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Principals of Evolution > Sexual Selection > Flashcards

Sexual Selection Flashcards

1
Q

sexual dimorphism

A

a difference between the phenotypes of females vs males within a population

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2
Q

natural selection

A
  • a difference between the survival & reproduction of individuals with different phenotypes
  • usually refers to components of fitness other than mating success
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3
Q

sexual selection

A
  • a difference, among members of the same sex, between the average mating success of individuals with different phenotypes
  • a special kind of natural selection
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4
Q

what explains the differences between the sexes?

A

sexual selection, it must act differently on the sexes

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5
Q

why is sexual selection different between the sexes?

A

sperm are cheaper than eggs

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6
Q

sperm are cheaper than eggs

A
  • human eggs are 4000x larger than a sperm
  • women ovulate ~300 to 400 eggs in their lifetime
  • men make 10’s of millions of sperm everyday
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7
Q

reproductive success

A

the number of viable, fertile offspring produced

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8
Q

the sexes differ in reproductive investment

A
  • male reproduction is (often) limited by access to females eggs
  • females are (often) limited by the number of eggs she can nurture & rear to maturity
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9
Q

Bateman’s Principle

A
  • when one sex invests more resources into producing offspring, this sex will be a limiting resource over which the other sex will compete
  • access to mates will usually limit male reproductive success, but fecundity will usually limit female reproductive success
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10
Q

fecundity

A

number of pregnancies

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11
Q

Bateman’s Gradient

A

the slop of the best fit line relating reproductive output to mating opportunities

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12
Q

the slope of Bateman’s gradient

A
  • strongly positive for males & horizontal or weakly positive for females
  • predictions flow from differences in relative investment, not from gender
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13
Q

reproductive variance mating success & reproductive success

A
  • most males don’t mate & produce no offspring
  • most females do mate & produce many offspring
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14
Q

what is the cause of sexual selection?

A

Bateman’s Gradient

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15
Q

sexual selection reversed

A

when males invest more than females

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16
Q

sexual selection reversed: seahorses

A

female seahorses transfer eggs to males & males give birth

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17
Q

sexual selection reversed: broad-nose pipefish

A
  • after eggs are fertilized, male provides all parental care by carrying eggs in brood pouch
  • females need less time & energy to produce a clutch of eggs than it takes a male to brood them
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18
Q

what does reversed sexual selection mean for Bateman’s Gradient?

A

reproductive variance is reversed

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19
Q

reproductive variance reversed mating success & reproductive success

A
  • most males mate & produce several offspring
  • many females do not mate & produce zero offspring
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20
Q

when sexual selection is strong for one sex & weak for the other, we predict that…

A
  • members of the sex subject to strong sexual selection will compete for mates
  • members of the sex subject to weak sexual selection will be choosy, because it is more important to pick the right mate that is to mate frequently
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21
Q

forms of selection when sexual selection is strong for one sex but weak for the other sex

A
  • intrasexual selection
  • intersexual selection
22
Q

intrasexual selection

A

typically male-male competition

22
Q

example of intrasexual selection

A

elephant seal males fighting

23
Q

male-male competition

A

most extreme when males are territorial & can control a large number of females

24
Q

types of male-male competition

A
  • combat
  • defenses
  • indicators of strength
25
Q

types of male-male competition: combat

A
  • horns
  • antlers
  • pincers
  • large size
26
Q

types of male-male competition: defenses

A
  • armor
  • large body size
27
Q

types of male-male competition: indicators of strength

A

large body size

28
Q

other types of male-male competition

A
  • sperm competition
  • infanticide
29
Q

Galapagos Marine Iguanas

A
  • females lay one clutch of 1-6 eggs per year
  • males only contribute sperm
  • females mate once per year, males fight hard for that opportunity
30
Q

alternative male mating tactics: yellow morph

A
  • sneaker
  • mimics female behavior
  • mimics female coloration
  • not territorial
30
Q

alternative male mating tactics: orange morph

A
  • territory usurper
  • large size
  • high testosterone
  • large territories
31
Q

alternative male mating tactics: blue morph

A
  • mate guarder
  • cooperates with other blues
  • small territories
32
Q

sperm competition

A
  • increase ejaculate
  • mate guard
  • sperm plugs
  • inject hormones that influence the females reproductive behavior
33
Q

infanticide

A
  • 25% of all pups deaths
  • females return to breeding condition on average 8 months sooner
34
Q

intrasexual selection

A

female choice

35
Q

intrasexual selection: male red-collared widowbird

A
  • males in better condition have longer tails
  • males with longer tails attract more females to their territory due to female choice
  • harder to survive with longer tail
36
Q

intrasexual selection: female choice in the grey treefrog

A
  • females prefer long calls vs short calls
  • females will pass by short calls to approach long calls
37
Q

4 explanations of female choice

A
  • good genes
  • direct benefits
  • sensory bias
  • chase-away sexual selection
38
Q

good genes

A
  • certain traits indicate the bearer has good genes
  • females that prefer males with good indicator traits will have offspring with better genes
39
Q

good genes: prediction

A
  • offspring of males with good gene indictor traits will have increased survival of reproductive success
  • these are indirect genetic benefits to female fitnesses
40
Q

good genes: examples

A
  • the offspring of peacocks with more elaborate trains enjoy improved growth & survival
  • human women prefer men that have immune system genes that differ from their own
41
Q

the tadpoles of long-calling animals

A
  • grew faster
  • metamorphosed sooner
  • greater mass at metamorphosis
  • survived better
  • grew faster at metamorphosis
42
Q

direct benefits

A

females prefer males with resources or other attributes that help them now

43
Q

direct benefits: prediction

A
  • females provided with male resources should have higher fitness
  • this is a direct benefit to the female
44
Q

direct benefits with shrikes

A
  • male shrikes display their foraging success
  • females choose males with evidence of fewer parasites, diseases, etc
  • territory quality important for offspring success
45
Q

sensory bias

A

taking advantage of the female sensory system

46
Q

example of sensory bias

A
  • Tungara frog males call with a whine & a chuck. Females prefer the chuck but so do bats
  • detailed studies of the inner ear have shoqn that females are naturally sensitive to the chuck
47
Q

chase-away sexual selection

A
  • males evolve mechanisms that increase their reproductive success
    so females evolve counter adaptations, since what is good for the gander is not always good for the goose
  • then males evolve in response to the females
  • the result is continual selection & evolution, like an arms race
48
Q

chase away sexual selection in fruit flies

A
  • females prevented from evolving
  • some males selected for success in mating competitions
  • some males not sleected for success in mating competitions
49
Q

result of chase away sexual selection in fruit flies

A

slected males evolve seminal fluids that can kill females

Principals of Evolution (18 decks)

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