Molecular systematics of pikas (genus Ochotona) inferred from mitochondrial DNA sequences

The phylogenetic relationships among worldwide species of genus Ochotona we re investigated by sequencing mitochondrial cytochrome b and ND4 genes. Par simony and neighbor-joining analyses of the sequence data yielded congruent results that strongly indicated three major clusters: the shrub-steppe gro up, the northern group, and the mountain group. The subgeneric classificati on of Ochotona species needs to be revised because each of the two subgener a in the present classification contains species from the mountain group. T o solve this taxonomic problem so that each taxon is monophyletic, i.e., re presents a natural clade, Ochotona could be divided into three subgenera, o ne for the shrub-steppe species, a second for the northern species, and a t hird for the mountain species. The inferred tree suggests that the differen tiation of this genus in the Palearctic Region was closely related to the g radual uplifting of the Tibet (Qinghai-Xizang) Plateau, as hypothesized pre viously, and that vicariance might have played a major role in the differen tiation of this genus on the Plateau, On the other hand, the North American species, O. princeps, is most likely a dispersal event, which might have h appened during the Pliocene through the opening of the Bering Strait. The p hylogenetic relationships within the shrub-steppe group are worth noting in that instead of a monophyletic shrub-dwelling group, shrub dwellers and st eppe dwellers are intermingled with each other. Moreover, the sequence dive rgence within the sister tars of one steppe? dweller and one shrub dweller is very low. These findings support the hypothesis that pikes have entered the steppe environment several times and that morphological similarities wi thin steppe dwellers were due to convergent evolution. (C) 2000 Academic Pr ess.