TIERNEY, A.J.*; GUNARATNE, C.; JENNISON, K.; Colgate Univ., Hamilton, NY; Colgate Univ., Hamilton, NY; Colgate Univ., Hamilton, NY: Behavioral correlates of alternate male forms (Form I and Form II) in adult crayfish.

Male crayfish of the subfamily Cambarinae exist in two forms, Form I and Form II. Form I males are reproductively competent whereas Form II males resemble juveniles and are nonreproductive. Individuals molt seasonally from one form to the other, and the forms differ morphologically in the structure of the reproductive organs and in the chelae which are larger in Form I. We conducted two experiments to determine if the change in form is associated with changes in behavior in adult male Orconectes rusticus. In the first experiment, we measured behavioral differences between isolated Form I and Form II males, including the amount of time spent active (walking or climbing), in a shelter, and feeding. We also recorded the reactions of animals to a female crayfish. In the second experiment, we compared agonistic behavior and hierarchy formation in size-matched, intra-form groups of four crayfish. We found that Form II crayfish spent significantly more time in the shelter than Form I crayfish, which may reflect increased vulnerability to predation in this form. However, there were no significant differences in other behaviors, including activity level, feeding behavior, and interaction with the female. In the second experiment, Form I crayfish engaged in significantly more fighting bouts and fought for longer durations, causing more retreats and tailflips by subordinate animals. Males of both forms established a linear hierarchy in each of three successive days of testing, and Form I males took longer to establish a hierarchy each day than did Form II males. The apparent increase in aggressive behavior among Form I crayfish may be due to their need to outcompete other males for female mates.