Octopamine receptor gene influences social grouping in the masked birch caterpillar

Abstract

Objective Group-living plays a key role in the success of many insects, but the mechanisms underlying group formation and maintenance are poorly understood. Here we use the masked birch caterpillar, Drepana arcuata, to explore genetic influences on social grouping. These larvae predictably transition from living in social groups to living solitarily during the 3rd instar of development. Our previous study showed a notable shift in the D. arcuata transcriptome that correlates with the transition from grouping to solitary behavior. We noted that one differentially regulated gene, octopamine receptor gene (DaOAR), is a prominent ‘social’ gene in other insect species, prompting us to test the hypothesis that DaOAR influences grouping behavior in D. arcuata. This was done using RNA interference (RNAi) methods by feeding second instar larvae synthetic dsRNAs. Results RT–qPCR analysis confirmed a significant reduction in DaOAR transcript abundance in dsRNA-fed larvae compared to controls. Behavioral trials showed that caterpillars with reduced transcript abundance of DaOAR remained solitary throughout the observation period compared to controls. These results provide evidence that regulation of the octopamine receptor gene influences social grouping in D. arcuata, and that specifically, a decrease in octopamine receptor expression triggers the larval transition from social to solitary.

Towards an integrative approach to understanding collective behaviour in caterpillars

“…Using a time series of gene expression profiles, a set of genes with differential expression between solitary and grouped instars was identified. Although this gene set probably includes stage-dependent changes unrelated to the behaviour, subsequent functional analysis of one candidate gene, the octopamine receptor gene ( DaOAR ), suggests that expression levels of this protein alter larval gregariousness [ 73 ]. DaOAR is linked to changes in group behaviour in other insects [ 74 , 75 ], suggesting convergent mechanisms underpinning developmental transitions in collective behaviours.…”