BIOL 286: Lecture #4 Review (Selection)

frequency-dependent selection

A type of selection whereby the fitness of a phenotype depends on the frequency of that phenotype within a population

Types of frequency-dependent selection: (2)

(1) negative; (2) positive

negative frequency-dependent selection

A type of frequency-dependent selection whereby rare phenotypes are favored (i.e. fitness declines as the phenotype becomes increasingly common)

Explain negative frequency-dependent selection with respect to water boatman color.

Negative frequency‑dependent selection occurs when a phenotype gains a fitness advantage specifically because it is rare. In water boatmen

positive frequency-dependent selection

A type of frequency-dependent selection whereby common phenotypes are favored (i.e. fitness increases as the phenotype becomes increasingly common)

Explain positive frequency-dependent selection with respect to schools of fish.

In positive frequency‑dependent selection

directional selection

A type of selection whereby an extreme phenotype is favored

disruptive selection

A type of selection whereby intermediate phenotypes are selected against

stabilizing selection

A type of selection whereby intermediate phenotypes are favored

Explain stabilizing selection with respect to the birth weight of human infants.

Stabilizing selection acts on human birth weight because infants at the extremes—either very low or very high weight—show higher mortality and complication rates

sexual selection

A form of natural selection resulting from differences in fitness associated with non-random success in mating

Both . . . and . . . animals are under selection to maximize their reproduction

male; female

With respect to sexual selection

males typically maximize fitness by . . .

Explain males' vs. females' differential strategies to maximize fitness in the context of sexual selection.

In the context of sexual selection

Bateman's principle

Asserts that female reproduction is limited by the resources necessary to produce eggs whereas male reproduction is limited by access to females

For species where the female has higher reproductive investment

. . . is observed

female mate choice

Under Bateman's principle

For species where the male has equal reproductive investment compared to females (e.g. biparental care)

. . . is observed

For species where the male has higher reproductive investment

. . . is observed

Explain male mate choice with reference to Mormon crickets.

In Mormon crickets

Often

males have . . . in mating success (i.e. . . .)

Higher variance in mating success (due to sexual selection) can lead to . . .

sexual dimorphism

sexual dimorphism

Differences in physical characteristics between males and females of the same species

Explain why sexual dimorphism is more prominent in species where there is higher variance in mating success

such as due to sexual selection.

intrasexual selection

A direct competition among individuals of one sex (usually the males in vertebrates) for mates of the opposite sex.

intersexual selection

Selection whereby individuals of one sex (usually females) are choosy in selecting their mates from individuals of the other sex; also called mate choice.

Both intra- and intersexual selection result in . . . (e.g. . . . (4))

ornaments; large horns or antlers

There can be "conflict" between . . . and . . . selection

natural; sexual

Explain how there can be "conflict" between natural selection and sexual selection.

Mate choice in sexual selection may select for certain traits that increase reproductive success

ecotypes

Genetically distinct populations that have adaptations to the local environment

Ecotypes may vary in . . .

. . .

absolute fitness

The survivorship and reproduction of each genotype in a population; the genetic make-up of a population after selection compared to before selection

Absolute fitness equation: . . .

of genotype after selection / # of genotype before selection

relative fitness

The ability of one genotype to survive and reproduce relative to the most successful (i.e. most fit) genotype in the population; the absolute fitness of one genotype divided by the highest absolute fitness

Relative fitness equation: . . .

w = absolute fitness of genotype of interest / highest absolute fitness

selection coefficient (s)

The proportion of a genotype that is not represented in the next generation due to death or reproductive failure

The selection coefficient determines . . .

which genotype is selected against

Selection coefficient equation: . . .

s = 1 - w

A lower value of a selection coefficient indicates . . .; by contrast

a higher value indicates . . .

Multiple mechanisms of evolution can be acting . . . but can . . .

upon the same population; have opposite effects