06 August 2009

The 'two-headed' yellow-lipped sea krait?

The Yellow-lipped sea krait (Laticauda colubrina) is quite commonly seen on our shores. And I've seen it many times without realising that the snake has a trick up its tail!
Yellow lipped sea snake (Laticauda colubrina)
Dr Arne Redsted Rasmussen made the fist observation of this snaky trick during a research dive. He saw the venomous sea snake go head first into a narrow crevice. Then suddenly he was surprised to see the snake pull its head out, as if the snake had been able to very quickly turn around inside the crevice. Moments he realized that the "head" was in fact the tail.

A closer study of Yellow-lipped sea krait specimens revealed a bright yellow horseshoe marking on both its tail tip and snout, distinctive from the rest of its body. Analysis of other sea krait species from museum collections found a similar distinctive color pattern in nearly 100 such species.

"The value of such an adaptation is twofold; it may increase the chances of surviving predator attack by exposing a less 'vital' body part, but more importantly it may deter attack in the first place if attackers perceive the tail as the venomous snakes head," said Rasmussen.

Venomous Sea Snakes Play Heads Or Tails With Their Predators
ScienceDaily 6 Aug 09;
In a deadly game of heads or tails venomous sea snakes in the Pacific and Indian Oceans deceive their predators into believing they have two heads, claims research published August 5 in Marine Ecology.

The discovery, made by Dr Arne Redsted Rasmussen and Dr Johan Elmberg, showed that Yellow-lipped Sea Kraits (Laticauda colubrina) use skin markings and behaviour patterns to fool predators into thinking their tail is a second head, complete with lethal venom.

There are over 65 species of sea snakes in the tropical waters of the Southern Hemisphere, ranging from Africa to the Gulf of Panama. Most spend their entire lives in the sea, inhabiting shallow water and are active predators, feeding on small fish found around coral reefs. All sea snakes have extremely potent venom which is among the most toxic known in all snake species.

When hunting for food sea snakes probe crevices and coral formations, temporarily forcing them to drop their guard to threats from the surrounding waters and making them highly vulnerable to attack. However, the Yellow-lipped Sea Krait has been found to twist its tail so that the tip corresponds with the dorsal view of the head, which combined with deceptive colouring, gives the illusion of having two heads and two loads of deadly venom.

Apart from the Yellow-lipped Sea Krait the ecology of sea snakes has largely gone understudied, due mainly to their off-shore and nocturnal behaviour. Yet, despite the number of behavioural studies devoted to this species, the discovery of this false-head-behaviour is a hitherto overlooked anti-predator adaptation.

The discovery was made while senior author Arne Redsted Rasmussen was diving off the coast of the Bunaken Island in Indonesia. A large Krait was followed for thirty minutes, swimming between corals and crevices hunting for food. Rasmussen was momentarily distracted by a second snake, but when looking back he was surprised to see the "head" was facing him while the tail probed the coral. Rasmussen's surprise grew when he saw a second head emerge from the coral instead of the expected tail. It was only when the snake swam away that the first head was clearly seen to be a paddling tail.

To build upon this discovery researchers examined 98 Sea Kraits from three major museum collections in Paris, Berlin and Copenhagen while also monitoring the behaviour of wild Sea Kraits in Solomon Islands during the Danish Galathea 3 Expedition. The research confirmed that all snakes of this species had a distinctive colouration pattern, with a bright yellow horseshoe marking on the tip of the head and the tail. The yellow was deeper than the colours on the rest of the body and the black colorations were much longer than the dark bands on the rest of the body, highlighting the similarity between the head and the tail.

The reason for this mixture of behaviour and coloration results from a developed defence strategy needed when the snake is probing for prey. Despite being extremely venomous sea snakes are susceptible to attack from several predators such as sharks, large bony fishes, and even birds.

"The value of such an adaptation is twofold; it may increase the chances of surviving predator attack by exposing a less 'vital' body part, but more importantly it may deter attack in the first place if attackers perceive the tail as the venomous snakes head," said Rasmussen.

Similar defence mechanisms have been discovered in lizards, and some land snakes have developed ingenious camouflage deterrent behaviour strategies, but this defence has never been associated with other lethally venomous predators such as sea snakes.

Traditionally the only evidence of a defence behaviour strategy in sea snakes has been documented in individual cases, when a snake was exposed to and aware of an imminent danger. This research is the first record of a combined false-head-behaviour and false-head-camouflage defence strategy used as instinct when a snake is hunting for food.

"It is intriguing that this discovery is observed in this species, as one of the key differences between the Yellow-lipped Sea Krait and other sea snakes is that they spend almost equal time on land and in the sea," said Rasmussen. "They therefore live in two worlds where two very different rules of survival apply. It remains to be confirmed whether Sea kraits use their sea defence tactic of motioning their tails when on land."

Journal reference:

1. Rasmussen.A.R, Elmberg.J. 'Head for my tail': a new hypothesis to explain how venomous sea snakes avoid becoming prey. Marine Ecology, August 2009 DOI: 10.1111/j.1439-0485.2009.00318

Adapted from materials provided by Wiley-Blackwell, via EurekAlert!, a service of AAAS.

'Two-Headed' Snake Fakes Predators
Jeanna Bryner, livescience.com 5 Aug 09;
One species of venomous sea snake shows the advantages of being two-faced. This slithering reptile twists its tail so its hind end appears to predators as a second head.

The clever sea snake, called the yellow-lipped sea krait (Laticauda colubrina), relies on the ruse to keep it safe from sharks and other enemies. Even though L. colubrina packs some of the most potent venom, the animal becomes relatively defenseless while foraging, a time when its head is stuck in crevices of coral reefs rather than on the lookout for attacks.

The thinking goes, if predators detect a vigilant head they'll steer clear. Apparently the trick can even fools unsuspecting scientists.

Arne Redsted Rasmussen of the Royal Danish Academy of Fine Arts, School of Conservation in Copenhagen discovered the phenomenon while diving off the coast of the Bunaken Island in Indonesia. There, he watched as a yellow-lipped sea krait probed the crevices of corals. From his perspective, the snake seemed to be foraging with its tail, since its "head" was facing the scientist.

Shortly thereafter, the diving scientist watched as the snake pulled "another head" out of the crevice. He noted that each time the snake poked its snout into a coral opening, its tail twisted around the length of the snake's body and began to move about (like any head would) to, apparently, monitor the scene and keep a lookout for danger.

When the snake swam away, this perceived head showed itself as the snake's flattened paddle-like tail.

Rasmussen and Johan Elmberg of Kristianstad University College in Sweden found L. colubrina has a bright yellow horseshoe marking on both its tail tip and snout, distinctive from the rest of its body.

They also analyzed other sea krait species from museum collections, finding a similar distinctive color pattern in nearly 100 such species. The museum findings suggest other sea snakes might employ the guise observed in L. colubrine, the researchers say. But further studies are needed to firm up this hypothesis, Elmberg noted.

The new discovery will be published this week in the journal Marine Ecology.

"Two Headed" Sea Serpents Fool Attackers
National Geographic News 5 Aug 09;
August 5, 2009—Just as Hercules had the multi-headed hydra to contend with, ocean predators tussle with two-headed sea snakes—or so it appears.

Some sea snake species, such as Hydrophis pachycercos, have evolved so that sharks and other predators can't tell whether the serpents are coming or going, Johan Elmberg and Arne Rasmussen report in a new study today in the journal Marine Ecology.

When Rasmussen on a research dive in Indonesia, said Elmberg, who was not in the dive, "he saw a venomous sea snake go head first into a narrow crevice. Then suddenly he was surprised to see the snake pull its head out, as if the snake had been able to very quickly turn around inside the crevice."

Moments later Rasmussen, a biologist with the School of Conservation in Copenhagen, Denmark, realized that the "head" was in fact the tail.

While the yellow-lipped sea krait, a nocturnal, shallow-water snake, had been "probing the reef crevice" for fish, Elmberg, an ecologist at Kristianstad University in Sweden, said, "the tail was slowly writhing back and forth, much in the same way as the head moves on a vigilant and actively searching snake."

Later, after studying 98 preserved specimens of the roughly three-foot-long (meter-long) tropical species at three European museums, the researchers concluded that all yellow-lipped sea kraits have "two headed" tail patterns.

"We think these tail patterns and the writhing movements likely intimidate potential predators by fooling them into believing that the tail is actually the venomous head," Elmberg said.

Since then, in the South Pacific waters of the Solomon Islands and elsewhere, the team has found similar markings in other sea snake species, such as H. pachycercos.

And though Elmberg and Rasmussen haven't witnessed H. pachycercos wagging its tail like a head, they suspect it does.

—Matt Kaplan

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