Adaptation to parasites drive African fishes along different evolutionary paths

August 15, 2007

An international team of scientists from Canada (Université Laval), the U.K. (University of Hull, Cardiff University) and Spain (Doòana 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.

These results show that natural selection has driven the evolution of these genes in different direction between the two species. Furthermore, the researchers showed that infecting parasites found on the two species were significantly different, as predicted based on the known immune function of MHC genes. "The mechanisms having produced the hundreds of species of East African cichlid fishes in a relatively short period of time are unclear", says Jonatan Blais, the senior author of the paper." This is one of the first genetic adaptive differences between closely related East African cichlid species identified. As such, it improves our understanding of the recent evolution of this incredibly diverse group of fish by pointing to a trait that not only diverged for adaptive reasons but may also be involved in mating behavior."

"The precise role that this divergence played in the evolution of reproductive isolation has yet to be studied", comments Louis Bernatchez, co-author of the study." But it offers an exciting new perspective in the study of African cichlids speciation ".

Source: Public Library of Science

Explore further: Researchers publish reference genome of gulf pipefish

Related Stories

Researchers publish reference genome of gulf pipefish

December 22, 2016

University of Oregon biologists have produced a detailed genome of the snakelike gulf pipefish, delivering a new research reference tool to help explore an ancient fish family that includes seahorses and sea dragons and has ...

"Ladies choice" reigns in the greater sac-winged bat

December 22, 2016

Females of the greater sac-winged bat select their mating partner by smell and unerringly choose a male which differs from them the most in genetic terms. Females with more variants of olfactory receptors of the TAAR-group ...

DNA markers distinguish between harmless, deadly bacteria

December 19, 2016

The virulent pathogen that causes the disease tularemia, or "rabbit fever," was weaponized during past world wars and is considered a potential bioweapon. Through a new study of the coccobacillus Francisella, Los Alamos National ...

The unique visual systems of deep sea fish

December 22, 2016

If asked the colour of the ocean, most people would rightly say "blue." The reason is that pure water absorbs long wavelength red light very strongly, but lets the shorter blue wavelengths pass. If you cut yourself while ...

Recommended for you

Researchers zero-in on cholesterol's role in cells

January 17, 2017

Scientists have long puzzled over cholesterol. It's biologically necessary; it's observably harmful - and nobody knows what it's doing where it's most abundant in cells: in the cell membrane.

Strength of hair inspires new materials for body armor

January 17, 2017

In a new study, researchers at the University of California San Diego investigate why hair is incredibly strong and resistant to breaking. The findings could lead to the development of new materials for body armor and help ...

Moving up the food chain can beat being on top

January 17, 2017

When it comes to predators, the biggest mouths may not take the biggest bite. According to a new study from bioscientists at Rice University, some predators have their greatest ecological impacts before they reach adulthood.

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.