BIOL3046 Lecture Notes - Lecture 19: Operational Sex Ratio, Egg Cell
5 Jul 2018
School
Department
Course
Professor
Animal Behaviour BIOL3046 460381099
Lecture 9: Parental care and mating systems.
Concord fallacy
• Past investment alone is irrelevant to decisions about the future.
Operational sex ratio
• Sex ratio when pregnant females are taken out of the count.
• Pregnant females are unable to mate, therefore are not part of the operational sex ratio.
Every offspring has two parents
• Better care for young when sex ratio is even. both sexes better off staying together and
caring for young.
Female argument Concord fallacy.
• Females should be the caretakers because costs of producing ova exceed those of sperm
so not deserting offspring avoids females wasting the investment they’ve made in the
egg.
Male argument
• When females care more males will be looking for females, so males should compete
more and have
• less time to care.
• Fisher condition: males can’t reproduce faster than females if the sex ratio is even
therefore males with preferable traits should spend more time competing until finding a
mate becomes very hard then it is better to invest more in caring for offspring
(frequency dependence shifts levels of care).
• Male uncertainty that offspring is theirs when females are internally inseminated and
can mate multiply, will reduce selection on parental care. Example: Male songbirds
invest more in incubating eggs when females are more faithful.
Good to be faithful
• Females that are more monogamous tend to have males that invest more in incubation.
Example: Dunnock.
Good to be unfaithful
• Example: Dominant male chimp thinks he is the father of all young. Females mate with
other males who might take over the dominance of the group. This means that the other
Document Summary
Concord fallacy: past investment alone is irrelevant to decisions about the future. Operational sex ratio: sex ratio when pregnant females are taken out of the count, pregnant females are unable to mate, therefore are not part of the operational sex ratio. Every offspring has two parents: better care for young when sex ratio is even. both sexes better off staying together and caring for young. Concord fallacy: females should be the caretakers because costs of producing ova exceed those of sperm so (cid:374)ot deserti(cid:374)g offspri(cid:374)g a(cid:448)oids fe(cid:373)ales (cid:449)asti(cid:374)g the i(cid:374)(cid:448)est(cid:373)e(cid:374)t the(cid:455)"(cid:448)e (cid:373)ade i(cid:374) the egg. Example: male songbirds invest more in incubating eggs when females are more faithful. Good to be faithful: females that are more monogamous tend to have males that invest more in incubation. Good to be unfaithful: example: dominant male chimp thinks he is the father of all young. Females mate with other males who might take over the dominance of the group.
