Meeting Abstract

84.3  Thursday, Jan. 7  Allometry and Correlated Evolution in Fiddler Crab Major Claw Morphology GEORGE, Matthew N*; SWANSON, Brook O; Gonzaga University; Gonzaga University mgeorge3@gonzaga.edu

For males of many animal species, diverse and opposing selective pressures influence the morphology and function of secondary sex characteristics. In the genus Uca, male fiddler crabs exhibit a single enlarged claw used not only in the context of male-female signaling, but also in male-male combat. This dual utility of a single appendage presents an opportunity to study variation across species and investigate how the appendage’s dual roles as a weapon and a visual signal shape morphology. In this study morphology, and structural properties (resistance to puncture) of the major claw and carapace were sampled for 23 species within the genus. An estimation of claw closing force was also determined using these measurements. Our results show large variations in all morphological and structural variables across species, even after correcting for body size. The resistance to puncture of the major claw appears to scale as mass to the 2/3 power. Claw force production on the other hand shows positive allometry, scaling as mass to the 1.1 power. Correlations of size corrected, phylogenetically independent contrasts show a positive relationship between claw-closing force and resistance to cuticle puncture (species with forceful claws have resistant cuticles), suggesting that these are evolutionarily correlated traits. However, mass corrected claw area (an estimate of signal size) is inversely correlated with claw force production, suggesting an evolutionary trade-off between signaling and fighting.