Research reveals that lobsters avoid sick neighbors

Ever tried to avoid a coworker who comes into the office with a runny nose and the sniffles? Turns out that lobsters can do you one better.

A new study by researchers at Old Dominion University and the Virginia Institute of Marine Science shows that Caribbean spiny lobsters, normally gregarious creatures that live together in underwater caves, will avoid other lobsters that are infected with a lethal virus called PaV1. They do so weeks before the sick lobsters show any obvious outward signs of disease.

The research, by ODU scientist and lead author Mark Butler, ODU post-doctoral student Donald Behringer, and VIMS scientist Jeff Shields, appears in the May 25th issue of the prestigious international journal Nature.

"This is the first record of healthy animals avoiding diseased members of their own species in the wild," says Shields.

The researchers suspect that healthy lobsters are using their exquisite sense of smell to detect and avoid diseased neighbors, just like they do to choose mates, feed, and establish dominance hierarchies.

Butler, Behringer, and Shields have been studying the PaV1 virus in wild lobsters for several years, in an attempt to better understand the disease, how it spreads, and how it might affect the commercial exploitation of the species. The Caribbean spiny lobster (Panulirus argus) is a popular seafood item that is commercially fished throughout its range, with the bulk of landings from the Florida Keys.

Behringer first noticed the PaV1 virus while drawing blood during a separate study of how lobsters molt. He noticed that the blood of many lobsters was milky rather than clear, as in healthy lobsters.

During subsequent field studies, the researchers noticed that infected lobsters only rarely shared shelters with other lobsters, even though healthy lobsters generally prefer to live together in dens.

To test whether this could be explained by healthy lobsters avoiding diseased neighbors, they set up a laboratory experiment in which healthy and diseased lobsters were given a choice between an empty den and one containing either a healthy or a diseased individual.

What they found was telling—healthy lobsters avoided dens containing diseased lobsters, preferring instead to share dens with other healthy lobsters. Diseased lobsters did not discriminate between dens, regardless of whether the animal inside was sick or well.

Other evidence from the laboratory and field shows that avoidance of diseased neighbors likely helps curb the spread of disease in the wild. When healthy juvenile lobsters are confined in the lab with lobsters infected with the virus, more than 60% of them succumb within 80 days. The rate of infection in wild populations in Florida is only 7%. The avoidance of sick neighbors likely explains the difference.

The ability of healthy lobsters to detect and avoid infected, though not as yet infectious, neighbors provides an important evolutionary advantage, says Shields. Lobsters that have this ability are more likely to survive, breed, and pass on the trait to their offspring.