Friday, February 6, 2015

Circadian Rhythm eliminated in Pachon Eyeless Mexican Cavefish to conserve energy

Circadian Rhythm eliminated in Pachon Eyeless Mexican Cavefish
Source: PLOS ONE

Summary: The scientists who directed the research at hand used two types of Mexican tetra fish to conduct their study. One type of the Mexican tetra fish is full-eyed and lives near the surface of the water, while the second type is blind and resides in deep waters and caves. The study was used to examine the evolutionary adaptation in fish who live in total, or almost total, darkness.


As the two types of tetra fish have different variants in physicality, they also experience differences in daily light exposure, access and availability of food, and predation. Each of these factors may contribute to the adaptations that are seen among the populations of these fish. To properly study the evolutionary differences of being blind or not in the same category of fish, the scientists took the fishes to the labs. The authors of the article explored the adaptations and evolution of the fish by measuring amounts of oxygen consumption, or metabolic rates, of both types of fish at a fixed swimming speed under light and dark and continuous dark periods.

The scientists found that the Pachon cavefish use 27% less energy than the surface fish who could see, depending on light conditions, and the surface fish expended 38% more energy in the living conditions of the cavefish than the cavefish expend in total darkness. They also found that the surface dwelling fish displayed a circadian rhythm in metabolic rates (oxygen consumption) in light and dark, but also in periods of total darkness. On the contrary, the cavefish showed no circadian rhythm in metabolism, at all, regardless of light and dark or only dark photoperiods. To the scientists running this study this is a tell-tale sign that evolution has occurred in the cave-dwelling blind fish, as the loss of circadian rhythm enables them to conserve energy and thus survive better in the darker waters where less food is available. The authors of the article also believe that this characteristic of loss of circadian rhythm, may be a general attribute that all animals living in perpetual darkness eventually adapt, as any creature of the dark and deep would be limited to food and provisions.

Circadian rhythms are necessary for animals that live on the surface of the planet as those animals experience cycles of night and day, in which these rhythms tune the physiology of their daily activities. Many animals function differently, on an internal organ level, at night than they do during the day. These studies of the Mexican tetra fish show that animals living in total darkness do not need to ramp up their metabolism for a daytime that will not be coming, and instead lose the circadian rhythm and conserve energy as other animals do at night, expect these fish are in night-mode all the time.


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

5 comments:

  1. This is an interesting example of evolution occurring today. We can see that two types of the same fish have adapted to their environment by not only eliminating their eyesight but instead adapting their metabolism. This is interesting because most of the time we (general population and beginning biology students) overlook the differences we cannot see meaning brain function, metabolism, and heart function. Their adapting metabolism is truly ingenious and also provides evidence that natural selection is not random which is what we have been discussing in class recently.

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  2. This is very interesting because it shows how the fish truly have adapted to their environment to eliminate unnecessary energy expenditures. This study could potentially be applicable to neuroscience studies concerning the circadian rhythms of human beings and our individual energy levels.

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  3. I think this study shows just how unpredictable natural selection and evolution can be at times. Not many people would have expected that a seemingly fundamental process such as the circadian rhythm would be eliminated. In fact, when I read the title of the article, I thought that eliminating a necessary function such as the circadian rhythm would actually be harmful to the organism; instead, natural selection and evolution have surprised scientists by converting an apparent disadvantage into a survival edge.

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  4. I think this study shows just how unpredictable natural selection and evolution can be at times. Not many people would have expected that a seemingly fundamental process such as the circadian rhythm would be eliminated. In fact, when I read the title of the article, I thought that eliminating a necessary function such as the circadian rhythm would actually be harmful to the organism; instead, natural selection and evolution have surprised scientists by converting an apparent disadvantage into a survival edge.

    ReplyDelete
  5. I think this study shows just how unpredictable natural selection and evolution can be at times. Not many people would have expected that a seemingly fundamental process such as the circadian rhythm would be eliminated. In fact, when I read the title of the article, I thought that eliminating a necessary function such as the circadian rhythm would actually be harmful to the organism; instead, natural selection and evolution have surprised scientists by converting an apparent disadvantage into a survival edge.

    ReplyDelete