“Weekend Nanotech” – Bat Thermal Imaging

By Elf Eldridge 06/08/2011


Vampire Bats nose - laden with infrared sensors
Vampire Bat's nose - laden with infrared sensors. From Reference 1

This week has been a great week for interesting nanoscience, with Nature Nanotech being published with a couple of great articles that I will discuss in time (namely building glowing stuff with Quantum Dots and a DNA scaffolding and nanomachines made of neurodegenerative amyloid proteins – oh I cant wait! Perhaps a two post edition of “Weekend Nanotech” is in order) , but the articles that really caught my eye this week concerned vampire bats, snakes, and Arnold Schwarzenegger’s greatest movie – Predator.

For some time now we have known that vampire bats and snakes have the ability to see into the infrared[3]. However what Gracheva et al [2] showed in Nature this week was exactly how, at a nanoscale, bats are able to do this, what they may use it for, and some indication of the sort of resolution they have. They found that it was due to the presence of a slightly modified temperature sensor that occurs in many mammals: TRPV1. This temperature senor is an ‘ion channel’, a pore through the wall of a nerve that allows the nerve to convert some sensation (in this case temperature) to an electrical impulse via the process called ‘depolarization‘. What’s special about the vampire bat’s particular channel though, is that it’s sensitive to temperatures around 30 degrees Celsius, almost 10 degrees lower than the temperature most mammal’s sensors are sensitive to – and that bats have achieved this via natural ‘splicing’ of the DNA that codes for their version of the TRPV1, allowing them to alter it’s structure rapidly (in evolutionary time scales). This is all a bit hard to relate to though – so instead of going into too much detail, I’m going to invite you to imagine seeing with your nose so that other people look like this (hence the Predator reference):

Human as seen via infrared camera
Human as seen via infrared camera

Oh but this story gets better! The bats use this sense to locate the ‘warm parts’ on animals – specifically the areas free of hair and full of arteries fresh from the heart, after all, these are vampire bats! So now go back to the image above and imagine being able to pick out arteries and veins and areas of bare skin, JUST though watching the organism’s body heat. That’s something even Predator couldn’t do!

There are a couple of caveat’s here though: the ‘bat-vision’ is only sensitive to distances of around 30 cm away from the bat’s head [2] (but then again these creatures are fully capable of sonar so they certainly don’t need it for long distance location), and that it’s highly unlikely that the infrared vision is perceived anything like the image above. Their resolution is much lower than what we can manage with thermal cameras, but only because bats don’t need high resolution when they have already located their prey (it’s the same story for snakes [3])!

Finally, a random little factoid to round off the story. The ion channel sensor, TRPV1, is actually quite well known, particularly in humans , as it’s not only sensitive to temperature, but also to capsacins, the oil that makes chillis and capsicums spicy! So next time you’re eyes are watering after partaking of something delicious and spicy, and you feel the heat and tingle on your tongue, remember that vampire bats are so awesome that they can use that sensation to ‘see’*. Like predator. Then be very grateful that a ‘meal’ to them is only 25ml of blood [2]. And that they’re highly altruistic [4] and actually kinda cute!

*a further caveat: I should probably note that when the bat’s sensors are set off, it’s most likely NOT felt by them as a ‘burning sensation’ in their nose, as you would imagine. This would have pretty strong negative evolutionary selective pressures. It’s a great mental image though!

References:

1) M.B.Fenton “Heat-thirsty bats” Nature 476, 40-41 (2011) doi:10.1038/476040a

2) E.O.Gracheva et al. “Ganglion-specific splicing of TRPV1 underlies infrared sensation in vampire bats” Nature 476, 88-91 (2011) doi: 10.1038/nature10245

3) E.O.Gracheva et al. “Molecular basis of infrared detection in snakes” Nature 464, 1006-1011 (2010) doi:10.1038/nature08943

4) http://faculty.jsd.claremont.edu/dmcfarlane/Publications/DeNault%20andMcFarlane1995.pdf