A new study found that the eyeless Mexican cavefish is capable of using 30 percent less energy than its surface fish counterparts by deactivating its circadian rhythm.
Researchers from the Lund University in Sweden observed that the blind Mexican cavefish saves energy because it doesn't use a circadian clock. The circadian clock is the mechanism responsible for coordinating the body's functions with the day and night cycle of a certain environment. This is present in plants, animals, fungi and some kinds of bacteria.
The scientists found that the Mexican cavefish can control its metabolism without using a circadian clock after measuring the cavefish's rate of oxygen consumption and metabolic rate, and comparing it to that of a surface-dwelling fish.
Both species of fish were exposed to varying light and dark condition, imitating the 24-hour light cycle. The researchers also exposed them to complete darkness. The experiment showed that the surface-dwelling fish consumed more amounts of oxygen than the cavefish during daylight hours. The cavefish, on the other hand, consumed the same amount of energy whether it is light or dark, which was 30 percent lesser than the other fish.
"This is the same as if you or I were put in a dark room for a couple of days. We would show this kind of cycle, because we have this clock inside our bodies," said postdoctoral student in Lund's department of biology Damian Moran to LiveScience.
Moran explained that the cavefish's ability to save energy as part of its adaptation to the limited food supply in caves. The fish also evolved so that it could better survive the dark caves, such as their lack of eyes allowing them to channel their body's limited resources towards more useful biological functions.
But the researchers were particularly interested in the cavefish's use, or lack thereof, of circadian rhythm.
"We tend to assume that these rhythms are always adaptive, that they serve some really important purpose. But what happens in animals that don't have these cycles? It's a real conundrum," Moran told LiveScience.
Further findings of the study were published in the Sept. 26 issue of PLOS One.