SPECIATION IN SAPSUCKERS (SPHYRAPICUS) .3. MITOCHONDRIAL-DNA SEQUENCEDIVERGENCE AT THE CYTOCHROME-B LOCUS

We amplified and sequenced a 711 base-pair (bp) fragment of mtDNA at t he cytochrome-b locus to reexamine relationships within and among spec ies of Sphyrapicus and representatives of two other woodpecker genera (Melanerpes, Colaptes). Sequences were obtained from 10 individuals of 5 taxa: Red-breasted Sapsucker (S. ruber daggetti), n = 2; Red-naped Sapsucker (S. nuchalis), n = 2; hybrid of S. ruber daggetti x S. nucha lis, n = 1; Yellow-bellied Sapsucker (S. varius varius), n = 2; Willia mson's Sapsucker (S. thyroideus thyroideus), n = 2; and Red-bellied Wo odpecker (M. carolinus), n = 1. The Melanerpes sequence and a comparab le published sequence of Andean Flicker (C. rupicola) were used as out groups. Levels of mtDNA sequence divergence ranged from 0.0 to 0.6% wi thin species and 0.1 to 10.2% among species of Sphyrapicus, and from 1 2.5 to 14.5% between members of Sphyrapicus and the two outgroup speci es. One region of sequence (78 bp) was identified as being especially conserved. Branching topologies based on this study corroborated resul ts from a previous analysis of relationships in Sphyrapicus using allo zymes: the phenotypically dissimilar species ruber and nuchalis are mo st closely related; varius, which is very similar in appearance to nuc halis, branches off next; and thyroideus, the most divergent member of the quartet from the standpoint of plumage pattern and degree of sexu al dimorphism, is strongly differentiated genetically. Pairwise mtDNA distances within Sphyrapicus showed a strong curvilinear relationship with allozyme distances (r = 0.996). The monophyly of Sphyrapicus is r eaffirmed, with S. thyroideus closer to the ancestral species. Members of Sphyrapicus are more similar to Melanerpes than to Colaptes based on their mtDNA. Prior hypotheses regarding the evolutionary history of sapsuckers in North America are discussed. Despite the near genetic i dentity of ruber and nuchalis based on both allozymes and mtDNA sequen ces, and their tendency for limited hybridization in sympatry, an earl ier study of mating preference supports the biologic-species status of these taxa.