Expression analyses of chemosensory genes provide insights into evolution of gustatory receptor genes in the bumble bee Bombus impatiens

Abstract

Background

The chemoreceptor gene families, which include gustatory, ionotropic, and odorant receptor gene families, are highly conserved across the insects yet also contain many recently duplicated, species-specific genes in particular clades. Within the Bombini (bumble bee) clade, a set of recently duplicated genes in the gustatory receptor (Gr) gene family was identified, the functions of which are unknown. Recently duplicated genes are hypothesized to first evolve to serve non-essential functions, then subsequently evolve additional functions. We tested support for this hypothesis in the common eastern bumble bee, Bombus impatiens, by identifying recently duplicated Gr genes in this lineage and examining their tissue and caste expression patterns.

Results

We annotated twenty-one Gr genes in B. impatiens. Ten of these genes appear to be unique to bumble bees and more likely to be expressed in a subset of sensory organs compared to the conserved Gr genes, which were more broadly expressed across sensory organs. This finding provides support for the hypothesis that younger genes have narrower functions and subsequently become more generalized over time.

Conclusions

Recently duplicated genes can mediate behavioral and ecological shifts, making them intricately linked to evolutionary processes such as adaptation and diversification. Chemoreception mediates fundamental behaviors in bumble bees like finding mates, selecting suitable nest sites, and foraging resources. Despite this, the molecular basis of bumble bee chemoreception, and the importance of each chemoreceptor family to bumble bee behavior and ecology, are still relatively uncharacterized. This study helps to characterize how chemoreception evolves in bumble bees and provides a foundation for understanding what tissues are important for bumble bee chemoreception.