A test of genetic divergence of a bird existing in the Sichuan Basin and its surrounding mountain ranges

Island ecosystems, serving as natural laboratories, facilitate geographical isolation, ecological specialization, and species divergence. The Sichuan Basin, surrounded by mountain ranges, represents a typical continental island due to its marked environmental spatial heterogeneity. This heterogeneity may contribute to geographical isolation and habitat heterogeneity, resulting in genetic divergence within populations. Therefore, we used the White-browed Laughingthrush (Garrulax sannio) as a model specimen to investigate the genetic divergence in the Sichuan Basin and its surrounding mountain ranges, given its presence in various habitats within and beyond this basin. Employing a RAD-seq dataset of 140 G. sannio individuals from 17 distinct ecological zones in the Sichuan Basin and its surrounding mountain ranges, we conducted PCA, population structure analysis, phylogenetic tree construction, and gene flow analysis to comprehensively analyze G. sannio groups. Additionally, in conjunction with geographical and ecological data, we performed isolation by distance, isolation by environment, PCA, and latent factor mixed model analysis to identify factors influencing the genetic divergence among these G. sannio groups. In summary, the 17 G. sannio groups were categorized into high-elevation, medium-elevation, and low-elevation groups. Genetic divergence in G. sannio may be attributed to both geographical distance and key ecological factors, particularly elevation and key climatic variables. Notably, the high-elevation group exhibited a greater number of SNPs and selected genes associated with the key ecological factors compared to the low-elevation group. The ADCY9 gene and several associated key pathways were identified as crucial elements driving ecological adaptation (elevation and key climatic variables) in the high-elevation group. Furthermore, climate changes during the glacial cycles may have facilitated gene flow among these groups residing in the Sichuan Basin and its surrounding mountain ranges. Our findings provide evidence of genetic divergence in G. sannio influenced by the geographical distance and key ecological factors between the Sichuan Basin and its surrounding mountain ranges. These results lay the groundwork for future research on the molecular systematics of continental islands.