Population genetic structure and introduction history of an invasive species Coptodon zillii in southern China

Native to Africa and parts of the Middle East, Coptodon zillii has become widely established in southern China following its introduction for aquaculture. Although the species is now widespread, its population genetic structure and invasion history across southern China remain poorly understood, limiting the reconstruction of introduction pathways and the development of targeted management strategies. We analysed mitochondrial cytochrome b (Cytb) and nuclear ectodermal-neural cortex 1 (Enc1) variation in 760 individuals collected from 44 sites across 12 river systems. Cytb revealed low genetic diversity but pronounced geographic structuring, whereas Enc1 exhibited higher polymorphism and weaker spatial differentiation, with mainland populations generally harbouring greater nuclear diversity than those from Hainan Island. Significant population differentiation was detected for both markers but was substantially stronger for Cytb (F ST = 0.38) than for Enc1 (F ST = 0.13), highlighting contrasting mitochondrial and nuclear genetic patterns. Collectively, these findings are consistent with a complex invasion history that may have involved multiple introduction events, subsequent human-mediated translocations, and region-specific demographic processes, although additional genomic data will be required to distinguish among alternative historical scenarios. The markedly reduced nuclear diversity observed in Hainan populations is likewise consistent with founder effects following introduction. Overall, our results demonstrate the value of integrating mitochondrial and nuclear markers to reconstruct the invasion history of C. zillii and provide a genetic basis for region-specific surveillance and management aimed at preventing further introductions and limiting secondary spread.