Phylotranscriptomics Reveals Discordance in the Phylogeny of Hawaiian Drosophila and Scaptomyza (Diptera: Drosophilidae).

Abstract

Island radiations present natural laboratories for studying the evolutionary process. The Hawaiian Drosophilidae are one such radiation, with nearly 600 described species and substantial morphological and ecological diversification. These species are largely divided into a few major clades, but the relationship between clades remains uncertain. Here, we present new assembled transcriptomes from 12 species across these clades, and use these transcriptomes to resolve the base of the evolutionary radiation. We recover a new hypothesis for the relationship between clades, and demonstrate its support over previously published hypotheses. We then use the evolutionary radiation to explore dynamics of concordance in phylogenetic support, by analyzing the gene and site concordance factors for every possible topological combination of major groups. We show that high bootstrap values mask low evolutionary concordance, and we demonstrate that the most likely topology is distinct from the topology with the highest support across gene trees and from the topology with highest support across sites. We then combine all previously published genetic data for the group to estimate a time-calibrated tree for over 300 species of drosophilids. Finally, we digitize dozens of published Hawaiian Drosophilidae descriptions, and use this to pinpoint probable evolutionary shifts in reproductive ecology as well as body, wing, and egg size. We show that by examining the entire landscape of tree and trait space, we can gain a more complete understanding of how evolutionary dynamics play out across an island radiation.