5. Sexual Selection Flashcards
Why are females the choosier sex?
More investment (fewer but larger gametes) & stand to lose much more than males by making a bad mate choice.
Eggs
Nutrient rich, expensive, & few produced
Sperm
Nutrient poor, inexpensive,
& many produced
Gamete Argument:
How does a female maximize her reproductive success?
By finding the best-quality male to fertilize her limited number of eggs and NOT by mating with more than one male.
Gamete Argument: How do males maximize their reproductive success?
By maximizing the number of mates.
Costs of sperm production
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.
Gamete Counter Argument
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.
Intersexual Selection
Between sexes: Members of one sex choose which member of the opposite sex to mate with.
Intrasexual Selection
Within the sexes: Members of one sex compete with each other for access to the other sex.
Secondary Sex Characteristics
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
Dimorphism increases with…
…increased male-male competition.
Mate Gaurding
Keeping females busy, lure suitors away, seal female genitalia, & blocking. High cost for males.
The female mate choice is controlled by…
…genes, learning, & cultural transmission.
Direct Benefit Model of Mate Choice
Male provides good resources: Nupial gifts (spermatophore), parental care, shelter, & nest.
Good Genes Model of Mate Choice (aka Sexy Sons Hypothesis)
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
Mate Symmetry shows…
…developmental stability - the measure of how well an organism handles changing environments as it matures.
MHC (Major Histocompatibility Complex)
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
If MHC patterns are too similar…
…tissue can be rejected. Different MHC and the baby is more likely to be carried to term.
Handicap Principle
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.
Runaway Selection Model of Mate Choice
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
Sensory Exploitation Model of Mate Choice
Male novel traits can potentially tap into preexisting female neurological response biases. To qualify, preference should appear before the male trait arises.
Sexual Imprinting
Young individuals learn Mate Choice from interaction with adults.
Type of classical learning
Cultural Transmission
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.
Ovulating Stripper Study
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)
Dominance Hierarchy
Only dominant males mate
Fighting occurs to establish position
Some males form alliance
Male-Male Competition: Cuckoldry
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
