Adaptation to parasites drive African fishes along different evolutio...( Quebec City Canada - An internationa...)

Quebec City, Canada - An international team of scientists from Canada (Universit Laval), the U.K. (University of Hull, Cardiff University) and Spain (Do ana Biological Station), have discovered that a pair of closely related species of East African cichlid fishes a group of fish whose diversity comprising hundreds of species has puzzled evolutionary biologists for decades evolved divergent immune gene adaptations which might explain why they do not interbreed, despite living side by side.

The two species ( Pseudotropheus emmiltos and Pseudotropheus fainzilberi ) are found in the north western part of Lake Malawi. Until now, the only known difference between them was the color of their dorsal fin. Many researchers believe that African cichlids recognize conspecifics from these kinds of colour differences, which are thought to result from sexual selection. However, recent mate choice experiments have shown that female P. emmiltos recognize males of their own species from P. fainzilberi males based on olfactory communication rather than color.

Some of the genes known to influence mating behavior through olfaction in other vertebrate species are genes of the major histocompatibility complex (MHC). These genes code for receptor that bound molecules produced by infectious agents and present them to specialized cells of the immune system which then launch an immune attack on the microbes. They are the most diverse genes found in vertebrate genomes and individuals of some species, including humans, are able to "smell" other individuals variability at these genes and adjust their mate choice in order to optimize the effectiveness of their offspring's immune system. Analysis of MHC genes between P. emmiltos and P. fainzilberi revealed that the two species were genetically more different at these sites involved in contacting and presenting molecules to immune cells than at other sites of the gene's DNA sequence that do not play functional roles.'/>"/>