Rustin Reed and Dr. Duke S. Rogers, Department of Biology
We examined relationships among samples of the Dusky shrew (Sorex monticolus) in the Intermountain West, concentrating on Utah locations with the aim of clarifying the distribution of two continental groups identified in a recent study by Demboski and Cook (2001). Genealogies were derived from mitochondrial DNA sequence and phylogenetic analysis confirmed the split between continental samples of S. monticolus into northern and southern units. We were fortunate enough to present our results on a poster at the Evolution Conference 2009 in Moscow, Idaho. We are currently preparing a manuscript for publication in the Journal of Mammalogy.
As presently understood, the range of Sorex monticolus (Demboski and Cook, 2001 and including S. monticolus, S. bairdi, S. monticolus, S. neomexicanus and S. pacificus) encompasses the boreal and temperate rain forest regions from Alaska south to the montane sky islands in the southern Rocky Mountains of North America. Based on analysis of 801 base pairs of the cytochrome b (cyt-b) gene, Demboski and Cook (2001) identified several groups within S. monticolus including: a coastal group containing S. monticolus, S. bairdi and S. pacificus and distributed from south-east Alaska to Oregon as well as a geographically widespread continental group found from Alaska to Arizona and containing S. monticolus and S. neomexicanus. In turn, the continental group was split into two sub-groups: northern and southern. The Northern Continental group was distributed from northern Alaska to Idaho, whereas the Southern Continental group was present from locations in Arizona (including S. neomexicanus), Colorado, New Mexico and Utah. However, the amount of contact (if any) between these two groups was undetermined given the broad sampling effort. The purpose of this study was to present a preliminary phylogenetic analysis of cyt-b sequence data with the aim of clarifying the distributions of the Northern and Southern Continental groups.
We developed Cyt-b sequence data for an additional 194 samples of S. monticolus from the intermountain west. Using software analysis, tree reconstruction resolved three groups. Groups I and II (Figure 1: circles and squares, respectively) correspond to the Southern and Northern Continental groups as described by Demboski and Cook (2001). Based on additional sampling within Utah, we document eight locations (one from Wasatch County and seven from Garfield, Wayne, and Sevier Counties, Utah), in which the northern and southern groups co-occur (red stars). These two groups occur in nearby locations in Duchesne, Sevier, and Summit Counties, Utah. In addition, we found two partitions within the Southern Continental group that correspond to southwestern and central Utah (yellow circles) versus all other Southern Continental locations in Utah, Colorado, New Mexico and Arizona. These two groups also co-occur in 15 locations within Garfield, Wayne, Sevier and Beaver Counties as indicated by the blue circles.
The presence of dusky shrews representing both Northern and Southern Continental groups in cooccurrence indicates that these groups may represent unique units at the species-level. To test this hypothesis, we are evaluating relatively more rapidly evolving nuclear markers. It is not unrealistic to assume that the northern and southern groups were separated during the early to mid-Pleistocene and have recently come into secondary contact, although the precise timing of this event awaits fossil calibration and examination of multiple molecular markers. We hypothesize that Dusky shrews that currently occur in central and southwestern Utah were isolated as well, perhaps indicating a late Pleistocene refuge in southwestern Utah and/or southeastern Nevada. These results are similar to those described by Hafner and Sullivan (1995) for Ochotona princeps (American Pika) in which major groups in the Intermountain West all were represented in Utah. This pattern of high genetic diversity among montane organisms within the confines of Utah should be tested evaluating other co-distributed species.
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