No Olfactory Recognition of Shell Disease in American Lobsters,Homarus americanus

Abstract

Epizootic shell disease in the American lobster, Homarus americanus, is seriously affecting inshore populations in southern New England. The disease can change the biochemical profile of lobsters and could potentially change their urine and other body odors. In turn, this may affect social responses, including avoidance of diseased animals. Behavioral avoidance could reduce the spread of disease. We conducted odor choice tests with pairs of (size- and site-matched) healthy and shell-diseased males. The results showed that healthy intermolt females did not prefer the odor of healthy or diseased males significantly. In addition, we investigated the effect of shell disease on male dominance. Healthy males established dominance over shell-diseased males in 15 of 18 fights. Subsequent choice tests with the same male pairs again showed no significant difference between the time females spent with healthy versus diseased males, but they preferred dominant males slightly. Because most dominant males were healthy, it confers a slight advantage to healthy males. The results were similar for animals from 2 subpopulations, each with considerable incidence of shell disease. Behavioral disease avoidance mechanisms were not seen and may have not yet evolved, if this disease is a recent phenomenon. Also, the disease may be caused more by environmental conditions than by genetic predisposition or interanimal contact, making disease recognition irrelevant.