Working through polytomies: Auklets revisited

Polytomies, or phylogenetic “bushes”, are the result of a series of internodes occurring in a short period of evolutionary time (which can result in data that do not contain enough information), or data that have too much homoplasy to resolve a bifurcating branching pattern. In this study we used the Aethia auklet polytomy to explore the effectiveness of different methods for resolving polytomies: mitochondrial DNA gene choice, number of individuals per species sampled, model of molecular evolution, and AFLP loci. We recovered a fully-resolved phylogeny using NADH dehydrogenase subunit 2 (ND2) sequence data under two different Bayesian models. We were able to corroborate this tree under one model with an expanded mtDNA dataset. Effectiveness of additional intraspecific sampling varied with node, and fully 20% of the subsampled datasets failed to return a congruent phylogeny when we sampled only one or two individuals per species. We did not recover a resolved phylogeny using AFLP data. Conflict in the AFLP dataset showed that nearly all possible relationships were supported at low levels of confidence, suggesting that either AFLPs are not useful at the genetic depth of the Aethia auklet radiation (7–9% divergent in the mtDNA ND2 gene), perhaps resulting in too much homoplasy, or that the Aethia auklets have experienced incomplete lineage sorting at many nuclear loci.