Impact of crop exposure and agricultural intensification on the phenotypic variation of bees

Abstract

In a context of rapid global change, understanding how environmental stressors can impact phenotypic variation, and which phenotypic traits are predominantly affected can be particularly relevant. Indeed, potential phenotypic modifications could affect the functionality of traits from taxa that are in decline but that are keystone species in many ecosystems. In this study, we assessed the impact of environmental drivers and agricultural intensification on two crucial pollinator species: the honeybee (Apis mellifera) and the buff-tailed bumblebee (Bombus terrestris). Among eight countries representing four major European biogeographical regions [i.e., Boreal (Sweden and Estonia), Atlantic (Ireland and United Kingdom), Continental (Germany and Switzerland) and Mediterranean (Spain and Italy)] and two type of crops (i.e., apple orchards and oilseed rape) we assessed how landscape structure, latitude and pesticide management could impact their wing morphology. Two sampling sessions were conducted: the first one when the hives/nests were settled on the field (T0) and a second sampling session after the potential effect of agricultural intensification (T1). Using a dataset of more than 7238 wings, we measured the wing size, shape and asymmetry. We observed that, in several countries, a shift in most of the morphological traits occurred between T0 and T1. When focusing on the drivers of phenotypic variation in T1, the levels of significance for some potential drivers were sometimes high, while most of the variation remained unexplained. The latitude and, more rarely, grassland cover were found to partly explain the wing modifications. In light of these results, we conclude that phenotypic shifts can occur in a very short period, after encountering new field conditions. Further studies should be conducted to better understand which alternative drivers could explain morphological changes in the agro-ecosystem after crop exposition, as well as the potential consequences of these changes on foraging performance or pollination efficiency.