Infrared-sensing 'pit organs' around the nose help the vampire bat (Desmodus rotundus) to hunt down its prey. Credit: Pascual Soriano

Vampire bats hunt by detecting hot spots on their prey where blood flows close to the skin, but how they do it has long been a mystery. Now, researchers have found that the bats alter a sensor that evolved to detect dangerously high temperatures, tuning it to track down the much cooler body heat of prey.

The finding shows that the bats (Desmodus rotundus) use a mechanism different from that of the only other vertebrates that can detect infrared radiation — three families of snake. The discovery might also help the design of drugs that act on similar sensors in humans.

Vampire bats are known to detect infrared radiation from their prey using specialized 'pit organs' located around their noses. To pin down the molecular basis of the bats' ability, David Julius, a physiologist at the University of California, San Francisco, and his colleagues compared gene expression in the nerve fibres of bats' pit organs with that in nerve fibres from the creatures' spines.

They found that the bats produce two different forms of a heat-sensitive ion channel — a protein that controls the processes of cells — called TRPV1. In the spinal nerve fibres, the bats used the gene Trpv1 to express TRPV1 in its normal, full-length form. But in the nerve fibres of the pit organs, the animals used the same gene to produce a new, shorter form of the protein. The work is published in Nature today.1

The researchers had previously shown that snakes such as pit vipers have adapted a different ion channel — one that is usually insensitive to heat — to detect infrared radiation.2

Molecular thermostat

"The study shows how a specialised adaptation — infrared detection — can evolve by different genetic mechanisms in vampire bats and in the only other vertebrates capable of this sensory mechanism," says Gareth Jones, who studies bat behaviour at the University of Bristol, UK.

TRPV1 is found in all vertebrates. It detects heat that would be damaging to body tissues, triggering a painful, burning sensation. It normally activates at 43 °C and above. But the extra variant produced by the bats responds to a much cooler 30 °C.

"The channel is like a little thermostat," says Julius. Altering its structure by leaving out part of the gene tunes the ability of the channel to detect heat. By expressing different forms in different tissues, the bats have split the function of the sensor, maintaining its original function but also gaining the ability to detect body heat for more efficient hunting.

Julius hopes that the work will shed light on how heat sensors work in humans. It could also aid the design of drugs that suppress the activity of related ion channels, such as those involved in causing inflammatory pain.

Credit: Pascual Soriano