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The Enigmatic Aye-Aye: An Alcoholic Primate-Rodent Convergence

The aye aye is a primate that is a fusion of a lemur and a rodent and it puzzles scientists. / Photo by: Konstantin Kalishko via 123RF


There is one primate in particular whose evolution has been paralleled by human understanding of the animal in question: Daubentonia madagascariensis. Also known as the aye-aye, this primate is one we used to think was related to squirrels, and we used to relegate it to the status of a rodent. Scientists have since realized that it is, in fact, a primate in that they have relatively large brains compared to other mammals, they have opposable thumbs, and they rely heavily on stereoscopic vision as their primary sensory system. Along with Nycticebus coucang, aye-aye was just found by researchers from Dartmouth College to have the innate ability to discern the different concentrations of alcohol from one substance to another; both were also found to have predilections toward beverages with the highest available concentrations of said alcohol.


The aye-aye is especially bizarre, though, because its features do at least aesthetically betray its primatehood, but this has only made it a long-time target for evolutionists. Given that the primate track is our own evolutionary track, aye-aye represents a link in the chain that seems inscrutable at both first and second glances. A new study published by scientists from the University of York in England has revealed that the aye-aye is, in fact, adapting more and more to be like squirrels to the extent that the research team and others throughout the scientific community worldwide have begun to describe this as an “evolutionary convergence,” an otherwise phenomenologically improvable concept.

Aye ayes are known to be alcoholic primates and they search for any food that contains alcohol like fruits. / Photo by: johny007pan via 123RF


These little, alcoholic primates find alcohol wherever it can be found in nature—fruits, saps, fermented nectars, et cetera. New reports are indicating that this is, in fact, an extra source of calories for other non-human primates like Nycticebus coucang, also known as the slow loris, which is a nocturnal primate. Both, in fact, are nocturnal primates, and slow lorises frequently suck fermented nectar from the bertam palm indigenous to Southeast Asia, and its alcohol concentration averages around 0.6%. Aye-ayes are the largest lemur of the night, indigenous to Madagascar, and their behavior is reportedly similar. “Aye-ayes are essentially primate woodpeckers,” according to Nathaniel Dominy, a co-author on the Dartmouth paper.

One scientist described the hands of the aye aye and he told that it was different from other lemurs. / Photo by: Ryan Somma via Flickr


“They have an elongated, bony finger for detecting and extracting grubs from decaying tree trunks. It is puzzling that they can digest alcohol so efficiently,” Dominy adds. It’s one of many bizarre adaptations in the evolutionary progression of aye-ayes, and they apparently spend around a fifth of their total feeding time during wet seasons just on the so-called traveler’s palm from which they extract fermented nectar. The York study, meanwhile, examined the evolution of the aye-aye more broadly yet more pointedly, and rather than comparing them to another kind of primate, they compared the aye-aye to squirrels. Led by Philip Cox of Hull York Medical College, the team imaged the skulls of a squirrel and an aye-aye via high-res microCAT scan. This enabled them to map out and model the apparent convergence of the two species’ evolutionary tracks, so to speak.


The York paper reads: “The aye-aye is a highly unusual lemuriform primate that has evolved a dentition similar to that of rodents: it possesses large, ever-growing incisors which it uses to strip the bark from trees in order to feed on wood-boring beetle larvae.” They created 3D reconstructions of the mandibles and skulls of both squirrels and aye-ayes, and they did the same for a plethora of closely related rodents and primates. “Indeed, such is the similarity that some of the earliest classifications of the aye-aye placed it in the squirrel genus Sciurus. We aimed to test the degree of convergence between the skulls and lower jaws of squirrels and the aye-aye.”


They also took coordinates from those 3D models and input them into a data analysis program. They mapped out the evolutionary trees of the Sciurus squirrels and the aye-aye so that they could see the areas in which various squirrel species inclined toward the aye-aye. The ancestries don’t align in any way or have any known connection in history, yet the skull and jaw of the aye-aye converged with those of several squirrel species. These findings imply the demand for greater bite force affected this adaptation in the aye-aye, and they also suggest that, just for meeting this demand, the entire skull and jaw structures were adapted. It’s not an adaptation that’s easily explained, yet it remains easier to explain than the aye-aye’s affinity for alcoholism.


“If the nectar is fermented, then the hyper-efficient alcohol digestion would make ecological sense,” says Samuel Gochman, the Dartmouth study’s lead researcher. “Since we didn’t have access to such flowering trees for the study, instead, we tested whether aye-ayes are attracted to alcohol in a nectar-simulating solution of sucrose.” They carried out multiple-choice experiments for feeding two aye-ayes and one slow loris at the Duke Lemur Center based in North Carolina. Aye-ayes distinguished between tap water and various sucrose compounds with differing levels of alcohol concentration, and they adjusted intake to get the most alcohol they could, dispensing with water altogether. Afterward, aye-ayes were fingering the empty containers like they wanted more, and they showed no physical or behavioral indications of inebriation.



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