Molecular Evolution for the Chemoreceptor Gene Families in the Common Eastern Bumblebee, Bombus impatiens

The common eastern bumblebee, Bombus impatiens, is widely used for commercial green house pollination in California and Mexico with considerable economic benefits in the specialty crop industry. Studying chemoreceptor gene families within bees is important for understanding the molecular and neural mechanisms beneath their communicative and social behaviors. Major components of chemoreceptor genes include odorant receptors (Ors) and gustatory receptors (Grs). Insect odorant receptors serve vital roles in communication and environmental signal recognition. The gustatory receptor genes are related to different functions in taste. I used previously published chemoreceptors from the European bumblebee, Bombus terrestris, as a template for TBLASTN searches against the assembled B. impatiens genome sequence. I annotated 159 Ors and Dr. Hugh Robertson annotated 24 Grs in the B. impatiens genome, revealing that some of these chemoreceptors have undergone recent duplications. Then I used phylogenetic analysis by maximum likelihood (ML) and positive selection analysis (PAML) to identify amino acid locations bearing the signature of positive selection in these chemoreceptor gene families in B. impatiens. I found evidence for positive selection in the Grs but not the Ors.The identification of chemoreceptor gene families in B. impatiens provides resources for comparative genomics, specifically in social insect communication. These resources will contribute to deeper study of the complex social behavior of B.impatiens.Ope