Lack of sex could be a signpost to extinction

Researchers from Imperial College London believe that when species become asexual they could be on their way to extinction.

The research, published in PLoS Pathogens, looks at the genetic structure of Penicillium marneffei, an asexual fungus. The researchers found that although P. marneffei spores were able to spread over large distances on currents of air, they were not able to 'invade' the new environments in which they landed.

P. marneffei is a fungus which causes disease in people with damaged immune systems, such as HIV/AIDS patients, and it is only found in parts of south-east Asia.

Dr Mat Fisher, first author on the paper, from Imperial College London, says: "We believe the failure of P. marneffei to adapt to new environments is because the fungus has largely dispensed with sexual reproduction. Without sex, you will not have the mixing of genes it causes, something all organisms need in order to be able to adapt to new environments."

The researchers used DNA typing to show that different clones of the fungus are found in different environments, and believe that the adaptation of the fungus to these environments is limiting their ability to adapt to other areas. They believe this is why P. marneffei is only endemic to a relatively small area of south-east Asia.

Evolutionary theory predicts that while asexual organisms can initially prosper and outcompete their sexual cousins, they ultimately pay the price for being unable to adapt through the recombination of genes caused by sexual reproduction.

Even though the fungus makes spores which can spread over very large distances, the researchers found that all the samples from any given location were genetically very similar. This led them to the conclusion that the fungus becomes highly adapted to its local environment, making it highly successful there, but stopping it spreading to other areas.

Dr Bill Hanage, one of the paper's authors, from Imperial College London, adds: "By being asexual, P. marneffei is not only limiting its ability to adapt, it may be at risk of becoming extinct. If it is unable to adapt to new environments, it will be unable to adapt to changes in its current environment. While becoming asexual may provide short term advantages to a species, in the long term, they are likely to end up in evolution's ultimate dustbin - extinction."

The study was funded by a Wellcome Trust Biodiversity Fellowship.