Peromyscus sp.

Peromyscus sp.

Currently, there is not a definitive name available for populations from the southwestern Yukon region that were found to be distinct from other members of the P. maniculatus species group by Wike (1998), Lucid and Cook (2007), and this study. The Yukon specimens genetically are different from populations of P. keeni to the south and from populations of P. maniculatus - like forms to the southwest and southeast that are now referable to P. sonoriensis. Wike (1998) eludes to the fact that the name P. arcticus might serve as a valid name for this distinct taxon. Although initially described as Hesperomys leucopus arcticus (Mearns 1890:285), this taxon later was treated as a subspecies, Peromyscus maniculatus arcticus (Osgood 1900:33). Later, Mearns (1911), based on “opinion 4” by the International Commission of Zoological Nomenclature (1910) realized that P. m. arcticus represented a preoccupied name that had been proposed by Coues (1877). Further, Mearns (1911) recognized that P. m. arcticus was problematic since the name referred to a specimen from Labrador (presumably assignable to a taxon from eastern Canada; most likely P. m. maniculatus); consequently, he described a new taxon (P. m. borealis) for the Yukon material and subsumed P. m. arcticus under this new subspecies and lists Fort Simpson, Yukon Territory, Canada as the type locality.

Based on the data presented by Wike (1998), Lucid and Cook (2007), and this study, the situation is further complicated by the fact that populations formerly referred to P. m. borealis are now assigned to P. sonoriensis (e.g. P. s. borealis). In fact, some of the samples, included herein (those assignable to P. s. borealis) are located only 235 km from the type locality of P. s. borealis at Ft Simpson, Yukon Territory; whereas the closest population of the seemingly new species (P. sp.; Lapie River; 8.5km West of Ross River) is located nearly 600 km to the west. However, it does not seem appropriate, at this time, to simply refer this new identified species to P. sp. until addition specimens in the vicinity of the type locality of P. s. borealis can be examined. Therefore, we have not provided a formal description for the putative new species; instead we off a brief discussion of how it differs, genetically, from the two species (P. sonoriensis and P. keeni) that geographically are in close proximity to P. sp.

Justification for a new taxon. —Examination of Cyt b sequences obtained in this study indicated that P. sp. differs from P. sonoriensis and P. keeni (two species geographically located to P. sp.) by 4.80% and 4.66% respectively. Genetic differentiation (= 0.92%) based on DNA sequences obtained from 28 individuals of P. sp. indicated a low level of genetic divergence for members of the P. maniculatus species group. This species exhibited a similar level of genetic divergence as did P. gambelii and P. labecula; two species that also occupy a fairly restricted geographic area.

Distribution of P. sp. —Occurs in the southwestern portion of the Yukon province (Wike 1998; Lucid and Cook 2004; Sawyer et al. 2017; this study). Specifically, it appears that P. sp. is distributed along the lower elevations associated with the western portion of the Klondike and Yukon Plateaus, bounded by the Ogilvie Mountains in the north, the Saint Elias Mountains to the south, and Pelly Mountains to the east. Further it appears that P. sonoriensis occupies the regions to the northeast and southwest of Haines Junction; whereas P. keeni is distributed further to the east and south. Further collecting in the southern Yukon is necessary to determine the distributions of the three species (P. keeni, P. sonoriensis and P. sp.) occupying this area.

Remarks. —Thirty-eight samples examined in this study were assigned to P. sp. Genetic divergences detected among the three species (P. keeni, P. sonoriensis, and P. sp.) occupying the Yukon and surrounding areas are similar to those detected among other recognized species in the P. maniculatus (Hogan et al. 1997; Greenbaum et al. 2017; this study), P. boylii (Bradley et al. 2014, 2017), and P. mexicanus (Bradley et al. 2015) species groups; and considerably less than reported for the P. truei (Durish et al. 2004) species group. Further these results are in agreement with characteristics of genetic species as presented in Bradley and Baker (2001) and Baker and Bradley (2006). Divergence estimates obtained herein suggested that P. sp. diverged from a common ancestor of the P. keeni clade approximately 1.12 mya.