Male mating success in a fiddler crab: a lesson in sample sizes

Autotomy and regrowth of a body part occurs in many animal species. It is costly to regrow the limb and there are often additional long-term costs in, for example, limb strength, foraging efficiency and even mating success. In the fiddler crab Uca mjoebergi, 7 % of males have autotomized and regrown their large claw at some point in their lives. Previous work has shown that there is a great disadvantage to having a regenerated claw. While these males are able to attract mate-searching females to visit them, none of the 84 males observed to have mated in previously collected data had regenerated claws. Since females' final mate choice is based on burrow structure, it was assumed that males with regenerated claws had poorer burrows. Here we show that, by finding only three cases of a female mating with a regenerated claw male, that there is, in fact, no mating disadvantage to having a regenerated claw. We also show that the burrows of males with regenerated claws are no different than those of orginal-clawed males. This is a very clear reminder that sample size matters, especially when dealing with rare events.