Dental Evolution of the Meadow Vole (Microtus Pennsylvanicus) in Mainland, Peninsular, and Insular Environments in Southern New England

Analyses of morphological and mensural variation in the molar dentitions of several populations of Microtus pennsylvanicus inhabiting mainland, peninsular, archipelagic, and insular environments in southern New England enabled elucidation of recent evolutionary trends in those populations. Dental evolution in voles of the pennsylvanicus lineage of the genus Microtus generally proceeds toward increased occlusal complexity in mainland habitats but toward decreased occlusal complexity on islands. Intraspecific and interspecific interactions play important roles in determining dental complexity. Quantitatively, insular populations usually are more variable than mainland populations because of the more intense selective forces that exist in insular environments. Likewise, intense K-selection on islands, as compared with that on the mainland, is responsible for the fact that microtine rodents generally are larger on islands than on the adjacent mainland. Factors responsible for increased natural selection on islands are discussed, and analysis of intrapopulational variation is shown to be useful as a measure of the rate of evolution.