Abstract
Understanding how climatic change impacts biological diversity is critical to conservation. Yet despite demonstrated effects of climatic perturbation on geographic ranges and population persistence, surprisingly little is known of the genetic response of species. Even less is known over ecologically long time scales pertinent to understanding the interplay between microevolution and environmental change. Here, we present a study of population variation by directly tracking genetic change and population size in two geographically widespread mammal species (Microtus montanus and Thomomys talpoides) during late-Holocene climatic change. We use ancient DNA to compare two independent estimates of population size (ecological and genetic) and corroborate our results with gene diversity and serial coalescent simulations. Our data and analyses indicate that, with population size decreasing at times of climatic change, some species will exhibit declining gene diversity as expected from simple population genetic models, whereas others will not. While our results could be consistent with selection, independent lines of evidence implicate differences in gene flow, which depends on the life history strategy of species.
Highlights
Phylogeography has advanced our understanding of the spatial distribution of genetic diversity within and between species (Avise 2000)
Fossil relative abundances give a hint of the census size through time while genetic data should yield independent assessments of the effective population size
The relationship between these measures varies, most studies suggest that the estimate of effective size derived from ecological data is higher than that derived from genetic data
Summary
Phylogeography has advanced our understanding of the spatial distribution of genetic diversity within and between species (Avise 2000). Empirical evidence of temporal change in genetic diversity in a single locality over time has not yet been placed in a population genetic or phylogeographic framework over ecologically long periods of time. In this paper we attempt to determine variation in genetic diversity experienced by populations of two mammalian species in situ and to place that diversity in the context of a changing environment through time. We view this approach as ‘‘phylochronology,’’ or the study of populations in space and time using phylogenetic and population genetic methods. LateHolocene climatic change, including the Medieval Warm Period (1,150 to 650 years before present [ybp]) and Little Ice Age (650 to 50 ybp) (Soon and Baliunas 2003), affected the local abundances of common small mammals in a manner consistent with their habitat preferences (Hadly 1996)
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