Genetic analysis of song dialect populations in Puget Sound white-crowned sparrows

The relationship between cultural variation and biological variation among natural populations has been the subject of both theoretical and empirical study. Zonotrichia leucophrys pugetensis is one of three subspecies of white-crowned sparrow known to form geographical song dialects. We investigated whether these dialects correspond to genetic differences among Z. l. pugetensis populations. We compared allele frequencies at four microsatellite loci in males from 11 sites spanning six dialects over the subspecies' range in Oregon and Washington. Cluster analysis and genotype assignment tests indicated no tendency for sample sites within dialect areas to be genetically more similar than are sites from different dialect areas. AMOVA tests revealed high within-site variation and low but significant cross-site and cross-dialect-area variation. Finally, genetic distance between sites was not correlated with dialect differences when the effect of geographic distance was controlled statistically. We compare our finding of low genetic differentiation among Z. l. pugetensis dialect populations to results of previous studies on Z. l. nuttalli and Z. l. oriantha. Because genetic structuring appears weaker than cultural (song dialect) structure in this species, we discuss the behavioral mechanisms underlying dialect maintenance in the presence of apparent gene flow.