A Multidisciplinary Investigation of the Applicability of the Pleistocene Herpetofaunal Stability Model to Collared Lizards (Crotaphytus collaris)

Recent paleontological evidence suggests the North American herpetofauna has been remarkably stable taxonomically and biogeographically throughout the Pleistocene. However, this paper uses paleontological, ecological, and molecular genetic data to argue that the thermophilous and xerically-adapted Collared Lizard (Crotaphytus collaris) did not persist in the northern parts of its range during glacial phases of the Pleistocene. First, a careful review of the paleontological data used to support the stability model reveals no northern fossils unambiguously dated to glacial phases. Second, environmental conditions inferred for the Ozark Plateau and Flint Hills during glacial phases were not compatible with fitness requirements of collared lizards. Third, phylogeographic analyses of an intraspecific mtDNA gene tree suggest a recent invasion of the Ozarks and Flint Hills. Finally, microsatellite data are statistically consistent with a Holocene invasion but not with long-term occupation of the Ozarks or the Flint Hills by collared lizards. These combined data sets provide strong evidence that collared lizards are able to occupy northern parts of their range only during the warmer, drier interglacials. Other thermophilous and xerically-adapted reptilian species might be expected to show similar historical patterns.