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

Abstract

BackgroundPleistocene events have shaped the phylogeography of many taxa worldwide. Their genetic signatures in tropical species have been much less explored than in those living in temperate regions. We analysed the genetic structure of a Malagasy primate species, a mouse lemur with a wide distribution (M. murinus), in order to investigate such phylogeographic processes on a large tropical island. We also evaluated the effects of anthropogenic pressures (fragmentation/deforestation) and natural features (geographic distance, rivers) on genetic structure in order to complement our understanding of past and present processes of genetic differentiation.ResultsThe 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.ConclusionsThis 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.

Genetic data suggest a natural prehuman origin of open habitats in northern Madagascar and question the deforestation narrative in this region

“…Similar results have also been suggested for other primates [orangutans (81) and howler monkeys (82)]. In all these species [detection of a more ancient population size change is discussed elsewhere (46,47)], the population bottleneck has been reasonably attributed to recent human-driven changes.…”

“…submitted to different demographic histories with different time depths. Indeed, the genome retains the specific signature of major events, such as recent contractions (44,45) or ancient expansions (46). Reconstructing the demographic history of extant species may thus help to investigate how climate change and anthropogenic impact affected the dynamic of their habitat (42,47).…”

Geogenetic patterns in mouse lemurs (genus Microcebus ) reveal the ghosts of Madagascar's forests past

“…Thus, the results of our study would appear to agree with other work in which Quaternary climatic and vegetation changes have been invoked to explain patterns of diversity and speciation in different groups of lemurs (5) and in mouse lemurs in particular (31,55).…”

“…Thus, mouse lemurs are likely to track environmental variation with fine temporal resolution, with the added benefit of relatively precise generation times that can readily be translated parametrically in coalescent-based modeling methods. Some of these advantages for phylogeographic study in Madagascar have been noted by others (31). Notably, some species of mouse lemur can occur in high densities in degraded forests and along forest ecotones and can thrive in areas with invasive fruiting trees.…”

On the role played by the carrying capacity and the ancestral population size during a range expansion

“…Episodes of REs have been postulated for many species (Rendine et al, 1986;Ibrahim et al, 1996;Cavalli-Sforza and Feldman, 2003;Klopfstein et al, 2006;Boessenkool et al, 2009;Brown et al, 2010) but they have been quantitatively tested in a spatially explicit framework only in few studies (Barbujani et al, 1995;Hamilton et al, 2005;Ray et al, 2005;Francois et al, 2008;Neuenschwander et al, 2008;Gaggiotti et al, 2009;Schneider et al, 2010;Mona et al, 2013). REs leave distinct signatures in the genetic diversity of populations (Barbujani et al, 1995;Ray et al, 2003;Edmonds et al, 2004;Travis et al, 2007;Sousa et al, 2014), proceeding as a series of founder events followed by continuous migrations among neighboring demes (Austerlitz et al, 1997;Ray et al, 2003).…”