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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....

1) viability

2) fecundity

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


what is frequency independent selection?

Selective regime does not depend on the frequency of the allele in the population