Species integrity and origin of Oreochromis hunteri (Pisces: Cichlidae), endemic to crater Lake Chala (Kenya–Tanzania)
Extensive transfer of tilapia between lakes throughout East Africa has often led to hybridisation with indigenous fish populations. The endemic Oreochromis hunteri of Lake Chala, an isolated crater lake near Mount Kilimanjaro, is potentially susceptible to introgression from a species formerly identified as Oreochromis korogwe, introduced ~ 30 years ago. We combined whole-body geometric morphometry on 104 specimens of both taxa with molecular phylogenetic analysis of mitochondrial loci from 15 O. hunteri and 9 O. cf. korogwe specimens to assess whether hybridisation has occurred. Using fishes from Lake Jipe and Nyumba ya Mungu reservoir, we expanded our analysis to all four Oreochromis species currently inhabiting the Upper Pangani River system to determine the closest relative of O. hunteri, and hence the possible source population of the ancestral species that colonised Lake Chala. Our results indicate no interbreeding occurs between O. hunteri and O. cf. korogwe, and suggest O. jipe to be the closest living relative of O. hunteri. The introduced O. cf. korogwe is a phenotypically uniform but genetically variable population, the identity of which remains unknown. The high haplotype diversity of O. hunteri is consistent with fossil evidence indicating that its ancestor colonised Lake Chala at least 25,000 years ago.
KeywordsIntrogression Colonisation Crater lake Cichlids Geometric morphometrics
This study was carried out under Memorandum of Understanding A14/TT/0923 between Ghent University and the National Museums of Kenya (NMK), and institutional affiliation of DV with NMK. We thank Caxton Oluseno and the fishermen of lakes Chala and Jipe for assistance in acquiring fish specimens for this study, and the staff of the NERC Biomolecular Analysis Facility and the Nosil lab, both at the University of Sheffield, for support. We further thank three anonymous reviewers for their suggestions to improve this manuscript. This research was sponsored by the Ghent University Special Research Fund through Collaborative Research Activity ‘DeepCHALLA’, including PhD support to JD. MM received support from the Swiss National Science Foundation, the University of Sheffield, and the International Continental Scientific Drilling Program. The Euler HPC cluster at ETH Zürich was used for phylogenetic analyses. We thank Michael Matschiner for advice on the program Fitchi. The mitochondrial CR and ND2 sequences produced by this study are accessible through GenBank, and vouchers of all sequenced fish specimens will be archived at NMK.
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