Male flight distance and population substructure in the bumblebee Bombus terrestris

Bumblebees are important pollinators in natural as well as agricultural ecosystems. Estimates of foraging range, population size and genetic population structure so far have been based on worker samples alone. Here we include both males and workers in a population genetic analysis to infer the contribution of males to these important ecological parameters. The population genetic (microsatellite) analyses of Bombus terrestris L. populations on the island of Cabrera (Spain) and Halle (Germany) revealed high heterozygosities (0.60 +/- 0.08 to 0.77 +/- 0.13) and neither a deviation from Hardy-Weinberg equilibrium nor linkage disequilibrium. We detected five colonies (census population size) for the island population and 27 to 68 for the German mainland population. The genetic effective population sizes were N(e) = 7.5 for the island and 40.5 to 102 for the mainland population respectively. There was a significant genetic subdifferentiation between the male and the worker population samples, suggesting that males originated from different and/or more distant colonies than workers. Based on the colony numbers, we estimated the flight range of males, which ranged from 2.6 km to 9.9 km, much further than worker flight ranges. Bumblebee-mediated pollen flow will therefore be much further than expected based on the foraging range of workers alone if males also contribute to pollination.