Newly discovered cichlid fish biodiversity threatened by hybridization with non-native species - Data supporting published version

Invasive freshwater fish systems 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 that O. korogwe from 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 of O. korogwe x niloticus hybrids 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 southern O. korogwe populations most plausibly diverged
approximately 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.