PATTERNS OF MITOCHONDRIAL-DNA DIVERGENCE IN NORTH-AMERICAN CRESTED TITMICE

This survey of patterns of mitochondrial DNA variation in the Tufted Titmouse (Parus bicolor), Plain Titmouse (P. inornatus), and Bridled Titmouse (P. wollweberi) provides a critical assessment of genetic divergence in a well-defined taxonomic hierarchy of passerine birds. Maximum divergence between coexisting haplotypes was 0.16% and no more than two haplotypes were found in a local population sample. Divergence distances between taxa were calculated from matrices of 191 shared restriction fragments and 128 shared restriction sites. Distances calculated from proportions of shared sites tended to be higher than distances calculated from shared fragments. Divergence distances between species suggest origins in the Pliocene (wollweberi vs. bicolor and inornatus) and in the early Pleistocene (bicolor vs. inornatus). Comparisons of allopatric, conspecific populations confirm the low divergence value reported by Avise and Zink (1988) for P. b. bicolor versus P. b. atricristatus. Our calculated distance (0.006) for these two semispecies was the same as the distance between P. w. wollweberi versus P. w. phillipsi. In contrast, coastal inornatus (transpositus) exhibit species level divergence (p = 0.05) from interior inornatus (ridgwayi). This result supports the conclusions of other recent studies that suggest a long historical separation of coastal California populations from sister taxa in the Great Basin.