Natural History

From the BBC:

Madagascar’s mysterious aye aye warms up its extra-long finger when searching for dinner, scientists have found.

The lemur, the world’s largest nocturnal primate, taps its specialised middle finger on tree trunks to find nutritious beetle larvae.

Studying thermal images, researchers found that the digit was colder than the others but warmed by up to 6C during foraging.

Scientists suggest that the aye aye saves energy by keeping the digit cool.

The findings are published in the International Journal of Primatology.

The team from Dartmouth University in New Hampshire, US, wanted to investigate the surface temperature of sensitive structures.

The aye aye’s unusual middle finger has already been found to be super-sensitive to vibrations, so provided the perfect subject for their study.

“It was striking to see how much cooler the third digit was while not in use and how quickly it warmed to [match] the other digits when engaged in an active foraging task,” said graduate student Gillian Moritz, who carried out the study under the guidance of her supervisor, Dr Nathaniel Dominy.

When not in use, the finger appeared black on thermal images. This indicated a large difference in temperature between it and the white (hot) ears and eyes.

But when the animal was looking for food, the finger rose in temperature by up to 6C.

“We think the relatively cooler temperatures of the digit when not in use could be related to its [long, thin] form,” said Ms Moritz.

“This form results in a relatively high surface-to-volume ratio [but] such a ratio is bad for retaining heat.”

In order to sense the vibrations of beetle larvae through the bark of a tree, the finger is “packed with sensitive nerve endings”, the scientist explained.

Because of its specialist sense receptors, using this tapping tool is very costly in terms of energy.

“Like any delicate instrument, it is probably best deactivated when not in use,” Ms Moritz told BBC Nature.

The question of how the lemur controls the heat of a single digit remains unclear.

Ms Moritz suggested two explanations. The first was simply that the blood vessels that supplied the digit could be constricted or dilated.

The second more unusual possibility, she said, was that the creature might employ temperature control method that was linked to the flexibility of its finger.

Ms Moritz explained: “Because the finger is fragile and vulnerable to injury, it is often extended back and out of the way during locomotion and periods of inactivity,” she said.

This extension could cause a “kink” in the artery that supplies warm blood to the digit.

In the same way a bent garden hose supplies less water, the artery could supply less blood, keeping the finger much colder than its fully supplied neighbouring digits.

Aye ayes are the only primates known to have this strange adaptation.

The species is listed as Near Threatened by the International Union for Conservation of Nature (IUCN), mainly because of threats to its habitat.

But the odd-looking primate also suffers direct persecution. Superstition in Madagascar describes the species as a bad omen. Those that are pointed at by the creature’s mysterious finger are said to meet their death.

The reason why this particular animal has suffered persecution is, well, look at it.

If you didn’t know what this animal was, you would probably would think you were coming across some demon. Of course, in Western societies, we would call then extraterrestrials or genetic experiments gone awry.

In Madagascar, aye-ayes are considered bad omens, and they are killed on site.  And then they hand them up along roadsides so the evil spirit they are said to possess will be carried away. This is one major reason why aye-ayes are becoming more and more threatened. This issue would not be so much of a problem, but aye-ayes have virtually no fear of people and are rather curious animals– which means they wander into villages on a regular basis. One would think that the villagers’ extreme antipathy toward the aye-aye would exert a selection pressure on the population to make them a bit more wary of people, but they still wander into villages.  And they wind up like this:

It might difficult for some to recognize this animal as a primate, but if one accepts that lemurs are primates, then the aye-aye, which is a lemur, is a primate.

Not only do they have the bizarre middle finger, they also have rodent-like teeth. On a primate skull, this looks very strange.

Oh and here’s a close up of that hand– just so you can see how weird the middle finger is:

Aye-ayes are on of those bizarrely specialized animals– perhaps one of the most specialized of all primates.

Specialization is often a dangerous path in evolution, and as the forests that contain the trees that hold the insects that the aye-ayes have evolved to eat have been felled, they aye-aye may not have any other way of surviving.

The aye-aye is a primate that has evolved into a kind of nocturnal woodpecker.  Where the woodpecker has its sharp bill and long tongue, the aye-aye has its middle finger and rodent teeth.

Now, if people in Madagascar were just a bit more educated about what an aye-aye is, we might not have them hanging along roadsides.

If I were the aye-aye, I’d be giving these people the middle finger.

A warmed up middle finger.