Discrepant partitioning of genetic diversity in mouse lemurs and dwarf lemurs--biological reality or taxonomic bias?

Unequal degrees of taxonomic subdivision can pose problems for research that relies on cross-taxon comparisons of biogeographic patterns. Numerous species of lemurs have been described in recent years. These descriptions were unevenly distributed over the genera of lemurs as exemplified by the closely related mouse lemurs (Microcebus spp.) and dwarf lemurs (Cheirogaleus spp.). According to previous studies, these genera display striking differences such as many versus few species, small versus large distributions, and small versus large mitochondrial divergence within and between species. We questioned if these differences reflect the biological reality or a biased taxonomic subdivision, which might be partially due to relatively small amounts of available genetic data from dwarf lemurs. We complemented existing datasets with genetic data from 51 dwarf lemurs from nine sites in southern Madagascar. We analyzed the mitochondrial cytb gene and the nuclear loci adora3, fiba, and vWF. Based on a comparison of mitochondrial genetic data from both genera, we delineated eight hypothetical subgroups within two recognized Cheirogaleus species. We used mitochondrial and nuclear data to reconstruct species trees and to estimate divergence times between Microcebus species and Cheirogaleus subgroups. We further performed Bayesian species delimitations based on nuclear sequence data from Cheirogaleus subgroups. Strong signals in mitochondrial and nuclear data indicate the existence of deeply divergent, distinct groups within recognized Cheirogaleus species. Based on several lines of evidence, we conclude that the species diversity in Cheirogaleus has been underestimated so far. We delineate six species among the eight subgroups and provide a formal description for one new Cheirogaleus species.