A Glimpse Into Infrared Sensing

Fer-de-lance pit-viper; infrared sensing pits found below the eyes.

Not all snakes rely heavily on their pure vision to find and strike their prey. Pit-vipers and rattle snakes are able to sense the infrared radiation given off, in the form of heat, by mammals to find their next meal. But what genes had to evolve to allow these reptiles to sense that which is not visible to the naked eye? That would be the TRPA1 gene. Published in 2011, this study sequenced the genes of 24 snake species, which represented nine snake families as well as other non-snake outgroups. What they found, was that snake species that have the pit organs had a high positive selection for the TRPA1 gene, while the other species did not. This finding indicated that the TRPA1 gene only evolved in the species that are able to detect infrared. The TRPA1 gene codes for the TRPA1 protein, which are then showed to have some amino acid substitutions dependent on the high positive selection, or lack of high positive selection.

The specific proteins that the gene code for are receptor proteins. In humans, these receptors, also known as ion channels, drive the response that we have to spicy foods like wasabi. Dr. David Julius and his team found that TRPA1 evolved to be increasingly sensitive to heat, activating at temperatures as low as 80 degrees Fahrenheit (18 degrees cooler than the normal human body temperature).  This TRPA1 gene is described to be millions of years old, but the viper and other snake species that use infrared sensing are much younger in comparison.

I think that the analysis of the infrared sensing genes in the snake species as well as other animal species is a really great way to demonstrate evolutionary abilities of genetics. It's incredible the a gene that is also found in humans to be able to feel heat when tasting spicy things, can vary so differently as to code for infrared sensing organs in snakes. I think the New York Times article does the best job by stating "evolution of new abilities does not necessarily require new genes, but new variations of old genes".