Abstract
Bombus terrestris is a bumblebee with a wide geographic range, with subspecies showing a variety of local adaptations. Global export of commercially-reared B. terrestris started in the 1980s; the bees are a mixture of subspecies bred for ease of rearing, bivoltinism and large nests. This paper investigated whether the increase in bivoltinism in UK resident B. terrestris audax populations was related to introgression with imported foreign subspecies. Workers were collected from wild populations in London and Bristol, as well as two commercial suppliers. Fourteen microsatellite loci were used to study population structure, hybridisation and introgression. No introgression with commercial B. t. dalmatinus was detected in wild populations. Hence, the increase in winter activity appears unrelated to introgression.
Highlights
Bombus terrestris (Linnaeus 1758) is a large, highly abundant bumblebee with a wide distribution across Europe (Figure 1), where it can be found in a range of habitats, excluding arctic, alpine and desert regions (Rasmont et al 2008)
Through a behaviour known as buzz pollination, bumblebees are capable of pollinating several crops which cannot be effectively pollinated by honeybees, and are a cheaper alternative to mechanical pollination in which humans use mechanical, hand-held devices to manually pollinate such crops (Velthuis and Van Doorn 2006)
We aim to investigate whether hybridisation and consequent introgression with imported, non-native subspecies is underpinning the recent trend towards bivoltinism in British B. terrestris, by using microsatellite analysis to detect differences and similarities between wild winter and summer populations, and commercial, imported bumblebees
Summary
Bombus terrestris (Linnaeus 1758) is a large, highly abundant bumblebee with a wide distribution across Europe (Figure 1), where it can be found in a range of habitats, excluding arctic, alpine and desert regions (Rasmont et al 2008). Nine distinct subspecies have been described, with physiological and behavioural adaptations appropriate to their local environment, such as differences in colour pattern, pheromones and aggression (Rasmont et al 2008; Coppée 2010) Despite such variation, the vast majority of B. terrestris populations are univoltine, with queens emerging from diapause in the spring, Chosen for their ability to pollinate a wide range of plants and to thrive in a variety of environmental conditions, B. terrestris has been bred commercially since the 1980s for agricultural pollination services (Velthuis and Van Doorn 2006; Rasmont et al 2008). As well as colony size and domesticity, commercial populations were bred to discourage diapause, leading to colony initiation immediately after mating, which has a known genetic component (Beekman et al 1999; Velthuis and Van Doorn 2006) These mixed, domesticated colonies have been distributed worldwide, often with no regard for the impact on local, native bumblebee species. These domesticated bumblebee species could cause negative effects on local species and subspecies within their native range such as spreading disease, disrupting local genetic adaptation or outcompeting local populations (Ings et al 2006; Lecocq et al 2016; Chandler et al 2019)
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