If you startled a deer, you might not expect it to jump into the nearest pond and submerge itself for minutes.
But that is exactly what two species of mouse-deer in Asia do when confronted by predators, scientists have found.
One other African mouse-deer species is known to do the same thing, but the new discovery suggests all ruminants may once have had an affinity with water.
It also lends support to the idea that whales evolved from water-loving creatures that looked like small deer.
There are around 10 species of mouse-deer, which are also called ‘chevrotains’.
All belong to the ancient ruminant family Tragulidae, which split some 50 million years ago from other ruminants, the group that went on to evolve into cattle, goats, sheep, deer and antelope.
Each are small, deer-like creatures that unusually don’t have antlers or horns. Instead they have large upper canine teeth, which in the males project down either side of the lower jaw.
The largest species, which stands no more than 80cm tall, lives in Africa and is thought to be the most primitive of all mouse-deer. Known as the water-chevrotain, this animal likes to live in swampy habitats. When alarmed, it dashes for the nearest river where it submerges and swims underwater to safety.
All of the other species of mouse-deer, which live in southeast Asia and India and Sri Lanka were thought to be dry-land animals.
That was until researchers witnessed some remarkable behaviour during two separate incidents.
The first occurred in June 2008 during a biodiversity survey in northern Central Kalimantan Province in Borneo, Indonesia.
During the survey, observers saw a mouse-deer swimming in a forest stream. When the animal noticed the observers it submerged. Over the next hour, they saw it come to the surface four or five times, and maybe more unseen. But it often remained submerged for more than five minutes at a time.
Eventually the observers caught the animal, which they identified as a pregnant female, then released it unharmed.
Among the survey team was the wife of Erik Meijaard, a senior ecologist working with the Nature Conservancy in Balikpapan, Indonesia.
Meijaard knew of anecdotal reports by local people who described deer hiding in creeks and rivers when chased by their dogs. When he saw photos of the deer he identified it as a greater mouse-deer (Tragulus napu).
Coming up for air
The same year, Meijaard also heard reports of a mouse-deer in Sri Lanka that had also been seen swimming underwater.
Three observers saw a mountain mouse-deer (Moschiola spp) run into a pond and start to swim, hotly pursued by a brown mongoose. The mouse-deer submerged itself, and eventually the mongoose retreated. The deer left the water only to be chased straight back into it by the mongoose.
“It came running again and dived into the water and swam underwater. I photographed this clearly and it became clear to me at this stage that swimming was an established part of its escape repertoire,” says Gehan de Silva Wijeyeratne, who saw the incident.
“Seeing it swim underwater was a shock. Many mammals can swim in water. But other than those which are adapted for an aquatic existence, swimming is clumsy. The mouse-deer seemed comfortable, it seemed adapted,” he says.
Origins of whales
Meijaard, Wijeyeratne and Umilaela, who saw the submerged Bornean mouse-deer, describe both incidents in the journal Mammalian Biology.
“This is the first time that this behaviour has been described for Asian mouse-deer species,” says Meijaard. “I was very excited when I heard the mouse-deer stories because it resolved one of those mysteries that local people had told me about but that had remained hidden to science.”
“The behaviour is interesting because it is unexpected. Deer are supposed to walk on land and graze not swim underwater. But more interestingly for the zoologist are the evolutionary implications,” he says.
The behaviour bolsters one leading theory regarding the origin of whales.
In 2007, scientists led by Hans Thewissen of the Northeastern Ohio Universities College of Medicine in Ohio published details of a remarkable fossil called Indohyus.
This fossil was of a ruminant animal that looked like a small deer, but also had morphological features that showed it could be an ancestor of early whales.
A mouse-deer in Borneo caught having spent 60 minutes trying to hide underwater
Although speculative, that suggests that all early ruminants may also have led a partially aquatic lifestyle.
The discovery that two Asian species of mouse-deer are comfortable underwater shows that at least three species of modern tragulid share an aquatic escape behaviour.
Because these species diverged at least 35 million years ago, their ancestor also likely behaved in the same way, again bolstering the the idea that a deer-like ruminant may have evolved to produce the modern cetacean group of whales and dolphins.
Hippos, the closest modern relative of whales, also dive for water when threatened, a behaviour that may have been lost over time by other modern species such as sheep and antelope.
Monster fish killed after attacking Swiss swimmers
POLICE have ended the reign of terror of a huge fish that was attacking swimmers in a Swiss lake.
The zander, which was 70 centimetres long and weighed eight kilos was harpooned on after it bit six swimmers over the weekend, fish warden Fabio Croci said.
Two swimmers were treated in hospital for bite wounds up to 10 centimetres long after being attacked on Lac Majeur, which borders Italy.
Police divers at first tried to capture the carnivorous fish with a net, but when this failed they pursued the zander with a harpoon and managed to kill it.
The meat from the captured fish was served up to tourists at the lake.
“It is quite unusual for zanders to bite humans”, Mr Croci said, adding he suspected the fish was suffering from a hormonal imbalance which could be responsible for its aggression.
White humpback whale Migaloo has low sperm count
Migaloo, the white humpback whale that migrates along the east coast of Australia each year, may never reproduce because he could have a low sperm count, scientists fear.
The whale bears scars on his back from a collision with a boat propellor and scientists believe the way the scars have healed may provide an insight into his health.
Professor Peter Harrison, the director of Southern Cross University’s whale research centre in New South Wales, said the whale was “very special” but may never breed.
“The scarring pattern on his back where the trimaran dagger-board [centreboard] sliced into him indicates that he is not healing in the same way, with the dark pigment pattern that we’d expect from other humpback whales,” he told the Australian Broadcasting Corporation.
“And that sort of confirms… that he may well be albino. Now one of the things associated with albinism in mammals is that it quite often leads to low sperm count or sperm infertility.
“So it’s possible that Migaloo, although he is a fully grown male humpback whale and sings like all the other humpback whales, he may not be an effective reproducer.
“And that’s one of the interesting things about him, that we simply don’t know enough about him in terms of whether or not he’s able to father offspring.”
Migaloo, whose name means ‘white fella’ in an Aboriginal dialect, was first sighted in 1991. He is believed to be the only all-white humpback whale in the world and his status as a “special interest whale” means no one is allowed to get within 500 metres of him.
Every year he migrates back to breeding grounds along the Great Barrier Reef region off north-eastern Australia.
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