Researchers have new evidence to explain what keeps those fish quiet through the day and singing all night.
What affects this are the fishes’ light-driven internal clock and melatonin, a hormone best known for controlling sleep and wake cycles.
A single hum can last for minutes up to almost 2 hours. Neighbouring males may hum together in a chorus, there can be slight differences in hum frequencies make the sound even more eerie.
Andrew Bass of Cornell University and Ni Y. Feng, a former graduate student in the Bass lab, knew that the midshipman fish kept the rocky intertidal zone humming during the breeding season. To find out why the fish only sing at night, they first needed to get them to hum in the lab, where they could control the lighting and other factors.
The researchers’ studies now show that the fish continue to hum on schedule when kept in conditions of constant darkness. But their humming is suppressed when the lights are kept on, a condition known to reduce the production of melatonin. Indeed, when a group of fish kept in the light were given melatonin, their humming stayed at normal levels and even increased.
The researchers went on to show evidence that melatonin acts directly on the vocal circuitry in the midshipman’s brain.
The findings show the remarkable versatility of melatonin as a timing signal, the researchers say. Melatonin keeps birds quiet at night, but in the midshipman fish melatonin has just the opposite effect. But there are similarities too; in both species constant light and reduced melatonin action shortens the duration of individual vocal elements.
The researchers say that they’d like to continue to explore the molecular-level events in the brain that lead melatonin to act in opposing ways in diurnal versus nocturnal species. They also hope that their findings find out whether melatonin plays a role in calls of other animals, such as nightingales and many species of frogs and mammals.
