Cultural and Genetic Variation in Swamp Sparrows (Melospiza Georgiana)

The relationship between variation in a cultural trait, the songs of male swamp sparrows Melospiza georgiana, and genetic variation at nine polymorphic enzyme loci was examined using seven geographic locations covering a major portion of the breeding range of this species. Swamp sparrow songs exhibit geographical variation, and song populations at a location can remain relatively stable over a ten year period. Three measures of song syllable variation were used to examine the similarities between the song populations. Electrophoretic analysis suggested at least 3 groups of locations based on allelic frequency differences. Two of these groups are geographically extensive. The mean proportion of songs two locations share is related independently to the distance between the locations and to the similarity of their allele frequencies. The allele frequency similarity between two locations is not related to the geographic distance between them. A descriptive analysis of the relationship between song and genetic variation yielded two conclusions. First, two of the three population subdivisions exhibited a pattern of correlation between song syllable variation and genetic variation that may resemble character displacement. The similarity of song syllables at two locations may depend on the position of the two locations relative to the region where different allele-frequency groups come into contact. Second, this pattern of correlation did not hold for comparisons involving the third subdivision, and thus was not species universal in swamp sparrows. Song syllable variation may have different biological relevance in different geographical areas.