Phylogenetic Relationships of the Order Insectivora Based on Complete 12S rRNA Sequences from Mitochondria.

Despite numerous studies, there is no single accepted hypothesis of eutherian ordinal relationships. Among the least understood mammalian orders is the group Insectivora. Currently, molecular and morphological data are in conflict over the possible monophyly of the living members of Insectivora (lipotyphlans), and the relationships within the group remain largely unresolved. One of the primary criticisms concerning molecular analyses is the noticeable lack of data from a well-sampled group of lipotyphlan insectivores. The mitochondrial 12S rRNA gene has been widely used to resolve interordinal and intraordinal relationships across a variety of mammalian taxa. This study compares 118 complete mammalian 12S rRNA sequences, representing all of the 18 eutherian orders and 3 metatherian orders, and includes as well taxa from each of the six families of lipotyphlan insectivores. Insectivoran lineages are thought to have diverged concurrently with the general radiation of mammalian orders. This study suggests that the 12S rRNA sequences lack the ability to resolve relationships extending into this period. This would explain the polyphyly, unusual affinities, and low support derived in this and other studies employing 12S rRNA sequences to diagnose relationships among eutherian orders. The results of these analyses suggest that even extensive taxon sampling is insufficient to provide well supported groups among eutherian orders. Additional genes and species sampling will be necessary to elucidate whether the Insectivora form a monophyletic group.

A test of Archonta monophyly and the phylogenetic utility of the mitochondrial gene 12S rRNA.

The relationships within the superorder Archonta, which contains the orders Dermoptera (flying lemurs), Scandentia (tree shrews), Chiroptera (bats), and Primates, were examined through the analysis of five newly derived and complete mitochondrial 12S rRNA sequences. The new data is combined with 83 additional known mammalian sequences to provide a full phylogenetic sampling. Phylogenetic hypotheses are generated using PAUP 3.1.1 (Swofford [1993] Illinois Natural History Survey, Champaign, IL) through analyses of all characters equally weighted, transversions only, and the effect of alignment gaps on phylogeny. The Parsimony Jackknifer (Farris et al. [1996] Cladistics 12:99-124) was used to assess the level of ambiguity present in the sequence data, and therefore the strength of the tree topologies. The conclusions of Springer and Douzery (1996, J. Mol. Evol. 43:357-373) which states that 12S rRNA is reliable to a time depth of 100 mya is unsupported by these analyses. The usefulness of 12S rRNA to aid in solving Archonta relationships and others of similar time depth is found to be suspect.

Support for interordinal eutherian relationships with an emphasis on primates and their archontan relatives.

Current knowledge about mammalian interordinal relationships is growing rapidly; thus this contribution is an attempt to summarize the past 5 years of this literature. We have focused on the recent controversies in mammalian phylogenetics including hypotheses concerning the monophyly of Archonta, the diphyly of Chiroptera, and the polyphyly of Rodentia. All of these issues have been proposed recently, challenging these phylogenetic hypotheses. We have attempted to include all of the comprehensive analyses of eutherian mammal systematics with an emphasis on morphological and molecular data sets where discrete characters are listed so they could be compiled and used in support of interordinal relationships. Particular attention is given to determining which of the living eutherian orders is the closest relative to primates. In reviewing relationships among the mammals, we have focused on collating all of the available evidence so that one could know where each of the specific data sets is in support of the various relationships.