Widespread modified hairs in bees: An explanation for floral specialization?

One of the great debates among pollination biology is how bees specialize on their floral hosts. Currently, the conventional wisdom is that specialist bees largely lack morphological adaptations for harvesting pollen. Instead, recent hypotheses have emphasized behavioral and dietary specialization. A survey of bee taxa has uncovered the pervasive occurrence of morphological specialization in bees spanning every family except Stenotritidae. These morphological adaptations take the form of modified hairs that gather and hold pollen before transferring it to the scopal hairs. The modifications to the hairs typically take the form of apical hooks, curves, bends, or corkscrews. They are generally found on the venter of bees, and can occur on the head, mesosoma, metasoma, coxae, trochanters, foretarsi, and mouthparts. The size and spacing of these hairs appear to match with the morphology of the pollen the bee is specialized on, while the placement of the hairs matches up with the morphology of the flower. The widespread occurrence of these hairs offers a mechanism to help explain specialization in bees, and suggests that many bees that appear to lack specialized morphological characters are in fact tightly specialized on the morphology of their host pollen.