Two new species of cichlid fish from Lake Victoria are described by
biologists from Naturalis Biodiversity Center (Research Department
Marine Zoology) and the Institute of Biology Leiden (Section Integrative
Zoology), the Netherlands. One of these species is named in honour of
Tijs Goldschmidt, author of Darwin's Dreampond. This book, published in
nine languages, describes the dramatic extinction of hundreds of cichlid
species in Lake Victoria in the 1980s due to the introduced Nile perch
and other human induced environmental changes.
In 1985, Leiden biologists made a survey in the Tanzanian part of the
lake, with an old ferry as floating lab, to establish the status of the
rapidly declining cichlids. During this expedition Tijs studied the egg
spots on the anal fin of cichlids for their possible role in the rapid
speciation of these fish. In the Emin Pasha Gulf, among a species
nicknamed Haplochromis "argens," individuals were found with
aberrant egg dummies and lacking red in the fins. Just the kind of
example Tijs was looking for to test his theory of speciation by sexual
selection. The aberrant individuals were provisionally named H. "dusky argens." Both
"species" play a part in Tijs' PhD thesis and in other studies.
However, a taxonomic description was never made and whether H.
"dusky argens" was a separate species or a colour morph remained
unclear. In 1987, most cichlid species from the offshore waters of the
lake had disappeared, and with them the urge of taxonomic descriptions. Now,
25 years later, about a quarter of the cichlid species have recovered
in the "Nile perch desert," some of them became even more abundant than
in the past, but the former common H. "argens" is still extremely rare. The status of H. "dusky-argens"
is unknown as it was only caught in the remote Emin Pasha Gulf, which
is not sampled nowadays. Research on successfully resurgent species
shows that they were able to adapt morphologically to the new
environmental conditions. Their body shape, for instance, changed, so
that burst swimming to escape predators improved. Preliminary results
suggest that such a response is not found in H. "argens." The
above observations triggered the present taxonomic study as a baseline
for further research. It shows that several taxonomic characters differ
more between the co-occurring populations of H. "argens" and H. "dusky
argens" in the Emin Pasha Gulf, than between populations from different
locations. This suggests that they are indeed two species, which are
morphologically driven apart at places where they co-occur. In case of H. "argens" the nickname was upgraded to the formal name, while H. "dusky-argens" is now named H. goldschmidti.
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