Bizarre mammals call using quills

By Ella Davies
Earth News reporter
Sir David Attenborough describes how the tenrecs rub their spines together to communicate in the dark forest

Unique hedgehog-like mammals have been filmed using their quills to communicate.

A BBC film crew captured footage of the streaked tenrecs in the eastern rainforests of Madagascar.

By rubbing together specialised quills on their backs, the tenrecs made high pitch ultrasound calls to each other in the forest undergrowth.

The footage is the first of a mammal communicating in this way, a technique called "stridulation".

The lowland streaked tenrec (Hemicentetes semispinosus) resembles both a hedgehog and a shrew with black and yellow stripes, and is found only in Madagascar.

A film crew hoping to feature these visually striking animals in the BBC series Madagascar faced a number of challenges.

As eaters of invertebrates, particularly earthworms, the best time of year to film the tenrecs was the rainy season.

The time of day also played a considerable role.

"They're active during the day and during the night but they hide a lot so it can be difficult," said local conservation expert Dr Rainer Dolch who assisted the crew in their search.

Despite being crepuscular and used to twilight conditions, the streaked tenrecs were unconcerned by the crew's lights as they foraged on the forest floor.

However, recording the sounds the animals made required more sophisticated technology.

Streaked tenrecs are known to communicate using high-pitch tongue clicks when foraging but many of the sounds are beyond human hearing.

"Most of the sounds are too high for us to hear so we took a bat detector so that we could also pick up ultrasonic noises," said researcher Emma Napper.

Using the bat detector, the filmmakers found that the seemingly "quiet" mammals were constantly communicating.

Scientists have theorised that tenrecs could also be using high pitched calls to echolocate in the dark forest, finding their way with sound rather than sight in a similar way to bats.

The film crew were also hoping to record evidence of a particularly bizarre audio behaviour, unique to streaked tenrecs.

In the 1960s, streaked tenrecs were found to communicate using specialised quills on their backs, rubbing them together to make high pitch ultrasound calls.

The tenrec's pale 'stridulating' quills are very different to those found on the rest of its body.

Animals such as crickets, beetles and vipers are known to communicate by rubbing together body parts in behaviour known as "stridulation".

However, stridulation had never been filmed before in mammals.

The crew captured footage of the tenrecs rubbing together these specialist quills on their back as they foraged.

Few studies have been made to investigate why streaked tenrecs communicate both vocally and via their quills but they are currently the only mammals known to do so.

Streaked tenrecs raise their crown of spines when threatenedTheir main defence is thrusting these detachable spines into predatorsCommon predators of tenrecs include Malagasy civets, fossas and mongooses

Tenrecs are a diverse family of mammals that resemble shrews, mice and even otters.

There are approximately 30 species in Madagascar including the rare web-footed aquatic tenrec (Limnogale mergulus) and the spiny, rabbit-sized common tenrec (Tenrec ecaudatus).

The rich diversity of tenrecs on Madagascar is explained by scientists as evidence of the Darwinian theory of "adaptive radiation".

They propose that the tenrecs evolved from a single ancestor 60 million years ago, possibly a mammal that floated across the sea from mainland Africa.

With no other mammals on the island at the time, the different species of tenrecs are thought to have evolved into a diverse family as they adapted to Madagascar's wide variety of environments, free from competition.

Madagascar continues on BBC TWO at 2000 GMT on Wednesday, February 16.

View the original article here

This post was made using the Auto Blogging Software from WebMagnates.org This line will not appear when posts are made after activating the software to full version.

Mammals 'floated to Madagascar'

The ancestors of the current mammals found on the island of Madagascar could have been transported on floating vegetation from Africa, a study says.

Researchers modelled ancient ocean currents and found that favourable conditions existed in the same period as when mammals arrived on the island.

The idea of "rafting" first emerged in 1940, but some argued that a "land bridge" allowed animals to walk there.

The findings have been published online on the Nature website.

Madagascar, the fourth largest island on the planet, is deemed one of the world's biological hotspots.

Because of its isolation, most of its mammals, half its birds, and many of its plant species exist nowhere else on Earth.

The first mammals are believed to have appeared on the island about 60 million years ago, 100 million years after the landmass was thought to have separated from Africa.

This led to the emergence of two main hypotheses on how mammals managed to inhabit the island: via a "land bridge" or floating vegetation.

Ticket to ride

Using a climate model used by the Intergovernmental Panel on Climate Change (IPCC), co-author Matthew Huber - a palaeoclimate modeller at Purdue University in Indiana, US - adapted it to shed light on the past.

"I had been doing these simulations for some time," he told BBC News.

"The paper's lead author (Dr Jason Ali from the University of Hong Kong) asked me to look at the Madagascar region because he thought that the ocean currents were different during that time.

"I looked, and - sure enough - the ocean currents went in the opposite direction than they do today," he explained.

"The reason is primarily because, in the past, both Madagascar and Africa were 15 degrees further south.

This meant that the 430km (270 mile) Mozambique Channel that separates the two landmasses was located in a different ocean "gyre" (circular ocean current), which had an important impact on the direction and strength of the currents within the channel.

Dr Huber said that the model showed that this provided the right conditions to allow mammals to be transported across the channel.

"What the model suggests is that occasionally - say one month in 100 years - the currents were strong enough to allow a raft, for example a large log, carrying a family of lemurs to make the journey in about three weeks," he explained.

"Biologists and palaeontologists say that rafting is the only sensible way for this [dispersal] to have happened. But the problem has always been the currents."

"When you looked at present ocean currents, the journey is impossible. "So scientists have been stuck because when you are faced with impossibilities, what do you do?"

Current thinking

As a result, a number of scientists favoured the theory that a land bridge existed in the past.

But the theory would have required a "radical rethinking of the region's plate tectonics", Dr Huber explained.

"What we have done is resolved this conundrum by saying that ocean currents were actually different in the past.

"So it was possible - not probable, but possible."

The idea of mammals being transported on "rafts" of vegetation was first mooted back in 1940 by US researcher George Simpson.

He developed the "sweepstakes" hypothesis because the biodiversity on Madagascar was unique, lacking "megafauna" such as elephants, lions and zebras.

If the animals had reached Madagascar via a "land bridge" - meaning the landmass was connected to the African continent - Simpson argued that large mammals would have also made the journey.

He added that the match between the currents and the arrival of new mammals on Madagascar was "pretty good".

It is understood that the common ancestor of present-day lemurs arrived on Madagascar between 60 million and 50 million years ago; tenrecs (such as hedgehogs) appeared 42-25 million years ago, and rodents between 24 million and 20 million years ago.

"About 20 million years ago, the 'flow' of species stopped," Dr Huber observed.

"When I look at my simulations for 20 million years ago, the currents are going the same way as they do today."

He explained that change in the direction of the current in the Mozambique Channel was a result of the slow northward movement of Africa and Madagascar.

This meant that the influence of the southern oceanic gyre was gradually weakened, causing the "sweepstake" route to be closed.

He said: "The 'switch' might have turned off gradually between 50 million and 20 million years ago, but by 20 million years ago, the journey was impossible."