Sex-biased gene flow in spectacled eiders (anatidae): Inferences from molecular markers with contrasting modes of inheritance

Genetic markers that differ in mode of inheritance and rate of evolution (a sex-linked Z-specific microsatellite locus, five biparentally inherited mi crosatellite loci, and maternally inherited mitochondrial [mtDNA] sequences ) were used to evaluate the degree of spatial genetic structuring at macro- and microgeographic scales, among breeding regions and local nesting popul ations within each region, respectively, for a migratory sea duck species, the spectacled eider (Somateria fisheri). Disjunct and declining breeding p opulations coupled with sex-specific differences in seasonal migratory patt erns and life history provide a series of hypotheses regarding rates and di rectionality of gene flow among breeding populations from the Indigirka Riv er Delta, Russia, and the North Slope and Yukon-Kuskokwim Delta, Alaska. Th e degree of differentiation in mtDNA haplotype frequency among breeding reg ions and populations within regions was high (phi (CT) = 0.189, P < 0.01; p hi (SC) = 0.059, P < 0.01, respectively). Eleven of 17 mtDNA haplotypes wer e restricted to a single breeding region. Genetic differences among regions were considerably lower for nuclear DNA loci (sex-linked: phi (ST) = 0.001 , P > 0.05; biparentally inherited micro satellites: mean theta = 0.001, P > 0.05) than was observed for mtDNA. Using models explicitly designed for u niparental and biparentally inherited genes, estimates of spatial divergenc e based on nuclear and mtDNA data together with elements of the species' br eeding ecology were used to estimate effective population size and degree o f male and female gene flow. Differences in the magnitude and spatial patte rns of gene correlations for maternally inherited and nuclear genes reveale d that females exhibit greater natal philopatry than do males. Estimates of generational female and male rates of gene flow among breeding regions dif fered markedly (3.67 X 10(-4) and 1.28 X 10(-2), respectively). Effective p opulation size for mtDNA was estimated to be at least three times lower tha n that for biparental genes (30,671 and 101,528, respectively). Large dispa rities in population sizes among breeding areas greatly reduces the proport ion of total genetic variance captured by dispersal, which may accelerate r ates of inbreeding (i.e., promote higher coancestries) within populations d ue to nonrandom pairing of males with females from the same breeding popula tion.