Lecture 11 - evolution of stable biparental care Flashcards
why is the evolution of biparental care problematic ?
Parental care is costly and life history theory predicts that current investment should be traded off against future survival and reproduction. In systems with biparental care, each parent bears the costs of their own investment individually, while the benefits of their investment (i.e. offspring fitness) are shared= “A TRAGEDY OF THE COMMONS” (Hardin 1968)
what are 2 theoretical solutions to the investment game?
1) ‘sealed bid model’ (Houston and Davies 1985)
2) ‘negotiation model’ (McNamaara 1999)
describe the ‘sealed bid model’
- parents’ effort evolves through time
- Each parent has an optimal response to partner’s effort and an ESS may be reached at which there is stable investment by both parents
what are the other 3 possible outcomes of the sealed bid model?
1) Only female care
2) Only male care
3) The point when both parents provide care is unstable
describe sexual conflict over care in the penduline tit
male builds nest to attract female and she lays her eggs in it
- she may leave after laying eggs to leave male to do all the care
- or when she’s laying the eggs the male might leave
One or both parents desert during egg-laying:
- 50-70% female only care
- 5-20% male only care
- 30-40% both parents desert
for the penduline tit how is the strategy decided?
the best strategy depends on what the other options are e.g. if there is spare males the female will leave and vice versa - in this case both parents thing the best ESS is to abandon and find another mate
- biparental care in this system is very unstable
when thinking about the sealed bid model is an individual’s effort fixed? e.g. an individual’s effort may be repeatable across different breeding attempts and in a couple of cases has been shown to be heritable, i.e. partly genetically determined
NO – in most species, parents vary their effort in relation to: - nestling age - brood size - food supply - number of carers, etc
because the sealed bid is unrealistic due to individual efforts not being fixed, what new model did they come up with?
‘negotiation’ model
what is the ‘negotiation’ model
parents respond to each other in real time
- more inclusive of potential influences on parental effort
critically both the negotiation model and the sealed bid model predict what?
Stable biparental care evolves only when one parent compensates incompletely for reduced effort by partner
The general prediction of incomplete compensation has been empirically tested many times- what are the 4 types of studies?
(a) Removal experiments
(b) Handicapping experiments
(c) Testosterone experiments
(d) Meta-analysis
describe removal experiments
remove one parent, does other compensate incompletely by increasing their effort but not enough to make up for the shortfall?
describe a removal experiment study and what was the outcome?
Orange-tufted sunbirds
- remove male from nest
- ‘widowed’ female increases effort
- compensation incomplete
- total reduction in effort had a consequence for the chicks - reduction in body mass
does mate removal fulfil the negotiation theory?
doesnt fully
describe handicapping experiments?
reduce effort of one parent, does other compensate incompletely?
- put some weights on one of the parents making a handicapped parent - therefore reducing their effort
- or tie some wings together
- both only have short term effects
