Published May 10, 1956
University of Kansas
Lawrence, Kansas
PRINTED BY
FRED VOILAND, JR., STATE PRINTER
TOPEKA, KANSAS
1956
Subspeciation in the Meadow Mouse, Microtus pennsylvanicus, in Wyoming, Colorado, and Adjacent Areas
BY
SYDNEY ANDERSON
INTRODUCTION
In the region including Wyoming and Colorado, Microtus pennsylvanicus has been divided into two subspecies: the pale M. p. insperatus (J. A. Allen) inhabits the Black Hills of the northeasternmost part of Wyoming; the dark M. p. modestus (Baird) inhabits extensive areas in both Wyoming and Colorado. Initial examination of Microtus pennsylvanicus revealed that specimens from the Big Horn Mountains of north-central Wyoming (within the range of modestus as mapped by Hall and Cockrum 1952:407), in color at least, resemble the subspecies insperatus more than they do modestus, and that specimens from southwestern Wyoming are notably dark. Durrant (1952:363) noted that specimens from Utah are dark, and Davis (1939:315) did the same for specimens from near Pocatello, Idaho. It seemed, therefore, that dark color might characterize populations of a wide geographic region and distinguish them from modestus named from southern Colorado. Also, there seemed to be a hiatus of at least 180 miles between the ranges of modestus in northern Colorado and modestus in eastern Wyoming, and an even greater distance separating populations of modestus in northern Colorado from those in western Wyoming. Microtus pennsylvanicus has not been taken in central or southeastern Wyoming despite extensive collecting there, which yielded numerous records of other kinds of Microtus (M. longicaudus, M. montanus, and M. ochrogaster). Subsequent study revealed a pattern of geographic variation within the range now ascribed to modestus which, in my opinion, can be described best by the recognition of three new subspecies.
MATERIALS, METHODS, AND ACKNOWLEDGMENTS