Whole-genome resequencing reveals complex effects of geographical-palaeoclimatic interactions on diversification of moustache toads in East Asia

Contrast and Genomic Characterisation of Ancient and Recent Interspecific Introgression Between Deeply Diverged Moustache Toads (Leptobrachium)

Recent genomic analyses have provided new insights into the process of interspecific introgression and its consequences on species evolution. Most recent studies, however, focused on hybridization between recently radiated species, with few examining the genomic outcomes of ancient hybridization across deeply diverged species. Using whole genome data of moustache toads (Leptobrachium), we identified signals of three hybridization events among nine species that diverged at the Eocene. An ancient introgression from L. leishanense to the ancestral branch (C1) of L. liui introduced adaptive variants. The highly introgressed regions include genes with important functions in odorant detection and immune responses. These genes are preserved in all three descendent populations of L. liui_C1, and these regions likely have been positively selected over a long filtering process. A recent introgression occurred from L. huashen to L. tengchongense, with the introgressed regions being mostly neutral. Furthermore, one F1 hybrid individual was detected between sympatric L. ailaonicum and L. promustache. The signals of introgression largely disappeared after removing the hybrid individual, indicating an occasional hybridization but minimal introgression. Further examination of highly divergent but low introgressed genomic regions revealed both pre-mating isolation and genetic incompatibility as potential mechanisms of resisting introgression and maintaining species boundaries. Additionally, no large X-effect was found in these introgression events. Hybridization between deeply diverged amphibian species may be common, but detectable introgressions are likely less so, with recent introgression being mostly neutral and the rare ancient one potentially adaptive. Our findings complement recent genomic work, and together they provide a better understanding of the genomic characteristics of interspecific introgression and its significance in species adaptation and evolution.

Genetic diversity and haplotype distribution patterns analysis of cytb and RAG2 sequences in Rana hanluica from southern China

Rana hanluica: an endemic amphibian of China, is found in the hills and mountains south of the Yangtze River. In this comprehensive study, we collected 162 samples from 14 different localities to delve into the genetic diversity of Rana hanluica using mitochondrial Cytb and nuclear RAG2 as genetic markers. Our findings reveal that the Nanling Mountains, specifically regions like Jiuyi Shan, Jinggang Shan, Mang Shan, and Qiyun Shan, are genetic hotspots harboring remarkable diversity. The research results also indicate that there is gene flow among the various populations of the species, and no distinct population structure has formed, which may be due to migration. Moreover, populations in some regions, as well as the overall population, show signs of a possible genetic bottleneck, which we speculate may have been caused by climate change. However, given the exploratory nature of our study, further investigations are warranted to confirm these observations. Through phylogenetic analyses, we uncovered indications that R. hanluica might have originated within the Nanling region, dispersing along the east-west mountain ranges, with a significant contribution originating from Jiuyi Shan. The genetic distributions uncovered through our research reflect historical migratory patterns, evident in the distinct haplotypes of the RAG2 gene between the western and eastern parts of the studied area. Moreover, Heng Shan and Yangming Shan exhibited unique genetic signatures, possibly influenced by geographic isolation, which has shaped their distinct genotypes. The insights gained from this study hold profound implications for conservation efforts. By identifying regions rich in genetic diversity and crucial gene flow corridors, we can develop more effective conservation strategies. Preserving these genetically diverse areas, especially within the Nanling Mountains, is vital for maintaining the evolutionary potential of R. hanluica. In conclusion, our research has laid a solid foundation for understanding the genetic landscape of R. hanluica, shedding light on its origins, population structures, and evolutionary trajectories. This knowledge will undoubtedly guide future research endeavors and inform conservation strategies for this endemic amphibian.

Genomic analysis reveals deep population divergence in the water snake Trimerodytes percarinatus (Serpentes, Natricidae)

Although several phylogeographic studies of Asian snakes have been conducted, most have focused on pitvipers, with non-venomous snakes, such as colubrids or natricids, remaining poorly studied. The Chinese keelback water snake (Trimerodytes percarinatus Boulenger) is a widespread, semiaquatic, non-venomous species occurring in China and southeastern Asia. Based on mitochondrial DNA (mtDNA) and single nucleotide polymorphism (SNP) data, we explored the population genetic structure, genetic diversity, and evolutionary history of this species. MtDNA-based phylogenetic analysis showed that T. percarinatus was composed of five highly supported and geographically structured lineages. SNP-based phylogenetic analysis, principal component analysis, and population structure analysis consistently revealed four distinct, geographically non-overlapping lineages, which was different from the mtDNA-based analysis in topology. Estimation of divergence dates and ancestral area of origin suggest that T. percarinatus originated ~12.68 million years ago (95% highest posterior density: 10.36-15.96 Mya) in a region covering southwestern China and Vietnam. Intraspecific divergence may have been triggered by the Qinghai-Xizang Plateau uplift. Population demographics and ecological niche modeling indicated that the effective population size fluctuated during 0.5 Mya and 0.002 Mya. Based on the data collected here, we also comment on the intraspecific taxonomy of T. percarinatus and question the validity of the subspecies T. p. suriki.

Impacts of Quaternary glaciation, geological history and geography on animal species history in continental East Asia: A phylogeographic review

Continental East Asia has a mild Pleistocene climate and a complex recent geological history. Phylogeographic studies of animals over the last 30 years have produced several distinctive patterns. Glaciation refugia are numerous and are not restricted to any particular regions. Most of them are localized and species-specific, although several large refugia, for example the mountains of SW China, are shared by multiple species and have refugia-within-refugia. Furthermore, postglaciation range expansion events vary greatly in time, scale and direction. Large-scale south-to-north post-LGM expansions are few and mostly occurred in the northern regions. Additionally, several unique geographic features, including the three-step terrain of China and the northern arid belt, have significant impacts on many species histories. Overall, the impacts of Pleistocene glaciations, particularly the LGM, on species history vary drastically from nondetectable to significant. The impacts are the least for species from the southwestern region and are most dominant for species from the north. Geological events play a more significant role in shaping species history than Pleistocene climatic changes. Phylogeographic patterns among animals species are highly consistent with those of plants. Future phylogeographic endeavour in East Asia should be hypothesis-driven and seek processes that underlie common patterns. The wide use of genomic data allow accurate estimates of historical population processes and exploration of older history beyond the Pleistocene.