Adaptation and Natural Selection 12.4 Warning coloration in a western coral snake (Micrurus euryxanthus) C:\Figures\Chapter12\high-res\Evolution-Fig-12-04-0.jpg

The Outcome of Natural Selection Depends Upon: Relationship between phenotype and fitness. (2) Relationship between phenotype and genotype. Determine the relationship between fitness and genotype. Outcome determines if there is evolution

% survival to reproduction: A = 0.05 B = 0.10 12.2 Growth of 2 genotypes in an asexually reproducing population w/ nonoverlapping generations % survival to reproduction: A = 0.05 B = 0.10 Fecundity (eggs produced): A = 60 B = 40 C:\Figures\Chapter12\high-res\Evolution-Fig-12-02-0.jpg Fitness A = 0.05 x 60 = 3 Fitness B = 0.05 x 60 = 4

R = Per Capita Growth Rate = Represents Absolute Fitness The rate of genetic change in a populations depends upon relative fitness: Relative Fitness of A = Absolute fitness A Highest Absolute Fitness WA = 3/4 = 0.75 Often by convention, fitness is expressed relative to the genotype with highest absolute fitness. Thus, WB = 4/4 = 1.0

The fitness of a genotype is the average lifetime contribution of individuals of that genotype to the population after one or more generations, measured at the same stage in the life history.

12.3 Components of natural selection that may affect the fitness of a sexually reproducing organism C:\Figures\Chapter12\high-res\Evolution-Fig-12-03-0.jpg

12.1(1) Modes of selection on a heritable quantitative character C:\Figures\Chapter12\high-res\Evolution-Fig-12-01-1.jpg

12.1(2) Modes of selection on a polymorphism consisting of two alleles at one locus C:\Figures\Chapter12\high-res\Evolution-Fig-12-01-2.jpg

Individuals may differ in fitness because of their underlying genotype Incorporating Selection Individuals may differ in fitness because of their underlying genotype Genotype A1A1 A1A2 A2A2 Frequency p2 2pq q2 Fitness w11 w12 w22 Average fitness of the whole population: w = p2w11 + 2pqw12 + q2w22

Given variable fitness, frequencies after selection: Genotype A1A1 A1A2 A2A2 Freq p2 w11 2pq w12 q2 w22 w w w New allele frequencies after mating: p2 w11 pq w12 pq w12 q2w22 + + w w New Frequency of A1 New Frequency of A2

Fitness: Probability that one’s genes will be represented in future generations. Hard to measure. Often, fitness is indirectly measured: (e.g. survival probability given a particular genotype) WAA WAa Waa 1 1 1 + s Fitness is often stated in relative terms Selection coefficient gives the selection differential

Persistent Selection Changes Allele Frequencies (i.e. Evolution by Natural Selection) Strength of selection is given by the magnitude of the selection differential

Selection Experiments Show Changes in Allele Frequencies HW Cavener and Clegg (1981) Food spiked with ethanol

Selection can drive genotype frequencies away from Hardy Weinberg Expectations

Predicted change in allele frequencies at CCR5 High frequency (Europe) High selection/transmisson (Africa) Predicted change in allele frequencies at CCR5 High frequency (Europe) Low selection/transmisson (Europe) Low frequency (Africa) High selection/transmisson (Africa)