Allometry and sexual selection in the chela shape of the squat lobster, Munida rugosa

Sexual selection generally promotes the development of ornaments or weapons that improve an individual’s chance of mating. The squat lobster Munida rugosa exhibits a range of variation in chela (claw) morphology, with some individuals having a particular arched chela morphology, apparently specialized as a weapon. Geometric morphometric techniques were used to compare chela morphology across a wide size range and between sexes. The most fully developed arched morphology only occurred in large males, although not all large males possessed an arched claw, while smaller males retained straight, slender claws. Some large females exhibited a reduced version of the arched morphology. The pattern of occurrence of the arched morphology suggests that it is, or has been, subject to sexual selection through male–male competition for mates.