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Title: Conservation and modification of genetic and physiological toolkits underpinning diapause in bumble bee queens

Author
item AMSALEM, ETYA - Pennsylvania State University
item GALBRAITH, DAVID - Pennsylvania State University
item CNAANI, JONATHAN - Israel Agricultural Research Organization (ARO)
item Teal, Peter
item GROZINGER, CHRISTINA - Pennsylvania State University

Submitted to: Molecular Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/6/2015
Publication Date: 11/11/2015
Citation: Amsalem, E., Galbraith, D.A., Cnaani, J., Teal, P.E., Grozinger, C.M. 2015. Conservation and modification of genetic and physiological toolkits underpinning diapause in bumble bee queens. Molecular Ecology. 24:5596-5615.

Interpretive Summary: Diapause is a key adaptation that allows insects to survive unfavorable conditions and inhabit an array of environments. While many of the conserved suite of genes that regulate diapause are similar between species, it is not known which genes affect diapause in social insect species. In social insects such as bees, these genes additionally may also be related to caste differences. In this study, scientists including an ARS scientist in Gainesville, FL examined the suites of genes affecting diapause in bumblebee queens. While some genetic mechanisms affecting diapauses were conserved between flies and bumblebees, a substantial number of transcripts were distinct in bumblebees. There was also substantial overlap between genes related to caste determination and diapause of bumblebees. A better understanding of the mechanisms associated with survival during advance conditions can provide insight in optimized management methods.

Technical Abstract: Diapause is the key adaptation allowing insects to survive unfavourable conditions and inhabit an array of environments. Physiological changes during diapause are largely conserved across species and are hypothesized to be regulated by a conserved suite of genes (a ‘toolkit’). Furthermore, it is hypothesized that in social insects, this toolkit was co-opted to mediate caste differentiation between long-lived, reproductive, diapause-capable queens and short-lived, sterile workers. Using Bombus terrestris queens, we examined the physiological and transcriptomic changes associated with diapause and CO2 treatment, which causes queens to bypass diapause. We performed comparative analyses with genes previously identified to be associated with diapause in the Dipteran Sarcophaga crassipalpis and with caste differentiation in bumble bees. As in Diptera, diapause in bumble bees is associated with physiological and transcriptional changes related to nutrient storage, stress resistance and core metabolic pathways. There is a significant overlap, both at the level of transcript and gene ontology, between the genetic mechanisms mediating diapause in B. terrestris and S. crassipalpis, reaffirming the existence of a conserved insect diapause genetic toolkit. However, a substantial proportion (10%) of the differentially regulated transcripts in diapausing queens have no clear orthologs in other species, and key players regulating diapause in Diptera (juvenile hormone and vitellogenin) appear to have distinct functions in bumble bees. We also found a substantial overlap between genes related to caste determination and diapause in bumble bees. Thus, our studies demonstrate an intriguing interplay between pathways underpinning adaptation to environmental extremes and the evolution of sociality in insects.