Sometimes the key to solving a medical problem turns up in unexpected places. For example, new discoveries about a fish's mating ritual may shed light on a cause of hearing loss in humans.
How a lovelorn fish could save human hearing. I'm Bob Hirshon and this is Science Update.
[Sound: Fish mating call]
Every summer, the male midshipman fish serenades potential mates with this high-frequency call. Now, scientists have found that a fertile female’s raging hormones actually help her hear it.
Neurobiologist Andrew Bass and his colleagues at Cornell University proved this by injecting non-fertile females with a fish hormone that's similar to estrogen.
And what we found, in fact, was that these hormones could induce an increase in the sensitivity of the female's ear, and we're very careful to boost the levels to levels that are similar to what are naturally found in females during the breeding season.
He says the findings may help women with a disease called Turner's Syndrome, which causes estrogen loss. These patients also tend to lose their hearing in high frequencies. The connection may lie in previously unexplained receptors for estrogen found in the human ear.
And what we discovered in fact is that the ear of this fish has the exact same kind of estrogen receptors. And that was an important discovery, because it really linked, at a very basic, molecular level, what's going on in the ears of humans and what can be happening in the ears of fish.
He says that estrogen therapy may someday protect or even restore these women's hearing. I'm Bob Hirshon for AAAS, the Science Society.
Making Sense of the Research
How do you get from the love call of a fish to treating hearing loss in humans? The answer actually requires several steps, many of which came before the experiment you just heard about.
Every spring and summer, the male midshipman fish migrates from deep offshore waters to shallow, rocky areas, in preparation for the mating season. The males dutifully carve out a nest and then sing to attract mates. When a fertile female hears the male's love song, she finds his nest, drops her eggs there, and takes off. The male fertilizes the eggs, and another mating season comes to a swift and rather unromantic end.
What's interesting is that the males don't seem to attract non-fertile females–in other words, females that aren't carrying mature eggs. So Bass' team looked into that first. They found that the females' hearing is actually different in the mating season than it is during the rest of the year: during the mating season, they are more sensitive to the higher frequency sounds in the males' calls.
It was already known that females' hormone levels change throughout the year as well. Bass and his colleagues put two and two together, and wondered if the changes in hormones were responsible for the changes in hearing sensitivity. That's what led to the experiment described in the Science Update report. They actually injected non-fertile females with an estrogen-like hormone, and found that their hearing switched over to the "mating season" mode.
Human females certainly don't need to be sensitive to men's high-frequency mating calls. But humans do have receptors in their ears that respond to estrogen–the very same receptors found in the ears of the female midshipman fish. Dr. Bass says that these estrogen receptors may be very common throughout the animal kingdom. In fact, even though we think of animal species as very different from each other, their similarities generally outweigh their differences.
Nobody is sure if the estrogen receptors in human ears serve a practical purpose. It's possible that they're just remnants of our evolutionary past. But the fact that Turner's syndrome, a genetic condition that causes estrogen loss in women, also results in the loss of high-frequency hearing, suggests that the receptors may still function in a similar way. If that's the case, then correcting the estrogen levels in Turner's syndrome patients may improve their hearing as well. But strangely, some studies have linked hormone replacement therapy to hearing loss in other women. Clearly, more work must be done in order to pinpoint the way hormones affect our hearing.
Now try and answer these questions:
- How does the female midshipman fish's hearing change over the course of a year?
- How did Bass and his colleagues show that hormones were responsible for the changes?
- What is the potential connection to Turner's syndrome? What experiments might confirm that estrogen loss actually causes the hearing deficits in this disorder?
- What does this study suggest about the evolution of animal species?
The National Geographic News article Sex Tips for Animals: A Lighthearted Look at Mating contains an overview of some unusual animal mating rituals and links to other stories.
The Turner Syndrome Society contains information and research news about the disorder.