Abstract
Chinese honey bees (Apis cerana cerana Fabricius, 1793) are crucial native pollinators in China, with substantial ecological and economic value. Their morphological traits may vary along altitudinal gradients, particularly in hilly regions such as Wanyuan City, Sichuan Province, which provides typical suitable habitat for a locally thriving ecotype known as the Wanyuan honey bee. To elucidate its adaptive variation across environmental gradients, this study investigated the morphological and genetic diversity of this ecotype along an altitudinal transect in Wanyuan. A total of 656 worker individuals from 15 sampling sites (565-1611 m) were analyzed for 13 morphological traits and mitochondrial DNA (tRNAleu-COII fragment) sequences. Results revealed significant altitudinal clines in morphology: Honey bees from mid-altitude sites exhibited larger body size for several traits, while low-altitude bees possessed a significantly higher number of hindwing hamuli. Key taxonomic indices like the cubital index and proboscis length also varied significantly with altitude. Genetic analysis identified 25 haplotypes with high haplotype diversity and nucleotide diversity, indicating substantial genetic variation. Population differentiation was generally low, with one site (Yinbazhai, 900 m) showing relatively higher distinctiveness. The detected high gene flow suggests frequent genetic exchange among most populations. These findings demonstrate that the Wanyuan honey bee exhibits clear altitudinal adaptation in morphology while maintaining high genetic diversity and connectivity. This study provides a crucial scientific basis for the conservation and sustainable management of this genetic resource by highlighting the importance of its population-specific adaptations and genetic structure.