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

<p><span><span><span><span><span><span><span><span><span><span><span>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 <i>Peromyscus leucopous</i> (white-footed mouse) and <i>Microtus pennsylvanicus</i> (meadow vole) from urban populations had significantly greater cranial capacity than their rural counterparts, but the opposite was true for <i>Eptesicus fuscus</i> (big brown bat). We found no difference in relative cranial capacity across time in any of the small mammal species. Our results suggest that a larger cranial capacity is selected for in an urban environment and reinforces the hypothesis that behavioral flexibility is important for animals to adapt to novel environments.</span></span></span></span></span></span></span></span></span></span></span></p>