1
Q
sexual dimorphism
A
a difference between the phenotypes of females vs males within a population
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
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
4
Q
what explains the differences between the sexes?
A
sexual selection, it must act differently on the sexes
5
Q
why is sexual selection different between the sexes?
A
sperm are cheaper than eggs
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
7
Q
reproductive success
A
the number of viable, fertile offspring produced
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
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
10
Q
fecundity
A
number of pregnancies
11
Q
Bateman’s Gradient
A
the slop of the best fit line relating reproductive output to mating opportunities
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
13
Q
reproductive variance mating success & reproductive success
A
- most males don’t mate & produce no offspring
- most females do mate & produce many offspring
14
Q
what is the cause of sexual selection?
A
Bateman’s Gradient
15
Q
sexual selection reversed
A
when males invest more than females
16
Q
sexual selection reversed: seahorses
A
female seahorses transfer eggs to males & males give birth
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
18
Q
what does reversed sexual selection mean for Bateman’s Gradient?
A
reproductive variance is reversed
19
Q
reproductive variance reversed mating success & reproductive success
A
- most males mate & produce several offspring
- many females do not mate & produce zero offspring
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
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
types of male-male competition
- combat
- defenses
- indicators of strength
25
types of male-male competition: combat
- horns
- antlers
- pincers
- large size
26
types of male-male competition: defenses
- armor
- large body size
27
types of male-male competition: indicators of strength
large body size
28
other types of male-male competition
- sperm competition
- infanticide
29
Galapagos Marine Iguanas
- 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
alternative male mating tactics: yellow morph
- sneaker
- mimics female behavior
- mimics female coloration
- not territorial
30
alternative male mating tactics: orange morph
- territory usurper
- large size
- high testosterone
- large territories
31
alternative male mating tactics: blue morph
- mate guarder
- cooperates with other blues
- small territories
32
sperm competition
- increase ejaculate
- mate guard
- sperm plugs
- inject hormones that influence the females reproductive behavior
33
infanticide
- 25% of all pups deaths
- females return to breeding condition on average 8 months sooner
34
intrasexual selection
female choice
35
intrasexual selection: male red-collared widowbird
- 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
intrasexual selection: female choice in the grey treefrog
- females prefer long calls vs short calls
- females will pass by short calls to approach long calls
37
4 explanations of female choice
- good genes
- direct benefits
- sensory bias
- chase-away sexual selection
38
good genes
- certain traits indicate the bearer has good genes
- females that prefer males with good indicator traits will have offspring with better genes
39
good genes: prediction
- offspring of males with good gene indictor traits will have increased survival of reproductive success
- these are indirect genetic benefits to female fitnesses
40
good genes: examples
- 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
the tadpoles of long-calling animals
- grew faster
- metamorphosed sooner
- greater mass at metamorphosis
- survived better
- grew faster at metamorphosis
42
direct benefits
females prefer males with resources or other attributes that help them now
43
direct benefits: prediction
- females provided with male resources should have higher fitness
- this is a direct benefit to the female
44
direct benefits with shrikes
- male shrikes display their foraging success
- females choose males with evidence of fewer parasites, diseases, etc
- territory quality important for offspring success
45
sensory bias
taking advantage of the female sensory system
46
example of sensory bias
- 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
chase-away sexual selection
- 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
chase away sexual selection in fruit flies
- females prevented from evolving
- some males selected for success in mating competitions
- some males not sleected for success in mating competitions
49
result of chase away sexual selection in fruit flies
slected males evolve seminal fluids that can kill females
Principals of Evolution
flashcards
Decks in class (18)
# Cards
-
8/29 notes43
-
8/31 notes48
-
Tree of Life Notes98
-
Fossils Notes25
-
The Origins of Life Notes35
-
An Explosion of Life17
-
Natural Selection34
-
Population Genetics I: Natural Selection73
-
Inner Reptile5
-
Population Genetics II: Genetic Drift19
-
Population Genetics III: Effective Population Size, Non-random Mating, Migration58
-
Quantitative Genetics53
-
Quantitative Genetics II33
-
Life History Evolution49
-
Kin Selection & Social Behavior36
-
Sexual Selection51
-
Why Sex?16
-
Final Exam154
