Population genetics and taxonomic signatures of wild Tilapia in Japan based on mitochondrial DNA control region analysis

Abstract

Non-native tilapia species were repeatedly introduced to Asian and South American countries because of their adaptiveness to new environments and new environmental conditions. Such founder populations rapidly adapted by evolving outstanding ecological and physiological features, making them highly successful invaders throughout the tropical and subtropical regions. In Japan, nine tilapia species were introduced. In recent years, several established populations were introgressed by accidental release of aquaculture strains of Oreochromis niloticus, causing reductions in population sizes, genetic diversity, and genetic perturbation upon introgressive hybridization. This study aimed to assess the levels of genetic integrity, genetic population structure, and biogeographic relationships of wild tilapia species found in Japan. Phylogenetic and phylogeographic analysis based on mtDNA control region sequences yielded 52 distinct haplotypes, indicating significant differences in genetic variability among the analyzed populations. Analysis of molecular variance showed high levels of variation within populations, except for tilapia species representing reproductively incompatible taxonomic units to O. niloticus aquaculture stains. Overall, a significant genetic structure emerged among the 11 populations analyzed. Our results indicated that accidental release of O. niloticus via aquaculture contributed significantly to the current genetic differentiation among populations within a few generations, showing clear signals of mtDNA introgression across species boundaries.