Sexual Selection III (mating systems)

Question 1

what are the types of mating systems

Answer 1

• monogamy
• polygyny
• polyandry
• polygynandry

Question 2

mating systems: number of participants - monogamy

Answer 2

• 1 male
• 1 female

Question 3

mating systems: number of participants - polygyny

Answer 3

• 2 or more females
• 1 male

Question 4

mating systems: number of participants - polyandry

Answer 4

• 1 female
• 2 or more males

Question 5

mating systems: number of participants - polygynandry

Answer 5

• 2 or more females
• 2 or more males

Question 6

explain how monogamy is rare

Answer 6

• 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

Question 7

polygyny

Answer 7

• common in mammals
• common male-male fights (usually large and dominant males)

Question 8

polygyny - why are male-male fights common (what is the outcome)

Answer 8

• due to the big reproductive skew in males
• few males have large fitness and many have little/no fitness

Question 9

polyandry - Gunnison prairie dog example (benefits)

Answer 9

• 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

Question 10

polyandry - Jacanas example (outcome)

Answer 10

• 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)

Question 11

polygynandry - Bonobo example

Answer 11

• all males and females mate with multiple males and females
• all raise offspring communicably
• there is no aggression or violence

Question 12

when would sexual selection on females be expected to be strongest

Answer 12

• polyandry
• if assume equal sex ratio, lots of females have zero mates and some females have lots of mates
• creates a big skew

Question 13

when would sexual selection on the sexes be expected to be equal

Answer 13

• monogamy and polygynandry
• expect skew to be the same in both sexes bc they can all find mates

Question 14

Aside from mating system, what other factors might cause there to be stronger sexual selection on females than males

Answer 14

• 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

Question 15

male parental investment > female parental investment - pipefish experiment

Answer 15

• 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

Question 16

explain sexual dimorphism in humans

Answer 16

Males are on average taller than women

Question 17

what factors could limit studying sexual selection in humans

Answer 17

limited to correlated studies bc of ethical reasons

Question 18

what selective pressures could have lead to dimorphism in humans

Answer 18

• inter- and intrasexual

Question 19

sexual dimorphism in humans - is there more selection on men than there is on woman to have multiple partners?

Answer 19

• the studies are limited and ones that we have show conflicting findings
• Finland: yes
• Tanzania: no

Question 20

what are the 2 hypothesis for why men are taller than woman

Answer 20

intersexual selection: woman prefer taller men
- intrasexual selection: taller men win fights

Question 21

sexual dimorphism in humans: intrasexual - men do compete over access to mates, but so do women. do men compete more intensely?

Answer 21

• 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

Question 22

sexual dimorphism in humans: intrasexual - is there a fitness advantage to contest behavior for males

Answer 22

• yes
• research shows more competitive males (killers and zealous warriors) have more offspring

Question 23

sexual dimorphism in humans: intersexual - female choice

Answer 23

• yes
• Polish men that have children are taller than men without
• same in the US at West Point

Question 24

sexual dimorphism in humans - what about selection on woman

Answer 24

• 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