Geographic and nongeographic variation in the genus Microtus (Mammalia: rodentia) in West Virginia

Geographic and nongeographic variation was assessed on 12 cranial and 4 external characters in approximately 400 specimens of Microtus (M. ochrogaster, M. chrotorrhinus, M. pinetorum, M. pennsylvanicus) in West Virginia. Univariate and multivariate statistical analyses were used to examine age-related variation, sexual dimorphism, elevation and geographic variation and litter size for each species of Microtus in the state. Cranial characters were more beneficial than external in detecting variation. Examination of data for each species of Microtus studied demonstrated that values and trends in variation is a specific rather than a generic trait. Age-related variation was present in some, but not all species for individual characters. Sexual dimorphism was not demonstrated on a large scale. No evidence of geographic variation was shown. The mean litter size was 4.43 +/- 1.20 for M. pennsylvanicus. No evidence of geographic variation was found in the average litter sizes