Introduced cichlid provides new insight

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A Malawian mbuna released to a new site in Lake Malawi in the 1960s has provided scientists with an opportunity to monitor how species change over time.

A race of Cyphotilapia afra was introduced into a new location at Mitande Point in Thumbi West Island, Lake Malawi, by a fish exporter and set up a breeding population in the lake which has gradually grown over the years.

A group of scientists from the University of New Hampshire in the USA have been monitoring the population for several years to see how it has been changing. Their findings are published in the latest issue of the journal Molecular Ecology.

By 2001, the C. afra population had colonised the whole perimeter of Thumbi West Island, but despite only having 20 years or so to evolve, the fish at the north and south sides of the island had already diversified.

By collecting afra from six sites around the island the group were able to show that the population had split into two genetically distinct populations with phenotypes present that vary in dorsal fin colour.

The team also found a number of hybrids between Metriaclima zebra and C. afra on the south coast. The waters on the south side of the island are rougher and more turbid, and the group says that the fish may be hybridising as a result of this.

Lake Victoria cichlid expert, Ole Seehausen, now at the University of Hull, has shown that a similar thing can occur in Lake Victoria. Murky water, it seems, causes the visual mate recognition system of cichlids to breakdown, leading to an increase in hybridisation.

For more details read the paper: Streelman, JT., Gmyrek, SL., Kidd, MR., Kidd, C., Robinson, RL., Hert, E., Ambali, AJ., Kocher, TD. (2004) - Hybridisation and contemporary evolution in an introduced cichlid fish from Lake Malawi National Park. Molecular Ecology, 2004. Aug; 13 (8) 2471-2479.