Environmental differences explain subtle yet detectable genetic structure in a widespread pollinator

BackgroundThe environment is a strong driver of genetic structure in many
natural populations, yet often neglected in population genetic studies.
This may be a particular problem in vagile species, where subtle structure
cannot be explained by limitations to dispersal. Consequently, these
species might falsely be considered quasi-panmictic and hence potentially
mismanaged. A species this might apply to, is the buff-tailed bumble bee
(Bombus terrestris), an economically important and widespread pollinator,
which is considered to be quasi-panmictic at mainland continental scales.
Here we aimed to (i) quantify genetic structure in 21+ populations of the
buff-tailed bumble bee, sampled throughout two Eastern European countries,
and (ii) analyse the degree to which structure is explained by
environmental differences, habitat permeability and geographic distance.
Using 12 microsatellite loci, we characterised populations of this species
with Fst analyses, complemented by discriminant analysis of principal
components and Bayesian clustering approaches. We then applied generalized
dissimilarity modelling to simultaneously assess the informativeness of
geographic distance, habitat permeability and environmental differences
among populations in explaining divergence. ResultsGenetic structure of
the buff-tailed bumble bee quantified by means of Fst was subtle and not
detected by Bayesian clustering. Discriminant analysis of principal
components suggested insignificant but still noticeable structure that
slightly exceeded estimates obtained through Fst analyses. As expected,
geographic distance and habitat permeability were not informative in
explaining the spatial pattern of genetic divergence. Yet, environmental
variables related to temperature, vegetation and topography were highly
informative, explaining between 33 and 39% of the genetic variation
observed. ConclusionsIn contrast to previous studies reporting
quasi-panmixia in continental populations of this species, we demonstrated
the presence of subtle population structure related to environmental
heterogeneity. Environmental data proved to be highly useful in
unravelling the drivers of genetic structure in this vagile and
opportunistic species. We highlight the potential of including these data
to obtain a better understanding of population structure and the processes
driving it in species considered to be quasi-panmictic.