Eyeless Mexican cavefish eliminate circadian rhythm to save energy

Mexican tetra
A closeup of our Blind Cave Fish, for the mexican tetra page. Credit: CC BY-SA 3.0

Eyeless Mexican cavefish show no metabolic circadian rhythm in either light and dark or constant dark conditions, according to a study published September 24, 2014 in the open-access journal PLOS ONE by Damian Moran from Lund University, Sweden, and colleagues.

The Mexican tetra has two variants, a fully-eyed fish living close to the surface and a blind, deep water, cave-dwelling fish. Scientists in this study used these two fish to study in fish residing in near or total darkness. The two fish types experience differences in daily light exposure, food availability, and predation, which all may influence adaptation. The authors explored these evolutionary differences in laboratory-based experiments by measuring (oxygen consumption) of both Pachón cave and surface fish at a fixed swimming speed under light and dark and constant dark photoperiods.

Researchers found that the eyeless cavefish use ~30% less energy than surface fish, depending on lighting conditions. Surface fish displayed a circadian rhythm in oxygen consumption on a light-dark cycle, and they found that this metabolic rhythm persists even in constant darkness. Cavefish, however, show no circadian rhythm in metabolism, in either light-dark or constant dark conditions. The authors propose that this loss of a circadian rhythm enables cavefish to save energy. The authors suggest that elimination of the circadian rhythm in metabolism could be a general feature of animals that live in perpetually dark, food-limited environments, such as caves or the deep sea.

Damian Moran added: "While animals that live on the planet's surface need autonomous to tune their physiology to their daily activities, the results of our study show that animals that live in environments without 24 hour cycles can save energy by not ramping up their metabolism needlessly for a day that will never arrive."

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Circadian clocks in a blind fish

More information: Moran D, Softley R, Warrant EJ (2014) Eyeless Mexican Cavefish Save Energy by Eliminating the Circadian Rhythm in Metabolism. PLOS ONE 9(9): e107877. DOI: 10.1371/journal.pone.0107877
Journal information: PLoS ONE

Citation: Eyeless Mexican cavefish eliminate circadian rhythm to save energy (2014, September 24) retrieved 16 September 2019 from https://phys.org/news/2014-09-eyeless-mexican-cavefish-circadian-rhythm.html
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Sep 24, 2014
This still does not explain why animals in pellucid environments don't have eyes. "Evolution" addicts will wheeze that they don't need them, so "evolution" removed them. But "evolution" doesn't act that way, only by adaptive advantage. In an environment without light, it doesn't matter if an animal has or doesn't have eyes or bright coloration. So there should be no proclivity for "evolution" to remove eyes and bright color! And even here, the claimed energy saving is from not adopting a circadian rhythm. But an animal with eyes in a totally black environment supposedly can lose their circadian rhythm. It's not necessary to lose eyes or coloration.comment

Sep 24, 2014
mmmm, I can't go an hour without my "Evolution" injected straight into my veins, otherwise I start wheezing like a fat 13 year old on track day.

Sep 25, 2014
this begs the question, could we evolve to lose a circadian rythm by living in perpetual LIGHT!!!!!.

Sep 25, 2014
This still does not explain . . .

Aside from operating them, growing eyes takes resources. And I didn't really need to explain that to you. To what extent is this obdurate attitude of yours toward evolution synthesized, and to what extent an inimical part of your aberrant mental process? The same process that regularly dishes out unwanted helpings of all that paranoid schizo conspiracy theory stuff of yours

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