Cryptic lineages and hybridization of the predaceous chub Parazacco spilurus (Actinopterygii, Cypriniformes, Xenocyprididae) in Hong Kong

Abstract

Fine-scale genetic studies are essential for understanding population connectivity and formulating appropriate conservation measures for freshwater inhabitants. Despite their significance, such studies remain relatively limited in South China and Asia in general. We examined the genetic structure of the predaceous chub Parazacco spilurus in Hong Kong by incorporating genetic data from both mitochondrial (control region and cytochrome b oxidase gene) and nuclear (recombination-activating gene 1) DNA markers. We identified two highly divergent lineages having discrete distribution ranges with limited overlap near two reservoirs located in north-eastern (Plover Cove Reservoir) and south-eastern (Tai Tam Tuk Reservoir) Hong Kong. Each lineage is further divided into sublineages with geographical association. As such, gene flow is highly restricted at both sublineage and population levels. Despite the presence of sublineages, inter-lineage divergence is far greater than that divergence within lineage. It also exceeds the species divergence in closely related cyprinid genera, suggesting that the two lineages recovered potentially represent two distinct species. Yet genetic analyses based on the nuclear marker indicated a low degree of hybridization between the lineages at two closely situated localities. This study provides insights on the possible direction of conservation plans for P. spilurus in Hong Kong and South China.