Elucidating the genes governing rostrum formation in weevils (Coleoptera: Curculionoidea)

Weevils (Coleoptera: Curculionoidea) are a diverse group of extant organisms and are associated with all major groups of plants and plant tissues. The weevil rostrum is a key evolutionary innovation that has enabled this group to feed on and oviposit in nearly all plant tissues, giving rise to diverse life histories and tremendous diversity in rostrum form. Insights into comparative development of the rostrum will provide insight into the evolution of this key structure that may be responsible for the explosive radiation of the lineage. Although weevils are an enormous group and countless species are significant agricultural pests, no weevil species have been utilized in developmental studies. In order to better understand the formation and evolution of this structure, histological examinations have been made in a phylogenetic context for comparing the internal structure of the rostrum in adults. Transcriptomes from the developing head tissue of 4 weevil species, representing disparate clades and divergent rostral forms, and 1 outgroup (non-weevil species) have also been produced in de novo assemblies. While there are difficulties in assessing similarities and differences among transcriptomes from divergent taxa, this study illustrates the use of transcriptomics across wide phylogenetic distances to identify genes responsible for key evolutionary innovations. Through this study, it is now becoming apparent which genes are responsible for differentiation of derived and ancestral features, as well as those that have produced the profound phenotypic diversity observed in the rostrum. While much remains to be done, closer inspection of these genes and gene pathways will permit a better understanding of the genetic framework that permitted the diversification of such an immense lineage as the weevils.