Large mountains make small barriers: Species composition and spatial dynamics history of the Odorrana schmackeri complex in the karst area of Guizhou, China

Aim Species delimitation is the basis for identifying diversity, and the genetic structure and demographic history of species can shed light on the effects of geological and historical climate change, thus allowing us to develop appropriate conservation and management strategies. In this study, we aimed to clarify the species composition and geographic distribution of the Odorrana schmackeri complex in the karst areas of Guizhou, explore the influence of geological and climatic events on its evolutionary and demographic history, predict the impact of future climate on the distribution area, and investigate the ecological niche differentiation of the complex. Location Karst areas of Guizhou Province, China. Methods Using three mitochondrial (12S, 16S, and ND2) and four nuclear gene (BDNF, RAG1, RAG2, and Tyr) sequences as genetic markers, Bayesian inference (BI) was used to infer phylogenetic relationships and BEAST was used to assess divergence times. We assessed and estimated demographic histories using neutrality tests, mismatch distributions, and Bayesian skyline plots (BSPs). Using a species distribution prediction model, past and future suitable ranges were assessed. Niche equivalency and similarity of the three species of the complex were examined using the R package "ecospat." Results The O. schmackeri complex in Guizhou Province consists of three species: O. kweichowensis, O. huanggangensis, and O. hejiangensis. Demographic analyses indicated that population expansion of O. kweichowensis and O. huanggangensis occurred during the late Pleistocene, coinciding with the expansion of suitable habitat during the last ice age and the mid-Holocene. Our projections suggest that potentially suitable habitat for all three species will contract under all future climate scenarios. The ecological niche similarity test showed significant climatic ecological niche differentiation between O. huanggangensis and O. kweichowensis, and between O. kweichowensis and O. hejiangensis. Main conclusions The Guizhou distribution of the O. schmackeri complex comprises three species, most of whose recent common ancestors diverged at the early Miocene (ca. 14.30 Ma) and split at the late Miocene (ca. 8-9 Ma). The Miaoling Mountains were not a geographical barrier to the dispersal of O. kweichowensis and O. huanggangensis, and the Dalou Mountains, Foding-Wuling-Leigong-Yueliang Mountains were geographical distribution boundaries in the formation of the current distribution of the three species in Guizhou Province. No population expansion was detected within O. hejiangensis. Population expansion in the late Pleistocene for O. kweichowensis and O. huanggangensis was less affected by the glacial period, and was related to the presence of refugia. Considering future climate change, the focus should be on suitable habitats, mainly in nature reserves. In conclusion, this study highlights the importance of the use of genetic markers for the identification of species in the complex, the small geographical barrier of the Miaoling Mountains, and the conservation of amphibians in karst areas.