Analysis of variation in lateral asymmetry of fiddler crabs Uca spp. and the ecological factors

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Males of fiddler crabs, Uca species, have a single enlarged claw used in courtship waving and fighting. The variation in handedness of the major claws and crab size were investigated for males of U.lactea complex and U.vocans complex. The original and regenerated claws were also distinguished morphologically for three subspecies of each complex. The comparisons in ratios of left-handed males between species, among subspecies, and among cohorts revealed that the ratio for U.lactea complex is quite stable at every level. On the other hand, a significant variation in ratio of left-handed males was detected among subspecies of U.vocans complex.Determining the costs of the courtship waving and fighting is critical to clarifying mechanisms that maintain the ratio of right-/left-handed males. The energy costs of male aggression and claw waving in a fiddler crab U.l.perplexa were estimated by examining blood glucose and lactate levels under natural conditions. The results of an enclosure experiment using opaque and transparent fences indicated that the waving display of the fiddler crab, as well as agonistic behavior, is energetically costly.The territorial males of U.l.perplexa fight their neighbours to demarcate and maintain territory boundaries. They also fight strangers that attempt to usurp their territories. Strangers pose a far greater threat than do neighbours since territory loss can be life threatening. Fights with strangers are, however, shorter than those between neighbours : the opposite of the commonly reported 'dear enemy' phenomenon. Fights with neighbours were significantly longer than those with strangers, but showed none of the patterns predicted for tests of strength. They were fundamentally different interactions. We argue that residents use aggression as a form of punishment against encroaching neighbours.