Geographic variation in weapon size and maximum strength among populations of the two-toned fiddler crab (Uca vomeris) - Integrative Ecology Lab Website at The University of Queensland

Male Uca vomeris strutting his stuff

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 our research, we are testing 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) as a function of population density and habitat variation. Fiddler crabs represent an ideal group for studying the evolution of weapon strength as males possess one enlarged and brightly coloured claw that is used both as a weapon during disputes (watch the video) with other males and to attract females during courtship.

So far we have examined 8 populations of U. vomeris in the creeks and bays along the south-east coast of Queensland between the Gold Coast and Bribie Island. Our predictions are that the increased competition that results from high population densities would be associated with larger relative claw sizes and greater weapon performance.


Candice and Ben "mudding"	Candice modelling Acme brand mudshoes

For each population, we are estimating population density and biomass to use as a proxy for the level of competition. We are also collecting approximately 100 males from each population and measuring body size, claw size and maximum claw closing strength for each individual using a custom built force transducer.

Measuring claw force of a male Uca vomeris with a custom-built force transducer

Update:

Current field work is looking at the level of interactions between males by recording behaviour using a camcorder and compiling a breakdown on how and for what period of time males interact with other crabs.

Further interests:

Colour variation of claws between populations and between different species.