K. Kullander et al., MOLECULAR PHYLOGENY AND EVOLUTION OF THE NEUROTROPHINS FROM MONOTREMES AND MARSUPIALS, Journal of molecular evolution, 45(3), 1997, pp. 311-321
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.