Chemosensory annotations in Neodiprion lecontei, a plant-feeding hymenopteran, and implications for the relationship between ecology and gene family size

Insects vary tremendously in their ecology and in the diversity of their chemosensory gene families. Because chemosensation is the primary way in which insects interact with their environment, gene family size may correlate with ecological guild or, within a particular guild, with the degree of niche specialization. For example, relative to other insects, the honeybee has a small gustatory receptor but expanded olfactory receptor family that may be directly related to a social, nest-dwelling lifestyle. To determine whether particular lifestyles are connected to specific, predictable changes in chemosensory gene families, it will be necessary to sample across different lifestyles and phylogenetic depths. Due to their ecological diversity and an abundance of annotated genomes, the Hymenoptera are emerging as a model for chemosensory gene evolution. Plant-feeding Symphytans, however, are entirely absent from these data. Here, we start to address this sampling gap by describing the gustatory receptor (GR) chemosensory gene family of the redheaded pine sawfly Neodiprion lecontei, an external folivore and pine specialist. Over 40 genes have been identified and include putative homologs of conserved GRs that are found across insects and the Hymenoptera. In terms of their number, size, structure, and phylogenetic patterns, our GR annotations are very consistent with high quality GR annotations from other insect genomes. These findings set the stage for future work that will examine the impact of different degrees of host specialization on chemosensory evolution in Neodiprion.