THE PHYLOGEOGRAPHIC PATTERN OF MITOCHONDRIAL-DNA VARIATION IN THE DALLS PORPOISE PHOCOENOIDES DALLI

We used 11 restriction endonucleases to study mtDNA variation in 101 D all's porpoises Phocoenoides dalli from the Bering Sea and western Nor th Pacific. There was little phylogeographic patterning among the 34 m tDNA haplotypes identified in this analysis, suggesting a strong histo rical connection among populations across this region. Nonetheless, mt DNA variation does not appear to be randomly distributed in this speci es. Both G(ST) and AMOVA uncovered significant differences in the dist ribution of mtDNA variation between the Bering Sea and western North P acific populations. These mtDNA results, coupled with differences in a llozyme variation and parasite infestation, support the demographic di stinctiveness of Bering Sea and western North Pacific stocks of Dall's porpoise. The lack of a strong phylogeographic orientation of mtDNA h aplotypes within the Dall's porpoise is similar to the pattern reporte d in other vertebrates such as coyotes, blackbirds, chickadees, marine catfish, and catadromous eels. Like Dall's porpoise, these species ar e broadly distributed, and have large populations linked by moderate t o high levels of gene flow. However, the more complex, deeply branched phylogenetic network of mtDNA haplotypes within Dall's porpoise, rela tive to these other vertebrates, suggests important differences betwee n these species in the forces shaping mtDNA variation. One such force is the effective size of female populations, which appears to have bee n comparatively large and stable in Dall's porpoise.