MOLECULAR PHYLOGENY AND EVOLUTION OF THE NEUROTROPHINS FROM MONOTREMES AND MARSUPIALS

We have investigated the phylogenetic relationships of monotremes and marsupials using nucleotide sequence data from the neurotrophins; nerv e growth factor (NGF), brain-derived neurotrophic factor (BDNF), and n eurotrophin-3 (NT-3). The study included species representing monotrem es, Australasian marsupials and placentals, as well as species represe nting birds, reptiles, and fish. PCR was used to amplify fragments enc oding parts of the neurotrophin genes from echidna, platypus, and eigh t marsupials from four different orders. Phylogenetic trees were gener ated using parsimony analysis, and support for the different tree stru ctures was evaluated by bootstrapping. The analysis was performed with NGF, BDNF, or NT-3 sequence data used individually as well as with th e three neurotrophins in a combined matrix, thereby simultaneously con sidering phylogenetic information from three separate genes. The resul ts showed that the monotreme neurotrophin sequences associate to eithe r therian or bird neurotrophin sequences and suggests that the monotre mes are not necessarily related closer to therians than to birds. Furt hermore, the results confirmed the present classification of four Aust ralasian marsupial orders based on morphological characters, and sugge sted a phylogenetic relationship where Dasyuromorphia is related close st to Peramelemorphia followed by Notoryctemorphia and Diprotodontia. These studies show that sequence data from neurotrophins are well suit ed for phylogenetic analysis of mammals and that neurotrophins can res olve basal relationships in the evolutionary tree.