YBAZETA, Gustavo; BAKER, Allan J.; Univ. of Toronto – Dept. of Zoology. ROM – CBCB; Univ. of Toronto – Dept. of Zoology. ROM – CBCB: Molecular biogeography of galaxiid fishes deduced using a Bayesian approach and a semi-parametric molecular clock

The galaxids are a group of freshwater fish with a Gondwanan geographical distribution. This distribution has fuelled the debate over speciation by vicariance vs. dispersal events. We used a bayesian approach to construct a well supported phylogenetic tree for this group. Based on this tree we used a semi-parametric approach of penalized likelihood to “smooth” the rates of substitutions across lineages and estimate the ages of the splits between species, including 95% confidence intervals. Our results indicate the rate of evolution for this group is 0.21% (0.17 – 0.27%), much slower than the standard 1% used in other vertebrates. A great majority of the speciation events in galaxiids are old enough to be attributed to vicariance via the fragmentation of Gondwanaland landmass. Only a few species have current distributions that require later dispersal events, and all involve reltively transoceanic dispersals of less that about 2000km.