Developmental genetics in a complex adaptive structure, the weevil rostrum

Abstract

statement This study begins exploring the development of a novel, complex structure in one of the largest families of organisms, the weevils. AbstractThe 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.

A new species of Proterhinus Sharp, 1878 (Coleoptera: Curculionoidea: Belidae) from Miti‘aro, Cook Islands, South Pacific

“…If these phenomena are operating in P. tauai, the benefits of the unknown trait under selection must presumably outweigh the costs involved with producing the exaggerated rostrum. Further work to explore this possible mechanism will require detailed investigation into the genes responsible for rostrum development (Davis 2018) and the genetic architecture of P. tauai.…”

Morphological and Molecular Perspectives on the Phylogeny, Evolution, and Classification of Weevils (Coleoptera: Curculionoidea): Proceedings from the 2016 International Weevil Meeting

“…He sequenced transcriptomes from the heads of developing weevils and functionally tested (by RNAi) genes for a role in head (and particularly rostrum) morphology and development. His results indicate a wide range of involvement for his previously identified candidate genes in development [17]. Notably, when the gene sex combs reduced (Scr) is knocked out, the posterior tentorial pits appear as paired (they are fused into a single pit in the wild-type), the gula appears (this also reverses the fusion of the ventral head sulci (the subgenal sulci reappear)) and the pleurostomal sulcus also reappears.…”

Phylogenomics of weevils revisited: data curation and modelling compositional heterogeneity

“…Weevils (superfamily Curculionoidea) represent a hyperdiverse and globally distributed group of phytophagous beetles, with approximately 62 000 described species in 5800 genera [1,2]. Most species of Curculionoidea can be easily recognized by their elongate rostrum, which has been suggested as a key innovation responsible for their success [3][4][5][6]. Indeed, the rostrum permitted weevils to access a greater variety of plant tissues than their relatives, particularly when coupled with the later appearance of an elongate scape (mostly in Curculionidae) allowing the antenna to fold posteriorly and for the rostrum to extend deeper into plant tissues while simultaneously preserving some motility from the pedicel to apex.…”