Madagascar: Life at an evolutionary tangent

26/02/2014 12:33

Written by Daniel Austin

Cast adrift in the Indian Ocean, Madagascar has been separated from other landmasses for longer than any other island on earth. For tens of millions of years evolution has been at play here in virtual isolation, heading off at a tangent from the rest of the world.

This lengthy geographical separation is key to the otherworldliness of Madagascar's wildlife today. Between 80 and 90% of the island's plants and terrestrial animals exist nowhere else.

Lemurs

There are no giraffes or elephants – nor are there lions or tigers. Indeed Madagascar has no native large mammals and no representatives of the cat or dog families at all. Numerous other globally widespread animal groups are also conspicuously lacking, and their absence has been a significant factor in allowing so many new species to emerge and thrive on this remarkable island.

The primates are a case in point: Madagascar is the exclusive home of around a quarter of all the primate species on our planet. Yet there are no monkeys and there are no great apes. Aside from humans – who are not thought to have settled the island until a mere 2,000 years ago – all of the primate inhabitants belong to a group known as lemurs. And they exist in glorious variety: more than one hundred different species and subspecies – big and small, nocturnal and diurnal, social and solitary, adorably cute and downright freaky...

Crowned lemur Madagascar by Natalia Paklina, ShutterstockCrowned lemur © Natalia Paklina, Shutterstock

A single common ancestor gave rise to the diverse potpourri of lemurs that populate Madagascar's forests today. Sometime between 40 and 60 million years ago, it is thought that this ancestral lemur – a single pregnant female or perhaps a couple huddled together – was swept out to sea in a violent storm on the African coast. The creature was washed up on the shores of Madagascar, having survived the ocean crossing against all the odds, probably by clinging to a raft of floating vegetation. It would have crawled up the beach sodden, exhausted, and entirely unaware of the pioneering significance of its arrival. It was to prove a fortuitous journey for its kind indeed, because not long afterwards they were wiped out on mainland Africa in the face of growing competition from their newly evolved and more advanced monkey cousins.

Madagascar, on the other hand, would have been a far more welcoming place for the new arrivals. With few potential predators, and an inviting array of different habitats and ecological niches to exploit, the early lemurs rapidly spread out and diversified into numerous different forms in a process biologists call adaptive radiation. Each new species became specialised in making the most of a different environment and finding nourishment from a different range of foods.

As a group the lemurs flourished. Some developed powerful back legs to propel them from tree to tree as they leapt through the rainforest canopy; others adapted to spend more time foraging on the ground. Some evolved highly sensitive sight and hearing to allow them to be active at night; while others sought safety in numbers and began to live in social groups. One species adopted a diet consisting almost exclusively of bamboo shoots, ingesting a dose of cyanide each day that would kill a human. Another opted to live a semi-aquatic lifestyle in the reed beds of Madagascar's largest lake.

Arguably the most specialised, and certainly the most bizarre, of them all is the aye-aye. It truly is unique, so much so that the first European scientists to receive a specimen from early explorers scratched their heads in bemusement and eventually classified it as a type of squirrel. Only after much debate and several reclassifications was it finally agreed that the aye-aye is in fact a kind of lemur. It is the sole species not only of its genus, but in its entire family, meaning there is nothing else in existence remotely like it.

Aye-aye Madagascar by Daniel AustinThe aye-aye might just be the most bizarre creature in Madagascar © Daniel Austin

Aye-ayes are nocturnal cat-sized creatures with shaggy black coats, spending much of their lives high up in the canopy of both deciduous forests and rainforests. They have continually growing incisor teeth just like rodents (part of the reason they were first thought to be squirrels), huge satellite-dish ears that can be swivelled to locate the faintest sound with pinpoint accuracy, and a long, skeletally thin middle finger. These features collectively constitute a specialised toolkit for the aye-aye's favourite activity: grub hunting.

Tapping rapidly on the bark of a tree, an aye-aye listens for the echo that indicates a hollow chamber within. So sensitive are its ears that they can detect the movement of grubs beneath the bark. Once such a snack has been located, the sharp teeth are used to gnaw a small hole into which the slim bony finger can be inserted to winkle the grubs out into the aye-aye's waiting mouth.

In this way, the species has evolved to fill the ecological niche typically occupied throughout the rest of the world by woodpeckers – a group of birds which has never found its way to Madagascar. It is little wonder that those early taxonomists had difficulty placing such an enigmatic creature in the system of biological classification!

Verraux's sifaka Madagascar by Daniel AustinIsalo National Park is a good place to spot Verraux's sifaka © Daniel Austin

Most of Madagascar's several dozen protected areas provide the visitor with plenty of opportunities for lemur-watching. Easily seen in the spectacular canyons of Isalo National Park in the central south, for example, are the iconic ring-tailed lemurs,handsome teddy-bear-faced Verreaux's sifakas, and ever-curious red-fronted brown lemurs. Three further species are active in the reserve by night. Isalo is a large national park famed for its dramatic scenery of majestic sandstone outcrops. The area is excellent for hiking and popular with botanists for its numerous succulent plants, several of which are endemic to the local area.

Even greater numbers of lemur species can be seen in Madagascar's lush rainforest reserves, which are found in the east and north of the country. Andasibe-Mantadia National Park is the most easily accessible, yet also among the most rewarding. The highlight here is the indri – the largest of all lemurs. These endangered animals live in small family groups and resemble oversized, enchantingly fluffy, black-and-white koalas. Every morning their eerie wailing carries for kilometres across the forest as the groups call to one another. Being woken by this hauntingly beautiful song is a memory that stays with many visitors forever. And seeing the indri is a truly unique Madagascar experience, for no zoo has ever succeeded in keeping this species alive in captivity.

Chameleons

Just like we saw in the lemurs, dozens of chameleon species have evolved to occupy nearly every habitat in Madagascar; almost half of all species in existence worldwide are native to this one island. And they are fittingly outlandish characters. Everyone knows chameleons possess the extraordinary ability to turn different colours – some species much more strikingly than others – but, contrary to traditional wisdom, their colour changes normally reflect their mood rather than an effort to match their background. Some, on meeting a potential mate, or when faced with a rival trespassing on their territory, will puff themselves up and explode into an alarming kaleidoscopic display of polychromatic emotional expression.

Parson's chameleon Madagascar by Daniel AustinThe Parson's chameleon © Daniel Austin

A chameleon's eyeballs are armour-plated, with only the small pupil exposed. The eyes swivel like gun turrets and operate independently so that one can be used to look forwards whilst the other keeps watch for any danger from behind. But once a chameleon spots potential prey – a juicy cricket, perhaps – the two roving eyes are coupled for binocular vision. Focussing on the target with both eyes allows a three-dimensional view, so that distance can be judged, which is critical for the creature to unleash its deadly weapon accurately.ameleons possess the extraordinary ability to turn different colours – some species much more strikingly than others – but, contrary to traditional wisdom, their colour changes normally reflect their mood rather than an effort to match their background. Some, on meeting a potential mate, or when faced with a rival trespassing on their territory, will puff themselves up and explode into an alarming kaleidoscopic display of polychromatic emotional expression.

The highly elastic tongue of a chameleon can typically be extended by a full body length. It is unleashed with impressive accuracy and lightning speed, taking just three hundredths of a second to hit its prey – faster than the perception of the human eye and, more importantly, faster than most insects' reactions. The tongue's tip is slightly sticky with mucus but actually grabs the prey by forming a suction cup. It is then swiftly reeled back in to be crunched up by strong jaws and a set of tiny sharp teeth.

At little more than two percent of the length of a giant Parson's chameleon, the pygmy stump-tailed chameleon is the world's smallest – and is another Madagascar resident. Considerably smaller even than some of the insects with which they share their forest floor habitat, these miniature lizards are among the tiniest of all reptiles, yet the keen-eyed guides at Montagne d'Ambre National Park in the far north of the country are adept at finding them for the delight and amazement of visitors.

Montagne d'Ambre is the oldest of the national parks, protecting an isolated area of montane rainforest with a well maintained trail system. There is a wonderful array of chameleons here, in addition to the pygmy stump-tail, as well as geckos and frogs in huge variety. Birding is good in the park, with a number of local endemics, lemurs are normally found, and the ring-tailed mongoose is also a frequent sighting. Among the plant life on show are the rarest baobab species, several palms, and countless beautiful orchids – with more than a thousand species, Madagascar has more orchids than the whole of mainland Africa.

Stump-tailed chameleon Madagascar by Daniel AustinThe stump-tailed chameleon is one of Madagascar's smallest chameleons © Daniel Austin

Now, more than ever, is the time to visit the country. Despite more than ninety percent of its original forest having been lost, Madagascar is still arguably the most important of all biodiversity hotspots. The diversity of flora and fauna is staggering, but increasingly under threat. As the country grapples with rising levels of poverty, a rapidly growing population in need of land for crops and charcoal to cook with, illegal logging of precious hardwoods, slash-and-burn agriculture, oil and mining projects with potential serious environmental impacts, land erosion, corruption and political difficulties, it is clear that massive conservation challenges lie ahead.

Ecotourism provides local employment and brings in much-needed revenue to help Madagascar tackle some of these issues, whilst at the same time reinforcing the message that the country's natural heritage is a valuable asset worth protecting.


This article first appeared in Compass magazine and is reproduced here with the kind permission of the editor.


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