Autotomy and running performance of fiddler crabs (Decapoda: Brachyura: Ocypodidae)

Abstract

The sexually dimorphic, enlarged major claw is a notorious trait among male fiddler crabs, but comes with potential locomotor costs. Possessing the ability to autotomize the enlarged claw is thus potentially advantageous to not only to escape a predator’s grip, but also to increase running performance. Previous studies concluded that autotomy either has no effect or even a negative effect on running performance. If the claw does not aid in locomotion, then shedding the enlarged claw that accounts for 40% of a fiddler crab’s mass should positively affect running performance. I therefore investigated autotomy and running performance in the Atlantic sand fiddler crab Leptuca pugilator (Bosc, 1801) with a focus on improving upon the methods of previous studies. Crabs were given substantial recovery time between collection, running trials, and autotomy induction. Maximum sprint speed was assessed by running crabs on a 1 m sand and mud track where individuals were significantly faster after autotomy of the enlarged claw (N = 64, t₆₃=-7.25, P < 0.001). Intact running velocity was furthermore a significant predictor of autotomized running velocity (R² = 0.194, P < 0.001). This study is the first to show a significant increase in fiddler crab sprint velocity after autotomy on a flat surface, and I propose where methodological pitfalls may have occurred in previous studies.