Sunday, August 29, 2010

Infrared "Vision" in Snakes

Seeing in the dark is (and is not) pittsville for snakes.  It's been so great that it's evolved more than once in pit vipers and in pythons.

Here's the organ:

Facts of note about the pit organ:

"Essentially, it allows these animals to “see” radiant heat at wavelengths between 5 and 30 μm to a degree of accuracy such that a blind rattlesnake can target vulnerable body parts of the prey at which it strikes"

"The facial pit actually visualizes thermal radiation using the same optical principals as a pinhole camera, wherein the location of a source of thermal radiation is determined by the location of the radiation on the membrane of the heat pit. However, studies that have visualized the thermal images seen by the facial pit using computer analysis have suggested that the resolution is actually extremely poor. The size of the opening of the pit results in poor resolution of small, warm objects, and coupled with the pit's small size and subsequent poor heat conduction, the image produced is of extremely low resolution and contrast. It is known that some focusing and sharpening of the image occurs in the lateral descending trigeminal tract, and it is possible that the visual and infrared integration that occurs in the tectum may also be used to help sharpen in the image. In addition, snakes may deliberately choose ambush sites with low thermal background radiation (colder areas) to maximize the contrast of their warm prey in order to achieve such a high degree of accuracy from their thermal “vision”."

"he organ is used extensively by them to detect and target warm-blooded prey such as rodents and birds, and it was previously assumed that the organ evolved specifically for that purpose. However, recent evidence shows that the pit organ may also be used for thermoregulation. In an experiment that tested snakes' abilities to locate a cool thermal refuge in an uncomfortably hot maze, all pitvipers were able to locate the refuge quickly and easily, while true viperswere unable to do so. This suggests that the pitvipers were using their pit organs to aid in thermoregulatory decisions."

"Take a whiff of mustard or wasabi and you’ll be hit with a familiar burning sensation. That’s the result of chemicals in these pungent foods hitting a protein called TRPA1, a molecular alarm that warns us about irritating substances. The same protein does a similar job in other animals, but rattlesnakes and vipers have put their version of TRPA1 to a more impressive and murderous purpose. They use it to sense the body heat of their prey.
Pit vipers are famed for their ability to detect the infrared radiation given off by warm-blooded prey, and none more so than the western diamondback rattlesnake. Its skills are so accurate that it can detect its prey at distances of up to a metre, and strike at objects just 0.2C warmer than the surrounding temperature. Against such abilities, darkness is no defence.
Like all pit vipers, the rattlesnake’s sixth sense depends on two innocuous pits located between their eyes and their nostrils. With two pits on either side of its head, the snake can even ’see’ heat in stereo. Each pit is a hollow chamber with a thin membrane stretched across it, which acts as an “infrared antenna”. It is loaded with blood vessels, energy-harvesting mitochondria and dense clusters of nerves. The nerves connect with the visual parts of the snake’s brain, allowing it to match up images of both heat and light."
"A single gene that encodes the TRPA1 protein was 400 times more active in the pit nerves than the spinal ones.
In humans, TRPA1 is activated by allyl isothiocyanate, the chemical that gives wasabi and mustard their kick."

"Two other groups of snakes, the pythons and boas, can detect infrared radiation, although their technology is 5-10 times less sensitive than the sophisticated viper hardware. They also have pits but theirs are spread across their snouts, are simpler in structure and have fewer nerve connections. But Gracheva and Ingolia found that they have independently co-opted the same molecule in their pursuit of hot sensory action, even though their ancestors diverged from those of vipers 30 million years ago."

"The membrane is only 15 micrometers thick and hangs freely suspended in the pit organ so that it is isolated by the air. Heat sensitive cells from the membrane react to differences in temperature of only a few millikelvins."

It's also interesting to note that some scientists think that the snake's brain might clean up the blurry images similarly to our brain scrubs out our blind spot, flips our eye's lens image reversal and how our mind accentuates borders.

Only Mammals Chew

Great stand up comedians have a gift at pointing out the obvious in everyday life and making everyone in the audience say in their mind, "That's so true!  I've never thought about that, but it's so true!"  This is one of those things.  Only mammals chew.

Try to think of an exception.  

I mean really chew.  Not tear up, bite through, or rip apart, but really gnaw, masticate, mash up.

How interesting.


Doesn't seem to be an easy answer, but some of it has to do with our endothermia - warm bloodedness.  To sustain warmbloodedness, which keeps enzymes and proteins at their optimal temperature for physiological fine tuning, we need constant energy inputs of high quality foods.  In contrast, reptiles, like snakes, can go months in a semi-dormant phase that doesn't require the constant fueling of the 'fire' of warmbloodedness.  Mammals can't.  A simple way of putting it is that reptiles can wait for their chemical digestion to break down their food, but mammals are in too much of a hurry (with exceptions).  We need it now and mechanical break down offers that.

Herbivorous mammal teeth:

Carnivorous mammal teeth (take note of molars, which semi-only occur in mammals):

Herbivorous reptile teeth:

Carnivorous reptile teeth:

There are two exceptions that I should mention, though.


Pretty much all birds, a few fish, a good number of insects 'chew' using a muscular sack in their gut called a gizzard.  This can use grit/pebbles or in the case of larger dinosaurs even up to stone size rocks to crush up their food.  There are even some insects and mollusks that use chitinous 'teeth' plates in their gut to 'chew'.

Some reptiles do chew.  Most notably dinosaurs like hadrosaurus.  Chewing in dinosaurs is one of the reasons it's been speculated that they might have been warm blooded.

Also, there was one crocodilian that was recently unearthed that seemed to have chewed as well:

Why this is neat:

It highlights how species are integrated systems.  Who would have thought that a tooth innovation might have started the whole process and paved the way for a metabolism innovation.

Link: Why do guys get sleepy after sex?

Saturday, August 28, 2010

Papa's Got Tatas - Male Lactation in Dayak Fruit Bat

Male mammals have nipples.  Some men get breast cancer and get mammograms.  Why don't they ever breast feed?  Well, there's one mammal that does!  It's the Dayak Fruit Bat of South East Asia.

Saturday, August 21, 2010

Gyroscopic Eyes - Vestibulo-ocular Reflex

If you're anything like me, learning this will only reinforce how little you actually know about the adaptations your body has that you constantly use thoughtlessly.  O, the wealth that you don't/can't even comprehend!!!

Please do this:

  • Go to a mirror.
  • Stare straight ahead.
  • Find a marking/discoloration on your iris or some distinguishing vein that you can watch during this process.
  • Rotate your head to the left and then the right taking notice of the compensatory motions of your eyes.

What do you see?

  • Now try it fast.
  • Slower.
  • See how far your eyes will rotate.

Think about it.  Your eye gyroscopes all the time and you've probably never really thought about how (or, at least, I didn't).


Here's the gist of what I understand to be happening.  Your inner ear is composed of channels filled with liquid that as we move cause slight currents to be detected by the minute hairs within the vestibule.

That information then follows the below path:

It then tells muscles wrapped around the eye to rotate the eye:
Notice the way the muscles wrap around the eye making it possible to rotate the eye.

The exceptions to this rule are worthy of note.   Ever felt like the room was spinning?  Maybe that's because your eyes were!!  When you drink, spin yourself, or put cold/warm water in your ear the brain receives some confusing signals that end up causing the vestibulo-ocular reflex to get a little wonky (called nystagmus).  Your eyes rotate when they shouldn't!!  Also, when a doctor is trying to to assess the severity of a brain injury and possibly determine if the patient is brain dead, rotating the head to see if the eyes rotate involuntarily is one method.  

Not even going to pretend I didn't steal this from Wikipedia:

"Using these direct connections, eye movements lag the head movements by less than 10 ms, and thus the vestibulo-ocular reflex is one of the fastest reflexes in the human body."