Newly discovered cichlid fish biodiversity threatened by hybridization with non-native species

Invasive freshwater fishes are known to readily hybridize with indigenous congeneric species, driving loss of unique and irreplaceable genetic resources. Here we reveal that newly discovered (2013-2016) evolutionarily significant populations of Korogwe tilapia (Oreochromis korogwe) from southern Tanzania are threatened by hybridization with the larger invasive Nile tilapia (Oreochromis niloticus). We use a combination of morphology, microsatellite allele frequencies and whole genome sequences to show thatO. korogwefrom southern lakes (Nambawala, Rutamba and Mitupa) are distinct from geographically disjunct populations in northern Tanzania (Zigi River and Mlingano Dam). We also provide genetic evidence ofO. korogwe x niloticushybrids in three southern lakes and demonstrate heterogeneity in the extent of admixture across the genome. Finally, using the least admixed genomic regions we estimate that the northern and southernO. korogwepopulations most plausibly diverged similar to 140,000 years ago, suggesting that the geographical separation of the northern and southern groups is not a result of a recent translocation, and instead these populations represent independent evolutionarily significant units. We conclude that these newly discovered and phenotypically unique cichlid populations are already threatened by hybridization with an invasive species, and propose that these irreplaceable genetic resources would benefit from conservation interventions.

Automated summary

In this study, newly discovered evolutionarily significant populations of Korogwe tilapia from southern Tanzania are threatened by hybridization with invasive Nile tilapia. Genetic analysis shows distinct differences between southern and northern populations of O. korogwe, with evidence of hybrids in southern lakes. This highlights the need for conservation interventions to protect these unique genetic resources.