Differences in the Use of Cheliped Autotomy by the Mud Fiddler Crab Uca Pugnax (Smith, 1870) (Decapoda, Ocypodidae) When Escaping Predation by the Blue Crab Callinectes Sapidus (Rathbun, 1896)

Autotomy of limbs has been observed for a variety of organisms and in some taxa has been shown to be an effective strategy for escaping predation. We investigated differences in the use of cheliped autotomy by small and large male fiddler crabs during predation events, and also assessed if autotomy of the major cheliped allowed male fiddler crabs to escape predation more often than females. The blue crab Callinectes sapidus was presented with 5 small and 5 large male mud fiddler crabs Uca pugnax (n = 60), and in a second experiment, 5 male and 5 female U. pugnax were presented to C. sapidus (n = 60). Large U. pugnax autotomized their major cheliped more often and survived compared to small U. pugnax (n = 22 pools, S = 96.5, p < 0.0001), although this difference was not significant when adjusted for the total number of attacks on each size (n = 22 pools, S = 45, p = 0.1467). There was no significant difference (n = 29 pools, S = 30.5, p = 0.4988) between the total number of unsuccessful attacks on male versus female U. pugnax. At least half of the males autotomized their major cheliped in unsuccessful attacks during the first (69%) and second (53%) experiments. The major cheliped of male U. pugnax is a prominent visual stimulus that may have initially attracted C. sapidus to this prey; however, autotomization potentially enabled male fiddler crabs to escape predation in over half of all unsuccessful attacks.