Microgeographic population structure of the seaside sparrow on the Texas Gulf Coast: A microsatellite analysis

The seaside sparrow is a small emberezine finch that occurs in salt marsh habitat from New Hampshire on the Atlantic Coast to Nueces Bay, in southern Texas. Two of the nine races recognized by the American Ornithologists Union in 1983 have been recently extirpated, and a third is recognized as highly vulnerable. Habitat loss and modification have been unequivocally identified as the major causes of extirpation. Seaside sparrow habitat in Texas has been severely impacted by agricultural, industrial, commercial, and residential development.; This study employed nuclear genetic markers to determine the degree to which habitat fragmentation had affected gene flow and population structure in a seven population assemblage.; The seaside sparrow population assemblage in this investigation demonstrated structure among and within subpopulations. Subpopulations, exhibited significant deviations from Hardy-Weinberg Expectations. Three of the five loci were significant at P-value < 0.004; and four of the seven populations were significant at P-value < 0.002. An overall F_ST of 0.0322 and Rho_ST of 0.0643 for all populations over all loci reveal moderate structure and indicate recent restriction of gene flow. Inbreeding coefficients for both allele identity (F_IS) and allele size (Rho_IS) were positive and considerable (0.1230 and 0.4484, respectively) indicating nonrandom association of alleles at the subpopulation level. Small population sizes along with isolation probably account for this observed structure.