PHYLOGEOGRAPHY, POPULATION-STRUCTURE AND DISPERSAL PATTERNS OF THE BELUGA WHALE DELPHINAPTERUS-LEUCAS IN THE WESTERN NEARCTIC REVEALED BY MITOCHONDRIAL-DNA

The recent evolutionary history, population structure and movement pat terns of beluga whales in the western Nearctic were inferred from an a nalysis of mitochondrial DNA control region sequence variation of 324 whales from 32 locations representing five summer concentration areas in Alaska and north-west Canada. Phylogenetic relationships among hapl otypes were inferred from parsimonious networks, and genetic subdivisi on was examined using haplotypic frequency-based indices and an analys is of variance method modified for use with interhaplotypic distance d ata. MtDNA relationships were characterized by a series of star-like p hylogenies which, when viewed in conjunction with information on haplo type frequency and distribution, suggested a rapid radiation of beluga whales into the western Nearctic following the Pleistocene, and an ea rly divergence of the Beaufort Sea from the Chukchi and Bering Seas su bpopulations. Overall nucleotide diversity was low (0.51%) yet all maj or summering concentrations were significantly differentiated (Phi(ST) = 0.33) from one another. Stratification of samples by gender and age from the three northernmost subpopulations suggested that female coho rts from neighbouring subpopulations were more differentiated than mal es. Further stratification of adult animals by age revealed that older adults were substantially less subdivided among locations than younge r adults, particularly for males, suggesting that dispersal, although limited, is biased toward older adult males. Overall, the patterns of mtDNA variation in beluga whales indicated that the summering concentr ations are demographically, if not phyletically distinct. Population s tructure appears to be maintained primarily by natal homing behaviour, while asymmetries in dispersal may be associated with the type of mat ing system.