Evolutionnary relationship of some beringian mammals [Relation évolutive de certains mammifères béringien].

Résumé

Beringia served as a bridge for intercontinental dispersal of mammals between Asia and North America at several different times during the history. Some taxa have diverged considerably since their earlier residence in Beringia while other more recent inhabitants are still considered conspecific throughout their Holarctic distribution. Certain ground squirrels of the genus Citellus provide excellent models for the study of evolutionnary relationships among past and presnt Beringian inhabitants. Chromosome, electrophoretically separable hemoglobins, transferrins and isozymes, and cranial measurements examined by multivariate statistical techniques were compared in populations of Holarctic Citellus parryi (2 n = 34) and in Asian C. undulatus and American C. columbianus, which both display 2 n = 32. After isolation by the Bering Strait for 12,800 years C. parryi has maintained similar chromosomes, and some (G6PD) in 10 proteins has undergone a change in electrophoretic mobility, but skull morphology has diverged. In the C. undulatus-C. columbianus complex there was no chromosomal divergence and Glemsa band patterns substantiate homology after isolation for at least 100,000 years. However, during this time two in 11 proteins (transferrin and albumin) have differentiated and cranial divergence has been striking. These data are applied to a zoogeographic reappraisal of the arctic and long-tailed ground squirrel group. The applicability of chromosomal, biochemical and numerical taxonomic techniques to similar zoogeograhic and evolutionary problems in Beringian species of Microtus, Clethrionomys and Ovisis is discussed