Abstract
One of the possible costs of the male fiddler crabs enlarged claw can be conspicuousness to predators. This hypothesis was tested using human observers as a model of visual predators. In the European fiddler crab, Uca tangeri Eydoux, the males' major claw is white contrasting with the orange-brownish colour of the carapace and of the feeding claw, and the mudflat background. The following morphotypes were created from close-up photographs taken in nature using an image processing software: male, male without claw, female, female with enlarged claw, male with enlarged claw of the same colour of the feeding claw, male with 75% sized claw, male with 50% sized claw. These morphotypes were then presented in a randomised order to students, using a psychology test software, which allows the measurement of response time in msec. The subjects were allowed to look at the images for an unlimited amount of time, until they detected the individual or until they decided to pass on to another image. Backgrounds (i.e. mudflat picture) without individuals were also presented as a control. Male crabs were detected significantly sooner than females. When we compared males with the claw removed with females with an enlarged claw added, the pattern is reversed and the latter are detected significantly faster. Thus, the enlarged claw seems to be the key feature that makes the individuals more conspicuous. Size and colour seem to be the main aspects of the claw's conspicuousness. The data of these experiments support the initial prediction of males being more conspicuous than females because of their enlarged claw. The possible costs and benefits of this trait, related to predation, are discussed.
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References
Andersson, M., 1994. Sexual Selection. Princeton University Press. New Jersey.
Backwell, P. R. Y. & N. I. Passmore, 1996. Development of asymmetry in the fiddler crab Uca cumulanta, Crane 1943 (Decapoda: Brachyura). Crustaceana, 34: 294–300.
Backwell, P. R. Y., P. D. O'Hara & J. H. Christy, 1998. Prey availability and selective foraging in shorebirds. Anim. Behav, 55: 1659–1667.
Bennet, A. T. D. & I. C. Cuthill, 1994. Ultraviolet vision in birds: what is its function? Vision Res, 34: 1471–1478.
Bennett, A. T. D., I. C. Cuthill & K. J. Norris, 1994. Sexual selection and the mismeasure of color. Am. Nat. 144: 848–860.
Bildstein, K. L., S. G. McDowell & I. L. Brisbin, 1989. Consequences of sexual dimorphism in sand fiddler crabs, Uca pugilator: differential vulnerability to avian predation. Anim. Behav. 37: 133–139.
Bradbury, J. W. & S. L. Vehrencamp, 1998. Principles of animal communication. Sinauer Associates, Sunderland, MA.
Cade, W., 1975. Acoustically orienting parasitoids: fly phonotaxis to cricket song. Science 190: 1312–1313.
Caravello, H. E. & G. N. Cameron, 1987. The effects of sexual selection on the foraging behaviour of the Gulf Coast fiddler crab, Uca panacea. Anim. Behav. 35: 1864–1874.
Christy, J. H., 1983. Female choice in the resource-defense mating system of the sand fiddler crab, Uca pugilator. Behav. Ecol. Sociobiol. 12: 169–180.
Christy, J. H., 1987. Female choice and the breeding behavior of the fiddler crab Uca beebei. J. Crust. Biol., 7: 624–635.
Clinton, W. L. & B. J. Le Boeuf, 1993. Sexual selection's effects on male life history and the pattern of male mortality. Ecology 74: 1884–1892.
Crane, J., 1967. Combat and its ritualization in fiddler crabs (Ocypodidae) with special reference to Uca rapax. Zoologica 52: 49–76.
Crane, J., 1975. Fiddler crabs of the world. (Ocypodidae, Genus Uca). Princeton University Press, New Jersey.
Cronin, T. W. & R. B. Forward Jr., 1988. The visual pigments of crabs I. spectral characteristics. J. Comp. Physiol. A 162: 463–478.
Cummins, D. R. & T. H. Goldsmith, 1981. Cellular identification of the violet receptor in the crayfish eye. J. Comp. Physiol. A 142: 199–202.
Dusenbery, D. B., 1992. Sensory Ecology. W. H. Freeman & Co, New York.
Endler, J. A., 1987. Predation, light intensity and courtship behaviour in Poecilia reticulata (Pisces: Poeciliidae). Anim. Behav. 35: 1376–1385.
Endler, J. A., 1992. Signals, signal conditions, and the direction of evolution. Am. Nat. 139: S125–S153.
Ens, B. J., M. Klassen & L. Zwarts, 1993. Flocking and feeding in the fiddler crab (Uca tangeri): prey availability as risk-taking behaviour. Neth. J. Sea Res. 31: 477–494.
Faria, M. M., 1994. Aspectos do comportamento das bocas-decavalete Uca tangeri (Eydoux), (Ocypodidae, Brachyura) no Parque Natural da Ria Formosa. Parque Natural da Ria Formosa.
Finger, E. & D. Burkhardt, 1994. Biological aspects of bird colouration and avian colour vision including ultraviolet range. Vision Res. 34: 1509–1514.
Formanowicz, D. R., Jr. & E. D. Brodie, Jr., 1988. Predation risk and forager escape tactics. Anim. Behav. 36: 1836–1860.
Greenspan, B. N., 1980. Male size and reproductive success in the communal courtship system of the fiddler crab Uca rapax. Anim. Behav. 28: 387–392.
Houde, A. E., 1997. Sex, Color, and Mate Choice in Guppies. Princeton University Press, Princeton, N.J.
Hyatt, G., 1975. Physiological and behavioural evidence for colour discrimination by fiddler crabs (Brachyura, Ocypodidade, genus Uca). In Vernberg, F. J., (ed.), Physiological Ecology of Estuarine Organisms. Univ. South Carolina Press, Columbia: 333–365
Hyatt, G. W., 1977. Field studies of size dependent changes in waving display and other behaviour in the fiddler crab, Uca pugilator, Bosc (Brachyura, Ocypodidae). Mar. Behav. Physiol. 4: 283–292.
Land, M. & J. Layne, 1995. The visual control of behaviour in fiddler crabs. I. Resolution, thresholds and the role of the horizon. J. Comp. Physiol. A 177: 81–90.
Latruffe, C., P. K. McGregor & R. F. Oliveira, 1999. Visual signalling and sexual selection in male fiddler crabs, Uca tangeri. Mar. Ecol. Prog. Ser. 189: 233–240.
Layne, J., M. Land & J. Zeil, 1997. Fiddler crabs use the visual horizon to distinguish predators from conspecifics: a review of the evidence. J. mar. biol. Ass. U.K. 77: 43–54.
Leggett, L. M. W., 1979. A retinal substrate for colour discrimination in crabs. J. Comp. Physiol. A 133: 159–166.
Martin, F. G. & M. I. Mote, 1982. Colour receptors in marine crustaceans: a second spectral class of retinular cell in the compound eyes of Callinectes and Carcinus. J. Comp. Physiol. A 145: 549–554.
Murai, M., S. Goshima & Y. Nakasone, 1983. Adaptive droving behavior observed in the fiddler crab Uca vocans vocans. Mar. Biol. 76: 159–164.
Oliveira, R. F & M. R. Custódio, 1998. Claw size, waving display and female choice in the European fiddler crab, Uca tangeri. Ethol. Ecol. Evol. 10: 241–251.
Oliveira, R. F., J. L. Machado, J. M. Jordão, F. R. L. Burford, C. Latruffe & P. K. McGregor, 2000. Human exploitation of male fiddler crab claws: behavioural consequences and implications for conservation. Anim. Conserv. 3: 1–5.
Rosenberg, M. S., 1997. Evolution of shape differences between the major and minor chelipeds of Uca pugnax (Decapoda: Ocypodidae). J. Crust. Biol. 17: 52–59.
Salmon, M., 1984. The courtship, aggression and mating system of a 'primitive' fiddler crab (Uca vocans: Ocypodidae). Trans. Zool. Soc. London 37: 1–50.
Scott, S. & M. I. Mote, 1974. Spectral sensitivity in some marine Crustacea. Vision Res. 14: 659–663.
Thurman, C. L., 1990. Adaptive coloration in Texas fiddler crabs (Uca). In Adaptive coloration in invertebrates, Proceeding of a symposium sponsored by the American Society of Zoologists 109–126.
Valiela, I., D. F. Babiec, W. Atherton, S. Seitzinger & C. Krebs, 1974. Some consequences of sexual dimorphism: feeding in male and female fiddler crabs, Uca pugnax (Smith). Biol. Bull. 147: 652–660.
Vehrencamp, S. L., J. W. Bradbury & R. M. Gibson, 1989. The energetic cost of display in male sage grouse. Anim. Behav. 38: 885–896.
Von Hagen, H.-O., 1962. Freilandstudien zur Sexual und Fortp-flanszungsbiologie von Uca tangeri in Andalusien. Z. Morph. Ökol. Tiere 51: 611–725.
Weygoldt, P., 1977. Communication in crustaceans and arachnids. In Sebock, T. A. (ed.), How Animals Communicate, Univ. Indiana Press, Indiana: 303–333.
Zeil, J., G. Nalbach & H.-O. Nalbach, 1986. Eyes, eye stalks and the visual world of semi-terrestrial crabs. J. Comp. Physiol. A 159: 801–811.
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Jordão, J.M., Oliveira, R.F. Major claws make male fiddler crabs more conspicuous to visual predators: a test using human observers. Hydrobiologia 449, 241–247 (2001). https://doi.org/10.1023/A:1017534228184
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DOI: https://doi.org/10.1023/A:1017534228184