Population genetics of a range-expanding bumblebee

Genetic bottlenecks suffered during colonisation events may hinder the ability of a species to establish in a new range. Such effects may be exaggerated in the eusocial Hymenoptera (ants, bees and wasps) because of their unusual system of sex determination, with low genetic diversity potentially leading to high frequencies of inviable or sterile diploid males. Despite this, social insects represent some of the most invasive species worldwide. Hence, there is special interest in the population genetic processes underlying the colonisation and establishment of social insects within new ranges.

The Tree Bumblebee represents one such range-expanding social insect, having rapidly expanded in range across the UK following its initial 2001 arrival. However, until recently, the population genetics of this range-expansion (i.e. whether the Tree Bumblebee suffered a loss of genetic diversity upon arrival to the UK) were relatively unknown.

By genotyping workers and males from a representative UK population, we recently showed that the UK Tree Bumblebee population exhibits relatively high genetic diversity at neutral microsatellite loci and the sex-determining locus, and relatively low levels of diploid male production. We therefore concluded that the Tree Bumblebee did not experience a genetic bottleneck on its arrival in the UK, and is likely still in genetic contact with continental European populations (through continued immigration of queens and/or males). Further, such evidence suggests that the Tree Bumblebee’s ecological success in the UK has not taken place against a background of low genetic variation, as is often seen in various invasive social insects.

I recently discussed this work on the Abstract Bioscience podcast, which you can listen to here.

Conflict resolution in a eusocial society

The high levels of co-operation observed in insect societies have led to them being described as ‘superorganisms’. However, given such societies are usually familial rather than clonal, potential for conflict between colony members exists. How societies are maintained in the face of such conflict represents a major question in social evolution.

In many social ants, bees and wasps, workers can lay haploid, male-destined eggs and directly compete with the queen over male production. In extreme cases, workers may even kill the queen to gain control over male production.

I’m interested in the outcomes of male production conflict in the Tree Bumblebee, a facultatively polyandrous bumblebee with colonies containing hundreds of workers. Such research involves the rearing of colonies from field-collected queens, number tagging and behavioural observations of the colony members, and genotyping to estimate levels of worker-produced males.