:: Current research project

Behavioural ecology and conservation of the fiddler crab Uca tangeri at the Ria Formosa Natural Park

Fiddler crabs encompass a wide variety of species, presenting a great deal of phenotypic variation in what regards to colour, size and behaviour. Nevertheless, they all share common characteristics, particularly in what regards to visual communication. Vision is extensively used by fiddler crabs in most of their social activities; however, waving is the visual display they are renowned for. This visual display is performed by males and it consists of the rhythmic and stereotyped elevation of the major claw. It is both used in a courtship context, to attract mates, and in a territorial context as a threat display to other males that may attempt to take over the signallers burrow. Although this visual display has been extensively studied by several authors in several fiddler crab species, especially in relation to its social context, some other aspects of this genus visual communication are still open for investigation.

In this study, the fiddler crab species Uca tangeri - the only fiddler crab species to occur in Europe, where they burrow in the mudflats and salt marshes of southern Spain and Portugal- was used as a model to address several of these questions. More specifically, the following issues were addressed: (1) characterization of four species of fiddler crabs’ spectral sensitivity and how it is adapted to visual communication; (2) how is crab body colouration perceived by conspecifics and potential avian predators and how is it adapted to the needs of both communicating with conspecifics and hiding from avian predators; (3) how much information is conveyed in the individual spatio-temporal features of the waving display and are there enough intra-individual differences to consider the hypothesis of a signature wave; (4) costs associated to the males’ enlarged claw used in the waving visual display: conspicuity to human observers and impairment of escape speed; (5) consequences of claw harvesting (a particular form of predation practiced by fishermen in this U. tangeri study population, where male enlarged claws are collected and crabs are released back in the mudflat to regenerate a new one): how it affects signalling ability and, consequently, population dynamics; (6) habitat structure: consequences of different densities of vegetation cover on visual communication.

Funded by: FCT - PRAXISXXI/BD/19835/99

:: Selected publications

- Cummings, M.E., Jordão, J.M., Cronin, T.W. and Oliveira, R.F. 2008. Visual ecology of the fiddler crab Uca tangeri: effects of sex, viewer and background on conspicuousness. Animal Behaviour 75: 175-188.

- Jordão, J.M., Cronin, T.W. and Oliveira, R.F. 2007. Spectral sensitivity of four species of fiddler crabs (Uca pugnax, Uca pugilator, Uca vomeris and Uca tangeri) measured by in situ microspectrophotometry. Journal of Experimental Biology 210: 447-453.

- Jordão, J.M., Curto, A.F. and Oliveira, R.F. 2007. Stereotypy and variation in the claw waving display of the fiddler crab Uca tangeri. Acta Ethologica 10: 55-62.

- Jordão, J.M. and Oliveira, R.F. 2005. Wandering in male fiddler crabs (Uca tangeri): alternative reproductive tactic or functional constraint? Behaviour 142: 929-939.

- Jordão, J.M. and Oliveira, R.F. 2001. Sex differences in predator evasion in the fiddler crab Uca tangeri (Decapoda: Ocypodidae). Journal of Crustacean Biology 21: 948-953.