Many insect species have been domesticated, and are widely propagated for use as biological control agents and crop pollinators. Domestic organisms are often genetically distinct from their wild conspecifics, as the process of domestication creates novel selection pressures. Thus, gene flow between domestic and wild populations may impact the genetic integrity of natural populations. The Common Eastern Bumblebee (Bombus impatiens) is a common native pollinator in the Northeastern United States that has been reared commercially since 1990. Our study evaluates 1) genetic differentiation between domestic and wild B. impatiens, and 2) introgression from domestic B. impatiens into wild populations using microsatellite markers.
Individuals were genotyped from three populations: from a domestic population produced by Koppert Biological Systems, from a wild population on a farm known to use domestic B. impatiens, and from a wild population on a relatively isolated wildlife preserve. Collections at study sites surrounding farms occurred after domestic hives have expired, to ensure bees were not sampled from artificial hives. Individuals were collected from 17 domestic colonies, and approximately 90 bees were collected from each field site. Workers were genotyped using four variable microsatellite loci previously described by Lozier et al. (2011).
Our results show moderate population differentiation between domestic populations and both wild populations at two microsatellite loci with Fst values between .05 and .15. However, there was no significant differentiation between the two wild populations (Fst < .05). We measured introgression using bayesian analysis of population structure to assign individuals to different clusters, or populations. Using a bayesian admixture analysis with informative priors (i.e, the model accounted for both hybridization between populations, as well as sampling locations), we found a model with two populations maximized the likelihood of the data. The domestic population showed a high proportion of membership in of one of these populations (71%), while the two populations of wild bumblebees showed low membership in this population (1.7-.001%). Preliminary results indicate if populations are hybridizing, introgression is low or nonexistent. However, in order to determine if these proportions are significant, it is necessary to run simulations.
Overall, we found that wild populations of bumblebees are genetically distinct from domestic bumblebees, though this differentiation is relatively low. We are currently expanding this study to incorporate five additional microsatellite markers, and to explore the significance of introgression using simulations.