Wednesday, February 22, 2012

Aye-Ayes Warm Up Specialized Middle Digit During Foraging

In the January 2012 issue of the International Journal of Primatology there is a fascinating article by Moritz and Dominy, a graduate student at Dartmouth and her advisor, who used infrared thermography (IRT) to visualize the surface temperatures of Aye-Ayes (Daubentonia madagascariensis) in order to answer questions about dynamic vascular supply during percussive and probative foraging. Aye-Ayes are the world's largest nocturnal primate, known for their use of a specialized middle digit to find and extract nutritious bettle larvae from tree trunks (see video). During foraging the Aye-Aye implements the digit by tapping it against a tree trunk up to 8 times/second, listening for the tiny change in resonance that indicate a hollow space within. Additionally, the finger contains many sensitive nerve endings that allow the Aye-Aye to sense the vibrations of beetle larvae through the trunk. These specialized sense receptors make the digit costly in terms of energy. Researchers hypothesized that the physiology of the digit might play an equally important role in foraging as auditory and sensory clues for "it [the digit] is a vital sensory tool that is expected to feature a high density of dermal mechanoreceptors that radiate heat and impose thermal costs under cool temperatures."

The team acquired IRT images of 8 Aye-Aye engaged in a variety of passive and probative behaviors. Findings are that the prominent middle digit of the Aye-Aye warms its surface temperature up to 6°C hotter in contrast to invariant surface temperatures of other digits during foraging. One explanation for the change in heat is constriction or dilation of the blood vessels that supply the digit. A second less likely explanation is that the creature might mitigate temperature changes through the flexibility of the digit. Moritz and Dominy acknowledge that the mechanisms behind these temperature fluctuations are unknown, through they indicate a unique, dynamic vascular supply that highlight the "thermal costs of a highly specialized sensory structure."

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