Evolutionary history of Microtus arvalis and Microtus agrestis

In recent years investigation of mechanisms of species’ responses to climate changes gained much scientific attention. One of the ways to learn about those mechanisms is to reconstruct species responses to climate changes that took place in a distant past, during the Late Pleistocene and Holocene when Earth witnessed many profound climate changes of various magnitudes. Recently it has been shown that multidisciplinary approach comprising analyses of DNA obtained from archaeological materials (ancient DNA) and direct radiocarbon dating allows for detailed reconstruction of species’ Pleistocene histories. The main goal of this project is to reconstruct evolutionary history of field (Microtus agrestis) and common voles (Microtus arvalis) during the last 50,000 years and to correlate it with available paleoclimate proxies. This will allow studying the impact of climatic oscillations of different magnitude on population dynamics of vole species. Recent studies of genetic diversity of contemporary voles populations has suggested that both species might be more susceptible to climate changes than previously thought and such investigation may reveal complex demographic history. We will also investigate whether both vole species have survived Last Glacial Maximum at high latitudes in cryptic northern refugia. This was suggested on the basis of distribution of contemporary genetic diversity but the evidence is not ultimate.

To achieve these goals we will analyse sequences of mitochondrial DNA cytochrome b fragment obtained from palaeontological remains of ca. 150 individuals of each species. Palaeontological material will come from various archaeological sites across Europe dated to the last 50,000 years. Bayesian and Maximum Likelihood approaches will be used to reconstruct phylogeny of each vole species. About 70 specimens will be radiocarbon dated to anchor these events in time. BEAST software will be used to estimate substitution rates of cytochrome b sequences and to date divergence of mitochondrial lineages. We will reconstruct changes in effective population size through time with Bayesian SkyGrid method. Approximate Bayesian Computations will be used to choose between alternative demographic scenarios. To estimate the impact of climate changes on the reconstructed demographic events we will compare the inferred timing of those events with palaeoclimate proxies such as oxygen isotopes record from Greenland ice cores and palynological profiles from different localities in Europe.

Recently, Late Pleistocene evolutionary histories of several extant and extinct species have been reconstructed in details, however large mammals such as woolly mammoths or cave bears got most of the attention. Frequently distinction between humans and climate as drivers of species extinction was examined. Small mammals are more susceptible to climate changes, and impact of humans on their populations is negligible, thus they are more suitable subject to study impact of climate changes on demographic processes. Both vole species are widespread in Europe and are important elements of temperate environments and demographic changes in their populations had bottom up effects on whole ecosystems. Comparison of the reconstructed evolutionary histories of two vole species with paleoclimate records may provide very important clues how temperate small mammal species responded to environmental changes and provide us with important guidance for planning conservation efforts in the currently fast changing environment.