Phylogenomics Controlling for Base Compositional Bias Reveals a Single Origin of Eusociality in Corbiculate Bees.

As increasingly large molecular data sets are collected for phylogenomics, the conflicting phylogenetic signal among gene trees poses challenges to resolve some difficult nodes of the Tree of Life. Among these nodes, the phylogenetic position of the honey bees (Apini) within the corbiculate bee group remains controversial, despite its considerable importance for understanding the emergence and maintenance of eusociality. Here, we show that this controversy stems in part from pervasive phylogenetic conflicts among GC-rich gene trees. GC-rich genes typically have a high nucleotidic heterogeneity among species, which can induce topological conflicts among gene trees. When retaining only the most GC-homogeneous genes or using a nonhomogeneous model of sequence evolution, our analyses reveal a monophyletic group of the three lineages with a eusocial lifestyle (honey bees, bumble bees, and stingless bees). These phylogenetic relationships strongly suggest a single origin of eusociality in the corbiculate bees, with no reversal to solitary living in this group. To accurately reconstruct other important evolutionary steps across the Tree of Life, we suggest removing GC-rich and GC-heterogeneous genes from large phylogenomic data sets. Interpreted as a consequence of genome-wide variations in recombination rates, this GC effect can affect all taxa featuring GC-biased gene conversion, which is common in eukaryotes

When different contact zones tell different stories: putative ring species in the Megachile concinna species complex (Hymenoptera: Megachilidae)

We examine the genetics, morphology and ecology of the widely distributed Megachile concinna species complex (Hymenoptera: Megachilidae), which is composed of numerous taxa of unclear taxonomic status in Africa and the Palearctic. In the Western Palearctic, three genetically distinct operational taxonomic units (OTUs) are found around the Mediterranean Sea: the western Mediterranean OTU M. pusilla, the eastern Mediterranean OTU M. anatolica and the predominantly Arabian OTU M. leucostoma. A morphological cline is present between anatolica and leucostoma in the Near East, despite a lack of mitochondrial introgression between the two; one nuclear marker suggests some gene flow between these OTUs. The contact zone between pusilla and leucostoma could not be sampled but phenotypic intergradation is also observed between these OTUs in northern Africa. In contrast, study of the contact zone between pusilla and anatolica indicates that both OTUs retain phenotypic and genomic integrity in sympatry over a contact zone spanning 1000 km. The arrangement of these three OTUs suggests a ring of interconnected populations around the Mediterranean Sea and sympatry between pusilla and anatolica at both ends of the ring in southeastern Europe. The latter two OTUs exhibit ecological differences, including phenology and host-plant preferences, which may contribute to their isolation. In addition, our results suggest that two OTUs, M. venusta and M. concinna, maintain genetic and phenotypic integrity in sympatry in parts of Africa; the latter is recognized as a valid species here. Lastly, our results indicate that two OTUs have been introduced independently into the New World, pusilla in North America and Argentina, and concinna in the Antilles