Hatching asynchrony decreases the magnitude of parental care in domesticated zebra finches: empirical support for the peak load reduction hypothesis. Ethology 120: 577-585 Mainwaring Lucy Hartley

Hatching Asynchrony Offspring from a single reproductive event hatch/born over extended period of time

Hatching Asynchrony Offspring from a single reproductive event hatch/born over extended period of time Hypotheses concerning the functional significance of hatching asynchrony fall into four broad types. Hatching asynchrony might: arise because of selection on the timing of events during the breeding cycle; facilitate the adaptive reduction in brood size; increase the energetic efficiency of raising the brood, or be non-adaptive and result from environmental or phylogenetic constraints . From Magrath 1990

Peak load reduction hypothesis

Hatching Asynchrony Title –Include the species name! First criticism one species one species not mentioned one species

Hatching Asynchrony -seems maladaptive – reduced survival of later born offspring Incubation behaviour ⇒ level of asynchrony ∴ hatching patterns should be an optimal strategy for parents AND Benefits offspring – reduces sibling competition & begging intensity ?

Hatching Asynchrony Support for hypotheses - mixed Mock & Schwagmeyer (1990) -Energy savings for parent - minimal -need large clutch size and extreme asynchorny Empirical support – depends on the species worked on

What does this have to do with load reduction hypothesis? Hatching Asynchrony Final point in introduction - -may have a role in sexual conflict -if parents provision differently ∴ have parent-offspring conflict & male-female conflict at the same time What does this have to do with load reduction hypothesis?

Species used and Hypotheses Domesticated Zebra finch – Taeniopygia guttata Replicating study done with wild finches -lay egg/day for 5 days -incubate from outset -early hatchlings get more food ⇒ grow larger Hypotheses 1) Parental feeding effort will be greater in synchronous broods 2) Male and female will differ in provisioning

♂ ♀ Materials and methods Nest box Used males and breeding females What does “breeding” female mean?

Materials and methods -took eggs each day & replaced with artificial egg - Put in a bowl to mimic nest conditions “turned daily to prevent the yolk from settling” ?? -no effect of manipulations on hatching success

Materials and methods Quantifying parental behaviour -videotaped for 3h – start between 9 and 10 -recorded when chicks were between 8 and 13 days old -chicks marked with white correction fluid Recorded 1) which nestling got food 2) Duration of regurgitation feeding 3) Maximum begging intensity score for each nestling

Materials and methods Quantifying parental behaviour Recorded 1) which nestling got food 2) Duration of regurgitation feeding 3) Maximum begging intensity score for each nestling Said this was a measure of feed load size 4 point scale

Materials and methods Statistics Tested covariance of a number of factors What they did is poorly explained

Materials and methods Statistics

Where is synchronous vs asynchronous? Results Where is synchronous vs asynchronous? No mention of females

Justification?? Equations?? r2 ?? p values??

Discussion 1. Main finding – parental feeding effort lower for asynchronous broods ??? Hatching asynchrony decreases the magnitude of parental care in domesticated zebra finches: empirical support for the peak load reduction hypothesis.

Discussion 1. Main finding – parental feeding effort lower for asynchronous broods 2. No benefits to nestlings from reduce parental workload 3. No difference in begging intensity between the hatching patterns -rejection of sibling rivalry reduction hypothesis

Discussion 1. Main finding – parental feeding effort lower for asynchronous broods 2. No benefits to nestlings from reduce parental workload 3. No difference in begging intensity between the hatching patterns -rejection of sibling rivalry reduction hypothesis 4. No support for the parentally-based favouritism hypothesis Not clear from their results if this is valid or not - Especially given the way they measured food delivery

Discussion Final point in discussion -dealing with domesticated birds -asynchrony good for parents but no advantage for offspring How does this related to theories of parent-offspring conflict?

Discussion Final point in discussion -dealing with domesticated birds -asynchrony good for parents but no advantage for offspring Compared their study to Gilby et al (2011) - similar result except for reduced begging in wild birds Domesticated Wild -ad lib food -search for food -frequent feedings -less frequent feedings -predator free -predator present -chicks beg more -chicks beg less

Discussion Are we then functionally dealing with the same species?

Discussion Is this evolution or just phenotypic plasticity? Are we then functionally dealing with the same species?

Questions??