2A Lecture Modes of Selection 10/5

what is fitness?

long-term reproductive success

what is the relationship between fitness and phenotype?

can be continuously increasing, decreasing, unimodal, and multimodal

what is a bimodal distribution?

two distinct phenotypes (make two distinct peaks)

What is directional stabilization?

• fitness and phenotype have a continuously increasing relationship (when one increases the other does)

• relationship btwn frequency and phenotype shifts to the right

What happened to the geospiza fortis (type of Darwin’s finch)?

• Two phenotypes (one w larger beak/one with smaller)

• drought occurred and birds with larger beak had higher frequency

• competition arrived and birds with smaller beak survived more —> higher frequency

What happened to the biston betularia (moths during industrial revolution)?

• smoke caused trees to darken

• darker moths selected for/ higher survival because they’re camouflaged

what is stabilizing selection?

• relationship btwn fitness and phenotype have a normal distribution

• relationship btwn frequency and phenotype have a narrower normal distribution

• less extremes

what is an example of stabilizing selection?

• clutch size = have as many offspring as you can in order to pass your genes/continue population, but also have enough that you are able to take care of

• number of spikes in a prickly cactus = cactus’ with super prickly spikes and cactus’ w no spikes won’t be able to survive → phenotype in the middle has a higher frequency

what is disruptive/diversifying selection?

• bimodal distribution for fitness and phenotype

• relationship btwn frequency and phenotype → initial has one phenotype that has high frequency but then frequency changes as more variation that’s being selected for occurs (two phenotypes that have high fitness)

what is an example of disruptive/diversifying selection?

• bird population → one bird has a small hue of blue on their head, another bird has a larger hue of blue on their head

• both birds have mating opportunities in the population

• may lead to speciation

what does natural selection require?

heritable phenotypic variation associated with differences in reproductive success

what are the 3 modes of selection?

• one extreme favored → directional

• intermediate favored → stabilizing

• both extremes favored → disruptive

is there a universally “best” phenotype?

no, fitness depends on the environment