Genetic Similarities between Subspecies of the White-Crowned Sparrow

Abstract

Tissue samples from 121 birds representing two subspecies of the Whitecrowned Sparrow, Zonotrichia leucophrys, and their zone of intergradation, were obtained from a linear series of eight localities along the Pacific coast of California and Oregon. The region sampled included all of the range of Z. 1. nuttalli, and a portion of the range of Z. 1. pugetensis. Allozyme variation at 46 presumptive gene loci was examined by means of starch gel electrophoresis; 15 of these loci (32.6%) were polymorphic. Allelic frequencies of these loci are reported here; they are used in an analysis of Wright's F-statistics and to estimate gene flow and indices of genetic distance. The population genetic structure of at least one deme within the zone of intergradation differs from that of the two intergrading subspecies, but the subspecies themselves apparently are not genetically differentiated from one another. This conclusion is supported by several lines of evidence: allelic frequencies of the subspecies are not significantly different, as determined by estimates of genetic distance; the association between interlocality F,, values and geographic distances is not significant, as measured by the Mantel test; and a reconstruction of the evolutionary relationships based on the genetic distances of Nei, Rogers, and Cavalli-Sforza and Edwards groups localities representing the two subspecies together, but separate from localities within the zone of intergradation. All lines of evidence suggest high levels of gene flow between the subspecies.