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

Abstract

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.

Assessing the genetic diversity of farmed and wild Rufiji tilapia (Oreochromis urolepis urolepis) populations using ddRAD sequencing

“…Therefore, hybridization between introduced and native tilapia species can severely impact the unique genetic diversity of the latter affecting their adaptation capacity toward changing environmental conditions (Deines, Wittmann, Deines, & Lodge, 2016). Even though the exact consequences of introduced tilapia species in Tanzania to the local fauna are unknown, habitat loss and significant decline of population size have been recently documented for the endemic Oreochromis hunter in Lake Chala, in Kilimanjaro Tanzania due to introduced tilapia species (Moser, van Rijssel, Ngatunga, Mwaiko, & Seehausen, 2019).…”

Ancient DNA is preserved in fish fossils from tropical lake sediments

“…Output from an initial mapping using BWA (settings aln -t 2 -n 0.05, seeding disabled) was deduplicated using Samtools (Li et al, 2009), 'bandia', which was recently introduced into Lake Chala and has also been called O. sp. 'blue head' (Moser et al, 2018) or O. cf. korogwe (Dieleman et al, 2018).…”

Preface: advances in cichlid research IV: behavior, ecology, and evolutionary biology

“…Here, two invasive species are now abundant, Oreochromis cf. korogwe (Lowe-McConnell, 1955) and Coptodon rendalli (Boulenger, 1897), and there are signs of the endemic Chala tilapia Oreochromis hunteri Günther, 1889 being in decline (Moser et al, 2019). Through a longitudinal study of diet using stomach content analysis and stable isotope ratios of carbon (d 13 C) and nitrogen (d 15 N), the authors found all three species to be primarily herbivorous, feeding on both benthic and planktonic food sources, and overlapping substantially in diet.…”