Handedness in fiddler crab fights     — ASN Events

Handedness in fiddler crab fights     (#533)

Daniela Perez 1 , Siobhan Heatwole 1 , Lesley Morrell 2 , Patricia Backwell 1
  1. Australian National University, Canberra, ACT, Australia
  2. University of Hull, Hull, United Kingdom

Bilateral animals presenting asymmetric morphological traits that are used as weapons are common, but it is not common for these weapons to occur on either the left or right side of the animal. The fiddler crab is one of these few exceptions. The male weapon is an enlarged claw that is used in male-male fights over territories, and is also used in courtship displays. The enlarged claw splits the populations in right and left-handed males. Fights can be classified as between same- or different-handed combatants. Fights escalate from pushing to the interlocking of claws (called grappling). Here we investigate the effect of handedness in fight outcome by inducing and observing inter-male contests. We recorded fight escalation level, duration, size, winner and tested whether these variables differ between same- and different-handed fights. Different-handed fights are more likely to escalate to grappling, suggesting that it is harder for the combatants to judge the opponents’ strength in this situation. We suggest that this is due to distinct positioning of same- and different-handed opponents resulting in distinct force mechanics. Since the likelihood of injury and energy expenditure are higher when opponents are different-handed, why are both fight types equally likely to happen? Finding a same-handed opponent may incur higher energetic costs than those incurred by fighting a different-handed male. Further investigations of handedness in fight outcome may shed light on the selective pressures causing and maintaining the handedness ratio in populations.