RESOLUTION OF PORTIONS OF THE KANGAROO PHYLOGENY (MARSUPIALIA, MACROPODIDAE) USING DNA HYBRIDIZATION

We generated a DNA hybridization matrix comparing eleven 'true' kangar oos (Macropodinae) and two outgroup marsupials, the rufous rat-kangaro o Aepyprymnus rufescens (Potoroinae) and the brush-tailed phalanger Tr ichosurus vulpecula (Phalangeridae). A small matrix included additiona l species of the genus Macropus (large kangaroos and wallabies). The r esults indicate that the New Guinean forest wallaby Dorcopsulus vanheu rni, and the quokka Setonix brachyurus, represent successively closer sister-groups of other macropodines. The remaining taxa examined form two clades: the tree kangaroo Dendrolagus matschiei with the pademelon s Thylogale and rock wallabies Petrogale, and Macropus including the s wamp wallaby Wallabia bicolor. The smaller matrix of five Macropus spe cies and Wallabia (with Dorcopsulus as an outgroup) pairs the red-neck ed wallaby M. rufogriseus and Parry's wallaby M. parryi, with the east ern grey kangaroo M. giganteus as their nearest relative; and associat es the red kangaroo M. rufus and wallaroo M. robustus, with Wallabia a s their sister-taxon. In the larger study, we found that inclusion of both outgroups provided little resolution among the macropodines, judg ing by jackknife and bootstrap tests. When Aepyprymnus was deleted, th e Dendrolagus-Thylogale-Petrogale association obtained; with Trichosur us eliminated instead, the Wallabia-Macropus group was recovered. Only analysis of the eleven ingroup taxa by themselves gave a topology whi ch supported both major clades. Our findings suggest that, at least fo r DNA hybridization studies, when ingroup taxa are separated by very s hort internodes experimental error in outgroup-to-ingroup distances ma y seriously compromise determination of ingroup affinities as well as the position of the root. We recommend that in such cases separate ana lyses with the outgroups sequentially eliminated and rigorous validati on of the topology at each step should be conducted. (C) 1995 The Linn ean Society of London