| I examined the distribution of genetic diversity among one northwestern US and six Canadian populations of a threatened songbird, the Brewer's sparrow (Spizella breweri breweri, Emberizidae, Passeriformes), using five primer pairs for microsatellite markers designed for other emberizine. DNA from almost all individuals amplified easily using an extraction protocol I developed and tested for small feather tissue samples. Three locus/population combinations displayed significant departures from Hardy-Weinberg equilibrium possibly suggesting a Wahlund effect or inbreeding. In addition, linkage disequilibrium was indicated for one population and three locus pairs possibly indicating an exchange of genes between genetically differentiated and isolated populations. Pair-wise estimates of FST across five loci ranged from 0 to 0.029, with only the latter value significant after sequential Bonferonni correction. An AMOVA suggested a small but significant proportion of total variation was attributable to population-level differentiation. Gene flow varied across pairs of populations, with Nem derived from Wright's FST ranging from ∼8 to ∼367, and using the private alleles method ranging from 2.2 to 4.8. Considered together these data suggest some viscosity of gene flow at fine geographic scales for certain population pairs, possibly as a cause of differences in dispersal coupled with strong breeding philopatry and increasing habitat fragmentation. |
