MBE Advance Access published online on March 15, 2007
Molecular Biology and Evolution, doi:10.1093/molbev/msm050
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RESEARCH ARTICLE |
Age of Cichlids: New Dates for Ancient Lake Fish Radiations
1 Department of Biological Sciences, University of Hull, Cottingham Road, Hull. HU6 7RX. United Kingdom
2 Institute of Zoology- Aquatic Ecology and Macroevolution, University of Bern, Baltzerstr. 6, CH-3012 Bern. Switzerland
3 EAWAG Ecology Center, Fish Ecology and Evolution, CH-6047 Kastanienbaum. Switzerland
4 School of Biological Sciences, Royal Holloway, University of London, Egham, Surrey, TW20 0EX. United Kingdom
5 School of Biological Sciences, University of Wales Bangor, Bangor, Gwynedd. LL57 2UW. United Kingdom
Corresponding author: Martin J Genner, School of Biological Sciences, University of Hull, Cottingham Road, Hull. HU6 7RX. UK. Tel: +44 (0) 1482 465962. Fax: +44 (0) 1482 465496. E-mail: m.genner{at}hull.ac.uk
Received for publication January 18, 2007. Accepted for publication March 4, 2007.
Timing divergence events allows us to infer the conditions under which biodiversity has evolved and gain important insights into the mechanisms driving evolution. Cichlid fishes are a model system for studying speciation and adaptive radiation, yet we have lacked reliable timescales for their evolution. Phylogenetic reconstructions are consistent with cichlid origins prior to Gondwanan landmass fragmentation 165-121 million years ago, considerably earlier than the first known fossil cichlids (Eocene). We examined the timing of cichlid evolution using a relaxed molecular clock calibrated with geological estimates for the ages of (i) Gondwanan fragmentation and (ii) cichlid fossils. Timescales of cichlid evolution derived from fossil-dated phylogenies of other bony fishes most closely matched those suggested by Gondwanan break-up calibrations, suggesting the Eocene origins and marine dispersal implied by the cichlid fossil record may be due to its incompleteness. Using Gondwanan calibrations, we found accumulation of genetic diversity within the radiating lineages of the African Lakes Malawi, Victoria and Barombi Mbo and Palaeolake Makgadikgadi began around or after the time of lake basin formation. These calibrations also suggest Lake Tanganyika was colonised independently by the major radiating cichlid tribes that then began to accumulate genetic diversity thereafter. These results contrast with the widely accepted theory that diversification into major lineages took place within the Tanganyika basin. Together this evidence suggests that ancient lake habitats have played a key role in generating and maintaining diversity within radiating lineages, but also that lakes may have captured pre-existing cichlid diversity from multiple sources from which adaptive radiations have evolved.
Key Words: molecular clock • Gondwanan fragmentation • fossil record • adaptive radiation • speciation
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