Genomic divergence and a lack of recent introgression between commercial and wild bumblebees (Bombus terrestris)

The global movement of bees for agricultural pollination services can affect local pollinator populations via hybridization. When commercial bumblebees are of the same species but of different geographic origin, intraspecific hybridization may result in beneficial integration of new genetic variation, or alternatively may disrupt locally adapted gene complexes. However, neither the existence nor the extent of genomic introgression and evolutionary divergence between wild and commercial bumblebees is fully understood. We obtained whole-genome sequencing data from wild and commercial Bombus terrestris collected from sites in Southern Sweden with and without long-term use of commercially imported B. terrestris. We search for evidence of introgression, dispersal and genome-wide differentiation in a comparative genomic analysis of wild and commercial bumblebees. Commercial B. terrestris were found in natural environments near sites where commercial bumblebees were used, as well as drifting wild B. terrestris in commercial bumblebee colonies. However, we found no evidence for widespread, recent genomic introgression of commercial B. terrestris into local wild conspecific populations. We found that wild B. terrestris had significantly higher nucleotide diversity (Nei's pi, pi), while the number of segregating sites (Watterson's theta, theta w) was higher in commercial B. terrestris. A highly divergent region on chromosome 11 was identified in commercial B. terrestris and found to be enriched with structural variants. The genes present in this region are involved in flight muscle contraction and structure and pathogen immune response, providing evidence for differing evolutionary processes operating in wild and commercial B. terrestris. We did not find evidence for recent introgression, suggesting that co-occurring commercial B. terrestris have not disrupted evolutionary processes in wild B. terrestris populations

SNP datasets from invasive Bombus terrestris on Tasmania, Australia

<p><span>Invasive species are predicted to adjust their morphological, physiological, and life-history traits to adapt to their non-native environments. Although a loss of genetic variation during invasion may restrict local adaptation, introduced species often thrive in novel environments. Despite being founded by just a few individuals, the bumblebee <em>Bombus</em> <em>terrestris</em> (Hymenoptera: Apidae) has successfully spread across the island of Tasmania (Australia) in less than 30 years, becoming abundant and competitive with native pollinators. We use RADseq to investigate what neutral and adaptive genetic processes associated with environmental and morphological variation allow <em>B. terrestris</em> to thrive as an invasive species in Tasmania. Across 15 sites, we found high gene flow with low genetic diversity, significant isolation-by-distance, and spatial variation in effective migration rates. A longitudinal band of restricted migration was evident across the mid-central region of Tasmania, corresponding to sites with high elevation, pastural land, low wind speeds and low precipitation seasonality. Tajima's D indicated a recent population expansion for central sites extending from the south to the north of the island. Significant selection signatures were found for loci in relation to precipitation, wind speed, and wing loading. Candidate loci were annotated to genes with functions related to </span><span>cuticle water retention and insect flight muscle stability. </span><span>Understanding how a genetically impoverished invasive bumblebee has rapidly adapted to a novel island environment provides further understanding about the evolutionary processes that determine successful insect invasions and the potential for invasive hymenopteran pollinators to spread globally.</span></p><p><span>Wild <em>B. terrestris</em> workers were sampled from 16 locations across the Australian continental island state of Tasmania and subsequently extracted for DNA (DNeasy Blood and Tissue extraction kit (Qiagen) and sent for RADseq at to Floragenex, Inc. (Portland, OR, USA). Samples were individually sequenced on an Illumina HighSeq 4000, generating 150bp paired-end reads with an average depth of coverage between 12–112x per sample. </span></p&gt

Genomic divergence and a lack of recent introgression between commercial and wild bumblebees (Bombus terrestris)

The global movement of bees for agricultural pollination services can affect local pollinator populations via hybridization. When commercial bumblebees are of the same species but of different geographic origin, intraspecific hybridization may result in beneficial integration of new genetic variation, or alternatively may disrupt locally adapted gene complexes. However, neither the existence nor the extent of genomic introgression and evolutionary divergence between wild and commercial bumblebees is fully understood. We obtained whole-genome sequencing data from wild and commercial Bombus terrestris collected from sites in Southern Sweden with and without long-term use of commercially imported B. terrestris. We search for evidence of introgression, dispersal and genome-wide differentiation in a comparative genomic analysis of wild and commercial bumblebees. Commercial B. terrestris were found in natural environments near sites where commercial bumblebees were used, as well as drifting wild B. terrestris in commercial bumblebee colonies. However, we found no evidence for widespread, recent genomic introgression of commercial B. terrestris into local wild conspecific populations. We found that wild B. terrestris had significantly higher nucleotide diversity (Nei's pi, π), while the number of segregating sites (Watterson's theta, θw) was higher in commercial B. terrestris. A highly divergent region on chromosome 11 was identified in commercial B. terrestris and found to be enriched with structural variants. The genes present in this region are involved in flight muscle contraction and structure and pathogen immune response, providing evidence for differing evolutionary processes operating in wild and commercial B. terrestris. We did not find evidence for recent introgression, suggesting that co-occurring commercial B. terrestris have not disrupted evolutionary processes in wild B. terrestris populations