A new study reveals thatPhreatichthys andruzzii, a blind fish from Somalia (Africa), has a rcircadian eloj that is governed for an extremely long period (up to 47 hours), and that accelerates with increasing temperature. “We wanted to know if blind fish, which live in an environment where there is no day and night cycle, still maintain a circadian clock that can be regulated by light,” Nicholas Foulke, a researcher at the University of Ferrara (Italy), told SINC. ) and co-author of a study published in the journalPLoS Biology.
The circadian clock is a physiological time mechanism that allows organisms to anticipate and adapt to the day and night cycle. The team of researchers from the University of Ferrara studied a specific species of cave fish, thePhreatichthys andruzzii, which has lived in isolation for two million years under the Somali desert, to learn how it has evolved over millions of years in underground environments.
The scientists’ starting point was to compare the circadian clock of this blind fish with that of a ‘normal’ fish, the zebrafish. They studied locomotor activity and clock gene expression in both species when exposed to a light-dark cycle. “While for the zebrafish they obtained a solid circadian clock synchronized with the light cycle, in the cavefish the same coincidence was not detected”, point out the experts.
However, in another comparative study where both fish were exposed to a time signal based on a regular diet, both zebrafish and cavefish showed synchrony in their circadian clock. The researchers concluded thatthe cave fish still had a clock that could be regulated by the feeding pattern, but not by the light. “This is extremely rare for circadian clocks in natural plants and animals,” says Foulke. Also, with a more detailed study they showed that the blind fish is governed by an abnormally long period. The most surprising thing is that the absence of readjustment with the light is not due to the lack of eyes, but totwo opsin mutations-molecules responsible for the initial cellular reactions involved in the perception of light- that make the clocks of most tissues do not react to light signals.Opsins are close relatives of the molecules that are present in our retinas and that they allow us to perceive different colors and form an image.
“The circadian clock of this fish works at a very long rate (47 hours) compared to the approximately 24 hour rate found in a normal circadian clock,” says Foulke, adding that “in addition, we have observed thatthe clock’s pace speeds up as the temperature rises. This is not the usual thing. Normally, the watch is adapted to run at the same speed in a normal range of temperatures. All the evidence points to this cave fish losing its watch. “
According to Foulke, this article is of great importance because it represents a “new and fascinating” reflection on how evolution in constant darkness affects animal physiology and because it is “the first genetic test of the identification of widely expressed photoreceptors in fish”. This study creates the framework for a more complete understanding of how circadian clocks respond to their environment.
