Cavefish study shows humans could evolve to sleep less

February 23, 2017

Pachón cavefish live in dark caves in Mexico and have lost their eyes completely
The caves have very little light and food and the fish evolved suppressed sleep
The lateral line is a line along a fish consisting of a series of sensory organs
These organs detect movements and pressure changes in the surrounding water
This makes them less able to block out the environment and so they loose sleep
This could shed light on how human brains could evolve to need less sleep too

Cecile Borkhataria For Dailymail.com

Published:
14:59 EST, 23 February 2017

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Updated:
15:03 EST, 23 February 2017

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Blind Pachón cavefish in Mexico have evolved to require very little sleep – and they could shed light on how human brains could evolve to need less sleep too.

Sleep in an essential behavior required by almost all animal – but animals have very big difference in how much sleep they need.

Researchers are investigating how sleep evolves and they’re using the cavefish as a model to understand how human brains could evolve very little sleep – just like the catfish.

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The Pachón cavefish live in deep, dark caves in central Mexico and have completely lost their eyes. The caves have very little food, oxygen or light – and because of this harsh environment they have evolved creative survival mechanisms including suppressed sleep

The researchers at Florida Atlantic University (FAU) studied Mexican cavefish to gain insight into the evolutionary mechanisms that regulate sleep loss.

The fish live in deep, dark caves in central Mexico and have completely lost their eyes.

The caves have very little food, oxygen or light – and because of this harsh environment they have evolved creative survival mechanisms including suppressed sleep.

They found that an inability to block out your environment is one of the ways to lose sleep.

‘Animals have dramatic differences in sleep with some sleeping as much as 20 hours and others as little as two hours and no one knows why these dramatic differences in sleep exist,’ said Dr Alex Keene, a co-author of the study and an associate professor in FAU’s Charles E.Schmidt College of Science.

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‘Our study suggests that differences in sensory systems may contribute to this sleep variability.

‘It is possible that evolution drives sensory changes and changes in sleep are a secondary consequence, or that evolution selects for changes in sensory processing in order to change sleep.’

Cavefish have evolved significant differences to surface dwelling fish because the cave environment is so different to the rivers inhabited by surface fish.

They have evolved differences in foraging and feeding behavior – making it possible that differences in food availability led to the evolution of sleep loss in cave populations.

(a,b) A surface cavefish that lives in rivers. (c,d) A Pachón cavefish that has no eyes. Cavefish have evolved significant differences to surface dwelling fish because the cave environment is so different to the rivers inhabited by surface fish. The cavefish have evolved differences in foraging and feeding behavior – making it possible that differences in food availability led to the evolution of sleep loss in cave populations

The researchers found that some cavefish populations evolved enhanced sensory capabilities which contribute to sleep loss, and sleep in cavefish can be changed and may be regulated by seasonal changes in food availability.

The specific population that researchers studied, the Pachón cavefish, lost sleep because of increased sensory input – but the other populations didn’t.

‘We were surprised to find that there are multiple independent mechanisms regulating sleep loss in different cave populations and this can be a significant strength moving forward,’ said James Jaggard, co-author and a graduate student at FAU working with Dr Keene.

There are more than 29 different populations of cavefish who all evolved independently, so the researchers were able to find out whether the different populations of fish evolved sleep loss through the same evolutionary mechanisms. The specific population that researchers studied, the Pachón cavefish, lost sleep because of increased sensory input

‘This means that there are many different ways to lose sleep or evolve a brain that sleeps less and we are going to search to identify these mechanisms.’

Previously, the researchers found that the cavefish evolved a very sensitive lateral line – a line along the side of a fish consisting of a series of sensory organs that detect movements and pressure changes in the surrounding water.

To conduct the study, the researchers recorded the catfish under infrared light in individual tanks.

Automated video software recorded when the fish were inactive, and they were considered asleep if they didn’t move for one minute.

WHAT IS THE LATERAL LINE?

The lateral line is a canal system made up of a series of receptors called neuromasts.

These neuromasts are arranged in an interconnected network along the head and body.

The canals are located just underneath the skin of the fish, and only the receptor part of each neuromast extends into the canal.

The lateral line system of a fish. (A) The bodily location of lateral lines. (B) Longitudinal section of a canal. (C) Superficial neuromast

Source: Britannica.com

‘Humans block out sensory cues when we enter a sleep-like state,’ said Dr Keene.

‘For example, we close our eyes and there are mechanisms in the brain to reduce auditory input.

‘This is one of the reasons why a sensory stimuli like someone entering a room is less likely to get your attention if you are asleep.

‘Our thinking was that cavefish have to some degree lost this ability and this drives sleep loss,’ he said.

The researchers recently created transgenic fish lines – when DNA from an animal is artificially introduced into a different species.

They want to use these fish lines to image their brain activity and genetically map differences in anatomy between the different cavefish populations.