Evolution of shape differences between the major and minor chelipeds of Uca pugnax (Decapoda: Ocypodidae)

Geometric morphometries were used to analyze shape differences between the major and minor chelipeds of the fiddler crab Uca pugnas. Although the major and minor chelipeds had similar allometric developmental trajectories. The form of the major cheliped was not all allometric extrapolation of the minor cheliped. The changes in shape associated with the formation of the major cheliped have functional relevance; they allow the major cheliped to produce relatively more power then the minor cheliped. This result suggests that selection for combat effectiveness has played an important role in the evolution of the major cheliped.