Living on the edge: first evidence for molecular edge effects in an animal population
Forest loss and fragmentation are predominantly anthropogenic processes causing massive biodiversity loss in tropical forests. A direct result of these processes is the creation of forest edges, which represent complex abiotic and biotic interactions between adjacent ecosystems separated by an abrupt transition. Although previous studies have documented patterns of plant and insect responses to edge effects, relatively little is known about how edge effects influence mammal ecology, biology, and genetics. The aims of our study were to assess the current state of theory on mammal responses to edge effects and to report novel results of the application of genetics in this important line of research. Current models focus almost exclusively on how edge effects influence animal biogeography (i.e. distribution, abundance, and species diversity). A critical, missing component in these models is that changes to animal movement patterns may result in population variation at the microhabitat level. We used population genetics tools to determine if molecular edge effects exist in Microcebus ravelobensis, a small, nocturnal, arboreal, endangered lemur species, endemic to the dry deciduous forests of northwestern Madagascar. M. ravelobensis was sampled in one edge and two interior habitats (500 and 1,400 m from the edge) in a continuous forest bordering abruptly on a savannah. A total of 41 individual mouse lemurs were genotyped with a suite of nuclear microsatellites to determine genetic diversity, genetic differentiation, and movements between the sites. We found that the overall genetic diversity was lower in the edge habitat compared to the two interior sites, and that all subpopulations showed relatively low genetic exchange and significant genetic differentiation, despite the short geographical distances that lie within the possible dispersal distance of single individuals. We interpreted these findings as the first signals of molecular edge effects, and also indicate the potential for local adaptation. Thus, existing models of edge effects should be updated to incorporate the possibility for molecular responses to habitat edges.