Evolution of dental traits since latest Pleistocene in meadow voles (Microtus pennsylvanicus) from Virginia

Abstract

Digitizing the third upper molars of Microtus pennsylvanicus reveals evolutionary change in some traits but stability in others during the last 30,000 years. Fossils from Strait Canyon, Virginia (radiocarbon dated between 29,870 + 1,800/-1,400 and 17,880 ± 150 yr B.P.) were compared with modern samples from the margin of the species' conterminous geographic range: Virginia, Colorado, Alaska, and Hudson Bay. Since the late Pleistocene a modification from narrow to wide teeth took place in the eastern populations but not in the western ones, and populations in Virginia apparently evolved wider confluence between triangles 1 and 2. Traits that remained stable through time in the Virginia area, but not necessarily elsewhere, include the numerical shape factors of the occlusal surface and the posterior loop. Potentially widespread stability is evident in the perimeter of the posterior loop relative to total tooth perimeter. Tooth length forms a geographic cline, in which both the fossil and modern populations from Virginia occupy the same position. A peripheral population from southern Colorado shows the most derived dental morphology. These morphological relationships suggest that mosaic evolution operates in arvicoline lineages and provide testable paradigms for future studies.