Selection for increased cranial capacity in small mammals during a century of urbanization

Urbanization is a selective force that is known to drive changes in the population dynamics of wildlife. How animals adapt to changing environmental conditions is crucial to their survival in these environments. Brain size, or cranial capacity, is a known proxy of behavioral flexibility, and can be used to assess how well a species has adapted to a particular environment. We examined cranial capacity changes in a time series of small mammal skulls collected from urban and rural populations in south western Pennsylvania. Urban skulls were collected from Allegheny county—an area that experienced rapid urbanization over the past century, and rural skulls from Powdermill Nature Reserve (Carnegie Museum), which has remained relatively unchanged forest over the same period. Our results show that Peromyscus leucopous (white-footed mouse) and Microtus pennsylvanicus (meadow vole) from urban populations had significantly greater cranial capacity than their rural counterparts, but the opposite wa...