1974) parent offspring conflict Trivers (1974) parent offspring conflict model is an amazing thingmodel is an amazing thing

You must think evolutionarilyYou must think evolutionarily

This stuff dovetails nicely with the stuff on This stuff dovetails nicely with the stuff on mating systemsmating systems