Sexual dimorphism, cheliped assymetry and selection pressure in , Uca spp

Croll, G.A. *; McClintock, J.B.: Sexual dimorphism, cheliped assymetry and selection pressure in , Uca spp.

Left-right claw asymmetry occurs in a variety of decapod species. The asymmetries can be present in early development or arise during sexual differentiation. In Uca spp., males have a dimorphic enlargement of one of the two chelipeds. The larger cheliped has been associated with male reproductive success as a result of female selection or advantage in male-male combat. Because the enlarged cheliped occurs on either the right or left side, selection pressure could produce populations with right or left cheliped dominance. To ascertain whether such selection pressure is acting on Uca longisignalis, U. minax, and U. pugnax, populations of fiddler crabs from four North American marshes were sampled; two on the coast of the Atlantic Ocean, one on the Chesapeake Bay and one on the coast of the Gulf of Mexico. There were no significant differences in the proportion of right or left enlarged chelipeds within males of all sampled species or within marshes (p>0.05). Similarly, when male crabs were grouped arbitrarily into two major cheliped size classes (equal to or greater than 20 mm and less than 20 mm) the proportion of right or left enlarged cheliped individuals was similar among each of the size groups (p>0.05). Mean major propodus size for males was similar for individuals with either right or left cheliped dominance within each of the three species and four marshes (p>0.05). It appears that among these three species of Uca, there is no selection for males with cheliped enlargement on either the right or left side .

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