Morphological Differentiation in White-footed Mouse (Mammalia: Rodentia: Cricetidae: Peromyscus leucopus) Populations from the New York City Metropolitan Area

Genetic studies have shown that New York City white-footed mouse (Peromyscus leucopus) populations exhibit substantial genetic structure and high levels of allelic diversity and heterozygosity. These studies have also identified mutations and genes involved in the divergence of urban and rural P. leucopus populations. To investigate whether morphological change mirrors the genetic differentiation observed in New York City P. leucopus populations, we conducted univariate and multivariate analyses on 4 external and 14 skull variables to compare urban, suburban and rural P. leucopus populations from in and around New York City. The only significant morphological differences among the three populations were in upper and lower toothrow lengths, both of which had high loadings in our principal components analyses. In general, rural individuals were found to have longer upper and lower toothrows than urban ones. This difference is likely due to the relationship between food quality and size of dental occlusal surfaces. Generally, lower quality food requires more chewing and its consumption is facilitated by larger occlusal surfaces. Our results suggest that urban mice consume a higher-quality diet or food that requires less chewing than their rural counterparts by making use of the availability of natural food sources in rich, vegetative understories characteristic of urban forest fragments. Our cluster analysis of the skull variables revealed that urban and suburban populations are more similar to one another than to the rural population.