Sexual Selection III (mating systems) Flashcards
what are the types of mating systems
- monogamy
- polygyny
- polyandry
- polygynandry
mating systems: number of participants - monogamy
- 1 male
- 1 female
mating systems: number of participants - polygyny
- 2 or more females
- 1 male
mating systems: number of participants - polyandry
- 1 female
- 2 or more males
mating systems: number of participants - polygynandry
- 2 or more females
- 2 or more males
explain how monogamy is rare
- no mammal has been found to be truly monogamous
- many social conflict behaviors evolved to prevent extra pair copulations (EPCs) in species with social monogamy
polygyny
- common in mammals
- common male-male fights (usually large and dominant males)
polygyny - why are male-male fights common (what is the outcome)
- due to the big reproductive skew in males
- few males have large fitness and many have little/no fitness
polyandry - Gunnison prairie dog example (benefits)
- females mate in multiples and results in them getting more offspring
- of those females than give birth, success of pups had increased with the number of males
polyandry - Jacanas example (outcome)
- females mate multiply
- all males get the chance to mate and are taking care of the nest
- results in a big reproductive skew in females
- lots of females have zero/little fitness and it selects for larger body size and selection of aggressive behaviors (like infanticide)
polygynandry - Bonobo example
- all males and females mate with multiple males and females
- all raise offspring communicably
- there is no aggression or violence
when would sexual selection on females be expected to be strongest
- polyandry
- if assume equal sex ratio, lots of females have zero mates and some females have lots of mates
- creates a big skew
when would sexual selection on the sexes be expected to be equal
- monogamy and polygynandry
- expect skew to be the same in both sexes bc they can all find mates
Aside from mating system, what other factors might cause there to be stronger sexual selection on females than males
- parental care
- Male parental investment per offspring may be = or > female parental investment
- If male invest > female invest, access to mates will be a limiting resource for females
male parental investment > female parental investment - pipefish experiment
- prediction: males are choosier bc they are investing more per offspring
- results: match prediction, males are very selective about female traits. females do not discriminate
explain sexual dimorphism in humans
Males are on average taller than women
what factors could limit studying sexual selection in humans
limited to correlated studies bc of ethical reasons
what selective pressures could have lead to dimorphism in humans
- inter- and intrasexual
sexual dimorphism in humans - is there more selection on men than there is on woman to have multiple partners?
- the studies are limited and ones that we have show conflicting findings
- Finland: yes
- Tanzania: no
what are the 2 hypothesis for why men are taller than woman
- intersexual selection: woman prefer taller men
- intrasexual selection: taller men win fights
sexual dimorphism in humans: intrasexual - men do compete over access to mates, but so do women. do men compete more intensely?
- assume that same-sex homicide = conflict
- it was found that in all cultures, male same-sex homicide is higher than female
- most perpetrators are in reproductive years (18-35)
- researchers argue that this is evidence of sexual selection for higher competition among men
sexual dimorphism in humans: intrasexual - is there a fitness advantage to contest behavior for males
- yes
- research shows more competitive males (killers and zealous warriors) have more offspring
sexual dimorphism in humans: intersexual - female choice
- yes
- Polish men that have children are taller than men without
- same in the US at West Point
sexual dimorphism in humans - what about selection on woman
- may be stabilizing selection on height of women
- woman of slightly less than average height had more children than wither shorter or taller woman
- due to natural selection (not sexual) bc those woman were healthier