Mountains, Lakes, and Ancient Drainage Networks Sculpt the Phylogeographic Architecture of the Stream Headwater Fish Acrossocheilus kreyenbergii in China.

BACKGROUND: Phylogeographic surveys of obligate freshwater fishes could serve as a pivotal lens through which the biological footprints of historic drainage rearrangements can be deciphered. METHODS: Focusing on the headwater-restricted cyprinid Acrossocheilus kreyenbergii in the Pearl, Yangtze, and Huai river basins, we examined variations in mitochondrial cytochrome b gene (Cyt b) to elucidate the phylogeographic architecture and evolutionary history of this stream fish in South-Central China through integrative analyses of phylogeny, ancestral area reconstruction, genetic structure, and population demography. RESULTS: A time-calibrated phylogeny recovered two primary lineages, K-I and K-II, which diverged ca. 2.15 Ma: K-I split into K-Ia (Huai River) and K-Ib (Yangtze-Poyang Lake catchment) at 1.53 Ma, whereas K-II gave rise to K-IIa, K-IIb, and K-IIc through sequential divergences at 1.29 Ma and 0.83 Ma, with K-IIa restricted to the Poyang Lake catchment. K-IIb was shared between the Poyang Lake catchment and the Qiupu River (Yangtze basin), and K-IIc was distributed in the Xijiang River (Pearl basin) as well as the Yangtze-Dongting Lake catchment. CONCLUSIONS: Our findings reveal that the phylogeographic architecture of A. kreyenbergii was sculpted by a succession of geologic and anthropocentric events: the Late-Cenozoic collapse of the Zhe-Min Uplift first fractured its range; the intervening Mufu-Lianyun-Luoxiao Mountains then acted as a persistent barrier; the large waters of Poyang and Dongting Lakes served as biological filters; and the 2200-year-old Lingqu Canal-constructed during the Qin dynasty-briefly re-established a corridor for gene flow. Together, these forces disrupted and reorganized the species' genetic connections, leaving a visible imprint today.