Comparative genetic analyses of historical and contemporary collections highlight contrasting demographic histories for the bumble bees Bombus pensylvanicus and B. impatiens in Illinois

摘要

Direct comparison of genetic patterns between museum specimens and contemporary collections can be a powerful approach for detecting recent demographic changes. Using microsatellite markers, we examined historical and contemporary genetic variation from an apparently declining bumble bee species, Bombus pensylvanicus, and from a stable species, Bombus impatiens, in central Illinois. For each species, we genotyped specimens from the Illinois Natural History Survey collected from three populations between 1969-1972 and from a resurvey of the same areas conducted in 2008. Population structure in B. pensylvanicus increased markedly over the last four decades (from θ_ST = 0.001 to 0.027) while no structure was detected in B. impatiens for either time period (θ_ST = _0.006 to _0.003). Changes in genetic diversity were not significant for either species, although small reductions were observed for B. pensylυanicus in all three populations. Coalescent simulations incorporating both contemporary and historical samples suggest that this small change is not surprising for recent population declines, as large reductions in genetic diversity were only apparent under the most severe bottleneck scenarios. These results demonstrate how comparisons of genetic patterns between temporal periods and species can help elucidate potential threats to popu_lation health and suggest several strategies that might be useful in the conservation of B. pensylυanicus in the Midwestern USA.