The origin and future of an endangered crater lake endemic; phylogeography and ecology of Oreochromis hunteri and its invasive relatives

Cichlids of the genus Oreochromis (“Tilapias”) are intensively used in aquaculture around the world. In many cases, when “Tilapia” were introduced for economic reasons to catchments that were home to other, often endemic, Oreochromis species, the loss of native species followed. Oreochromis hunteri is an endemic species of Crater Lake Chala on the slopes of Mount Kilimanjaro and is part of a small species flock in the upper Pangani drainage system of Tanzania. We identified three native and three invasive Oreochromis species in the region. Reconstructing their phylogeography, we found that O. hunteri is closely related to, but distinct from the other members of the upper Pangani flock. However, we found a second, genetically and phenotypically distinct Oreochromis species in Lake Chala whose origin we cannot fully resolve. Our ecological and ecomorphological investigations revealed that the endemic O. hunteri is currently rare in the lake, outnumbered by each of three invasive cichlid species. It is mitochondrially, phenotypically and trophically distinct from all others. The occurrence of the formerly abundant O. hunteri in such small numbers, its narrow habitat restriction and its limited morphological variability suggest recent population decline and loss of niche breadth in this critically endangered endemic cichlid species