Losing cichlid fish biodiversity: genetic and morphological homogenization of tilapia following colonization by introduced species

Among the many negative impacts of invasive species, hybridization with indigenous species has increasingly become recognized as a major issue. However, few studies have characterized the phenotypic outcomes of hybridization following biological invasions. Here we investigate the genetic and morphological consequences of stocking invasive tilapia species in two water bodies in central Tanzania. We sampled individuals from Mindu Reservoir on the Ruvu river system, and at Kidatu on the Great Ruaha-Rufiji river system. We screened individuals at 16 microsatellite loci, and quantified morphology using geometric morphometrics and linear measurements. In both the Mindu and Kidatu systems, we identified evidence of hybridization between indigenous Wami tilapia (Oreochromis urolepis) and the introduced Nile tilapia (Oreochromis niloticus) or blue-spotted tilapia (Oreochromis leucostictus). At both sites, purebred individuals could largely be separated using geometric morphometric variables, wit...