Developmental genetics in a complex adaptive structure, the weevil rostrum

The rostrum of weevils (Curculionidae) is a novel, complex, adaptive structure that has enabled this huge beetle radiation to feed on and oviposit in a wide spectrum of plant hosts, correlated with diverse life histories and tremendous disparity in rostrum forms. In order to understand the development and evolution of this structure, transcriptomes were produced in de novo assemblies from the developing pre-pupal head tissues of two distantly related curculionids, the rice weevil (Sitophilus oryzae) and the mountain pine beetle (Dendroctonus ponderosae), which have highly divergent rostra. While there are challenges in assessing differences among transcriptomes and in relative gene expression from divergent taxa, tests for differential expression patterns of transcripts yielded lists of candidate genes to examine in future work. RNA interference was performed with S. oryzae for functional insight into the Hox gene Sex combs reduced. Scr has a conserved function in labial and prothoracic identities, but it also demonstrates a novel role in reduction of ventral head structures, namely the gula, submentum, and associated sulci, in weevils. Ultimately, this study makes strides towards elucidating how the weevil rostrum initially formed and the profound phenotypic diversity it has acquired throughout the curculionoid lineages. It furthermore initiates a better understanding of the genetic framework that permitted the diversification of such an immense lineage as the weevils.\n\nSummary statementThis study begins exploring the development of a novel, complex structure in one of the largest families of organisms, the weevils.