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 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.

中文翻译：

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与非本地物种杂交威胁新发现的罗非鱼丽鱼科鱼类生物多样性

已知有侵入性的淡水鱼系统很容易与本地同属物种杂交，从而导致独特和不可替代的遗传资源的流失。在这里，我们揭示了与较大的入侵尼罗罗非鱼（Oreochromis niloticus）杂交威胁了新发现的（2013-2016）具有进化重要性的坦桑尼亚南部科罗威罗非鱼种群（Oreochromis korogwe）。我们结合形态学，微卫星等位基因频率和全基因组序列，显示来自南部湖泊（Nambawala，Rutamba和Mitupa）的O. korogwe有别于坦桑尼亚北部（Zigi河和Mlingano大坝）的地理分离种群。我们还提供了在三个湖泊中O. korogwe x niloticus杂种的遗传证据，并证明了整个基因组混合程度的异质性。最后，使用最少混合的基因组区域，我们估计北部和南部的O. korogwe种群最有可能在大约14万年前分离，这表明北部和南部群体的地理隔离不是最近易位的结果，而是这些种群代表了独立的进化重要单位。我们得出的结论是，这些新发现的和表型独特的丽鱼科鱼种群已经受到与入侵物种杂交的威胁，并提出这些不可替代的遗传资源将从保护措施中受益。这表明北部和南部各族群的地理隔离不是最近易位的结果，而是这些种群代表了独立的具有进化意义的单位。我们得出的结论是，这些新发现的和表型独特的丽鱼科鱼种群已经受到与入侵物种杂交的威胁，并提出这些不可替代的遗传资源将从保护措施中受益。这表明北部和南部各族群的地理隔离不是最近易位的结果，而是这些种群代表了独立的具有进化意义的单位。我们得出的结论是，这些新发现的和表型独特的丽鱼科鱼种群已经受到与入侵物种杂交的威胁，并提出这些不可替代的遗传资源将从保护措施中受益。