Handedness in fiddler crab fights

Abstract

Asymmetric weapons are common in bilateral animals and, in some species, they can occur 23 on either the left or the right hand side of the body (lateralisation). Fiddler crabs (Uca spp, 24 Decapoda: Ocypodidae) have an enlarged claw that is used in male-male combat over 25 territories, and in courtship displays. Males can be either right or left-handed, and most 26 species have a 1:1 ratio. Past studies have found little effect of handedness on fighting 27 success, fight duration or other measures of combat. Here we show that, while handedness 28 per se. does not affect fighting, handedness-matching has a significant effect. In Uca 29 mjoebergi, fights between different-handed males were more likely to escalate to grappling, 30 suggesting that it is harder for the combatants to determine the winner. We suggest that the 31 positioning of the claws during fighting creates distinct forces that result in different 32 outcomes for same-versus different-handed fights. This can represent a strong selective 33 pressure in populations with an uneven handedness distribution where handedness minority 34 will often engage in different-handed fights. We discuss these results in light of the selective 35 forces that may act on handedness distribution in fiddler crabs.

Behavioural lateralization in domestic pigs (Sus scrofa)—variations between motor functions and individuals

“…Alternatively, the population bias in tail curling may be the result of a morphological directional asymmetry, which is described as an inherited trait where most individuals are asymmetrical in one direction (Palmer, 2004). One example of this is claws of crabs that differ in size (Perez, Heatwole, Morrell, & Backwell, 2015). Future studies on the (muscular) structure of the tail would help increase our understanding of its function and determine if lateralized tail curling is the result of a morphological asymmetry or not.…”

The Emergence of the Bilateral Symmetry in Animals: A Review and a New Hypothesis

“…While the critical period for crusher determination is genetically determined, the actual trigger is influenced by experience [21]. A similar asymmetry is obtained for crabs [22]. Flat fish have a remarkable asymmetry with both eyes placed on one side of the head.…”

The functions of multiple visual signals in a fiddler crab

“…Like in fiddler crab claws, sexually dimorphic traits that are also used as weapons are selected for fight efficiency (Emlen, ). Thus, claw functionality and display is not only shaped through intersexual selection, but also constrained by fight efficiency and the coevolution of other body parts for balance (Bywater, Wilson, Monro, & White, ; Perez, Heatwole, Morrell, & Backwell, ). Future studies that address these points as well as investigations with other species that present the behaviour will be decisive to thoroughly unveil the adaptive significance of fiddler crab signal multiplicity.…”