MtDNA and nDNA corroborate existence of sympatric dwarf lemur species at Tsinjoarivo, eastern Madagascar.

Madagascar is a biodiversity hotspot, well known for its endemic primates, the lemurs. Numbers of recognized lemur species have increased drastically in some genera (e.g. Microcebus), while field-based studies revealed low species diversity in the dwarf lemurs (genus Cheirogaleus). Only three (C. medius, C. major, C. crossleyi) of seven described species have to date been identified in field-based studies. Blanco et al. (2009) reported two sympatric Cheirogaleus species at Tsinjoarivo based on morphological data, one of which they attributed to C. crossleyi and the other of which they described as C. sibreei-like, or possibly a new species. Based on comparative analyses of mtDNA (cytb) and nDNA (vWF, fiba, adora3), we confirm the presence of C. crossleyi and show that the C. sibreei-like individuals form a well-defined fourth clade, basal to the three recognized species. Whereas these molecular analyses demonstrate that a non-holotype museum specimen considered by Groves (2000) to belong to C. sibreei does not cluster with the C. sibreei-like individuals from Tsinjoarivo, morphometric analysis of one Tsinjoarivo individual, the C. sibreei holotype from Ankeramadinika, and samples of C. medius, C. major, and C. crossleyi strongly suggests that the fourth (and basal) clade is indeed C. sibreei. Tsinjoarivo therefore becomes the only known field site harboring C. sibreei today. Given ongoing forest loss and fragmentation at Tsinjoarivo we can surmise that this population, critical to our understanding of the evolution of the genus Cheirogaleus, is also critically endangered.