Relationships among didelphid marsupials based on sequence variation in the mitochondrial cytochrome B gene

Abstract

Variation in the mitochondrial cytochrome b gene (nucleotide and amino acid sequences) is evaluated for 9 genera and 15 species of American opossums in the family Didelphidae, using the American caenolestid rat opossum Lestoros and the New Guinean peroryctid bandicoot Echimypera as outgroups. Phylogenetic analyses (parsimony and distance) strongly support the monophyly of the Didelphidae and delineate two major clades; (1) Didelphis and Philander are strongly aligned sister taxa, with Metachirus weakly but consistently associated with them, and (2) Marmosa plus Micoureus, with Monodelphis falling outside that pair. The genera Marmosops, Caluromys, and Glironia exhibit varied relationships, depending upon the method of analysis and data (DNA or amino acid sequences) used, but generally are placed individually or in combinations near or at the base of the didelphid radiation. Some aspects of these relationships are consistent with current taxonomic views, but others are in marked contrast. Specifically, a clade comprised of the mouse opossums Marmosa, Micoureus, and Marmosops is strongly rejected by log-likelihood analysis, contrary to expectations from some current classifications. Also, the woolly opossums Caluromys and Glironia also do not form a sister-taxon relationship, as suggested by their placement in a subfamily separate from the remaining didelphids examined. However, such a relationship cannot be rejected from log-likelihood analyses. The relationships suggested from cyt-b sequences are strongly concordant with those based on DNA-DNA hybridization analyses. In addition to systematic and phylogenetic properties, molecular evolution of the didelphid cytochrome b gene sequence is characterized according to nucleotide bias and rate differentials at each codon position and across the entire sequence. © 1996 Plenum Publishing Corporation.