The vampire bat, Desmodus rotundus, must find a blood meal every one to two days to survive. Razor sharp teeth and infrared-sensing 'pit organs' surrounding its nose help the bat achieve this goal.
Credit: Pascual Soriano
Desmodus rotundus
Credit: Pascual Soriano
SYDNEY: Vampire bats use infrared radiation to locate blood hotspots on their prey, a new study has shown.
Vampire bats are well adapted for their bloodthirsty lifestyle, with an excellent sense of smell, good eyesight and anticoagulant-laced saliva. They use flight and echolocation to hunt and can also walk on the ground to stalk their prey.
New research has now confirmed that they have taken thermosensation to an extreme and developed specialised systems that allow them to detect infrared radiation (IR) from their prey.
The infrared signals are received through three leaf pits, approximately 1mm in diameter, which surround their noses and can change direction when the vampire bat is hunting. The only other vertebrates capable of detecting infrared radiation are boas, pythons and pit vipers, which also have pit organs.
"These snakes use IR to detect warm blooded prey, such as a mouse or squirrel at night or in a dark tunnel," said David Julius from the University of California, San Francisco, lead author of the study in the current issue of Nature.
A nose for blood
The leaf pits are stimulated by the trigeminal ganglia (TG) - a mass of nerve cells associated with the trigeminal nerves, which cause sensations in the face. The TG of vampire bats have large diameter neurons, like those of pit-bearing snakes, rather than the smaller trigeminal ganglia observed in fruit bats.
However, their dorsal root ganglia (DRG) - the nerve cells mass associated with the spinal nerves - are the size of the DRG of fruit bats.
The researchers sequenced the DNA from the TG and DRG of different bat species and found a variation of the receptor TRPV1, an ion channel that is activated by heat. The variation, TRPV1-S, was found in the TG of vampire bats, but was barely detected in fruit bat TG or DRG. This suggests that the neuron specialisation of TG in vampire bats evolved for infrared detection.
"The precise nature and development of the innervation [of the leaf pits] has not been known and so this study is a fascinating insight into the further complexity and sophistication of this sensory system," said Sue Hand from the University of New South Wales in Sydney, who was not involved in the study.
A relative of cows?
The researchers also analysed genetic material from cows, pigs, dogs and coast moles to determine if the variant appeared in any of the other Laurasiatheria mammals - a large group of placental mammals believed to have originated on the northern supercontinent of Laurasia 510 to 200 million years ago.
Julius said that cows and moles have a gene structure that makes it potentially possible for them to generate TRPV1 variants, but they may not exploit this possibility.
"In some animals, such as cows or dogs, the so-called splice variants do not differ in their temperature sensitivity, so even of they made these variants, there would presumably be no change in temperature sensing ability," he said.
These findings support recent suggestions that bats are more closely related to cows and moles than primates, which have traditionally been considered their closest relatives.
"Some interesting implications of this include that echolocating bats and dolphins are no longer at opposite ends of the placental family tree and perhaps apparently shared abilities may be due to inherited capacity rather than evolutionary convergence," Hand said.
