Molecular evolution is echoed in bat ears

Bats' ability to echolocate may have evolved more than once, according to research published this week by Queen Mary, University of London scientists. Species of bat with the ability to echolocate do not all group together in the evolutionary tree of life - some are more related to their non-echolocating cousins, the fruit bats. This has raised the question of whether echolocation in bats has evolved more than once, or whether the fruit bats somehow lost their ability to echolocate.

Writing in the journal Proceedings of the National Academy of Sciences, Dr Stephen Rossiter from Queen Mary's School of Biological and Chemical Sciences, along with Professor Gareth Jones from the University of Bristol and Professor Shuyi Zhang and Dr Li Gang from East China Normal University in Shanghai, studied a gene called Prestin that codes for a protein of the outer hair cells - the tiny structures in the inner ear that help to give mammals their sensitive hearing (Prestin is linked to deafness in humans).

They looked at the Prestin DNA sequence in a range of echolocating bats and fruit bats and found that parts of the gene appear to have evolved to be similar in the distantly related echolocating species. But they couldn't find any evidence of genetic changes in the fruit bat Prestin that might be expected from a loss of high frequency hearing.

Dr Rossiter explains: "If Prestin does indeed help bats to hear their high-pitched echoes, then these results appear to support the idea that echolocation has evolved more than once in bats. This apparent independent evolution of a trait in distant relatives is known as convergence, a term that is more commonly used to describe the physical features of species that live in similar habitats and face similar selection pressures, such as the spines of hedgehogs and porcupines."

Examples of convergence at a molecular level are very rare. Based on their results, Dr Rossiter and his colleagues warn of the potential problems of inferring true evolutionary relationships from genes that may be involved in important functions and, therefore, could be shaped by convergent evolution.

Dr Rossiter added: "If hearing were an Olympic event, echolocating bats would be strong medal contenders. Their ears are tuned to higher sound frequencies than those of any other mammals because they need to listen to the returning echoes of their ultra-sonic squeaks."

Source: Queen Mary, University of London