Phylogenomics reveals the history of host use in mosquitoes

Mosquitoes have profoundly affected human history and continue to threaten human health through the transmission of a diverse array of pathogens. The phylogeny of mosquitoes has remained poorly characterized due to difficulty in taxonomic sampling and limited availability of genomic data beyond the most important vector species. Here, we used phylogenomic analysis of 709 single copy ortholog groups from 256 mosquito species to produce a strongly supported phylogeny that resolves the position of the major disease vector species and the major mosquito lineages. Our analyses support an origin of mosquitoes in the early Triassic (217 MYA [highest posterior density region: 188-250 MYA]), considerably older than previous estimates. Moreover, we utilize an extensive database of host associations for mosquitoes to show that mosquitoes have shifted to feeding upon the blood of mammals numerous times, and that mosquito diversification and host-use patterns within major lineages appear to coincide in earth history both with major continental drift events and with the diversification of vertebrate classes.

The phylogeny and divergence times of leaf-mining flies (Diptera: Agromyzidae) from anchored phylogenomics

Leaf-mining flies (Diptera: Agromyzidae) are a diverse clade of phytophagous Diptera known largely for their economic impact as leaf- or stem-miners on vegetable and ornamental plants. Higher-level phylogenetic relationships of Agromyzidae have remained uncertain because of challenges in sampling of both taxa and characters for morphology and PCR-based Sanger-era molecular systematics. Here, we used hundreds of orthologous single-copy nuclear loci obtained from anchored hybrid enrichment (AHE) to reconstruct phylogenetic relationships among the major lineages of leaf-mining flies. The resulting phylogenetic trees are highly congruent and well-supported, except for a few deep nodes, when using different molecular data types and phylogenetic methods. Based on divergence time dating using a relaxed clock and model-based historical biogeography analysis, leaf-mining flies are shown to have diversified in multiple lineages since the early Paleocene, approximately 65 million years ago. Our study not only reveals a revised classification system of leaf-mining flies, but also provides a new phylogenetic framework to understand their macroevolution.

Single-copy nuclear genes resolve the phylogeny of the holometabolous insects

BACKGROUND

Evolutionary relationships among the 11 extant orders of insects that undergo complete metamorphosis, called Holometabola, remain either unresolved or contentious, but are extremely important as a context for accurate comparative biology of insect model organisms. The most phylogenetically enigmatic holometabolan insects are Strepsiptera or twisted wing parasites, whose evolutionary relationship to any other insect order is unconfirmed. They have been controversially proposed as the closest relatives of the flies, based on rDNA, and a possible homeotic transformation in the common ancestor of both groups that would make the reduced forewings of Strepsiptera homologous to the reduced hindwings of Diptera. Here we present evidence from nucleotide sequences of six single-copy nuclear protein coding genes used to reconstruct phylogenetic relationships and estimate evolutionary divergence times for all holometabolan orders.

RESULTS

Our results strongly support Hymenoptera as the earliest branching holometabolan lineage, the monophyly of the extant orders, including the fleas, and traditionally recognized groupings of Neuropteroidea and Mecopterida. Most significantly, we find strong support for a close relationship between Coleoptera (beetles) and Strepsiptera, a previously proposed, but analytically controversial relationship. Exploratory analyses reveal that this relationship cannot be explained by long-branch attraction or other systematic biases. Bayesian divergence times analysis, with reference to specific fossil constraints, places the origin of Holometabola in the Carboniferous (355 Ma), a date significantly older than previous paleontological and morphological phylogenetic reconstructions. The origin and diversification of most extant insect orders began in the Triassic, but flourished in the Jurassic, with multiple adaptive radiations producing the astounding diversity of insect species for which these groups are so well known.

CONCLUSION

These findings provide the most complete evolutionary framework for future comparative studies on holometabolous model organisms and contribute strong evidence for the resolution of the 'Strepsiptera problem', a long-standing and hotly debated issue in insect phylogenetics.