Mating behavior and methyl farnesoate levels in male morphotypes of the spider crab, Libinia emarginata (Leach)

Abstract

We presently recognize at least six male morphotypes in Libinia emarginata which differ with respect to their appearance and reproductive behavior. The primary reproductives have a large carapace, large claws and their exoskeletal epicuticle is worn away, giving them an “abraded” appearance. These animals also have large reproductive system indices (RI), and high methyl farnesoate (MF) blood levels. Smaller abraded males with short claws do not compete with the larger aggressive ones, but employ alternative tactics such as “sneak mating” and female mimicry. They also have large RIs and high levels of MF in their blood. Unabraded morphs of any size do not attempt to mate. Their MF levels are lower (usually one half that of the abraded males) as are their RIs, suggesting that they are in a state of reproductive diapause. Incompletely abraded males have intermediate levels of MF and will attempt mating in the absence of the large-claw abraded ones. This relationship between behavior and hormone level suggests that MF may be involved in determining the type of mating behavior displayed by the different male morphotypes.