Comparative Analysis of Escape Behavior in Male, and Gravid and Non-Gravid, Female Lobsters

Few studies exist in which the parameters of a single behavior have been quantitatively compared for male and female lobsters. Here, we have examined the effects of sex and gravidity on the parameters of the escape behavior of the American lobster, Homarus americanus, elicited by a visual threat. Both non-gravid females and male lobsters readily tailflipped in response to the stimulus, but gravid females failed, with one exception, to initiate a swim, even when stimulus strength was increased. Although the total distance swum by males and non-gravid females was not statistically different, males covered more ground in the initial power swim and during the subsequent swims than did non-gravid females. Males swam for a longer time, performing more tailflips, than females. Relative to their length and weight, males swam a greater distance at each stroke during the initial power swim and the subsequent swims, although, females might have compensated by swimming at a higher frequency. There were no significant differences in swimming velocity or acceleration, nor in the calculated force or work performed by the two sex classes (male and non-gravid females). Therefore, apart from egg-bearing, which severely inhibits the escape response, it remains to be seen whether the subtle physiological and anatomical sexual dimorphism that produces longer and more swim strokes in males but higher frequency tailflips in females results in the same chances of survival for the sexes.