Invasion success of the bumblebee, Bombus terrestris, despite a drastic genetic bottleneck.

In early 1992, the European bumblebee, Bombus terrestris, was first seen in Tasmania and currently has spread to most of the island. Here, we report on the genetic structure, using micro-satellites, of the invading population from samples collected in the years 1998-2000, a few years after the first sighting of the species in its new area. The data show that the Tasmanian population has a very low genetic diversity, with less than half of the allelic richness (Richness=2.89 alleles; H(exp)=0.591) and lower levels of heterozygosity as compared to populations in New Zealand (4.24 alleles; H(exp)=0.729) and Europe (5.08 alleles; H(exp)=0.826). In addition, the genetic data suggest that the invasion must have happened once, probably around late 1991, and was the result of very few, perhaps only two, individuals arriving in Tasmania. Furthermore, these founders came from the New Zealand population. Today, the population in the south of Tasmania seems to act as a source population from which individuals migrate into other parts of the state. A similar source-sink structure seems also the case for New Zealand. The data show that B. terrestris is a highly invasive species capable of establishing itself even after a dramatic genetic bottleneck. B. terrestris may be an invasive species due to the haplo-diploid sex determination system, which exposes recessive, deleterious mutations to selection. Offspring of such purged lines may then be able to tolerate high levels of inbreeding.

Queen-controlled sex ratios and worker reproduction in the bumble bee Bombus hypnorum, as revealed by microsatellites.

Social insect colonies provide model systems for the examination of conflicts among parties with different genetic interests. As such, they have provided the best tests of inclusive fitness theory. However, much remains unknown about in which party's favour such conflicts are resolved, partly as a result of the only recent advent of the molecular tools needed to examine the outcome of these conflicts. Two key conflicts in social insect colonies are over control of the reproductive sex ratio and the production of male offspring. Most studies have examined only one of these conflicts but in reality they occur in tandem and may influence each other. Using microsatellite analyses, the outcome of conflict over sex ratios and male production was examined in the bumble bee, Bombus hypnorum. The genotypes were determined for mother queens, their mates and males for each of 10 colonies. In contrast to other reports of mating frequency in this species, all of the queens were singly mated. The population sex ratio was consistent with queen control, suggesting that queens are winning this conflict. In contrast, workers produced over 20% of all males in queen-right colonies, suggesting that they are more effective in competing over male-production. Combining these results with previous work, it is suggested that worker reproduction is a labile trait that may well impose only small costs on queen fitness.