Drivers of genomic differentiation landscapes in populations of disparate ecological and geographical settings within mainland Apis cerana.

Elucidating the evolutionary processes that drive population divergence can enhance our understanding of the early stages of speciation and inform conservation management decisions. The honeybee Apis cerana displays extensive population divergence, providing an informative natural system for exploring these processes. The mainland lineage A. cerana includes several peripheral subspecies with disparate ecological and geographical settings radiated from a central ancestor. Under this evolutionary framework, we can explore the patterns of genome differentiation and the evolutionary models that explain them. We can also elucidate the contribution of non-genomic spatiotemporal mechanisms (extrinsic features) and genomic mechanisms (intrinsic features) that influence these genomic differentiation landscapes. Based on 293 whole genomes, a small part of the genome is highly differentiated between central-peripheral subspecies pairs, while low and partial parallelism partly reflects idiosyncratic responses to environmental differences. Combined elements of recurrent selection and speciation-with-gene-flow models generate the heterogeneous genome landscapes. These elements weight differently between central-island and other central-peripheral subspecies pairs, influenced by glacial cycles superimposed on different geomorphologies. Although local recombination rates exert a significant influence on patterns of genomic differentiation, it is unlikely that low-recombination rates regions were generated by structural variation. In conclusion, complex factors including geographical isolation, divergent ecological selection and non-uniform genome features have acted concertedly in the evolution of reproductive barriers that could reduce gene flow in part of the genome and facilitate the persistence of distinct populations within mainland lineage of A. cerana.

Defining honeybee subspecies in an evolutionary context warrants strategized conservation.

Despite the urgent need for conservation consideration, strategic action plans for the preservation of the Asian honeybee, Apis cerana Fabricius, 1793, remain lacking. Both the convergent and divergent adaptations of this widespread insect have led to confusing phenotypical traits and inconsistent infraspecific taxonomy. Unclear subspecies boundaries pose a significant challenge to honeybee conservation efforts, as it is difficult to effectively prioritize conservation targets without a clear understanding of subspecies identities. Here, we investigated genome variations in 362 worker bees representing almost all populations of mainland A. cerana to understand how evolution has shaped its population structure. Whole-genome single nucleotide polymorphisms (SNPs) based on nuclear sequences revealed eight putative subspecies, with all seven peripheral subspecies exhibiting mutually exclusive monophyly and distinct genetic divergence from the widespread central subspecies. Our results demonstrated that most classic morphological traits, including body size, were related to the climatic variables of the local habitats and did not reflect the true evolutionary history of the organism. Thus, such morphological traits were not suitable for subspecific delineation. Conversely, wing vein characters showed relative independence to the environment and supported the subspecies boundaries inferred from nuclear genomes. Mitochondrial phylogeny further indicated that the present subspecies structure was a result of multiple waves of population divergence from a common ancestor. Based on our findings, we propose that criteria for subspecies delineation should be based on evolutionary independence, trait distinction, and geographic isolation. We formally defined and described eight subspecies of mainland A. cerana. Elucidation of the evolutionary history and subspecies boundaries enables a customized conservation strategy for both widespread and endemic honeybee conservation units, guiding colony introduction and breeding.

Diversity and functional analysis of Chinese bumblebee gut microbiota reveal the metabolic niche and antibiotic resistance variation of Gilliamella.

Bumblebees play an important role in maintaining the balance of natural and agricultural ecosystems, and the characteristic gut microbiota of bumblebees exhibit significant mutualistic functions. China has the highest diversity of bumblebees; however, gut microbiota of Chinese bumblebees have mostly been investigated through culture-independent studies. Here, we analyzed the gut communities of bumblebees from Sichuan, Yunnan, and Shaanxi provinces in China through 16S ribosomal RNA amplicon sequencing and bacterial isolation. It revealed that the bumblebees examined in this study harbored two gut enterotypes as previously reported: one is dominated by Gilliamella and Snodgrassella, and the other is distinguished by prevalent environmental species. The gut compositions obviously varied among different individual bees. We then isolated 325 bacterial strains and the comparative genomic analysis of Gilliamella strains revealed that galactose and pectin digestion pathways were conserved in strains from bumblebees, while genes for the utilization of arabinose, mannose, xylose, and rhamnose were mostly lost. Only two strains from the Chinese bumblebees possess the multidrug-resistant gene emrB, which is phylogenetically closely related to that from the symbionts of soil entomopathogenic nematode. In contrast, tetracycline-resistant genes were uniquely present in three strains from the USA. Our results illustrate the prevalence of strain-level variations in the metabolic potentials and the distributions of antibiotic-resistant genes in Chinese bumblebee gut bacteria.

Gene reuse facilitates rapid radiation and independent adaptation to diverse habitats in the Asian honeybee.

Animals with recent shared ancestry frequently adapt in parallel to new but similar habitats, a process often underlined by repeated selection of the same genes. Yet, in contrast, few examples have demonstrated the significance of gene reuse in colonization of multiple disparate habitats. By analyzing 343 genomes of the widespread Asian honeybee, Apis cerana, we showed that multiple peripheral subspecies radiated from a central ancestral population and adapted independently to diverse habitats. We found strong evidence of gene reuse in the Leucokinin receptor (Lkr), which was repeatedly selected in almost all peripheral subspecies. Differential expression and RNA interference knockdown revealed the role of Lkr in influencing foraging labor division, suggesting that Lkr facilitates collective tendency for pollen/nectar collection as an adaptation to floral changes. Our results suggest that honeybees may accommodate diverse floral shifts during rapid radiation through fine-tuning individual foraging tendency, a seemingly complex process accomplished by gene reuse.