The Aye Aye (Daubentonia madagascarensis) is a strange, squirrel like primate unique to Madagascar. With its strange bright orange eyes, shaggy black fur and freakishly long finger, this elusive, nocturnal primate is unfortunately seen as a bad omen in the eyes of many Malagsy people. To add to this, its native forests are being cut down at an alarming rate, prompting the IUCN to list the aye aye as endangered in 2009 and place the primate on Appendix 1 of CITES. It is the world’s largest nocturnal primate and the only member of the lemur family Daubentoniidae, so the extinction of this species would be a terrible loss to the world’s biodiversity.
Image from Edge of Existence
Taxonomic controversy: the natural history of the aye aye
The aye aye was discovered by French zoologist Louis J.M Daubenton in 1780, hence the Latin name given to the species. Although no one really knows the exact reason for the unusual name aye aye, some people posited that the name is derived from the supposed ‘hai-hai’ call of the primate, but scientists studying the aye-aye have debunked this, saying the animal makes no such noise. Instead, it is suspected naturalist Pierre Sonnerat, who studied the animal in Madagascar, chose the name from the cries of fear this species evoked in villagers who viewed the aye-aye as a harbinger of death. In the dialect of local villagers, ‘heh-heh’ or ‘hey-hey’ is generally taken to mean ‘I don’t know’ and could have been the name given to the aye-aye by superstitious villagers, who either couldn’t explain what they had seen or didn’t want to speak its name out of fear.
An illustration of the lemur family tree. Those names with the crossbones next to them indicate the species is extinct. Image from ‘Phylogeny and divergence times of lemurs inferred with recent and ancient fossils in the tree.’ Herrera, J.P. and Davalos, L.M.
For many years there were arguments over the correct taxonomic position for this unusual looking primate. At one time classed as a marsupial, another time classed as a rodent due to its large front teeth, eventually the aye-aye was correctly placed into the Lemuriform primates, a lineage consisting of 5 main groups:
- Indriidae: (19 species in 3 genera) including the indris and sifakas.
- Lepilemuridae: (26 species in 1 genera) including the sportive lemurs.
- Cheirogaleidae: (30 species in 5 genera) including the dwarf and mouse lemurs.
- Lemuridae: (25 species in 5 genera) including the true and bamboo lemurs.
- Daubentonidae (1 species in 1 genera) including the aye aye.
Lemurs split off from the rest of the primate family along with the lorisiform group, which contains African and Asian nocturnal primates such as slow lorises, galagos and tarsiers. This split occurred between sixty six and eighty four million years ago, and led to the tooth combed primate clade, or strepsirrhini, a sister clade to all the other primate species. Once lemur ancestors reached Madagascar and it split away from Africa and India, around 50 million years ago, the lemur species we see today began to evolve. The Daubentonidae arose early in lemur evolutionary history, being the first to diverge. Fossil remains discovered in the South of Madagascar revealed there is an extinct species of aye aye that once roamed the island; the giant aye aye (Daubentonia robusta), which was estimated to be 2-2.5 times larger than the extant species, although this is just a hypothesis, as only fossil fragments have ever been found, such as a mandible and part of an eye socket. This creature lived until fairly recently (well, at least in evolutionary terms!), present on the island in the last 2000 years, and no one knows exactly what led to its extinction, although we can make a fair guess that humans had a hand in it somewhere, as we so often do unfortunately!
Habitat and Ecology
The aye aye can be found across the whole of Madagascar, albeit in very fragmented, low-density populations. Although there have been improvements in population studies over the years as Madagascar and its habitat becomes more accessible to researchers, this elusive animal, with its nocturnal nature and large ranges, is still a tricky one to study. They are found mainly in the eastern rainforest belt and the dry forests of the north-western and northern regions of the island, although there are small populations elsewhere. In the 1960’s, two populations of 9 individuals were introduced to the island of Nosy Mangabe, off the North-eastern coast of Madagascar, and the island Ile Roger, although recent reports from scientists and locals suggests the animals there are long gone, and only the Nosy Mangabe population still exists. Unfortunately, despite their extensive range, Madagascar has lost 37% of its biodiversity rich forests between 1973 and 2014, with an estimated deforestation rate of 1.1% per year between 2010 and 2014. And despite the best efforts of NGOs and conservationists, this trend seems set to continue.
Aye aye aye! What weird physiology!
Given the odd appearance and physiology of the aye-aye, it is easy to understand why early naturalists couldn’t agree on where to place this unusual mammal. Like rodents, the aye aye’s chisel like front teeth never stop growing, likely an adaptation to their diet of food with tough shells and to allow them to gouge out trunks for access to food inside. Not only are their teeth distinctly rodent like, but their skull and muscular structure is too; the facial muscles are designed to help the aye-aye to gnaw away at wood and swivel their ears to listen for larvae prey too! Their especially tough, adapted skull can buffer the worst of the blows of repeatedly chiselling away at trunks. Their large ears are also a special adaptation; most scientists believe aye-ayes can hear larvae moving around inside wood cavities as a kind of echolocation. In many behavioural studies they would only be attracted to logs containing live insects, despite the fact the logs were all the same visually. Relative to their size and lifestyle, the aye-aye has a high level of encephalization, or brain development. This may be due to their feeding ecology, using complex sensory-motor skills to forage for and extract food, although behavioural studies testing advanced tool use suggest that this behaviour is simply trial and error and not proof of advanced cognition. Brainy they may be, but not so bright perhaps?
Knock on wood: dinnertime for the aye-aye
An aye-aye using its fantastically adapted middle finger to forage inside a branch.
Perhaps the most unusual (and that’s saying something!) aspect of aye-aye physiology is their hands, with the long middle finger accounting for 45% of the trunk length, proportionally the longest digit of any primate. This probelike middle finger is vital for this species’ feeding ecology, a behaviour called ‘tap-foraging’. The aye-aye crouches low to a branch and it gently taps the wood with its long middle finger, nose down and ears pointing forwards as they listen for the quiet sounds of bark beetle larvae trundling through cavities in the wood. Once they have located a juicy bug, they use their chisel teeth to gnaw a hole, then use their specialised middle finger to scoop out their snack. This is why this middle finger has independent digit control to allow the aye-aye to get into places few other primates could; no larvae are safe! They are also known to forage nectar from the bright blue flower Ravenala madagascariensis and use their specialised digit to reach in between the petals and get a sugary treat. In fact, specialised opsin genes, which are involved with vision and across the tree of life play an important role in animal sensory systems, found in the aye-aye give the species sensitivity to blue wavelengths, which may help them to locate the blue flowers whose nectar they love so much. Some scientists hypothesise however that this specialised vision is actually used to detect urine markings, which may play an important role in mating behaviour or communication between individuals.
And the aye-aye keeps surprising us! As recently as 2019, primate researcher Adam Hartstone Rose and his team at North Carolina State University discovered a previously unknown ‘pseudo-thumb’, a tiny sixth digit that sprouts out of their palms, whilst dissecting an individual that had died from natural causes in the wild. CT scans revealed that this ‘pseudo-thumb’ can move in three directions and even has its own fingerprint! The other curious features of the aye-ayes’ hand has long overshadowed this little nub of bone, and now researchers want to view aye-ayes climbing in the wild as they suspect it helps this arboreal primate cling onto branches whilst it uses that swivelling finger to ferret out dinner.
A close up of the pseudothumb and the fleshy pad above it. Image from researcher Adam Hartstone Rose
Fading forests and Fady; the struggle for aye-aye survival
Although long considered to naturally exist at low densities, as scientific research became more accessible in Madagascar, conservationists soon realised the situation for the aye-aye was more dire than initially thought, prompting the IUCN to list the species as endangered in 2008. It now holds the dubious privilege of being in the top 25 most endangered primates in the world.
The aye-aye naturally occurs at low densities as it has one of the largest range requirements of any species in the Lemuriform clade and this need for space is possibly the most significant issue facing the primate right now. Madagascar is suffering from serious deforestation, with the particularly devastating slash and burn forestry the key tactic amongst locals to clear land for agriculture of important cash crops such as vanilla, clove, cashew, and coffee. Ecologically important trees are felled for raw materials for boats and houses in huge numbers annually, and more still are burned to produce charcoal. The once lushly forested island is now 80% prairie, with these ecologically bereft ecosystems unable to support more than the most basic grasses, as essential nutrients and soil support have been stripped away. Unfortunately, the issues facing Madagascar’s forests are complex. The island has long been burdened with serious economic decline and debt, with poverty crippling the locals, their only way out of such desperate situations to cut down the forests for crop production. There are 144 protected parks in Madagascar, with aye-ayes persisting in many of them, but in 2020 even the president of Madagascar admitted that these areas are failing to preserve ecosystems and their biodiversity. A fair assessment, given that in 2018 the country lost the largest proportion of tropical forest of anywhere in the world. Longstanding poverty and social inequalities are understandably competing with conservation for funding. More communication between conservationists and locals is ultimately needed to ensure there is a balance between protecting the vital biodiversity in Madagascar without disadvantaging local people already suffering abject poverty in some parts of the island.
Madagascar is an island rich with cultural traditions, and unfortunately some of these legends have put the aye-aye’s survival at risk. Although some species of lemur are sacred, as Malagsy beliefs state loved ones often turn into the charismatic primates, and therefore protected from hunting, unfortunately the aye-aye does not benefit from this cultural protection. Considered ‘Fady’ or taboo, with its strange looks and elusive nature, the aye-aye is often considered a harbinger of death, and whichever village it approaches will immediately suffer a terrible fate. Often, aye-ayes are killed before they can supposedly enact their terrible magic on the village, and their carcasses displayed on a post. There are frequently killed as they are viewed as a pest, or even for their meat in areas where food can be scarce: it’s unlikely you would get as filling meal from an aye-aye!
Despite all these pressures, there is hope for the world’s most unusual primate. In 2020, a study on cultural attitudes towards the aye-aye had some surprising results. Despite the well-known fear of the aye-aye, in the survey of local attitudes, the survey found that only 47% of respondents had a negative opinion of the aye-aye, with the remaining 53% feeling neutral or even positive towards the aye-aye. This may not seem so great but given the long-standing cultural traditions on Madagascar and lack of education around the primate, this is a really surprising result. In fact, many villagers reported being pleased to see the aye-aye around their farms as they have been observed acting as pest control for several important crops, most notably clove trees, where they feed on the larvae of pest insects and keep their numbers manageable. More people than expected showed a genuine curiosity in the aye-aye and the important ecological role it has. This is extremely positive news and the perfect place to kick start community-based conservation.
The IUCN has always highlighted the importance of population monitoring in conservation; without understanding the structure and numbers of populations, it is almost impossible to enact good conservation management. Some species can be tracked relatively easily, but a nocturnal primate is not one such species. In the case of the aye-aye, new technologies like eDNA are proposed to be the way forward to monitor and understand aye-aye populations. eDNA, or environmental DNA, involves taking samples from the environment, from soil, water, vegetation and a plethora of other sources (even the air in some cases!) and extracting DNA from it. Any time an organism interacts with its environment it expels DNA into the environment, and so this DNA can be investigated, and the organisms present in a location revealed, without ever having to see the animal or even traces of it, such as tracks or faeces, which can be notoriously unreliable depending on the animal. With this technique, scientists can use databases of genetic information to trace the individual down to the genus level, taking a lot of the guesswork out of field science!
The aye-aye is also an EDGE species, classed by the Zoological Society of London as Evolutionarily Distinct and Globally Endangered. Given that the aye-aye is the only extant species of its genus left, it isn’t surprising that this bizarre little animal fits into this programme. In fact, it ranks as number 16 on the EDGE list of endangered mammals. EDGE fellow Rotsinomena Andriamisedra has been employed by ZSL to carry out research on the aye-aye and working with the Group d’Etude et de Reserche sur les Primates out of Manombo Forest Reserve, she is working with communities to improve education and carry out research to better understand the ecology and status of the aye-aye. Check out her project work at https://www.edgeofexistence.org/fellow/rotsi-andriamisedra/
As a kind of insurance policy for this struggling species, as of 2019 there are 50 aye-ayes in captivity in various zoological institutes around the world. In the 1970s breeding programmes were set up at several accredited institutions, including Durrell Wildlife Conservation Trust and London Zoo. In fact, on the 19th of May this year (2021), Sally the aye-aye gave birth to a baby as part of the European breeding programme. However, despite these small successes, there is yet to be a 2nd generation born since the programme’s initiation in the 1970s. This makes every aye-aye born a very precious thing indeed.
Conservation tips, organizations and heroes!
- The Durrell Conservation Trust: a part of the Madagascar Fauna group, the trust has worked since 1964 to learn more about captive breeding in the aye-aye, as well conducting research and habitat protection programmes. Many Madagascan students have enrolled in Durrell’s International Training Centre and have taken the vital conservation skills they learned home.
- The Lemur Conservation Foundation: set up in Mykka city in Florida by museum educator Penelope Brody Sanders in 1996, which a centre now in Madagascar. The foundation aims to educate people about lemurs and the trails they are facing in the wild, as well as conducting extensive behavioural and ecological research to improve outcomes for all lemur species. Check out their work at https://www.lemurreserve.org/research/. You can adopt a lemur through their website and help them fund vital lemur research and conservation.
- For anyone who lives in the Sarasota-Bradenton area, they offer husbandry internships and volunteering positions if you want to muck in!
- If you also want to help the vital Madagascan rainforests, visit the rainforest trusts’ Madagascan forest project at https://www.rainforesttrust.org/projects/saving-the-lost-forest-of-madagascar/ to learn how they are empowering the local Bara people to find workable solutions to deforestation. They have links to donate and other ways you can get involved to help the cause of our precious rainforests.
- A great way to help the aye-aye is simply to spread the word about these awesome creatures and bust those myths about them! The more people hear about this crazy little critter, the more people can help the cause! In fact, why don’t you send this episode to a friend and educate them about the weird and wonderful aye-aye.
References
Aylward, M.L. Sullivan, A.P. Perry, G.H. Johnson, S.E. and Louis Jr, E.E. (2018) ‘An environmental DNA sampling method for aye-ayes from their feeding traces.’ Ecology and Evolution, 31(8)
Feistner, A.T.C. and Carroll, J.B. (1993) ‘Breeding aye-ayes: an aid to preserving biodiversity.’ Biodiversity and Conservation, 2, pp 283-289
Horvarth, J.E. Weisrock, Embry, S.L. Fiorentino, I. Balhoff, J. Kappeler, P. Wray, G. Willard, H. and Yoder, A. (2008) ‘Development and application of a phylogenetic toolkit: resolving the evolutionary history of Madagascar’s lemurs.’ Genome Research, 18(3), pp 489-499
http://www.edgeofexistence.org/species/aye-aye/
https://ielc.libguides.com/sdzg/factsheets/ayeaye/taxonomy
https://www.iucnredlist.org/species/6302/16114609
https://www.nationalgeographic.co.uk/animals/2019/10/bizarre-primate-has-newly-discovered-digit
Mittermeier, R.A. Konstant, W.R. Hawkins, F. and Louis, E.E. (2010) Lemurs of Madagascar, Conservation International Tropical
Morris, P.J.R. Cobb, S.N.F. and Cox, P.G. (2018) ‘Convergent evolution in the Euarchontoglires.’ Biology Letters
Neudert, R. Ganzhorn, J.U. and Watzold, F. (2017) ‘Global benefits and local costs- the dilemma of tropical forest conservation: a review of the situation in Madagascar.’ Environmental Conservation, 44(1), pp 82-96
Perry, G.H. Louis Jr, E.E. Ratan, A. Bedoya-Reina, O.C. Burhans, R.C. Lei, R. Johnson, S.E. Schuster, S.C. and Miller, W. (2013) ‘Aye-aye population genomic analyses highlight an important center of endemism in northern Madagascar.’ Proceedings of the Natural Academy of Sciences, 110(15), pp 5823-5828
Perry, G.H. Martin, R.D. and Verrelli, B.C. (2007) ‘Signatures of functional constraint at aye-aye opsin genes: the potential of adaptive colour vision in a nocturnal primate.’ Molecular Biology and Evolution, 24(9), pp 1963-70
Randimbiharinirina, R.D. Richter, T. Raharivololana, B.M. Rastsimbazafy, J.H. and Schußler, D. (2021) ‘To tell a different story: unexpected diversity in local attitudes towards endangered Aye-ayes Daubentonia madagascariensis, offers new opportunities for conservation.’ People and Nature
Sterling, E. and Mccreless, E. (2007) ‘Adaptations in Aye-aye; a review.’ Lemurs
Yoder, A.D. and Yang, Z. (2004) ‘Divergence dates for Malagasy Lemurs estimated from multiple gene loci: geological and evolutionary context.’ Molecular Ecology, 13(4), pp 757-73
