A genome-wide analysis of structure and evolution in Irish and British populations of Bombus terrestris (L. 1758) : implications for genetic resource conservation

Abstract

Insect pollinators play vital regulatory roles within ecosystems and provide humanity with essential services that support our health, wellbeing, and economies. Despite their importance, reported declines at regional and national levels have raised concerns over the continuation of such benefits. Island pollinator populations are of particular conservation interest as they may harbor lower genetic diversity due to restricted gene flow caused by geographical barriers, which may in turn influence local selective processes. In this study, we investigated the population structure and potential targets of selection within the genomes of a bumblebee subspecies, Bombus terrestris audax, native to the islands of Ireland and Great Britain. In particular, we compared the genomes of wild-caught populations from each island alongside representatives of other European subspecies and commercial imports to ascertain patterns of historical admixture. Our analysis identified a largely genetically distinct population of B. t. audax on the island of Ireland, with weak evidence of admixture. In addition, we find differential signatures of positive selection between the two island populations in genes associated with neurology and development, indicating potential local adaptation. Furthermore, we identified an extremely polymorphic region on chromosome 10 with evidence of shared haplotypes in both wild and commercial bees, which may represent long-standing genetic variation at the continental level or potential localized admixture between wild and commercial bees. Collectively, our findings inform on the genetic distinctiveness of these island bumblebees, emphasizing the applied need to genetically characterize natural populations to ensure the conservation of genetic resources—in the context of this study, by informing risk-assessment and management of commercial bumblebees. In addition, our study reinforces the utility of genomic approaches in the biomonitoring of isolated or regionally adapted insect pollinator populations, which will contribute towards the effective conservation of these ecologically vital organisms.