Bigger bees bumble by barriers, end up with lower population genetic differentiation

Population structure is the core of ecological genetics, as it’s practiced today. Genetic differentiation between populations in different places is our null hypothesis and one of our most widely used indirect signals that environmental factors are impacting the evolution of those different populations. Oh, and it’s also a first step to the origin of new species.

The huge body of published datasets testing for population structure is a great resource for synthetic work, that identifies broad general patterns about population genetic processes. Last year we saw one such study link locomotion mode and genetic differentiation — confirming that bird populations are less likely to differentiate, given a particular geographic distance, than populations of land-bound vertebrates. Now, freshly out in Molecular Ecology, we have a similar project in a more specific taxonomic scope: bees.

Wild pollinators, you may have heard, are under considerable threat from a variety of factors linked to human activity, including loss of habitat and the widespread use of pesticides. The population genetic structuring of bee populations, and what broad ecological factors impact that structuring, can inform how we protect them — whether we expect a species to have the diversity to respond to environmental changes, or whether we expect it to become fragmented given a particular level of habitat fragmentation, say. Margarita M. López‐Uribe and her coauthors address this by compiling genetic differentiation estimates from 42 bee species. They tested effects of species body size (bigger bees can generally fly farther), diet breadth, and sociality on differentiation.

The results varied among three measures of genetic differentiation the authors considered, but they found consistent effects of bee body size — bigger species had lower genetic differentiation. For two of three measures (Jost’s D and G_ST), there was also a significant effect of sociality, in which solitary species had somewhat higher differentiation than social ones.

That’s a fairly tidy synthetic result, and it should be helpful in providing baseline expectations about population genetic structure in bee species for which actual genetic data aren’t available. That said, there’s a lot of scatter in the data assembled by López-Uribe and her coauthors — so for species of particular concern, it’ll still probably be better to get the data than to use the "predictions" generated by this study.