Predicting potential hybridization between native and non-native Rhodeus ocellatus subspecies: The implications for conservation of a pure native population in northern Kyushu, Japan

Hybridization between native and non-native fishes is a serious global problem. Thus, there is a need to develop monitoring methods for predicting potential hybridization to evaluate the risk of genetic introgression and to identify important areas for conservation of pure native populations. Here, we developed a prediction model for intersubspecific hybridization, based on distribution and genetic data. We selected Rhodeus ocellatus kurumeus and R. ocellatus ocellatus as the native and non-native subspecies, respectively. First, we developed generalized linear models (GLMs) for the species habitat requirements by using presence/absence data and environmental variables. The best-fit models showed river length gave conflicting effects for the two subspecies. Next, we developed a GLM using the ratio of non-native haplotypes in mitochondrial DNA as an objective variable, with the predicted probabilities of the occurrence of each fish and spatial information as explanatory variables. The best-fit model selected the distance from the center of native distribution and the non-native habitat requirement as key factors. Our findings indicate that hybridization occurs highly and/or initially near the margin of native distribution where non-native habitat requirements are available. Our model could identify sites in native habitats with very low potential risk for genetic invasion as important areas for conservation of pure native populations.