Flashcards in Fitness and Selection Deck (29):
what is selection?
the nonrandom differential survival and reproduction of particular phenotypes
what does the strength of selection depend on?
the heritability (h^2) and on the degree of difference in fitness among phenotypes
h^2 = Vg/(Vg + Ve)
so the larger Vg is relative to Vp then the more effective selection will be
phenotypes have varying consequences for fitness
what is fitness?
the average reproductive output, R, of all organisms bearing the genotype
it's defined for a genotype and pertains to a particular situation in a certain place at a particular time
because of environmental effects, R will not be uniform among all bearers of a genotype
what is reproductive output?
how many eggs are produced?
what is the probability of fertilization?
reproductive output of a genotype is the individual effort of all organisms bearing that genotype
if there is small environmental impact then there will be less variance in output among bearers of a genotype
what two variables shape population structure?
# of individual having offspring
# of reproductive propagules
what is the upper limit on reproductive output per cycle?
(# of reproducers) x (# of eggs)= upper limit on reproductive output per cycle
what three factions influence growth rate?
number of cycles per year
- anual, seasonal, lunar
number of cycles per female lifespan
- fertility over time
age of sexual maturity
what are 6 factors that effect fitness?
1) # of reproductive females
2) # offspring per cycle
3) # cycles per unit time
4) # cycles per female lifetime
5) death rate of reproductive individuals
6) survival rate of offspring
change in any of these factors will change population growth profile
what two kinds of factors influence population size?
density independent and density dependent factors
both limit the natural, genetically determined potential for population increase
what is a density independent factor? examples?
effect is the same regardless of population size or density
increase mortality across the population, thus decreasing the # of reproductive females
ex. environmental phenomena like drought, long winters, hurricanes
what is a density dependent factor? examples?
effect is modulated depending on population size or density
density dependent factors integrate resource availability and competition with population growth
ex. supply of food or other resources --> resources aren't limited for smaller populations but may become limiting as population increases
ex. disease --> spreads more effectively with more people
what governs R?
genotype governs R!
fitness is determined by the reproductive output, R, for each genotype
the average R of the entire population, all genotypes, determines population fitness
what are the components of fitness? does having a certain allele impact....
3) mating success
4) gamete viability
5) fertilization success
fitness is the sum of fitness components at each of these stages
what is viability?
probability that individual bearing genotype will survive
what is fecundity?
number of gametes per individual
fruitfulness and fertility, the ability to produce abundant healthy growth or offspring
what is mating success?
number and quality of mates
what is gamete viability?
alleles impact the longevity or quality of the egg or sperm
what is fertilization success?
alleles impact the probability that fertilization will take place
what is relative fitness? what's the symbol for it?
relative measure of survival and reproduction (W)
W of best genotype AA, Aa = 1
W of other genotype aa = 1-s
what is the selection coefficient? whats the equation?
reduction in fitness relative to best genotype (s)
W +s = 1
always a value between 0 (no selection) and 1 (complete mortality)
if s = 0 then it means no selection
what is differential survival and reproduction?
non random process through which pre-existing variation is sorted
what is directional selection?
if individuals at one extreme of the range of phenotypes of fittest
what is purifying selection?
if the allele being reduced in frequency is lethal
- directional selection will act to reduce # of recessive alleles
ex. taller birds fitter than shorter birds
what is disruptive selection?
if 2 or more discontinuous phenotypes are fittest
Homozygous phenotypes fitter than heterozygote --> allele frequencies will be maintained but not phenotype frequencies
what is stabilizing selection?
if the intermediate phenotype is fittest
heterozygote phenotype is fitter than homozygotes and the frequency of homozygotes is therefore reduced
what is positive selection?
When selection acts to favor a phenotype or genotype, selection is positive
what is negative selection?
When selection acts to eliminate a phenotype or genotype, selection is negative
what is frequency dependent selection?
Selective regime and its impact differ depending on the frequency of pheno- or geno-types