Population genomics of introduced Nile tilapia Oreochromis niloticus (Linnaeus, 1758) in the Democratic Republic of the Congo: Repeated introductions since colonial times with multiple sources

19 pages, 5 figures, 4 tables, supporting information https://doi.org/10.1111/mec.16479.-- Data Accessibility: Genotype data are available on DataDryad (https://doi.org/10.5061/dryad.sxksn035k)

During colonial times, Nile tilapia Oreochromis niloticus (Linnaeus, 1758) was introduced into non-native parts of the Congo Basin (Democratic Republic of the Congo, DRC) for the first time. Currently, it is the most farmed cichlid in the DRC, and is present throughout the Congo Basin. Although Nile tilapia has been reported as an invasive species, documentation of historical introductions into this basin and its consequences are scant. Here, we study the genetic consequences of these introductions by genotyping 213 Nile tilapia from native and introduced regions, focusing on the Congo Basin. Additionally, 48 specimens from 16 other tilapia species were included to test for hybridization. Using RAD sequencing (27,611 single nucleotide polymorphisms), we discovered genetic admixture with other tilapia species in several morphologically identified Nile tilapia from the Congo Basin, reflecting their ability to interbreed and the potential threat they pose to the genetic integrity of native tilapias. Nile tilapia populations from the Upper Congo and those from the Middle–Lower Congo are strongly differentiated. The former show genetic similarity to Nile tilapia from the White Nile, while specimens from the Benue Basin and Lake Kariba are similar to Nile tilapia from the Middle–Lower Congo, suggesting independent introductions using different sources. We conclude that the presence of Nile tilapia in the Congo Basin results from independent introductions, reflecting the dynamic aquaculture history, and that their introduction probably leads to genetic interactions with native tilapias, which could lower their fitness. We therefore urge avoiding further introductions of Nile tilapia in non-native regions and to use native tilapias in future aquaculture efforts

We would like to acknowledge the financial support of the Belgian Science Policy (BELSPO) through JEMU (Joint Experimental Molecular Unit), Belgian Federal Science Policy Office (BRAIN-be Pioneer Project BR/132/PI/TILAPIA), EMBRC Belgium—FWO project GOH3817N, European Research Council project (no. 683210), Research Council of Norway (no. 250548/F20), VLIR-UOS South Initiative ZRDC2014MP084, the OCA type II project S1_RDC_TILAPIA and Mbisa Congo project (2013-2018), the last two being framework agreement projects of RMCA with the Belgian Development Cooperation, and the Czech Science Foundation (P505/12/G112—European Centre of Ichtyoparasitology ECIP). M.G. was supported by the Bijzonder Onderzoeksfonds (BOF-project 7NI02) of Hasselt University for the analysis, interpretation of data and writing of the manuscript. M.W.P.J. was supported by a BOF Reserve Fellowship from Hasselt University. M.P.M.V. received travel grant K220314N from the Research Foundation—Flanders (FWO-Vlaanderen) and support from the Belgian Directorate-General for Development Cooperation and Humanitarian Aid (CEBioS programme at the Royal Belgian Institute of Natural Sciences), and was financed by the Special Research Fund of Hasselt University (BOF20TT06)

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