The bat with the incredibly long tongue

A rare South American bat turns out to have a spectacularly long tongue. At up to 150% the length of its body, it is proportionally the longest of any mammal.

The bat appears to have evolved its incredible tongue in order to feed exclusively from a tubular flower found in the "cloud forests" of Ecuador.

Nectar bats’ tongues have tiny hairs on the end, which they use to mop up nectar and pollen from within flowers. The plants gain from this relationship by depositing pollen on the bat’s head, which it spreads from flower to flower.
Anoura fistulata is only the size of a mouse, but its tongue is around 8.5 centimetres long – more than double the tongue-length of similar nectar bats. Compared with its body, a tongue of this size is second only to the chameleon in terms of vertebrates, and it is the longest of all the mammals.

“It’s like a cat being able to lap milk from two feet away,” says Nathan Muchhala of University of Miami, Florida, US, who first discovered the species in 2003.

Close to heart
Such a small animal has had to evolve a way to store the tongue. “I had all sorts of theories, such as perhaps the tongue folded up inside, or coiled, or maybe its lower lip was critical somehow,” says Mucchala.

It turned out that the tongue extends down into the bat’s chest, and its base is between the heart and sternum. When extended, it stretches by up to three times its stored length.

Muchhala measured the bats’ tongues by training them to drink sugared water from a tube, which was approximately the diameter of a McDonald’s drinking straw.

The straws resemble a flower from the region, called centropogon nigricans, which has a funnel-like neck called a corolla, at the base of which is its nectar.

Competitive advantage
This flower is unique because it relies exclusively on fistulata to pollinate it. Most plants in the region have evolved so all nectar bats can feed from them, but this flower’s neck is too long for other bats to reach down with their tongues.

Such a close co-evolutionary relationship is rare, says Muchhala. It occurs in other species – some plants have evolved so that only hummingbirds can feed from them – but this is the first known example of a flower pollinated by only one species of bat. The flower gains an advantage over other species of plant in the region because it does not have to compete with them to attract the nectar bats.

The finding is also an example of convergent evolution, where two unrelated organisms independently evolve similar traits as they adapt to similar environments, says Muchhala. Other animals such as scaly anteaters have evolved similarly long tongues, which they use to feed.

Journal reference: Nature (vol 444, p 701)
http://www.newscientist.com/article/dn10721?DCMP=NLC-nletter&nsref=dn10721