sexual selection, gene flow, and genetic drift

lect. 12, bio 121

sexual dimorphism

distinct differences in size/appearance/behaviour/physiology between male and females

intrasexual and intersexual

2 mechanisms of sexual selection

intrasexual selection

competition between 2 individuals of same sex for mates (usually males)

intersexual selection

when one member of one sex (usually female) chooses a member of the opposite gender as a mate

asymmetry in gametes- cheap sperm and costly eggs

why did darwin think females were more choosy than men?

male signals to female that they would provide better direct/indirect benefits

what would make one male more enticing to a female than another male?

resources, protection, parental care, fertility

direct benefit examples

phenotypes, looking healthy- no parasites, good immune system, non-damaged DNA

indirect benefit examples

phenotypic variation amongst individuals in population, heritable variation, differences in fitness (phenotype)

3 requirements for evolution by sexual selection

gene flow

movement of genes into/out of a population

organism leaves and moves to new population, organism does not leave but gametes move

how does a gene flow occur?

can introduce new alleles into a population, make different populations more genetically similar

gene flow implications for evolution

genetic drift

changes in allele frequencies in a population over time due to chance events (random differences)

super strong- loses genetic diversity/variation more quickly

what effect does genetic drift have on small populations?

speciation

small, isolated population may diverge genetically from other larger populations due to genetic drift

bottleneck event and founder event

2 special opportunities for genetic drift to occur

bottleneck effect

effect occurs when a population’s size is substantially reduced for at least one generation (wildfire, flood)

founder effect

effect occurs when a new population is started by a few members of original population in new location