Genetic footprints of demographic expansion in North America, but not Amazonia, during the Late Quaternary

Abstract

The biotic consequences of climate change have attracted considerable attention. In particular, the "refugial debate" centers on the possible retraction of habitats to limited areas that may have served as refuges for many associated species, especially during glaciations of the Quaternary. One prediction of such scenarios is that populations must have experienced substantial growth accompanying climatic amelioration and the occupation of newly expanded habitats. We used coalescence theory to examine the genetic evidence, or lack thereof, for late Pleistocene refugia of boreal North American and tropical Amazonian mammals. We found substantial and concordant evidence of demographic expansion in North American mammals, particularly at higher latitudes. In contrast, small mammals from western Amazonia appear to have experienced limited or no demographic expansion after the Late Pleistocene. Thus, demographic responses to climate change can be tracked genetically and appear to vary substantially across the latitudinal gradient of biotic diversity.

Fig. 1.

(A) Map of North America indicating areas considered in the analyses. In the case of the long-tailed vole, the sample from the Southern Rockies was analyzed separately from those from the remaining Southwest. (B) Map of western Amazonia indicating the area and sampling localities considered in the analyses and the proposed Inambarí Refuge (8, 38). (C) Estimates of the exponential growth parameter g for boreal mammals, analyzed separately for each of the areas outlined in A and for mammals of western Amazonia. All estimates of g are color-coded as follows, regardless of symbol shape: gray, g < 3 standard deviations above 0; yellow, g between 3 and 6 standard deviations above 0; orange, g > 6 standard deviations above 0.