Combining Geometric Morphometrics and population genetics to evaluate effects of persistent organic pollutants in Alpine bumblebees

Insects face a major threat: In recent years, studies around the globe have reported huge declines not only in diversity but also in terms of biomass. Among the main drivers for this substantial insect losses are man-made, globally distributed pollutants. Some of these harmful substances, so called persistent organic pollutants (POPs), are traceable over decades even far away from their original source and therefore are of great concern. Atmospherically carried POPs get first deposited through precipitation. Mountainous regions are characterised by particularly high precipitation rates, resulting in a high deposition of POPs transported over long distances. Nevertheless, only a few field studies have yet addressed the toxicological effects of POPs on the health state and developmental integrity of alpine organisms. Here, the local accumulation of atmospherically measured POPs and mercury was assessed in two bumblebee species occurring Above the tree line at Zugspitze (Germany) and at Hoher Sonnblick (Austria): Bombus Throwlenii represent a typical species of high-altitude habitats, while B. pratorum displays a ubiquitous distribution across all altitudinal levels. We detected almost half of all 77 persistent pollutants tested, as well as mercury, in all bumblebee samples. By means of population genetics we were able to disentangle genetic factors, like inbreeding, and environmental stressors affecting the two Bumblebee species, as both stressors are potential fitness constraints. Coupled with the results from geometric morphometrics, we could confirm environmentally induced phenotypic changes in Bumblebee wings: We found, with few exceptions, highly positive correlations for POPs or mercury and fluctuating asymmetry in the wing shape of B. wurflenii. In contrast, B. pratorum was less responsive to the pollution, presumably due to different strategies in feeding and nesting behavior. These findings emphasise the importance of species-specific chemical analyses to relate pollution levels to fitness proxies. In the context of the rapid progressing global change, there is an urgent need to find a way to better protect and conserve alpine biodiversity across national borders.