BioEd Online

Caribbean spiny lobsters have a cunning way to avoid catching disease: they seem to be able to sniff out the scent of illness in their peers before infected neighbours show any symptoms. The normally gregarious animals can then stay well clear of the sickly.

Such a trick is unusual in the animal world. Some female creatures seem to be able to sniff out sickness in potential mates to avoid breeding with diseased males. And researchers think they have seen bullfrog tadpoles steering clear of illness. But nothing has been so dramatic as the lobster case, says Donald Behringer from the Old Dominion University in Norfolk, Virginia.

Behringer and his colleagues stumbled upon the avoidance tactics of Panulirus argus while studying the crustaceans in their seagrass home off the Florida Keys.

They noticed that all the lonesome lobsters had one thing in common: milky white blood oozing beneath their tails. This is a telltale sign of Panulirus argus virus 1 (PaV1), the only virus known to infect lobsters, explains Behringer.

To investigate, Behringer's group infected 16 lobsters with PaV1 in the lab. They then presented both healthy and infected lobsters with a choice of dens: either an empty house, or a den already occupied by a healthy or an infected lobster. "We basically gave the lobsters 48 hours to decide on a shelter," explains Behringer.

Leave me alone

As expected, the healthy lobsters avoided dens with an infected occupant, but preferred sharing with a healthy individual over having a den to themselves. Infected lobsters, on the other hand, showed no preference for one den over another. They had either lost the ability to stay away from diseased animals, or simply stopped caring about who they hung around with.

Interestingly, healthy lobsters seemed to make the choice to avoid an infected creature before any symptoms showed up. Nearly 70% of healthy animals spurned those that had carried the virus for just four weeks. By the time symptoms struck at six weeks, 100% of healthy lobsters stayed away, the researchers report in Nature¹.

Behringers' group thinks that P. argus is using chemical cues, rather than visual ones, to sniff out danger. Exactly how they manage to do this remains a mystery.

But the trick has an obvious benefit: keeping lobsters clear of fatally infected individuals. The effect of this on disease transmission isn't yet known.

Sadly the study won't help hungry diners to pick the healthiest lobster from the restaurant tank. This virus only seems to strike juvenile lobsters, when they are just a few centimetres long, notes Behringer. The bigger beasts offered up to diners are unlikely to be diseased, even if they are lurking alone in the corner of the tank.

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