Convergent evolution of specialized bee traits for pollen collection from nototribic flowers

Bees and certain pollen wasps have independently evolved specialized morphological traits to effectively collect pollen from nototribic flowers or those with anthers and styles positioned on the upper side of bilaterally symmetrical blooms. These flower types are common in the Lamiaceae, Fabaceae, and Scrophulariaceae. We surveyed the literature and examined museum specimens to compile a global list of bee species exhibiting facial adaptations associated with nototribic pollination. We also assessed the occurrence of these floral specializations in relation to body size, nesting ecology, and geographic distribution. We document and categorize various morphological modifications, including flattened facial regions, rugose integuments, and specialized hairs (e.g., hooked, wavy, or proclinate). In addition, we mapped the presence of these traits onto the bee phylogeny. Our findings suggest that these adaptations have evolved convergently across multiple biogeographic regions, particularly in the Holarctic and Neotropics. Although behavioral observations remain limited, preliminary evidence suggests additional behavioral adaptations that facilitate effective pollen collection and removal.