'Echoes' in bat and dolphin DNA

Scientists have found a striking similarity in the DNA that enables some bats and dolphins to echolocate.

A key gene that gives their ears the ability to detect high-frequency sound has undergone the exact same changes over time in both creatures.

The researchers report their findings in the journal Current Biology.

It may be the first time that identical genetics has been shown to underpin the evolution of similar characteristics in very different organisms.

Nature is full of cases where the path taken by evolution has resulted in the same traits, or phenotypes, developing independently in diverse animal groups.

Examples would include the tusks displayed by elephants and walruses, or the bioluminescence seen in fireflies and jellyfish.

"It's common on a morphological scale but it's assumed not to occur at a DNA level because there are so many different ways to arrive at the same solution," explained Dr Stephen Rossiter of Queen Mary's School of Biological and Chemical Sciences.

"The fact that we're able to link convergence of the DNA with a phenotype I think is unique, and in such a complex phenotype as hearing as well," he told BBC News.

Animal and human

Many bats and toothed whales like dolphins have exceptional hearing, and are able to track down their prey by emitting high-frequency noises and then listening for the echoes that bounce back.

Critical to echolocation are tiny hairs in the inner ear that move in response to sound.

Their keen performance is driven by a particular protein known as prestin, which in turn is encoded by a gene, also known as prestin.

Those bats that echolocate use high-frequency sound to track small prey

Two studies published this week in Current Biology find that this gene in bats and dolphins has picked up the same mutations over time.

"We've found a whole suite of amino acid changes that are common to these two groups that have evolved in parallel, convergently," Dr Rossiter said.

Both research teams also have evidence showing that these changes to prestin were selected for, suggesting that they must be critical for the animals' echolocation for reasons the researchers do not yet fully understand.

"The results imply that there are very limited ways, if not only one way, for a mammal to hear high-frequency sounds," said Professor Jianzhi Zhang of the University of Michigan, US, who led the other study.

This type of research is a beneficiary of the immense and ongoing effort to understand human genetics, which finds interesting targets for biologists from many fields to follow up.

Mutations in the prestin gene in humans have been shown to be associated with the loss of high-frequency hearing. It was this revelation that initiated the study of prestin's role in echolocation.

Music therapy 'may help cut tinnitus noise levels

Individually designed music therapy may help reduce the noise levels experienced by people who suffer from tinnitus, say German researchers.

They altered participants' favourite music to remove notes which matched the frequency of the ringing in their ears.

After a year of listening to the modified music, individuals reported a drop in the loudness of their tinnitus.

The researchers said the "inexpensive" treatment could be used alongside other techniques to relieve the condition.

It could significantly complement widely-used and rather indirect psychological treatment strategies Dr Christo Pantev Westphalian Wilhelms University

It is thought that around 1-3% of the population have chronic ringing in their ears which is significant enough to reduce their overall quality of life.

Writing in the Proceedings of the National Academy of Sciences, the researchers said although the cause of tinnitus remains unknown, it has been shown that the part of the brain that processes sounds is frequently disrupted in people with the condition.

The theory behind the new technique is that removing the spectrum of noise associated with tinnitus from the music reduces activity in the brain relating to that frequency, alleviating the condition.

Therapy

The 39 patients who took part in the study all had chronic tinnitus for an average of five years but had no other hearing problems.

They were split into three groups and were offered either the modified music therapy, a dummy version of music therapy or usual treatment.

Participants listened to the music for an average of 12 hours a week and by the end of the study, those who had been given the tailored music reported a significant drop in the level of the ringing they heard compared with those listening to the dummy version.

Study leader Dr Christo Pantev, from Westphalian Wilhelms University in Munster, said the approach specifically targeted the part of the brain responsible for tinnitus.

"The notched music approach can be considered as enjoyable, low cost, and presumably causal treatment that is capable of specifically reducing tinnitus loudness.

"It could significantly complement widely-used and rather indirect psychological treatment strategies."

Dr Ralph Holmes, director of biomedical research at deaf and hard of hearing charity, RNID, said he would look in detail at the findings.

"While we find it encouraging there is new investment in treatment for tinnitus, we know there is no proven 'cure'.

"This seems to be similar to tinnitus retraining therapy which is one of the most common ways of managing the condition."