Michael G. Branstetter | bioRxiv Science

bioRxiv2016

Phylogenomic Analysis of Ants, Bees and Stinging Wasps: Improved Taxon Sampling Enhances Understanding of Hymenopteran Evolution

The importance of taxon sampling in phylogenetic accuracy is a topic of active debate. We investigated the role of taxon sampling in causing incongruent results between two recent phylogenomic studies of stinging wasps (Hymenoptera: Aculeata), a diverse lineage that includes ants, bees and the majority of eusocial insects. Using target enrichment of ultraconserved element (UCE) loci, we assembled the largest aculeate phylogenomic data set to date, sampling 854 loci from 187 taxa, including 30 out of 31 aculeate families, and a diversity of parasitoid outgroups. We analyzed the complete matrix using multiple analytical approaches, and also performed a series of taxon inclusion/exclusion experiments, in which we analyzed taxon sets identical to and slightly modified from the previous phylogenomic studies. Our results provide a highly supported phylogeny for virtually all aculeate lineages sampled, supporting ants as sister to Apoidea (bees+apoid wasps), bees as sister to Philanthinae+Pemphredoninae (lineages within a paraphyletic Crabronidae), Melittidae as sister to remaining bees, and paraphyly of cuckoo wasps (Chrysidoidea). Our divergence dating analyses estimate ages for aculeate lineages in close concordance with the fossil record. Our analyses also demonstrate that outgroup choice and taxon evenness can fundamentally impact topology and clade support in phylogenomic inference.

Evolutionary Biology↗

bioRxiv2016

Into the tropics: phylogenomics and evolutionary dynamics of a contrarian clade of ants

AimThe standard latitudinal diversity gradient (LDG), in which species richness decreases from equator to pole, is a pervasive pattern observed in most groups of organisms. Despite its commonness, an increasing number of non-conforming lineages have been identified, presenting a challenge for general explanations of the standard LDG. Although problematic, documenting and studying these contrarian groups can help us to better understand LDGs generally. To that end we identify the ant tribe Stenammini, a diverse lineage with over 400 species, as a contrarian clade, and we attempt to explain the groups atypical diversity pattern using a historical approach. We evaluate the following alternative hypotheses: time-for-speciation/center-of-origin (TFS/COO), niche conservatism, and differences in diversification rate.\n\nLocationGlobal.\n\nMethodsWe examine the shape of the LDG in Stenammini by plotting latitudinal midpoints for all extant species. We then infer a robust phylogeny using a phylogenomic approach that employs ultraconserved element loci and we use the phylogeny to estimate divergence dates, biogeographic history, and ancestral habitats. We also test for diversification rate heterogeneity across the tree and among lineages within the tribe.\n\nResultsStenammini has a skewed inverse latitudinal diversity gradient with an extratropical richness peak in the northern temperate zone. Our phylogenomic approach resulted in a robust phylogeny revealing five major clades and several instances of non-monophyly among genera (Goniomma, Aphaenogaster). The tribe and most major lineages originated in the temperate zone and inhabited temperate niches. Crown Stenammini dates to 52 Ma (Eocene Climatic Optimum) and most major lineages appeared soon after during a period of global cooling. Despite its temperate origin, the group invaded the tropics at least six times, but failed to diversify greatly there. Across the tree diversification increased from 17.2-1.9 Ma following the Mid-Miocene Climatic Optimum, and among lineages there was a rate increase in Holarctic Aphaenogaster + Messor just prior to 17.2 Ma.\n\nMain ConclusionsOur results suggest that time, niche conservatism, and increased diversification have all contributed to the inverse latitudinal gradient in Stenammini. Among these processes, niche conservatism may be less important given that the tribe has dispersed to the tropics multiple times.

Evolutionary Biology↗