5. Sexual Selection

Question 1

Why are females the choosier sex?

Answer 1

More investment (fewer but larger gametes) & stand to lose much more than males by making a bad mate choice.

Question 2

Eggs

Answer 2

Nutrient rich, expensive, & few produced

Question 3

Sperm

Answer 3

Nutrient poor, inexpensive,

& many produced

Question 4

Gamete Argument:

How does a female maximize her reproductive success?

Answer 4

By finding the best-quality male to fertilize her limited number of eggs and NOT by mating with more than one male.

Question 5

Gamete Argument: How do males maximize their reproductive success?

Answer 5

By maximizing the number of mates.

Question 6

Costs of sperm production

Answer 6

High cost of spermatophore production, successive spermatophores can become smaller, high cost of production can reduce life span of males with high mating rates, & sperm counts may reduce the life span in males with high mating rates.

Question 7

Gamete Counter Argument

Answer 7

Some males are prudent in their allocation of ejaculates (i.e. male selectivity) and females of some species can be fertilized by more than one male.

Question 8

Intersexual Selection

Answer 8

Between sexes: Members of one sex choose which member of the opposite sex to mate with.

Question 9

Intrasexual Selection

Answer 9

Within the sexes: Members of one sex compete with each other for access to the other sex.

Question 10

Secondary Sex Characteristics

Answer 10

Sexual phenotypes in addition to genitalia: plumage, colors, courtship displays used to attract mates or battle rivals.

These are favored by natural selection because of their effects on mate choice

Question 11

Dimorphism increases with…

Answer 11

…increased male-male competition.

Question 12

Mate Gaurding

Answer 12

Keeping females busy, lure suitors away, seal female genitalia, & blocking. High cost for males.

Question 13

The female mate choice is controlled by…

Answer 13

…genes, learning, & cultural transmission.

Question 14

Direct Benefit Model of Mate Choice

Answer 14

Male provides good resources: Nupial gifts (spermatophore), parental care, shelter, & nest.

Question 15

Good Genes Model of Mate Choice (aka Sexy Sons Hypothesis)

Answer 15

Indirect benefit

Offspring, not mates, will benefit.

Females pick males best suited for their environment which can be indicated by physical traits (color, size, MHC complex, symmetry) or behavior (mating displays)

Color may symbolize a healthier mate with less parasites

Question 16

Mate Symmetry shows…

Answer 16

…developmental stability - the measure of how well an organism handles changing environments as it matures.

Question 17

MHC (Major Histocompatibility Complex)

Answer 17

MHC - Set of genes involved in disease resistance; proteins produced by MHC genes guide body in identifying “self” vs “foreign” invaders

Animals prefer mates with different MHC than their own as offspring will have a whole new set of MHC - great for immune protection

Question 18

If MHC patterns are too similar…

Answer 18

…tissue can be rejected. Different MHC and the baby is more likely to be carried to term.

Question 19

Handicap Principle

Answer 19

Honest signals should be costly to produce and should be reliable indicators about the condition of the male (coloration) therefore it’s impossible to really cheat certain attributes.

Question 20

Runaway Selection Model of Mate Choice

Answer 20

Involves two sets of alleles: one set that codes for the male trait & one set that codes for preference of trait - females pass along both to offspring.

Males produce trait that females desire and females choose that trait.

Extreme versions of trait appear over time

Question 21

Sensory Exploitation Model of Mate Choice

Answer 21

Male novel traits can potentially tap into preexisting female neurological response biases. To qualify, preference should appear before the male trait arises.

Question 22

Sexual Imprinting

Answer 22

Young individuals learn Mate Choice from interaction with adults.

Type of classical learning

Question 23

Cultural Transmission

Answer 23

Female mate preference is affected by preference of other females in the population.

Males probability of being preferred increases as a result of having been preferred in the past.

Question 24

Ovulating Stripper Study

Answer 24

Ovulating strippers were consistently given higher tips/hour

Men can respond to ovulation via olfactory stimuli by becoming more loving and jealous of other men (mate guarding)

Question 25

Dominance Hierarchy

Answer 25

Only dominant males mate

Fighting occurs to establish position

Some males form alliance

Question 26

Male-Male Competition: Cuckoldry

Answer 26

Satellite Male - Acts peripherally to dominant male. Doesn’t use mating displays but may ambush female who have been drawn by dominant male

Sneaky Male - Sneak past Male using female coloration then mate with female under disguise