Density-dependent unidirectional hybridization between the Japanese pond turtle, Mauremys japonica, and the exotic Reeves' pond turtle, Mauremys reevesii, in Japan, inferred from molecular and morphological analyses.

This article focuses on the widespread hybridization between the indigenous Japanese pond turtle (Mauremys japonica) and the introduced Reeves' pond turtle (Mauremys reevesii) in Japan. Using mitochondrial DNA (mtDNA), microsatellite markers, and morphometric analyses, the study reveals bidirectional hybridization with hybrids often possessing the mtDNA of the locally rarer species, and that later-generation hybrids (F2 and beyond) outnumber first-generation hybrids (F1). The research also identifies two mtDNA lineages of M. reevesii (Korean and Chinese), noting a recent range expansion of the Chinese lineage linked to increased introgression into M. japonica. Morphological traits, especially plastron shape, correlate significantly with genetic introgression, suggesting reproductive interference by the dominant species as a key driver of hybridization, with implications for conservation strategies targeting the near-threatened native M. japonica.