Frequency and latency of autotomy of a sexually selected fiddler crab appendage

Autotomy is a predator defence mechanism by which individuals voluntarily release an appendage to escape a predator or escape a fouled moult. The decision to autotomize is driven by the costs of autotomy (i.e., the loss of the appendage) vs. the risk of predation. In many cases, autotomized appendages have few alternative functions, yet male fiddler crabs autotomize the sexually selected large claw that is critical for mate attraction. We conducted an experiment with Austruca mjoebergi to understand the role of claw autotomy by males during the mating season. Males more readily autotomized a leg relative to the enlarged claw, reflecting the much greater cost of being without the major claw. Larger crabs had a lower probability of claw autotomy than did small crabs, reflecting the greater fitness cost of claw autotomy experienced by larger crabs. The sexually selected fiddler crab claw is a multifunction structure with benefits that may outweigh the survival probability resulting from autotomy when individuals are threatened by predation.