Genetic structure and gene flow in an endangered native tilapia fish (Oreochromis esculentus) compared to invasive Nile tilapia (Oreochromis niloticus) in Yala swamp, East Africa

Abstract

The introduction of invasive Nile tilapia (Ore- ochromis niloticus), and the rapacious predator Nile perch (Lates niloticus), into Lake Victoria resulted in a decline in population sizes, genetic diversity and even extirpation of native species which were previously the mainstay of local fisheries. However, remnant populations of native fish species, including tilapia, still persist in satellite lakes around Lake Victoria where they may coexist with O. niloticus. In this study we assessed population genetic structure, diversity, and integrity of the native critically endangered Singidia tilapia (O. esculentus) in its refugial populations in the Yala swamp, Kenya, and contrasted this diversity with populations of the invasive tilapia O. nil- oticus in satellite lakes (Kanyaboli, Namboyo and Sare) and Lake Victoria. Based on mtDNA control region sequences and eight nuclear microsatellite loci, we did not detect any mtDNA introgression between the native and the invasive species in Lakes Kanyaboli and Namboyo, but did find low levels of nuclear admixture, primarily from O. niloticus to O. esculentus. Some genetic signal of O. es- culentus in O. niloticus was found in Lake Sare, where O. esculentus is not found, suggesting it has recently been