We see snakes

Model explains infrared vision of snakes

Catching prey with infrared vision: Until now it was unclear how the pit organ of snakes enables them to see infrared. Now a new model could explain this ability. According to this, the cells in the pit organ act like a pyroelectric material - they convert heat into electricity and thus generate the electrical signals of this sensory organ. Experiments must now clarify whether and how exactly this process takes place in the snakes' pit organ.

Snakes are feared predators in the animal kingdom - they usually bite so quickly that their prey hardly has a chance. Certain species - such as the pit viper, boa constrictor and pythons - are also able to use infrared vision to catch their prey with enormous accuracy, even in the dark. Fossil finds show that there were snakes millions of years ago that could perceive even the smallest temperature fluctuations with their infrared vision.

Snake species that hunt in the dark have so-called pit organs - hollow chambers enclosed by a thin membrane - on the upper and lower jaw: These sensory organs are equipped with infrared receptors and give the animals a three-dimensional thermal image of their environment. The reptiles convert the infrared rays from organisms into electrical signals so that, among other things, they can “see” their prey in the dark.

How do snakes convert the infrared rays?

But how do the cells inside the pit organ convert heat radiation into electricity? A research team led by Faezeh Darbaniyan from the University of Houston got to the bottom of this question. The researchers already knew that hard, brittle tissues like crystals have pyroelectric properties: They can convert heat into electricity. But animal tissues are actually too soft for this form of heat conversion.

"The cells in the pit organ are not pyroelectric materials," confirms Darbaniyan's colleague Pradeep Sharma. “We could explain the infrared detection of snakes if there was a hard, pyroelectric material in their pit organ, but no one has ever found one.” So the researchers used a theoretical model to investigate whether there is a way, and how soft organic materials can have a pyroelectric effect.

Soft material can also have a pyroelectric effect

And indeed: as the scientists found with the help of their model, the cells in the snake's pit organ must also behave like a pyroelectric material. “Our solution is deceptively simple,” explains Sharma.

The decisive prerequisite is therefore that static electrical charges can form and hold in the material - in this case in the tissue of the pit organ. "Then you have to make sure that the material is soft enough that it allows large deformations in terms of shape and size and that it is temperature-sensitive," explains Sharma. Because these temperature-related deformations then bring the static charges into contact with one another and thus generate the electrical signals.

As the scientists have calculated, the small amounts of heat captured by the snakes' pit organ would be sufficient to trigger such a pyroelectric reaction in the organ's cells. They have already started to recreate this system in the laboratory using artificial materials.

Point of contact for further investigations

"We're pretty sure we've uncovered at least part of the mechanism by which these snakes can see in the dark," says Sharma. How exactly the pyroelectric reaction works in the tissues and cells of the snake has yet to be investigated. Earlier studies suggested that certain ion channels in the membrane of pit organ neurons play an important role in their function. However, it is unclear whether these channels are also involved in the pyroelectric effect.

So more laboratory experiments are still needed to confirm whether the research team's mechanism really takes place in the cells of the pituitary organ's membrane. "Now that we've developed a model for it, other scientists can work on it and carry out experiments to confirm or refute our theory about the infrared sense of snakes," says Sharma. (Matter, 2020, doi: 10.1016 / j.matt.2020.09.023)

Source: University of Houston, Cell Press

October 27, 2020

- Anna Bolten