The wonderfully weird world of tenrecs

With just a quick glance at the image above, it's easy to see how someone could mistake a hedgehog tenrec for an actual hedgehog. 

But what makes these lookalikes peculiar is that they last shared a common ancestor some 160 million years ago. In fact, tenrecs are more closely related to elephants than they are to hedgehogs!

Discover why these unusual mammals deserve more of the limelight.

What is a tenrec?

Tenrecs are a group of mammals mainly found on Madagascar. Like many of this large island's plants and animals, most species of tenrec are endemic, meaning they aren't naturally found anywhere else in the world.

What do tenrecs eat and what eats them?

For the most part, tenrecs eat invertebrates, such as worms, insects and their larvae, though some are known to eat small vertebrates, such as baby snakes and amphibians.

Tenrecs are food for birds of prey, snakes and possibly fossa too. They are also sometimes killed by domestic cats and dogs, and small individuals may even be eaten by larger members of their species. 

How many tenrec species are there?

There are about 36 species of tenrec, all belonging to a family called Tenrecidae. But despite being close relatives, these animals don't look much like one another at all.

'Tenrecs are wonderfully weird,' says senior researcher Dr Natalie Cooper, who's spent time in Madagascar studying these animals. 'They are my favourite group of mammals.'

Tenrecs range from species the size of a small dog to tiny shrew-like creatures that Natalie describes as being 'about the size of a Wotsit crisp'. In between there are species that look a lot like moles, rodents and hedgehogs. Then there are some species that are so unique looking that there's nothing on Earth you can directly compare them to. 

This is unusual! Take hummingbirds for example, they are a large group of around 360 species that all belong to the family Trochilidae. Like tenrecs, these birds are closely related, and while they vary a little from species to species, they generally have quite a similar body plan - being small with a long, pointed beak.

The tenrec family doesn't share a body shape blueprint in the same way. Instead, they are an amazing example of adaptive radiation or divergent evolution.

Madagascar broke off from mainland Africa around 170 million years ago. In the time since, it's thought that the ancestors of some of modern-day Madagascar's wildlife, including tenrecs, inadvertently reached the island having rafted across the Mozambique Channel. From there, the tenrecs' ancestors would have adapted to the variety of habitats on Madagascar, slowly diverging into the multitude of different looking species we see today.

While tenrec species might not look much like one another, they do bear striking similarities to other animals not found on Madagascar.

For example, there's the greater hedgehog tenrec, Setifer setosus, and the lesser hedgehog tenrec, Echinops telfairi, which – as their names suggest – both look unmistakably like hedgehogs, with backs covered in short, sharp spines.

There are also about 20 species of shrew tenrec that for most people would be impossible to tell apart from actual shrews - species belonging to the family Soricidae.

Despite looking similar, these tenrecs aren't actually closely related to any of the animals they look like. For example, by looking at the mammal family tree, we can see that the lineages that led to tenrecs and hedgehogs split about 160 million years ago.

In fact, tenrecs belong to the order Afrotheria, which includes several mammals that are either found in Africa or that originated from the continent. This means tenrecs are more closely related to animals such as elephants, manatees and aardvarks than they are to any of the mammals they look like.

So how have tenrecs ended up looking so much like hedgehogs, shrews, rodents and moles? Scientists think the answer is convergent evolution. 

What is convergent evolution?

Convergent evolution is when animals evolve similar solutions to similar problems.

In natural selection, selection pressures cause an animal to adapt to a particular environment. These could be in response to the habitat, food or predators for example.

In the case of tenrecs, this would mean that these animals faced selection pressures on Madagascar that were similar to those experienced by animals in other parts of the world. In response, over time they adapted to take similar shapes and forms to survive in similar ways.

For example, the ancestors of hedgehogs and hedgehog tenrecs likely evolved their similar spiny armour in response to needing a way to protect themselves from predators.

Moles and mole tenrecs mostly live underground. To successfully survive in this subterranean habitat, both have evolved modified forelimbs that help them to dig efficiently.

Tenrecs aren't the only example of convergent evolution. Dolphins and the group of ancient marine reptiles ichthyosaurs are another example. They evolved similar streamlined body shapes to help them to move swiftly through water.

Colugos, sugar gliders, greater gliders and flying squirrels are another example. These have all evolved big flaps of skin to help them move through the air between trees. The tiny dinosaur Amboptyrex also evolved a similar approach 160 million years ago during the Jurassic Period.

Tenrecs and their unique abilities

A few tenrec species have developed characteristics not commonly seen in other mammals.

Lowland streaked tenrecs make ultrasonic noises

The lowland streaked tenrec, Hemicentetes semispinosus, is covered in spines, which it mostly uses for defence. It will raise up its spines and jump at prospective predators to ward them off.

'They're like a hedgehog crossed with a shrew, crossed with fury,' jokes Natalie. 'They are very angry little things.'

However, some of the spines have another use. The group of closely gathered spikes on its lower back rub together to make sound. This is known as stridulation and is something also seen in insects, such as cicadas, which use their wings to make a buzzing sound. 

Humans can't hear the noises tenrecs make with their spines. It's thought that the tenrecs might be using these ultrasonic sounds to communicate with their young as they traverse the dense understory of their forest habitat.

One seemingly conspicuous thing about lowland streaked tenrecs is their colour. With their spiny bodies and their bold black-and-yellow stripes that are reminiscent of a bumblebee or wasp, these animals look like something straight out of the world of Pokémon.

The reason for their bright colours is a bit of a mystery. Conspicuous colouration or markings, known as aposematic colouration, is often evolved to put off predators, but scientists aren't certain whether that's why it evolved in these tenrecs. They might seem highly visible, but surrounded by leaves on the forest floor, they're probably still quite well camouflaged.

'It might just be one of those evolutionary quirks,' says Natalie. 'Not everything we see in the natural world is selected for, some of it persists because it doesn't make any difference to the survival of individuals one way or the other.'

Common tenrecs have loads of babies

Tailless tenrecs, Tenrec ecaudatus, are the largest species in the Tenrecidae family. They can grow up to 39 centimetres in length, making them about the size of a small dog.

Despite Tenrec ecaudatus also being known as the common tenrec, this species actually has several uncommon characteristics, and in fact holds two quirky records. Firstly, they produce the most offspring of any mammal, having up to 30 babies at a time. Secondly, they have the most nipples of any species of mammal - a staggering 36 of them!

Natalie says, 'A lot of tenrecs' life history traits - such as how many babies they have, how long they gestate them for and how long they look after them for - just doesn't really fit with other small mammals'.

Shrew tenrecs and echolocation

Scientists think that some shrew tenrecs can echolocate and that they potentially use this ability to find food, a bit like bats do. It's something Natalie spent time researching in Madagascar.

'The more research we did, the more it seems lots of small mammals can - it's partly about how you define echolocation and how you detect it.'

Experiments in the 1960s found that tenrecs were able to find food even when they couldn't see, suggesting that they're able to echolocate. But it's quite hard to prove it.

'When you put the tenrecs in a lab setting and they're walking around, you can just hear their little nails on the surfaces as they move. You can't necessarily hear or record the sub-vocalisations they're making,' explains Natalie.

Are tenrecs endangered?

Habitat loss and fragmentation are among the greatest threats to tenrecs' survival. Tenrecs are mostly found in intact forests, which are dwindling in Madagascar due to widespread deforestation. The country has lost about 40% of its forests in the last 50 years, and non-native plants, such as eucalyptus, have been introduced to try and solve the island's forestry issues.

Other threats to tenrecs include uncontrolled fires, the introduction of non-native animals and being hunted for bushmeat. The web-footed tenrec, Microgale mergulus, which is a semi-aquatic species, reportedly also falls foul of eel and crayfish traps, drowning when it gets stuck inside.

In the longer term, climate change is expected to alter tenrecs' habitats and ranges. Some experts have expressed concern for mountain-dwelling species in particular, as they have less opportunities to disperse, so could be more vulnerable to any change in the climate.

Only six species of tenrec are considered to be threatened with extinction, but experts think that even species currently categorised as Least Concern on the IUCN Red List are probably in decline due to continued habitat loss.

As with many of Madagascar's plants and animals, tenrecs need to be monitored and protected to ensure their survival.