"The Age of Cichlids......

New cichlid species and taxonomy
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Thomas Andersen
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"The Age of Cichlids......

Post by Thomas Andersen » Sat Jun 30, 2007 1:49 am

......New Dates for Ancient Lake Fish Radiations" by Genner, Seehausen, Lunt, Joyce, Shaw, Carvalho and Turner (2007) Molecular Biology and Evolution vol. 24(5), 1269–1282.

Abstract: Timing divergence events allow 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 121–165 MYA, 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 1) Gondwanan fragmentation and 2) cichlid fossils. Timescales of cichlid evolution
derived from fossil-dated phylogenies of other bony fishes most closely matched those suggested by Gondwanan
breakup 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 colonized 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 and also that lakes may have captured preexisting cichlid diversity from multiple sources from which
adaptive radiations have evolved.

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