prelim 2 (adaptation/speciation 1 - pop genetics 4) Flashcards
sexual selection
type of selection resulting from differences among individuals in their ability to mate or
fertilize eggs
- gives rise to diversity in morphology + behavior
individuals possessing traits that help them reproduce will be favored by sex selection
two fold cost of sex
asexual organisms can multiply faster than sexual organisms.
costs of sex
- finding an appropriate mate
- parents are less related to their offspring (r = 1 in asex but here r = 0.5)
- risk of contracting STDs
why is sex common
- gene recombination for genetic exchange; allows for the weeding out of deleterious mutations
- combining favorable mutations more quickly
- allows for faster adaptation again thru
reshuffling of genetic diversity
cost of asexual reproduction
- entire genome passed down generations
- deleterious mutations accumulate
- accumulation results in genetic load
sexual dimorphism
phenotypic difference between the male/female in population
- size, color, behavior, physiology
sex selection trade offs
investment strategies differ between species and the sexes
anisogamy
gametes are different sizes
- egg tends to be larger; female might need to have diff life history strategy to account for energy
- fruit fly exception w the v long sperm
internal fertilization
in females usually; evolved multiple times
- sets up different level of investment
- females have large energetic investment; specialized adaptations for offspring care in females
- internal fertilization means those carrying are certain of their offspring
operational sex ratio
ratio of males to females available for reproducing at given time
- how strong sexual selection is
male biased OSR and stronger sexual selection on males (bc females get pregnant) - when there is larger male population and females are not reproductive due to pregnancy and other
variance in reproductive succes
higher male variance in a more male-biased OSR
- stronger sex selection in males
- lower variance in female reproductive success
male-biased OSR
males are most likely to maximize fitness by fertilizing eggs
females invest in choosing good mates, producing good eggs, provisioning offspring
females-biased OSR
females control territories: invest in attracting mates bc there are more female than male
males: invest in high quality mates and offspring care
strength of sexual selection
higher in mating system where variance in reproductive success is higher
-* stronger in species that mate w multiple during fertile period
- members under stronger selection = mating competition; weaker selection = mate choice
cryptic females choice
females can store sperm and decide later which to use more of
geographical barriers= extrinsic
mountains, rivers, oceans, physical separation
- allopatric and peripatric
intrinsic = reproductive barriers
difference in attraction and stuff
or infertile children
- parapatric and sympatric speciation
allopatric speciation
ancestral pop divided by extrinsic barrier
peripatric
small number of individuals cross a barrier and are separated geographically
- founder affect?
vicariance
formation of geographic barriers that separate a population
dispersal and colonization
populations become separate by dispersal to new areas
parapatric speciation
occurs when species is spread out over large geographic area that causes differences; mate with ones closer to them until they diverge more and more
sympatric speciation
some individuals begin to exploit a new niche and mate with other occupying the same niche
behavioral isolation
utilize different mate recognition system
prezygotic barrier
occur prior to the fertilization of the egg
- ecological isolation: habitat isolation, temporal isolation, pollinator isolation
- behavioral isolation, copulatory behavior isolation, mechanical isolation, gametic isolation
- mechanical isolation
copulatory behavioral isolation
behaviors mate may need to perform during copulation to entice the partner
habitat isolation
breeds in different locations or prefer different microhabitat
mechanical isolation
the species genitalia compatibility
temporal isolation
species breed in different seasons and/or time of day
pollinator isolation
species pollinated by different organism
post zygotic isolation
hybrid infertility or inviability, ecological hybrid inviability, behavioral sterility
hybrid inviability
ecological hybrid inviability
behavioral sterility
hybrids are not able to reproduce
hybrids are not able to survive as well in either of the parent habitats
hybrids can’t obtain mates
hybrid zones
areas where two populations meet, interbreed, create hybrid offspring
- primary and secondary zone
primary zone =
secondary zone
when two populations that have been physically separated come back together
phonetic species concept
define species using morphological traits
disadvantages:
- same species can be morphologically distinct
- cryptic species=morphologically similar but genetically distinct
phylogenetic species concept
species as ‘tips’ on the phylogenetic tree
limitation = relies on accurate phylogeny
biological species concept
species = groups of potentially or actually interbreeding populations
advantage = no problems w different morphological problems
disadvantage = unclear potential interbreeding definition
heterozygote advantage
a1a2 allele result in diff phenotype then homozygous and give it a fitness advantage
additive inheritance system
makes heterozygotes intermediate phenotype and intermediate fitness
can be a1 or a2 additive & advantageous depending which allele is advantageous
selection differential
The difference between the mean of the initial population and the mean of the reproducing individuals of the population/the mean of the population after selection
response to selection
difference between the mean of the initial population/before selection and the mean of the offspring of the population/mean of the next generation
heritability (h^2?)*
how heritable a trait is? LOL
R = h2*S
proportion of population variation in a trait that comes from genetic factors
graph of midparent against midoffspring: slope = heritability; more heritable when slope is positive and points are close to the line
directional selection
when selection favors phenotypes at one end of a distribution
- mean changes but the variation may stay the same
stabilizing selection
selection favors values toward the middle of the distribution
- the mean stays the same but there is less variation in the population
disruptive selection
favors phenotypes at both ends of the distribution = bimodal
the mean may stay the same if equal distribution on both sides, variance increases
darwin logic: critical ingredients to natural selection
fact 1= species have great potential fertility that their population size would increase exponentially if all born reproduced successfully
fact 2 = populations normally display stability in size
fact 3 = natural resources are limited and remain ~constant in a stable environment
fact 1+2+3 = inference `; more individuals are produced than can be supported meaning there’s a struggle for survival and only a small survival and progeny of each generation
fact 4: no two are the same; variability
fact 5: variation is heritable
4+5 = inference 2; survival is not random but depends on heritability constitution of the surviving
- unequal survival = natural selection
Inference 3 = over generations process of natural selection leads to gradual change of populations
darwins postulates (3)
- individuals are variable in some traits
- some of this variation is heritable
- there’s a struggle for survival or reproduction in which some fare better than others
traits selection may operate on
morphological
behavioral
physiological
causes for phenotypic variation
genetics
environment
interactions between the two
*measurement error
*developmental stages = ontogenetic
mechanisms of evolution
natural selection
gene flow
genetic drift
mutation
frequency dependent selection
when fitness of a genotype depends on its frequency
- negative and positive
negative frequency dependent
phenotype has greatest selective advantage if it is rare
- ex: viruses against antibodies
positive freq dependent
phenotype is more advantageous if common; higher commonness = higher fitness
truths about natural selection
- is not forward looking, does not act “for the good of the species”
- actos on individuals of certain phenotypes
- depends on environmental conditions of the moment
life history traits*
timing and duration of key events during a lifetime that can influence an organism’s fitness
- age, time of reproduction, number and size of offspring, lifespan
inclusive fitness
sum of indirect and direct fitness
direct fitness
contribution individual makes to gene pool through own offspring
indirect fitness
genes being represented in gene pool from their relatives but not own offspring
antagonistic pleiotropy
when a genetic variant w beneficial effect on one trait also has a detrimental effect on another
ex: selection for trait early in life causes shortened overall lifespan (senescence)
senescence
a decline with age in per capita reproductive performance, physiological function, or prob of survival
- selection is weaker on traits that favor later life survival; absent or very weak on post-reproductive traits
kin selection
can favor behaviors that reduce direct fitness if indirect fitness is greater or increased
Hamilton’s rule
R - relatedness coefficient
B - benefit to recipient
C - cost to donor
rB > C
life history tradeoffs
based on - current reproductive success, future “ “, and likelihood of surviving
eusociality
highest level of organization of a society - insect colonies
post-copulatory mating competition
sperm competition
- produce a lot
- remove sperm already present
- prevent the next
more competition where females were polyamorous
mates under stronger sexual selection will
compete: mating competition
members under weaker sexual selection will
be choosier: mate choice
sexual conflict
interests of mating partners are opposed
- example w the ducks
- antagonistic coevolution
- cannibalism
“antagonistic coevolution”
aka evolutionary arms race
- ex of the female vagina evolving to decreased forced copulations and the male penis also evolving
- antagonistic coevolution b/w parasite and host
muller’s ratchet
when asexual beings may accumulate deleterious mutations
red queen effect
proposes that organisms must constantly adapt, evolve, and proliferate not just for continuous reproduction but to merely survive within their competitive habitats
runaway selection
a mechanism whereby a secondary sexual trait expressed in one sex becomes genetically correlated with a preference for the trait in the other sex
fusion
if divergence in allopatry results in no prezygotic or post zygotic isolation and the barrier is removed fusion occurs
heterozygote advantage
heterozygous has the highest fitness compared to both homozygous
additive fitness pattern
heterozygous has an intermediate fitness level between the two different homozygous
- advantageous genotype reaches fixation faster than recessive and advantageous
dominant and advantageous
homozygous dom and heterozygous have the same and higher fitness than homozygous recessive
- population will never go to fixation in dominant allele
- frequency increases quickly
recessive and advantageous
homozygous recessive has highest fitness; hetero and homozygous dom are lower
- may reach fixation but it would take a much longer time
- frequency doesnt increase for a whole and then inc sharply
polygenic traits
traits determined by the contribution of many independent genes
microevolution
A change in the relative frequencies of alleles in the gene pool of a population
founder effect
founder events involve mvt to a new uncolonized area
- is a type of bottle-neck
- population that experiences higher effects of genetic drift
- population w diff allele frequencies from original
mutation role in evolution
introduce new source of variation
