DRIES, L.A.: Swords, Roots and Reliability: the DNA Phylogeny of Xiphophorus revisited

Since the publication of Harvey and Pagel’s book, there has been a resurgence in the use of the comparative method in evolutionary biology. This approach is critically dependent on a reliable and accurate phylogeny, thus many investigators rely on previously published phylogenies of their groups of interest. Swordtails and platyfishes (Xiphophorus) have been used in many comparative studies, particularly those examining the evolution of exaggerated traits in males and the corresponding preferences in females. Prior to 1994, there was an accepted phylogeny for Xiphophorus based on a variety of characters. That phylogeny was challenged with the publication of a DNA sequence-based phylogeny that presented a different picture of evolutionary history, casting doubt on previous conclusions about the pattern of evolutionary change in the group. The conflict between these two phylogenies has not been resolved, leaving some investigators in a quandary over which to use, or worse, resulting in the exclusive use of the DNA phylogeny. Given the importance of phylogeny in comparative studies this conflict deserves re-examination. I will present the results of extensive reanalyses of the DNA data to ask, 1) is the 1994 phylogeny reliable, and 2) should it be used in comparative studies?