Microtus richardsoni DeKay 1842

Microtus richardsoni DeKay 1842, Zoology of New York, Part I, Mammals: 91.

Type Locality: Canada, Alberta Prov., vicinity of Jasper House (as interpreted by Bailey, 1900:60).

Vernacular Names: North American Water Vole.

Synonyms: Microtus arvicoloides (Rhoads 1894); Microtus myllodontus Rasmussen and Chamberlain 1959; Microtus principalis Rhoads 1895 .

Distribution: Wet subalpine and alpine meadows of Rocky Mountains, from S British Columbia and Alberta, Canada, to W Wyoming and C Utah, USA; and of Cascade Mountains, from SW British Columbia south through WC Oregon.

Conservation: IUCN – Lower Risk (lc).

Discussion: Senior synonym of the type (= arvicoloides) of Aulacomys . In early classifications (Bailey, 1900; Miller, 1896), richardsoni was placed with Old World water voles in the subgenus Arvicola (including Aulacomys) of Microtus, a relationship reaffirmed by Hooper and Hart (1962) and followed by others, with Arvicola employed either at the subgeneric (Hall, 1981) or generic level (Jones et al., 1975). Substantial evidence argues the retention of richardsoni within Microtus and the restriction of Arvicola to Old World forms (Carleton, 1981; Conroy and Cook, 2000 a; Gromov and Polyakov, 1977; Hinton, 1926 a; Jannett, 1997; Koenigswald, 1980; Repenning, 1980; Zagorodnyuk, 1990). Hoffmann and Koeppel (1985) further suggested the autochthonous origin of M. richardsoni in North America from an early stock that also gave rise to M. xanthognathus, an idea consistent with the biochemical similarity of richardsoni to certain New World Microtus (Nadler et al., 1978) and with Zagorodnyuk's (1990) usage of the subgenus Aulacomys; cytochrome b sequence data, although also supporting a North American origin, disclose nearest kinship to M. (Pitymys) pinetorum (Conroy and Cook, 2000 a) . See Ludwig (1984, Mammalian Species, 223).