Week Five Flashcards
What did Robert Trivers derive from Bateman’s principles?
He figured out that the principles were not from innate male/female differences, but from who invests more energy into reproduction.
-He reasoned that in species where the sexes reverse roles, with males investing more into offspring than females do, we should see a reversal in the pattern of the Bateman gradient.
What is a reversal in Bateman’s Principles?
Females have more variance in # of offspring than males do.
Females have more variance in # of mating partners than males do.
Females benefit strongly from increased partners.
Which sex is the ‘limiting resource’ in a given population?
The sex that invests the most in the progeny will be the limiting resource in reproduction.
This sex should be the choosier, the other being the more strongly sexually selected and therefore more invested in intrasexual competition and displays.
Why is there a role reversal in Sea Kangaroos?
Hippocampidae and Syngnathedae are a couple species where males ‘get pregnant’
- Eggs are moved from the female to male via a tube-like ovipositor.
- -> Seahorse males hold eggs in a pouch, where they are fertilized
- -> Sea dragons carry the eggs on their backs
What is Paternity Assurance?
Male nest-building and nurture probably evolve from cooperative rearing, to further assure paternity.
- -> If the odds of being cuckolded are great, then better to make the female deposit her eggs with you, unfertilized.
- -> Investing in offspring that are not yours is a bad outcome for males.
How do brown-headed cowbirds (brood parasite) increase their fitness?
They do not raise their own young, instead laying their eggs in the nest of other bird species.
- -> Therefore, the young are not exposed to species-typical visual and auditory information like other birds.
- -> They develop singing, social and breeding behaviors of nestmates.
–> Even evolve to have eggs that look like other bird, so that the female guarding the nest will not destroy it.
Why do sticklebacks SEEM to counter Bateman’s principles?
They build nests and tend to the eggs of females.
- Yet they are still the showier sex and females are the choosier sex.
this is because males can care for 8+ broods of eggs simultaneously.
What are some criticisms of Bateman’s Principles?
He had other unpublished results showing that females benefited from multiple partners.
- People think that stereotypes limit exploration of diversity.
- Also implies that sperm are cheap and mating is without risks.
- -> Large # of sperm transferred for each ejaculate
- -> STDS
Also implies that only benefits available to females come from mate choice.
- ‘good genes’, better territories and so on
- overlooks the potential benefits of polyandry to females
What did Brown et al. study with regards to Bateman’s principles?
Studied the evolution of human sex to discover links to Bateman’s principles.
According to Brown et al. do humans follow Bateman’s principles?
Males do have a higher variance in the number of offspring produced than females do.
- Variable and related to mating system.
- Far from universal predictor but some have argued them for behavior.
Males in western populations do have higher variance in # of mates than females (based on remarriage rates), but difficult to assess.
- In polygyny systems, most breeding males are still monogmous, even if polygyny is permitted.
- Although polygyny exists for 83% of the societies surveyed, these are small populations.
According to Brown et al. do humans follow Bateman’s gradient?
There is a closer correlation between the number of mates (MR) and reproductive success (RS) in males than in females.
-Evidence is positive but weak.
Might depend on the cost of child rearing and other factors.
- IF demand for paternal investment is high, may lead to a diminishing returns relationship between MR and RS for men.
- Do “wives” cooperate in polygyny to make a more productive, wealth-enhancing unit? Fitness gains could accelerate with MR.
What evidence/data sets support the Bateman gradient in humans?
Several data sets show positive Bateman gradient for men in offspring #
- -> None show this for women, although other benefits to polyandry may exist.
- -> Few data are available on fertility gains from extra-partner mating in humans.
Outline the parish records from C18th - 19th Norway used to study the Bateman gradient in humans.
Contrasted a fishing community (low wealth disparity) vs. an agricultural community (high wealth disparity)
-Looked at reproductive success in single marriage and with remarriage.
Study found that:
- Sexual selection was strongest upon the wealthy, for both men and women,
- For men the greatest contributor to “breeding success” in remarriage was age differential to second spouse.
- For women the greatest contributor was their own age, with 35 being optimal.
-Both men and women “benefitted” equally from remarriage, as measured by the Bateman Gradient.
