From ABC News in Science, 25 September 2014:
The eyeless, cave-dwelling form of the Mexican tetra fish (Astyanax mexicanus) has surrendered its circadian rhythm for the sake of saving energy in its pitch-black habitat.
The absence of a day/night cycle in the cave-dweller’s metabolism has resulted in a 27 per cent saving in energy use, the scientists report today in PLoS ONE.
Most animals have a clear day/night circadian rhythm to their metabolism says lead author and fish biologist Dr Damian Moran, now a senior scientist at Plant and Food Research New Zealand.
“The reason why the metabolism is ramped up for day-active animals is that they are preparing for foraging, digestion and are anticipating all these physiological processes that they need to be ready for,” he says.
However the cave-dwelling, eyeless form of the tetra appears to have eliminated that cycle, and as a result, uses significantly less energy over a 24-hour period compared to its surface-dwelling counterpart.
“These cave fish are living in an environment without light, without the circadian presence of food or predators, they’ve got nothing to get ready for, so it looks like they’ve just chopped away this increase in anticipation for the day,” Moran says.
Instead, the cave-dwellers exist in a more steady metabolic state that is somewhere between asleep and fully active.
“They live a demand-led life rather than an anticipation-led life.” Read more.