Phylogenetic and phylogeographic insights into the origin of Madagascar's shrews

Abstract

Madagascar is a biodiversity 'hotspot' about 400 km off the southeast coast of Africa. All the mammals on Madagascar have diversified from within one of four ancestral lineages (Goodman and Benstead, 2005). This is remarkable because Madagascar separated 100 million years before the divergence of most mammalian orders (Krause, 2003). With the arrival of humans on Madagascar several new species were introduced (Duplantier and Duchemin, 2003), including one or possibly two introduced species of shrews (family Soricidae) Suncus murinus and Suncus madagascariensis. Although once believed to be a subspecies of the Old World S. etruscus, Suncus madagascariensis is currently believed to be endemic to the island, but this has never been tested (Goodman et al., 2003). I examined the phylogeny and phylogeography of the shrews occurring on Madagascar, using the mtDNA gene ND2 and a higher-level study utilizing the 16S rRNA subunit. No phylogeographic structure was recovered across the island using ND2 for either species of shrew on Madagascar. The higher-level analysis using the 16S shows little variation between S. madagascariensis and S. etruscus. Collectively, my results strongly suggest that S. madagascariensis is in fact a junior synonym of the S. etruscus and does not warrant species status. Both species of shrews that occur on Madagascar can therefore be considered introduced.