# Morphological and Genetic Variation of the Chinese Honey Bee (Apis cerana cerana Fabricius, 1793) in Wanyuan, Southwest China

## TL;DR

This study explores how Chinese honey bees in Wanyuan adapt to different altitudes, showing changes in body traits and maintaining genetic diversity.

## Contribution

The study reveals altitudinal morphological and genetic adaptations in a local ecotype of Chinese honey bees.

## Key findings

- Mid-altitude bees showed larger body size, while low-altitude bees had more hindwing hooks.
- Genetic diversity was high with 25 haplotypes and strong gene flow between populations.
- One site at 900 m showed slight genetic distinctiveness despite overall connectivity.

## Abstract

This study investigated how the Chinese honey bee (Apis cerana cerana Fabricius, 1793) adapts to different altitudes in Wanyuan, Sichuan. We collected 656 bees from 15 sites (565–1611 m) and measured 13 body traits and analyzed mitochondrial DNA. We found clear changes in bee shape with altitude: mid-elevation bees were larger in several traits, while low-elevation bees had more hindwing hooks, likely helping them fly in dense vegetation. Key identification traits also varied with elevation. Genetically, the population showed high diversity with 25 haplotypes, and most groups were well connected through gene flow, though one site at 900 m was slightly distinct. Overall, the Wanyuan honey bee displays noticeable physical adjustments to altitude while maintaining strong genetic connectivity across the landscape. These insights can help guide local conservation and sustainable use of this valuable honey bee resource.

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.