Microgeographic Variation of Morphometric and Electrophoretic Characters in Peromyscus leucopus

Abstract

White-footed mice, Peromyscus leucopus, from a small geographic area (<12 kM2) in N-central Kansas were analyzed for patterns of morphological and electrophoretic variability. Peromyscus leucopus were collected from five areas of favorable habitat separated to varying degrees by unfavorable habitats: croplands, pastures, and roads. Populations sampled were assumed to be relatively isolated. Results showed little subdivision; no significant morphological variation occurred among areas and there were only slight differences at one genetic locus. Lack of differentiation is likely due to dispersal although trapping efforts in unfavorable habitats in this general region seldom yield any P leucopus. Age, but not sex, had a significant effect on morphological variation in Peromyscus leucopus; this pattern was the same for all samples. White-footed mice in N-central Kansas were larger than those from the eastern and southern portions of the range -a macrogeographic pattern of size variation that fits a reformulation of Bergmann's Rule. INTRODUCTION White-footed mice, Peromyscus leucopus, occur in woodlands and brushy habitats in much of the eastern two-thirds of the United States (Baker, 1968). In arid regions of the range, populations are restricted to riparian woodlands, scattered patches of shrubs and trees, and planted woodlands (e.g, shelterbelts) on farmsteads (Fleharty and Stadel, 1968), although individuals are occasionally found some distance from trees (Choate and Fleharty, 1975). Isolation among populations in areas of favorable habitat is likely related to the magnitude of barriers to dispersal (unfavorable habitat). To assess differentiation among populations of P leucopus under these conditions, we examined morphological and electrophoretic characteristics of samples from five localities within a small geographic area (< 12 kM2) in N-central Kansas. These samples were from five areas of favorable habitat separated by unfavorable habitats-pastures, croplands and roads. Our objectives were to: (1) describe aspects of morphological and electrophoretic variation; (2) examine effects of age and sex on morphological variation; (3) estimate the degree of subdivision among populations, and (4) compare P leucopus from this region to those from other parts of the distributional range. STUDY SITE AND METHODS Peromyscus leucopus were live-trapped in five areas of wooded habitat which were interspersed among mixed grass prairie, cropland and additional woodland within the total study site (< 12 kM2). Samples 2 and 3 were from shelterbelts and 1, 4 and 5 were from wooded areas along streams (Fig. 1). Sampling areas were separated by grassland and/ or cropland except for 4 and 5 which were separated by an elevated unpaved road. Two study areas, 2 and 5, were sampled in 1976 (2A and 5A) and 1977 (2B and 5B); the other three were sampled only in 1977. Specific localities and sample sizes (N) were (all 'Present address: Department of Biology, Southwest Missouri State University, Springfield 65804.