Genetic structure of muskrat (Ondatra zibethicus) and its concordance with taxonomy in North America.

Extrinsic factors such as physical barriers play an important role in shaping population genetic structure. A reduction in gene flow leading to population structuring may ultimately lead to population divergence. These divergent populations are often considered subspecies. Because genetic differentiation may represent differences between subspecies, patterns of genetic structure should reflect subspecies groupings. In this study, we examine the contemporary population genetic structure of muskrat (n = 331) and assess the relevance of 4 geographically distinct subspecies designations across northern North America using 9 microsatellite loci. We predicted that patterns of gene flow and genetic structure would reflect the described subspecies. We found evidence of genetic differentiation between western and eastern regions, and muskrats from Newfoundland (NF) showed significantly lower genetic diversity than central regions. A strong isolation by distance pattern was also detected within the eastern cluster. Our results did not differentiate Ondatra zibethicus spatulus (northwest) from O. z. albus (central), but they suggest a distinction between O. z. obscurus (NF) and O. z. zibethicus (east). This study highlights the need for more phylogenetic studies in order to better understand intraspecific divergence and the genetic characterization of subspecies.