Topic 9 Population subdivision and gene flow

• a large population composed of 2 or more partially/completely isolated subpopulations • mating within the metapopulation is NOT random

-groups of indiv. that mate randomly with each other (in absence of inbreeding and assortative mating)

-refers to the fact you almost never have a single panmictic population but rather subpopulations **population subdivision reduces heterozygosity (perception) -e.g. earth worms (poor dispersal abilities) –> 2 subpopulations vs. 1

the perception of a heterozygote deficit caused by treating 2 separate subpopulations as a single population

• quantifies the (avg reduction) changes in heterozygosity WITHIN subpopulations • as a result of factors such as inbreeding, outbreeding, and assortative mating • range: -1 to 1 -changes due to all factors: inbreeding, outbreeding, assortative mating

• quantifies the proportion of the total reduction in expected heterozygosity at the metapopulation level, which occurs as result of population subdivision alone • range: 0 to 1 • due to differences among subpop’ns (not w/in) • def’n 2: proportion of total genetic variation in the metapopulation due to differences in allele freq’s among the subpop’ns

• quantifies the total decrease in heterozygosity (HW deviation) at the metapopulation level as a result of: a) any deviations WITHIN each subpopulation (e.g. inbreeding, etc), and b) due to subdivision w/in the metapopulation

• another way of measuring population differentiation • the larger the value of Nei’s D, the greaterthe difference in allele frequencies among populations and subpopulations • range: 0 to infinity -in allozyme data: gives number of allelic substitutions at a locus

• Fst variant • advantage: unlike Fst, Nst can be used for haploid (as well as diploid) • Fst only works for diploid -considers both haplotype freq’s, and the sequence divergence b’w those haplotypes to quantify pop’n diff’s

• Fst variant • advantage: unlike Fst, Nst can be used for haploid (as well as diploid) -considers only haplotype freq’s (diff’s among pop’s) to quantify pop’n diff’s

genetically similar haplotypes co-occur w/in subpop’ns, but dissimilar haplotypes occur b/w pop’ns

genetically divergent haplotypes co-occur w/in subpop’s, but at different frequencies

• a special variant of X2 (squared) test - useful b/c it can be applied to any type of data: allozymes, microsatellites, and chloroplasts