Speciation and gene flow in two sympatric small mammals from Madagascar, Microgale fotsifotsy and M.soricoides (Mammalia: Tenrecidae).

Abstract

Madagascar's shrew tenrecs (Mammalia: Tenrecidae; Microgale, Nesogale) represent an excellent system for studying speciation. Most species are endemic to the island's eastern humid forests, a region renowned for high levels of biodiversity and a high rate of in situ diversification. We set out to understand the speciation dynamics in a clade of recently described taxa: Microgale fotsifotsy and M.soricoides, which have nearly identical distributions in the moist evergreen forest, and M.nasoloi, which occurs in the western dry deciduous forest. A phylogenetic analysis using mitochondrial DNA data recovered two distinct clades of M.fotsifotsy: a south clade that is sister to, and broadly sympatricwith, M.soricoides, and a north clade that is sister to the dry-forest and distantly allopatric species M.nasoloi. To better understand this result, we analysed cranioskeletal measurements and performed demographic analyses using nuclear sequence data from ultraconserved elements. Nuclear data did not support a sister relationship between M.soricoides and the south clade of M.fotsifotsy but did demonstrate introgression between these clades, which probably explains the discordance between nuclear and mitochondrial phylogenies. Demographic analyses also revealed the absence of gene flow between the north and south clades of M.fotsifotsy. Morphometric data revealed several major differences between M.soricoides and M.fotsifotsy, as well as more subtle differences between the two clades of M.fotsifotsy. In light of these results, we treat the south clade of M.fotsifotsy as a new candidate species. Our findings demonstrate the utility of integrating multiple data types to understand complex speciation histories, and contribute to a growing body of evidence that species diversity on Madagascar is underestimated.