Alternate mating strategies of polymorphic males of Libinia emarginata appear to depend on methyl farnesoate

The spider crab Libinia emarginata has six male morphotypes that differ with respect to their appearance and reproductive readiness. Large abraded males compete actively for females and have the largest claws and reproductive system indices and highest methyl farnesoate (MF) blood levels. Smaller abraded males with short claws attempt mating in the absence of large abraded males but employ the alternative tactics of sneak mating and female mimicry when large aggressive males are present. Unabraded morphs of any size do not attempt to mate, either in competition or in isolation with receptive females. Their MF levels are lower (usually one-half that of abraded males) indicating that they are in a state of reproductive diapause. Incompletely abraded males have intermediate levels of MF and are moderately active in reproduction. These data suggest that MF may be involved in directing the reproductive behavior of different male morphotypes.