Differences in proportional claw size among left- and right-handed Atlantic sand fiddler crabs Leptuca pugilator (Bosc, 1801) (Decapoda: Brachyura: Ocypodidae)

Abstract

Abstract The sexually dimorphic, enlarged major claw is a prominent feature among fiddler crabs and acts as both a sexual signal and weapon. Most often the enlarged claw occurs on the left and right sides of fiddler crabs in relatively even proportions (40–60%), but populations exhibit an extreme right handedness bias (> 90%) in a few cases. The mechanisms maintaining relatively even handedness proportions among fiddler crabs remains debatable, but from an evolutionary perspective it should be maintained through an evenness in fitness (reproduction and survival) between left- and right-handed crabs. I investigated handedness ratios and claw to body size in a Leptuca pugilator (Bosc, 1801) population on Sapelo Island, Georgia, USA. In collecting 417 adult male crabs, there was a slight right-hand bias (54%, χ 2= 2.9376, P = 0.087), which was similar to the previous study of this population 17 years prior. I nevertheless found right-handed crabs had significantly smaller claw size relative to their carapace size (P = 0.018). Overall, this study documents inequality in the body proportions between left- and right-handed L. pugilator within a population operating at a slight right hand-bias. I discuss how my study contributes to previous discussions on handedness bias in fiddler crabs as well as potential mechanisms that control its widespread handedness evenness.