Fitness and Selection

Question 1

what is selection?

Answer 1

the nonrandom differential survival and reproduction of particular phenotypes

Question 2

what does the strength of selection depend on?

Answer 2

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

Question 3

what is fitness?

Answer 3

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

Question 4

what is reproductive output?

Answer 4

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

Question 5

what two variables shape population structure?

Answer 5

# of individual having offspring
# of reproductive propagules

Question 6

what is the upper limit on reproductive output per cycle?

Answer 6

(# of reproducers) x (# of eggs)= upper limit on reproductive output per cycle

Question 7

what three factions influence growth rate?

Answer 7

number of cycles per year
- anual, seasonal, lunar

number of cycles per female lifespan
- fertility over time

age of sexual maturity

Question 8

what are 6 factors that effect fitness?

Answer 8

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

Question 9

what two kinds of factors influence population size?

Answer 9

density independent and density dependent factors

both limit the natural, genetically determined potential for population increase

Question 10

what is a density independent factor? examples?

Answer 10

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

Question 11

what is a density dependent factor? examples?

Answer 11

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

Question 12

what governs R?

Answer 12

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

Question 13

what are the components of fitness? does having a certain allele impact….

Answer 13

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

Question 14

what is viability?

Answer 14

probability that individual bearing genotype will survive

Question 15

what is fecundity?

Answer 15

number of gametes per individual

fruitfulness and fertility, the ability to produce abundant healthy growth or offspring

Question 16

what is mating success?

Answer 16

number and quality of mates

Question 17

what is gamete viability?

Answer 17

alleles impact the longevity or quality of the egg or sperm

Question 18

what is fertilization success?

Answer 18

alleles impact the probability that fertilization will take place

Question 19

what is relative fitness? what’s the symbol for it?

Answer 19

relative measure of survival and reproduction (W)

W of best genotype AA, Aa = 1

W of other genotype aa = 1-s

Question 20

what is the selection coefficient? whats the equation?

Answer 20

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

Question 21

what is differential survival and reproduction?

Answer 21

non random process through which pre-existing variation is sorted

Question 22

what is directional selection?

Answer 22

if individuals at one extreme of the range of phenotypes of fittest

Question 23

what is purifying selection?

Answer 23

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

Question 24

what is disruptive selection?

Answer 24

if 2 or more discontinuous phenotypes are fittest

Homozygous phenotypes fitter than heterozygote –> allele frequencies will be maintained but not phenotype frequencies

Question 25

what is stabilizing selection?

Answer 25

if the intermediate phenotype is fittest

heterozygote phenotype is fitter than homozygotes and the frequency of homozygotes is therefore reduced

Question 26

what is positive selection?

Answer 26

When selection acts to favor a phenotype or genotype, selection is positive

Question 27

what is negative selection?

Answer 27

When selection acts to eliminate a phenotype or genotype, selection is negative

Question 28

what is frequency dependent selection?

Answer 28

Selective regime and its impact differ depending on the frequency of pheno- or geno-types

Question 29

what is frequency independent selection?

Answer 29

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