Signals of recent spatial expansions in the grey mouse lemur (Microcebus murinus)

The analysis of the mitochondrial D-loop sequences of 195 samples from 15 study sites (10 from a continuous forest and five from isolated forest fragments) from two adjacent Inter-River-Systems (IRSs) revealed that forest fragmentation and the river restrict gene flow, thereby leading to an increased genetic differentiation between populations beyond the effect of isolation-by-distance. Demographic simulations detected signals of two successive spatial expansions that could be preliminarily dated to the late Pleistocene and early Holocene. The haplotype network revealed geographic structure and showed deep molecular divergences within and between the IRSs that would be congruent with a two-step colonization scenario.This study supports the hypothesis of a relatively recent spatial expansion of the grey mouse lemur in northwestern Madagascar, which may also explain why this taxon, in contrast to its congeners, has not yet undergone allopatric speciation in the studied area and possibly across its presently wide range.Pleistocene events have shaped the phylogeography of many taxa worldwide [1]. Particular emphasis has been put on these dynamics in temperate regions [2]. Tropical biomes have also been shown to have undergone complex ecological dynamics following worldwide Pleistocene climate changes [3], but their genetic signatures in present-day natural populations are much less explored. The genetic structure of natural populations is not only shaped by these ancient processes but also by ongoing natural (e.g. migration, genetic drift) and more recent anthropogenic factors [4].One model region for the study of the combined effects of ancient and recent factors is Madagascar. This island has been isolated from all other landmasses during the last 80 million years (My) and different vertebrate groups have undergone complex phylogeographic histories [5]. Moreover, Madagascar has been strongly affected by anthropogenic disturbances during the last 2000 years following t