Horned ghost crabs change camouflage from day to night

By Ella Davies, Reporter, BBC Nature

Horned ghost crabs change their appearance from day to night for camouflage, a study has revealed.

The species Ocypode ceratophthalmus builds burrows on beaches from Japan to East Africa to shelter from predators.

Researchers investigating young crabs' defences found they fine-tune their brightness to mimic their background.

The crabs reflected changes in their environment throughout the day, becoming lighter in the daytime and darker at night.

The findings are published in the Biological Journal of the Linnean Society.

Horned ghost crabs are named for their eyestalks which extend upwards resembling horns. The crabs are mostly active at night and juveniles are slightly translucent.

Dr Martin Stevens, working for the University of Cambridge, undertook the study with colleagues from the National University of Singapore.

Continued:  http://www.bbc.co.uk/nature/22025789

Sea hares' sticky defence uncovered

By Michelle Warwicker, Reporter, BBC Nature

The sea hare, a soft-bodied marine creature, uses a sticky secretion to fool hungry predators, say scientists.

The slow-moving animals are known for defending themselves by squirting an off-putting mixture of purple ink and a white substance called opaline.

However, exactly how this sticky opaline is used to deter predators was previously unknown.

Now scientists have shown the substance coats predators' antennae, deactivating their chemical senses.

Researchers suggested that with their sense of smell blocked predators lose their appetite and spend a long time cleaning themselves of the sticky coating, allowing the sea hares to escape.

Sneaky predator avoidance

The team from Georgia State University, Atlanta, US said that their study is the first time "sensory inactivation" as a defence against predators has been shown in an experiment.

Details of their findings are published in the Journal of Experimental Biology.

Continued:  http://www.bbc.co.uk/nature/21929070

Social butterflies find safety in numbers

Some butterflies find it safer to hang out in a gang, collectively creating a big visual 'stop sign' to keep predatory birds at bay, say researchers.

Entomologist Susan Finkbeiner, of the University of California, Irvine, and colleagues, report their findings today in Proceedings of the Royal Society B: Biological Sciences.

"It's the exact same butterfly that roosts with the same individuals in the same place," says Finkbeiner. "Some even roost on the exact same part of the branch every night, as if their name was written on it."

Scientists have known for 150 years that come sundown, many species of butterflies of the genus Heliconius bed down in gangs of about 4 to 15 individuals.

"It's really unique in butterflies because most adult butterflies tend to be solitary. Any social behaviour among butterflies is really rare," says Finkbeiner.

Until now, the reason behind this unique communal roosting behaviour has remained a mystery.

Now, Finkbeiner and colleagues have investigated and found that it's all about safety in numbers.

The researchers investigated two hypotheses: First, that the butterflies were hanging out together so they could share information about foraging sites.

This is known, for example in groups of birds that roost together and follow their roost mates to foraging sites.

Second, that the grouping helped the butterflies to fend off predators, who tend to attack first thing in the morning.

Finkbeiner says the butterflies are actually loaded with cyanide, because of the passion vine they feed on as larvae, and are coloured brightly to warn off bird predators.

It is possible that by joining together they enhance their bright warning signal, she says.

Read on:  http://www.abc.net.au/science/articles/2012/03/21/3459526.htm

'Flying plankton' escape predatory fish

Tiny shrimp-like creatures called copepods break through the ocean's surface and leap through the air to escape predators, US scientists say.

They have been investigating how the brightly-coloured Pontellid copepods, which live close to the surface, are so abundant yet so conspicuous to fish.

Writing in Proceedings of the Royal Society B, the scientists say copepods travel further in air than in water.

Predators are also left confused about where they will land, they say.

Almost all commercially important fish, including cod, pollock and whiting, feed on copepods.

There are reports from the late-19th Century of copepods breaking through the water surface but observers at the time thought this was to allow them to moult.

A later report proposed jumping was part of an escape from predators but was not confirmed.

Read on:  http://www.bbc.co.uk/news/science-environment-17430640

Giant squid eyes are sperm whale defence

By Richard BlackEnvironment correspondent, BBC News

The world's biggest squid species have developed huge eyes to give early warning of approaching sperm whales.

Colossal and giant squid both have eyes that can measure 27cm (11in) across - much bigger than any fish.

Scientists found that huge eyes offer no advantages in the murky ocean depths other than making it easier to spot enormous shapes - such as sperm whales.

Writing in current Biology journal, they say this could explain the equally huge eyes of fossil ichthyosaurs.

Lead scientist Dan Nilsson from Lund University in Sweden was present at the unique dissection of a colossal squid performed four years ago in New Zealand.

There, he examined and handled the eyes - in particular, the hard parts of the lens.

Read on:  http://www.bbc.co.uk/news/science-environment-17365736

Eat and Let Die: Insect Feeds On Toxic Plants for Protection from Predators

ScienceDaily (Feb. 21, 2012) — Certain insects, such as the African variegated grasshopper (Zonocerus variegatus) or the cinnabar moth (Tyria jacobaeae), native in Europe and Asia, feed on toxic plants in order to protect themselves from predators. A working group at the Botanical Institute at Christian-Albrechts-Universität zu Kiel (CAU), together with scientists from Technische Universität Braunschweig and the City University College, New York, have published findings on this phenomenon.


The Kiel scientists from the field of biochemical ecology have been studying for more than ten years how particular insects ingest plant toxins and store them within their own bodies. These toxins, the so-calledpyrrolizidine alkaloids, are found for example in ragwort (Senecio jacobaea), a common wild flower in Eurasia. These plants have been repeatedly in the news over the past few years, e.g. as contaminants in rocket lettuce or as compounds causing intoxication of grazing livestock. The scientists now showed that the African grasshopper has developed a specific enzyme, allowing it to store plant toxins for self defence. An almost identical enzyme was found a few years ago in the European cinnabar moth. "The most exciting aspect of this finding is that evolution has developed such a complex mechanism twice in two very different species," says Professor Dietrich Ober, head of the working group in Kiel.


Read on:  http://www.sciencedaily.com/releases/2012/02/120221090240.htm

Crafty Caterpillars Mimic Each Other to Avoid Predators

Scientists have long documented mimicry in adult butterflies, but new research shows that caterpillars also use this defense mechanism to deter predators.


To protect themselves from hungry predators, caterpillars have evolved a number of defenses. Some caterpillars physically camouflage themselves to look like bird droppings or sticks, while others have developed fake eyes to scare off birds. Some caterpillars even have chemical defenses gained from poisonous plants, which they then broadcast to predators with a bright warning coloration.

Although many adult butterflies employ mimicry — where one species develops warning color patterns similar to another species' — to quickly teach predators which insects to avoid, scientists have observed few definitive cases of caterpillars using this strategy.

"Mimicry in general is one of the best and earliest-studied examples of natural selection, and it can help us learn where evolutionary adaptations come from," University of Florida biologist Keith Willmott said in a statement.

Read more here:
http://www.livescience.com/17647-caterpillar-mimicry-predation.html

How Crabs Avoid Getting Eaten

Despite their simple compound eyes crabs have evolved a smart way to tell the difference between friend and foe, new scientific research has revealed.

Scientists from The Vision Centre have found that fiddler crabs quickly learn to recognize if an approaching creature is a threat, a mate or a harmless passer-by – according to its direction of approach.

“Fiddler crabs have extremely poor sight, with no depth perception and no ability to see in detail,” says Ms Chloe Raderschall, a researcher from The Vision Centre and The Australian National University. “In a situation where every ‘blob’ that moves in the environment can be a threat, they have to strike a balance between succumbing to paranoia – and ending up as bird feed.

“Crabs achieve this through a process called habituation where they learn from repeated events to differentiate threats from harmless objects. Humans too use habituation: for instance we learn to ignore the sound from an air conditioner once we grow accustomed to it.

‘We found that crabs have a very selective and finely tuned habituation response – instead of relying solely on the physical appearance of an object, they associate the object with its past behavior in their living environment, such as its direction of approach.”

In the study, the researchers used dummy predators to approach groups of fiddler crabs from two different compass directions.

“We did two dozen runs of a dummy approaching from direction A without attacking the crabs, and within five runs, the crabs started to ignore it,” Ms Raderschall explains. “When we switched to another dummy coming from direction B, the crabs were scared witless and headed straight to their burrows.”

When the researchers switched back to direction A, they found the crabs did not attempt to escape, indicating that they clearly distinguish between the dummies approaching from the two directions, she says.

“As both dummies were identical and there was no difference in the timing of their movements, we conclude that the crabs used the direction of approach to determine whether an approaching object was a threat or not.”

Ms Raderschall explains that this finding confirms that crabs have an extremely specific habituation response. This contradicts previous assumptions found in most text books that habituation is a simple learning mechanism based mostly on physical appearances.

“Their identification of a dangerous or harmless object is closely associated with their memory of how the object behaves, rather than how it looks.

“Apart from very simple visual cues, they don’t really have other ways to detect predators, and this study provides clues as to how animals with relatively poor vision can adapt and survive over time.”

The paper ‘Habituation under natural conditions: model predators are distinguished by approach direction’ by Chloe A. Raderschall, Robert D. Magrath and Jan M. Hemmi was published on 23 November 2011 in The Journal of Experimental Biology.

The study was conducted in the Research School of Biology at The Australian National University.

The Vision Centre is funded by the Australian Research Council as the ARC Centre of Excellence in Vision Science.

Source: redOrbit (http://s.tt/14ewu)
http://www.redorbit.com/news/science/1112429177/how-crabs-avoid-getting-eaten/index.html