Testing the Influence of Habitat Structure and Geographic Distance on the Genetic Differentiation of Mouse Lemurs (Microcebus) in Madagascar

Abstract

The evolution of the high level of microendemism in Madagascar’s biota remains poorly understood. Allopatric speciation or adaptations to local conditions along continuous gradients are two mechanisms that could have contributed to the extraordinary radiation of lemurs. Here we tested whether mouse lemurs (Microcebus griseorufus) occurring across three adjacent but distinct vegetation formations (ranging from dry forest to spiny bush) in southwestern Madagascar showed signs of genetic differentiation that could be interpreted as incipient speciation and adaptation to different environmental conditions using analysis of molecular variance and distance-based redundancy analysis. In the context of a mark-recapture study, mouse lemurs were captured with Sherman live traps set eight times for four nights per trapping session in standardized trapping grids in the three vegetation formations between October 2007 and February 2009. For genetic analyses, we used tissue samples from 41 female and 35 male M. griseorufus. Genetic differentiation between demes as estimated by amplified fragment length polymorphism (AFLP) data (as parental markers) and mitochondrial D-loop sequences (as maternally inherited markers) was more pronounced in philopatric females than in males, which are the dispersing sex in this species. In single-factor analyses, isolation-by-ecology had about the same statistical effect as isolation by distance, but isolation-by-ecology was no longer significant once isolation by distance was taken into account. Despite some differentiation between local demes, STRUCTURAMA, a Bayesian approach for inferring population structure from genetic data, assigned all individuals to a single population. Thus, we did not find evidence for incipient ecological speciation as a result of adaptation to the three investigated habitat types on a small geographic scale based on the available samples.