Shrews (genus: Sorex), among the smallest mammals, have high metabolic rates, short generation time, and high mutation rates. Patterns of genetic differentiation provide insight into biogeographic structure and the response of organsims to environmental change, so the rapidly evolving shrew is an excellent model for interpreting fine scale response of vertebrates to environmental change. Population and community structure have been dynamic since the last glacial maximum (LGM), often following a latitudinal shift in response to changing climate. However, sometimes populations become isolated in discreet areas due to elevational shifts in response to changing climate and these organisms are now found in disjunct “sky island” refugia. Molecular signatures for these disjunct populations reflect their demographic history. Signatures of shrews occurring in the Jemez Mountains of New Mexico were explored and revealed that individuals thought previously to be Sorex cinereus (occurring in the Sangre de Cristo Mountains) are actually a close relative, S. haydeni. Sorex haydeni is a mesic grassland species of the central Great Plains whereas habitat in the Jemez Mountains is semi-arid to mesic coniferous forest and montane meadows. We investigate phylogeographic structure across these species to understand their history. We test competing hypotheses that this population is either a relict from cooler climates of LGM versus a more contemporary colonization event. Mitochondrial DNA sequences were obtained through standard laboratory procedures and phylogeographic and population genetic parameters were generated.
All shrews of S. cinereus and S. haydeni tested from northern New Mexico resulted in two discreet populations with no overlap in distributions. The Jemez Mountains was represented only by S. haydeni, an extension of the known range of this species and a geographically disjunct population, whereas the Sangre de Cristo Mountains were represented by S. cinereus. Genetic signatures of both species suggest persistence of these populations in New Mexico although relatively lower genetic diversity in the Jemez Mountains also indicates limited population size and a potential historical bottleneck. Within S. haydeni, the Jemez Mountain population represents a distinct evolutionary clade due to isolation from populations further north. These findings have implications for the conservation of peripheral populations and understanding the response of southwestern montane mammals to environmental change.