Mammalian Molecular Systematics with Emphasis on the Insectivore Order Lipotyphla
Abstract: Insectivore classification has been one of the most controversial problems in mammalian systematics. Evolutionary relationships among the six extant families, Talpidae (moles), Soricidae (shrews), Erinaceidae (hedgehogs), Tenrecidae (tenrecs), Chryosochloridae (golden moles), and Solenodontidae (solenodons), have remained uncertain based on morphological data. Animals classified within the order Lipotyphla have been considered to be among the most primitive living eutherian mammals. However, the six extant families are speciose, geographically widespread and adapted to a wide range of ecological niches. The combination of "primitive" and various specialized morphological characters has made classification of lipotyphlans particularly difficult. This work addressed the phylogenetic relationships among the Talpidae, Soricidae, Erinaceidae, and Tenrecidae based on mitochondrial (mt) DNA sequence data. Complete mt genome sequences of a European mole (Talpa europaea) and a lesser hedgehog tenrec (Echinops telfairi) were determined, as well as the cytochrome b (cyt b) and partial NADH5 mt gene sequences of a shrew (Sorex araneus). Three methods of phylogenetic analysis were used: maximum parsimony, neighbor joining and maximum likelihood (ML). The effect of rate heterogeneity on tree topology and branch lengths was explored under ML. In addition, the complete mt genome of an African cane rat (Thryonomys swinderianus) was sequenced to address the issue of the phylogenetic position of Erinaceidae at the base of Eutheria. Monophyly of Lipotyphla was not supported based on analyses of 12 mt protein coding genes. Talpidae was found as an outgroup to the Cetferungulata rather than as an ancient lineage in Eutheria. Analyses of cyt b and NADH5 data indicated strong support for a sister taxon relationship between Talpidae and Soricidae (superfamily Soricoidea). Chiroptera was outgroup to Soricoidea, forming the clade Volantiterranea, new. A sister taxon relationship between Tenrecidae and Talpidae was significantly rejected. There was moderate support for the placement of the Tenrecidae within Afrotheria together with Tubulidentata (aardvark) and Proboscidea (elephant). The basal position of Erinaceidae was supported by all approaches except ML + rate heterogeneity. The discrete gamma model of rate heterogeneity disproportionately increased the long branches at the base of Eutheria relative to those at the top of the tree highlighting the potential for misleading results and the need for more dense taxon sampling near the base of the tree.
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