Death of a dreampond

Africa's largest lake was once a biologist's dream pond, offering rare glimpses into vertebrate speciation and the dynamics of sexual versus natural selection, via the hundreds of endemic and often highly colourful cichlids that danced in its waters. Following the introduction of the Nile perch, a two metre long predatory fish that some people thought would make good sport, the barely ploughed depths of the lake's biodiversity was soon reduced to a dismal dump of alien cannibals, as the perch began to feed on alternate foods such as prawns and on each other, having exhausted the lineages of hundreds of cichlid species. Not surprisingly, midge populations along the lake's coasts exploded, as few small fish were left to consume insect larvae.

"Within a single decade," writes Dutch biologist Tijs Goldschmidt, who studied this community in the 1980s, "the differentiated biotic community that had coevolved over a period of at least fourteen thousand years, and perhaps even hundreds of thousands of years, had changed into an impoverished mess."

The Nile perch is now an ineradicable feature of Lake Victoria, a fitting tribute to the indiscriminate pride of men whose folly overruled their freedom. Nearby, the shore-dwellers of Tanganyika and Malawi have mercifully discovered the livelihoods afforded in catching their technicolour cichlids for export to aquarists. Here, at least, a handful of small fish are being truly transformed into a breadbasket that feeds a multitude.

Comments

It's the same all over =/.

[Tyrone]

With the current silting of the lake the sexual selection barriers keeping species is collapsing resulting in mass "hybridization" that is rendering the current "species" extinct. Of course these hybrids are fully fertile which may indicate that the "speceis" weren't real "species" at all. As consequence it may turn out there is only 1 "species" endemic to in Lk. Victoria and those phenotypes the Nile Perch has taken out were just fanciful forms of the same species. So was anything really renderred extinct at all?

Hmmm... something to ponder.

[budak]

The Victorian cichlids offer several problems for taxonomists. Firstly, that little research was done until the late 70s, resulting in a sudden explosion of new 'species' that remained undescribed for want of manpower. There is of course the introduction of the Nile perch, which compounded taxonomic attempts. Goldschmidt's own multi-year survey of one tiny bay revealed that the cichlids there diverged into several ecological niches with corresponding adaptive morphologies: 134 species of fish eaters, 16 detritius feeders, 10 algae raspers, 2 plant eaters, 21 snail eaters, 21 open water zoo plankton feeders, 29 insect eaters, 3 prawn feeders, 1 crab predator and over 50 with unknown habits. It could be said that within each dietary group, the 'flock' is dynamic, and normal species 'barriers' are liable to be broken thanks to factors such as female preferences, turbidity, predator influences, egg-spot size.... but the specific boundaries between flocks of vastly divergent dietary and ecological forms are concrete and irreversible.

[Tyrone]

obtained from here
Proc R Soc Lond B Biol Sci. 2004 Dec 7;271(1556):2445-52.

Intraspecific sexual selection on a speciation trait, male coloration, in the Lake Victoria cichlid Pundamilia nyererei.

Maan ME, Seehausen O, Soderberg L, Johnson L, Ripmeester EA, Mrosso HD, Taylor MI, van Dooren TJ, van Alphen JJ.

Department of Animal Ecology, Institute of Biology, University of Leiden, PO Box 9516 2300 RA Leiden, The Netherlands. maan@rulsfb.leidenuniv.nl

The haplochromine cichlids of Lake Victoria constitute a classical example of explosive speciation. Extensive intra- and interspecific variation in male nuptial coloration and female mating preferences, in the absence of postzygotic isolation between species, has inspired the hypothesis that sexual selection has been a driving force in the origin of this species flock. This hypothesis rests on the premise that the phenotypic traits that underlie behavioural reproductive isolation between sister species diverged under sexual selection within a species. We test this premise in a Lake Victoria cichlid, by using laboratory experiments and field observations. We report that a male colour trait, which has previously been shown to be important for behavioural reproductive isolation between this species and a close relative, is under directional sexual selection by female mate choice within this species. This is consistent with the hypothesis that female choice has driven the divergence in male coloration between the two species. We also find that male territoriality is vital for male reproductive success and that multiple mating by females is common.

You may also want to see: Seehausen O, Schluter D. (2004) Male-male competition and nuptial-colour displacement as a diversifying force in Lake Victoria cichlid fishes. Proc R Soc Lond B Biol Sci. 271(1546):1345-53.

Bottom line: "Speciation" is driven by mate choice, not habitat or ecological niche based on current research. Wayne Leibel reviewed the research in a TFH column back in 2003 or 2004... can't recall.

Once the pond clears the females will pry the "species" apart once more. And this time they will be Nile Perch resistant.

tt4n