DNA HYBRIDIZATION, THE COMPRESSION EFFECT, AND THE RADIATION OF DIPROTODONTIAN MARSUPIALS

Advocates and adversaries of single-copy DNA hybridization find both promise and pitfalls in the application of this technique to phylogenetic reconstruction. Measurement error, biased sampling of sequences, and homoplasy reduce the additivity of DNA hybridization data, although numerical corrections exist. If distortions of hybridization data can be rectified, pairwise tree construction algorithms should provide reliable estimates of phylogeny. We used single-copy DNA hybridization studies to elucidate interfamilial relationships within diprotodontian marsupials. Peroryctes longicauda, a peramelid, was included as an outgroup. To improve their additivity, data were corrected for nonreciprocity (the compression effect), reduced normalized percentages of hybridization, and homoplasy. Results of DNA hybridization experiments suggest an initial radiation of diprotodontian marsupials into three major lineages: (1) vombatiforms, (2) macropodids, and (3) phalangeroids plus petauroids. Subsequent diversification occurred first in the phalangeroid-petauroid group, second in vombatiforms, and last in macropodids. Within the phalangeroid-petauroid clade, phalangerids and burramyids form one monophyletic group whereas acrobatids, petaurids, and pseudocheirids form a second. This branching pattern obtains for both uncorrected and corrected data.