Heterospecificity of body pollen varies across and within functional groups of pollinators

Abstract Selection pressures exerted by pollinators are widely regarded as key drivers of the evolution of floral phenotypes. To capture presumed similarities in these selective forces, pollinators have traditionally been organized into functional groups, often corresponding to taxonomic classifications. However, given the likely diversity of foraging behavior among pollinators, groupings based solely on taxonomy or morphology may not adequately reflect variation in pollen transfer efficiency, particularly in terms of heterospecific pollen transfer (HPT) potential. To explore this possibility, we assessed how 11 groups of insect pollinators in a Japanese satoyama landscape, classified by both taxonomy and putative behavioral differences, varied in the heterospecificity of pollen on their bodies. Despite being collected from flowers of the same Ligustrum trees in close proximity, the body pollen profiles of these insects significantly differed—both among and within the 11 groups—in terms of the proportion of heterospecific (non-Ligustrum) pollen, the composition of pollen species, and the diversity of pollen species. Notably, marked variations were found within bees, flies, and beetles, as well as between males and females of the same bumble-bee species. Based on these data, we discuss how the observed variations could offer new insights into conventional views on functional groups of pollinators, which are largely based on taxonomy or morphological/size similarities.