Abstract
BackgroundCichlids are a prime model system in evolutionary research and several of the most prominent examples of adaptive radiations are found in the East African Lakes Tanganyika, Malawi and Victoria, all part of the East African cichlid radiation (EAR). In the past, great effort has been invested in reconstructing the evolutionary and biogeographic history of cichlids (Teleostei: Cichlidae). In this study, we present new divergence age estimates for the major cichlid lineages with the main focus on the EAR based on a dataset encompassing representative taxa of almost all recognized cichlid tribes and ten mitochondrial protein genes. We have thoroughly re-evaluated both fossil and geological calibration points, and we included the recently described fossil †Tugenchromis pickfordi in the cichlid divergence age estimates.ResultsOur results estimate the origin of the EAR to Late Eocene/Early Oligocene (28.71 Ma; 95% HPD: 24.43–33.15 Ma). More importantly divergence ages of the most recent common ancestor (MRCA) of several Tanganyika cichlid tribes were estimated to be substantially older than the oldest estimated maximum age of the Lake Tanganyika: Trematocarini (16.13 Ma, 95% HPD: 11.89–20.46 Ma), Bathybatini (20.62 Ma, 95% HPD: 16.88–25.34 Ma), Lamprologini (15.27 Ma; 95% HPD: 12.23–18.49 Ma). The divergence age of the crown haplochromine H-lineage is estimated to 22.8 Ma (95% HPD: 14.40–26.32 Ma) and of the Lake Malawi radiation to 4.07 Ma (95% HDP: 2.93–5.26 Ma). In addition, we recovered a novel lineage within the Lamprologini tribe encompassing only Lamprologus of the lower and central Congo drainage with its divergence estimated to the Late Miocene or early Pliocene. Furthermore we recovered two novel mitochondrial haplotype lineages within the Haplochromini tribe: ‘Orthochromis’ indermauri and ‘Haplochormis’ vanheusdeni.ConclusionsDivergence time estimates of the MRCA of several Tanganyika cichlid tribes predate the age of the extant Lake Tanganyika basin, and hence are in line with the recently formulated “Melting-Pot Tanganyika” hypothesis. The radiation of the ‘Lower Congo Lamprologus clade’ might be linked with the Pliocene origin of the modern lower Congo rapids as has been shown for other Lower Congo cichlid assemblages. Finally, the age of origin of the Lake Malawi cichlid flock agrees well with the oldest age estimate for lacustrine conditions in Lake Malawi.
Highlights
Cichlids are a prime model system in evolutionary research and several of the most prominent examples of adaptive radiations are found in the East African Lakes Tanganyika, Malawi and Victoria, all part of the East African cichlid radiation (EAR)
We provide a new relative divergence time frame for the African Pseudocrenilabrinae and especially for the mtDNA lineages belonging to the EAR, which is critical in the context of clarifying the phylogeographic history and origin of the famous adaptive radiations of Lakes Tanganyika (LT), Lake Malawi (LM) and Lake Victoria (LV) and of several smaller haplochromine lineages
The alternatively calibrated BEAST runs (Calibration Set 1–11 and Sets 13–17) yielded maximum-clade credibility (MCC) trees which were largely identical to the topology of the Maximum likelihood (ML) tree
Summary
Cichlids are a prime model system in evolutionary research and several of the most prominent examples of adaptive radiations are found in the East African Lakes Tanganyika, Malawi and Victoria, all part of the East African cichlid radiation (EAR). The age of endemic Lake Malawi lacustrine cichlid lineages has previously been constrained in molecular clock analyses [15, 16] to be younger than the postulated complete desiccation of Lake Malawi either at around 1.6– 1.0 Ma, or at the post-drought re-establishment of truly lacustrine conditions at 1.0–0.57 Ma [24] This approach is in conflict with a recent study reporting continuous sedimentation in the geological LM basin over the last 1.3 Ma, i.e. raising doubts about the previously used LM calibration points [25] the use of the sedimentology-based lake age estimates as molecular clock calibration points for the origin of cichlid taxa endemic to large and paleogeographically complex rift lakes appears problematic and might result in highly misleading node age estimates
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