Meeting Abstract

25.8  Monday, Jan. 5  Geographic variation in weapon size, strength and colouration among populations of the two-toned fiddler crab (Uca vomeris). BYWATER, CL*; WHITE, C; WILSON, RS; University of Queensland; University of Queensland; University of Queensland c.bywater@uq.edu.au

Males of many species possess specialized weapons that are often displayed to resolve territorial disputes without direct physical contact. Theory predicts that the evolution of increased weapon size should be associated with increased competition for resources and weapon strength should increase simultaneously with size (reliable signals). In this study, we tested this association by examining inter-population variation in the size and maximum strength of the enlarged claw of the two-toned fiddler crab (Uca vomeris) and examined its association with population density, habitat variation and weapon colouration. Fiddler crabs represent an ideal group for studying the evolution of weaponry as males possess one enlarged and brightly coloured claw that is used both as a weapon during disputes with other males and to attract females during courtship. We examined ten populations of U. vomeris in the creeks and bays along the south-east coast of Queensland between the Gold Coast and Noosa. We predicted that the increased competition that results from high population densities would be associated with larger relative claw sizes and greater strength. For each population, we estimated population density and quantified the habitat type, orientation and average tidal exposure. We collected more than 100 males from each population and measured the body size, claw size and maximum claw closing strength for each individual using a custom built force transducer. We will discuss the variation observed among populations in relative and absolute size of their weaponry and its association with maximum strength, weapon colouration and population density.