Extensive Protein Similarity of the Hybridizing Chickadees Parus atricapillus and P. carolinensis

Abstract

Starch gel electrophoresis of proteins was used to assess genetic differentiation and introgression across a contact zone between Parus atricapillus and P. carolinensis. Little or no differentiation was found at 35 presumed genetic loci, even between distantly allopatric population samples. Nei's (1978) genetic distance (D) was <O.001 for all comparisons. In contrast, Parus gambeli, another chickadee known to hybridize with atricapillus, was well differentiated at 3 loci (D - 0.065). While the data suggest that atricapillus and carolinensis are closely related, they do not allow conclusions on the extent of introgression across the contact zone. The implications of these data are discussed in the light of the emerging pattern of isozyme variation in birds. Received 26 August 1985, accepted 28 March 1986.