Population genomic structure in Goodman’s mouse lemur reveals long-standing separation of Madagascar’s Central Highlands and eastern rainforests

The Central Highland Plateau of Madagascar is largely composed of grassland savanna, interspersed with patches of closed-canopy forest. Conventional wisdom has it that these grasslands are anthropogenic in nature, having been created very recently via human agricultural practices. Yet, the ancient origins of the endemic grasses suggest that the extensive savannas are natural biomes, similar to others found around the globe. We use a phylogeographic approach to compare these two competing scenarios. By sampling multiple populations of Goodman’s mouse lemur (Microcebus lehilahytsara), a small-bodied nocturnal primate, we reconstruct the phylogeographic and demographic history of these “environmental metronomes” to estimate the time at which their populations diverged, and thus proximally, when their habitats would have become fragmented. We applied coalescent methods to RADseq data to infer phylogenetic relationships, population structure, and migration corridors among sampling sites. These analyses indicate that forest fragmentation occurred rapidly during a period of decreased precipitation near the last glacial maximum and would have affected both the Central Highlands and eastern forests. Though there is clear genomic structure separating the populations of the Central Highland from those of the eastern rainforests, there is also evidence of historical migration between them. Findings support the hypothesis that the Central Highland savanna predates human arrival, indicating that it is a natural landscape that has long impacted the population dynamics of Goodman’s mouse lemur, and by extension, other forest-dwelling organisms in Madagascar.

First experimental evidence for olfactory species discrimination in two nocturnal primate species (Microcebus lehilahytsara and M. murinus)

Olfactory communication is highly important for nocturnal mammals, especially for solitary foragers, but knowledge is still limited for nocturnal primates. Mouse lemurs (Microcebus spp.) are nocturnal solitary foragers with a dispersed lifestyle and frequently use chemo-sensory signalling behaviour for governing social interactions. Different mouse lemur species can co-occur in a given forest but it is unknown whether olfaction is involved in species recognition. We first screened 24 captive mouse lemurs (9 M. murinus, 15 M. lehilahytsara) for their olfactory learning potential in an experimental arena and then tested the species discrimination ability with urine odour in an operant conditioning paradigm in four individuals. The majority of the screened animals (75%) did not pass the screening criteria within a 2-week test period. However, all four final test animals, two M. murinus and two M. lehilahytsara, were successfully trained in a 5-step-conditioning process to reliably discriminate conspecific from heterospecific urine odour (requiring an overall median of 293 trials). Findings complement previous studies on the role of acoustic signalling and suggest that olfaction may be an important additional mechanism for species discrimination.