SANTINI, F; University of Toronto: Was the fish specific genome duplication the cause of the high diversity of teleost fishes?

During the past few years a number of genomic studies have corroborated the idea that a duplication of the entire genome happened in the ancestor of teleost fishes. Comparing the high species diversity as a whole of the teleostean clade when compared to the pre-teleostean actinopterygian lineages (approx. 25000 teleost species, versus a few dozen actinopterygian species), several authors have claimed that the high diversity of teleost fishes is due to this fish-specific genome duplication, even though no causal mechanism for this has ever been proposed. These claims, however, do not take into consideration many recent � and even not-so-recent � advances in phylogenetic and paleontological studies of actinopterygian fishes. In fact, as I will show, 1) most pre-teleostean lineages have in the past been much more species-rich than they are now; 2) most teleostean diversity is found within two clades that originated at least 100 million years after the fish-specific genome duplication; 3) the origin of both these clades likely coincides with the invasion of new environments; and 4) the diversification of these lineages was probably mostly due to ecological, factors, such as the availability of new food sources (i.e., after the evolution of herbivory). While the fish-specific genome duplication may have provided the genetic basis that allowed the diversification of teleost fishes to occur, possibly through the development of preadaptive morphological or physiological features, there is as yet no evidence that the fish-specific genome duplication was the cause of such diversification.