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

Abstract

Background The 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. Results Genetic 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. Conclusions In 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.

Selection despite low genetic diversity and high gene flow in a rapid island invasion of the bumblebee, Bombus terrestris

“…The initial introduction of just two or three queens to Tasmania likely led to the low genetic diversity we observed (Schmid‐Hempel et al., 2007; Figure 1, Figure S5 in Appendix S1; site pairwise F ST −0.0031 to 0.014, global F ST 0.005). However, our values are within the range of similarly low F ST values observed in invasive B. terrestris populations in Japan (pairwise F ST between two sites = 0.006, Nagamitsu & Yamagishi, 2009), native populations in continental Europe (global F ST = 0.005, Estoup et al., 1996) and Eastern Europe (global F ST = 0.006, Glück et al., 2022). Other Bombus species show similarly low genetic differentiation in continental Europe, such as B. lapidarius (global F ST = 0.003, Theodorou et al., 2018), B. hortorum in Belgium (global F ST = 0.010) and B. sylvarum (global F ST = 0.029, Maebe et al., 2019).…”

High genetic connectivity of two pollinating flies despite urban disturbance

“…Previous studies highlighted that isolation by environmental distance can occur in the absence of isolation by geographical distance or by resistance (Glück et al, 2022). Glück et al (2022) found that environmental differences accounted for over 30% of the genetic divergence observed among buff‐tailed bumblebee [ Bombus terrestris (Linnaeus, 1758)] populations across Romania and Bulgaria, although population structure was subtle ( F ST < 0.07) and not detected by Bayesian clustering. Environmental heterogeneity was suggested to act as a selective pressure against dispersers, which would result in a disruption in genetic connectivity whereby divergence in neutral markers can arise through genetic drift.…”