Getting out of bed some days feels like too much effort. If only night lasted all day, just like it does for the blind Mexican cavefish. Like the fish, you just might save some energy by living in an endless night.
The Mexican tetra (Astyanax mexicanus) is a species of fish found in the southern United States and parts of Mexico. It takes two forms, or ‘morphs’ – one with good vision and one that develops without eyes. While the sighted morph swims in streams exposed to sunlight, the blind morph can be found underground in lightless caves, finding its way by detecting changes in the surrounding water pressure.
A world without sunlight is also a world without the predictable rhythm of night and day. Many living things – from humans to flowers, and even a number of microscopic organisms – have chemical processes that roughly match the 24 hour patterns of night and day. These processes help prepare you with a boost of energy during the times of day you need it most.
Called a circadian rhythm, this body clock doesn’t rely on you checking your watch or even seeing the Sun. It is kept in check by periods of light and dark. If you’ve ever had jet lag, you’ve experienced your circadian rhythm telling you to sleep or eat at odd times of the day.
Yet the Mexican cavefish lives in darkness, so does it even have a circadian rhythm? To find out, Swedish biologists compared the blind morph with the sighted morph, and found that the blind morph does not have this internal body clock. It also uses less energy than the sighted morph, by not having to prepare for daylight.
Next time you oversleep, you've got a new excuse. Tell your teacher you’ve become a blind Mexican cavefish and lost your body clock!
Blind Mexican cavefish live in an endless night. Image: Wikimedia Commons/H. Zell BY-SA
Quiz questions
Where in your body would you find your sphenoid bone?
The microbe Thiomargarita namibiensis holds the record for being what? Is it a) the fastest single celled organism, b) the most common organism, or c) the most massive bacterium?
What period came before the Cretaceous period?
What are the three most common elements in the Milky Way galaxy?
What do cosmologists study?
Try this: Burning cold
Submerge ten nails in hot water, and ten nails in ice water.
Try touching the two groups of nails separately.
Arrange the nails so that the warm nails alternate with the cool nails. Place your palm on top of the row of nails. How does it feel?
You will need
20 large nails (10 cm or longer)
Ice water
Hot tap water
Two plastic containers (large enough to hold the nails)
A flat surface
What to do
Fill the plastic container with warm water from the tap. It should be hot enough to touch without causing pain – add some cold water if it’s too hot.
Submerge ten of the nails in the hot water.
Fill the second plastic container with ice water.
Submerge the other ten nails in the ice water.
Wait ten minutes, then pour out the water from both containers.
Lightly touch one of the hot nails. It should be quite warm, but not enough to cause pain.
Lightly touch one of the cold nails. Likewise, it should be quite cool to the touch and not painful.
Arrange the ten cold nails on a flat surface so they all line up parallel.
Lay your hand across the row of nails, palm down. How does it feel?
Repeat steps 8 and 9 with the ten warm nails.
Arrange the nails so that the warm nails alternate with the cool nails. The nails should go cool, warm, cool, warm, and so on. Try to do this quickly to prevent the temperature of the nails changing too much.
Place your palm on top of the row of nails again. How does it feel?
What’s happening?
Separately, the temperatures of the cool nails and the warm nails feel quite harmless. The cool nails should be between 5 °C and 15 °C, while the warm nails should be about 40 °C to 50 °C – not hot or cold enough to cause damage. Combining them sends mixed temperature signals to your brain, causing an uncomfortable sense of mild burning.
Perhaps you’ve experienced a similar sting of pain when you’ve eased a cold foot into a warm bath on a chilly winter’s day. The odd sensation caused by the alternating nails is called the thermal grill illusion, and dates back to 1896 when a Swedish doctor named Torsten Thunberg experimented with the sensation of temperature.
The reasons for this lie in how the brain decides when a temperature should be avoided. We have two types of thermoreceptor (nerves that detect temperature change). One type sends lots of messages to the brain as it warms, and slows down when it cools. The other type does the opposite. Faced with both warming and cooling close together, our brain makes a judgment that says we’re feeling a painful temperature.
Applications
In 2011, Swedish neuroscientists wanted to see exactly what was going on in our brain. They made a thermal grill illusion from plastic and silver, to ensure it wouldn’t be affected by a magnetic resonance imaging (MRI) scanner, and set it to work on some volunteers.
They found that the thalamus structure in the brain was rather busy when the illusion was on. This lump of tissue acts as a relay station, sending sensations from the body to other sections of the brain. It has also been linked to central pain syndromes.
Researching unpleasant sensations can be a rather tricky business for neuroscientists. Creating discomfort with an illusion is a neat way to do experiments without harming volunteers.
What do you think of when you hear a storm is coming? Create a work of art and enter the 2014 Australian Meteorological & Oceanographic Society Art Competition to win great prizes. The competition is open to primary and secondary students to year 10, and welcomes entries of visual art works, including photographs.
The sphenoid bone is in your skull, behind your eyes.
Thiomargarita namibiensis holds the record for being the most massive bacterium. It can grow as long as 0.75 mm and as wide as 0.3 mm.
The Jurassic period came before the Cretaceous period.
The three most common elements in the Milky Way galaxy are hydrogen, helium and oxygen.
Cosmologists study the origins, growth, structure, and end of the universe as a whole.
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