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An astonishing example of evolutionary convergence – why primate aye-aye is so similar to a squirrel?

Posted August 2, 2018

Aye-aye is the most unusual looking primate in the world with its bony fingers large eyes and fuzzy fur. Sadly, aye-aye is endangered due to loss of habitat and, believe it or not, being persecuted as a harbinger of evil. Interestingly, aye-aye was first thought to be related to squirrels, when it was brought from Madagascar to Europe in 1780. Now scientist from University of York took a look at how these unusual features developed.

Aye-aye is commonly targeted by locals in Madagascar because of superstitious beliefs. Image credit: Klaus Rassinger (Museum Wiesbaden) via Wikimedia (CC BY-SA 4.0)

Of course, aye-aye is not a rodent – it is a primate – it was correctly identified by the mid-19th Century. But still, it does look like a squirrel a lot, which shows how unrelated species can develop similar features. Now scientists used high-resolution microCT scanning to image the skulls of both squirrel and aye-aye. They mapped and modelled evolutionary convergence in their appearance. It turns out, a lot of similarities result from the need of high bite force. Squirrels need it to crack nuts and aye-aye uses its teeth to bite into tree bark to feed on wood-boring beetle larvae.

Even though these two species are unrelated and feed on different food, the way they are using their front teeth is similar. Furthermore, the force needed to crack a nut and to bite through the tree bark is also almost the same. This means that both species evolved similar features, which is an example where environmental factors override ancestry. And it is not the only example of evolutionary convergence known to science. For example, dolphins and sharks are also unrelated – one is a mammal and the other one is a fish. But they evolved to be almost the same shape due to living in the same environment. In the same way aye-aye looks like a squirrel, because both animals need strong jaws.

Scientists didn’t even need animal models for this research – they just borrowed skulls from a museum and made computer models of them. Dr Philip Cox, senior author of the study, said: “Our study shows the extent to which functional pressures, such as having to eat mechanically demanding food, can significantly alter an animal’s skeleton and result in distantly-related species evolving to resemble one another very closely”.

Aye-aye is now endangered. Around 50 aye-ayes are in the zoos around the world, but in the wild in Madagascar they are often targeted by locals. They believe aye-ayes mark people for death by pointing their fingers to them. Farmers think that aye-ayes are responsible for poor harvests. These are the reasons why aye-ayes are commonly killed on sight in Madagascar, but they are also in danger of extinction because of deforestation.


Source: University of York

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