evolution final 2023

coincidental evolution hypothesis

human virulence is side effect of traits that are adaptive in the pathogen's normal habitat, for pathogens that do not usually have a human host

short-sighted evolution

pathogens that live for many generations in single host aren't under selection for transmissibility

trade-off evolution

damage to host is acceptable if it increases the chances of transmission to new hosts

hemagglutinin

coat protein that helps virus bind to host cells, recognized by the host immune system

pandemic strains

strains that are rapidly acquiring amino acid substitutions in sites under positive selection

antigenic sites

parts of the protein of the virus that the immune system recognizes and remembers

biological species concept

Species is a group of populations whose members have the potential to produce fertile offspring.

phylogenetic species concept

defines a species as the smallest group of individuals that share a common ancestor

morphological species concept

characterizes a species by body shape and other structural features

lateral transfer species concept

species concept using bacteria and lateral gene transfer

allopatric speciation

formation of species with physical isolation

sympatric speciation

formation of new species in the same range- due to other barrier

polyploidy

condition in which an organism has extra sets of chromosomes, can create rapid sympatric speciation

vicariance

allopatric speciation that occurs when something in the environment separates organisms of the same species into separate groups

dispersal

the movement of organisms from one place to another to create new species

divergence

must occur to split species after isolation. reasons- adaptation to different habitats, assortative mating, more mutations

reinforcement occurs

hybrids have reduced fitness

hybrid zones

where geographic ranges of 2 species overlap

disparity

morphological differences between taxa

diversity

number of taxa and relationships between taxa

morphospaces

ranges of trait values may be occupied or not, usually uneven- theoretical range is broader than observed range

punctuated equilibrium

Pattern of evolution in which long stable periods are interrupted by brief periods of more rapid change

phyletic gradualism

Species evolve by the accumulation of many small changes over a long time period

adaptive radiation

rapid increase in disparity and diversity, driven by ecological opportunity or morphological innovation

one island model

most gene flow is from continent to island. every individual that comes from mainland significantly impacts allele frequencies in island gene pool, way less impactful for mainland gene pool

two island model

2 islands gene pools are more equally influence by each other

genetic drift

describes the effect of random chance on allele frequencies. random

sampling error

= xbar - mu

mu

actual mean

xbar

sample mean

founder effect

example of genetic drift, allele frequencies of those who migrate may not represent frequencies of population

allopatric speciation

The formation of new species in populations that are geographically isolated from one another.

random fixation

probability of an allele becoming fixed due to random chance is equal to its starting frequncy

Loss of heterozygosity

happens on the way to fixation

H g+1 means

heterozygosity in the next generation

Hg+!

= Hg (1- 1/2N)

Fst means

fixation index, models loss of heterozygosity in isolated subpopulations

Fst

= (Ht-Hs)/Ht

Ht

expected heterozygosity if entire population is in HWE, 2pq

Hs

observed average heterozygosity across all subpopulations

neutral loci

loci that are not under selection give better idea of when and how fast drift acts, good for molecular clock

nonrandom mating

both sexual selection and inbreeding

inbreeding

mating with genetic relatives, exacerbated by small population sizes, does not change allele frequencies but increases proportion of homozygotes

inbreeding depression

result of increased homozygosity, deleterious recessive alleles are more likely to be expressed in this population

linkage disequilibrium

When a pair of alleles from two loci are inherited together in the same gamete more/less often than random chance would expect, increased by inbreeding

haplotype

multilocus genotype of a chromosome or gamete

linked loci

physically proximate, less likely to be separated by crossing over during meiosis

linkage equilibrium

genotype of a chromosome at one locus is independent of its genotype at the other locus

D means

coefficient of linkage disequilibrium

g

frequency of each haplotype in population

D

=gABgab - gAbgaB

r

recombination rate, probability of crossing over

sexual reproduction

reduces LD by crossing over during meiosis generating new haplotypes

the older the mutation

the less closely linked it is to a certain haplotype

common and strongly linked alleles

young and under positive selection

mullers ratchet

describes accumulation of deleterious mutations in an asexual population and loss of genetic diversity to drift

Quantitative traits

traits that show continuous variation ex. height, controlled by many different loci and environmental factors

M

marker locus, helps identify loci that contribute to quantitative trait. if M predicts average phenotype, marker is linked to quantitative trait locus

QTL

quantitative trait loci

V

variance

broad sense heritability

V genetic / V phenotypic

V phenotypic

Vg + V environmental

H

= Vg/ Vg+Ve

h^2

narrow sense heritability, equal to slope of least-squares regression line on plot of midparent and midoffspring trait values

Vg>Ve

trait is more heritable, identical twins will have more similar trait values than dizygotic twins

t bar

mean trait value of population

t star

mean trait value of individuals that reproduce

selection differential

the difference between the mean of the group selected for reproduction and the mean of the entire population, s = tstar-tbar

selection gradient

plots relative fitness vs trait value, connects trait value to fitness

breeders equation

calculates response to selection

breeders equation actual

R = h2s

directional selection

changes the average trait value, moves curve over

stablizing selection

decreases variance of trait without changing the average trait value

adaptation

trait or integrated suite of traits that increases the fitness of its possessor, process in which a lineage evolves a trait that confers higher fitness

determine what trait is for, show that individuals with the trait contribute more genes to future generations than individuals lacking it

how to test if trait is adaptive

typically female

higher investing parent

typically male

lower investing parent

heavy investing parent limits

reproductive success limited by resources and time

light investing parent limits

reproductive success limited by number of mates

intersexual selection

sex with heavy investment in offspring is choosy about mating, one sex exacting selection on another

intrasexual selection

sex with light investment in offspring will compete to mate, same sex exacting selection on each other

intrasexual selection can lead to

adaptations for display or combat, sneaky behaviors

sneaker males

"sneak" in and mate with females when the dominant or territorial male is not looking, do not fight or display. can be equally fit as competitive strategies

sperm competition

competition between sperm of different males to fertilize eggs

infanticide

individual killing the offspring of other males to increase own fitness

preference

daughters preferred trait value often matches brothers measured trait value, increases likelihood of brothers mating success. "sexy sons hypothesis"

why does preference exist

arbitrary, exploit sensory biases, increases resources available, signals that individual has good genes

mutually beneficial behavior

benefits fitness of actor and recipient, ex. communal nesting

selfish behavior

benefits actor at expense of recipient, ex. cane toad eggs eat each other

altruistic behavior

benefits recipient at expense of the actor, ex. ground squirrel alarm calls

spiteful behavior

harms both actor and recipient, ex. bacteria making toxins that kill other strains of their species

direct fitness

Individual's own reproductive success

indirect fitness

reproductive success of relatives

inclusive fitness

direct fitness + indirect fitness

Hamiltons rule

predicts when altruistic behavior will occur, B*r - C > 0

r

relatedness

c

cost of direct fitness actor gives up

b

benefit of direct fitness recipient gains

relatedness definition

probability that shared allele is identical by descent

identical by descent

shared allele is shared because was present in an ancestor