John H. Christy
Address: Smithsonian Tropical Research Institute,
Attn: John H. Christy
9100 PANAMA CITY PL
Washington DC 20521-9100
Telephone: +507 212.8720
FAX: +507 212.8790
Note to students:
Thank you for your interest in my research and in working with me.
Volunteers and Interns: I am not accepting new volunteers or interns at this time.
Pre- and Postdoctoral Fellows: I am available to serve as a STRI advisor to pre- and post-doctoral fellows doing research in most areas of animal behavior and intertidal marine biology. Please contact me well in advance of fellowship application deadlines so that we have time to discuss your interests and proposal.
The evolution of animal communication with emphasis on sexual selection, courtship and the behavioral mechanisms of mate choice in fiddler crabs, genus Uca.
The timing of reproduction by intertidal crabs and the dispersal ecology of crab larvae.
The behavioral and evolutionary ecology of marine invertebrates.
Multiple modes of sexual selection on a male trait. Courting males of about 17 species of fiddler crabs build sand or mud structures at the opening of their burrows to which they attract females for mating. Through direct observation and field experiments we are studying three causes of sexual selection of structure building in Uca beebei and Uca musica:
1) the differential attractiveness of structures, compared to unadorned burrow openings, to mate-sampling females,
2) the differential utility of structures as visual guideposts that males use to find their own burrows when courtship has produced errors in their non-visual orientation mechanism, which is based on path integration,
3) the differential effects of structures on the rate males detect, encounter and court females. Ultimately we hope to parse and measure the effects of each mode of sexual selection on structure building and design.
Selection of mating preferences.
We have shown experimentally that structures build by male fiddler crabs attract mate sampling females. Such preferences usually are thought to arise and be maintained by selection that is a consequence of mating males with the preferred trait. In this case, however, our studies strongly suggest that structures co-opt for mate choice a response that is selected by predation. Through field experiments we have shown that structures are attractive to males and females of species who don't build them, that females of structure building species do not prefer the structures built by males of their own species and that natural objects such a stones, shells and bits of wood are as attractive or more attractive than are male-built structures. Together the evidence indicates that male built structures elicit landmark orientation, the tendency of fiddler crabs to move toward and hide behind objects when they are at risk moving on the surface away from burrows, as are mate sampling females. Females who approach structures may benefit directly by reducing their mate search costs. We have shown that structure building is a condition-dependent trait suggesting that females may also benefit indirectly by mating structure builders. However such possible indirect benefits appear to be a fortuitous effect, rather than a cause of the evolution of the differential response to structures.
Deceit in animal communication.
Fiddler crabs frequently use deception in both courtship and competitive interactions. Currently, our studies on this topic include the use by male Uca musica of displays that startle females into their burrows to mate, as do avian predators, and the construction by juvenile female Uca beebei of mud chimneys that elevate their burrow opening above the visual field of competitors, primarily juvenile males, and thereby hide their burrow allowing these females to maintain burrow ownership without having to defend their burrow in a fight they are sure to loose.
Many intertidal estuarine crabs release their larvae at night near the time of high tide on the days of the biweekly tidal cycle with the larger amplitude nocturnal ebb tides. Consequently their larvae are transported rapidly at night to deeper coastal waters where they develop. Evidence is accumulating that this timing pattern allows newly hatched larvae to escape heavy predation by diurnally feeding planktivorous fish that are most abundant is shallow water. A study of the reproductive timing of Uca musica has provided a new line of evidence that supports this predator escape hypothesis. The larvae of this species are small, red and have short spines, characters that make them very vulnerable to fish predation and the timing of larval release follows the above pattern. Egg hatching and larval release marks the end of a period of embryonic development, the duration of which depends on the temperature of the sediment where females incubate their eggs. Due to seasonal cold water up-welling in the Bay of Panama, sea and sediment temperatures vary annually by 4 - 6 oC. By monitoring daily both temperature and the timing of courtship, mating and ovulation over a 17 month period we have found that adults change when they court and mate to compensate for the effects of temperature on the duration of incubation so that females release larvae on the larger amplitude nocturnal ebb tides in the biweekly cycle year-round. The mechanism that gives rise to this remarkable temperature-dependent phase shift in adult reproductive cycles remains completely unknown.
Education and Degrees
B.A., Lewis and Clark College, 1970.
Ph. D., Cornell University, 1980.
Christy, J. H., P. R. Y. Backwell and U. Schober. 2003. Interspecific attractiveness of structures built by courting male fiddler crabs: experimental evidence of a sensory trap Behav. Ecol. Sociobiol. 53:84-91
Christy, J. H., J. Baum and P. R. Y. Backwell. 2003. Attractiveness of sand hoods built by courting male fiddler crabs Uca musica: test of a sensory trap hypothesis. Anim. Behav. 66:89-94.
Christy, J. H., P. R. Y. Backwell, S. Goshima, and T. J. Kreuter. 2002. Sexual selection for structure building by courting male fiddler crabs: an experimental study of behavioral mechanisms. Behavioral Ecology 13:366-374.
Backwell, P. R. Y, J. H. Christy, S. R. Telford, M. D. Jennions and N. I. Passmore. 2000 Dishonest signaling by a fiddler crab. Proc. Royal Soc. B. 267:1-6
Christy, J. H. and S. G. Morgan. 1998. Estuarine immigration by crab postlarvae: mechanisms, reliability and adaptive significance. Mar. Ecol. Prog. Ser. 174:51-65
Strumbauer, C., J. S. Levinton and J. H. Christy. 1996. Molecular phylogeny of fiddler crabs: test of the hypothesis of increasing behavioral complexity in evolution. Proc. Nat. Acad. Sci. USA 93:10855-10857.
Morgan, S. G., and J. H. Christy. 1995. Adaptive significance of the timing of larval release by crabs. American Naturalist 145:457-479.
Christy, J. H. 1995. Mimicry, mate choice, and the sensory trap hypothesis. American Naturalist 146:171-181.
Christy, J. H. 1983. Female choice in the resource-defense mating system of the sand fiddler crab, Uca pugilator. Behavioral Ecology and Sociobiology 12:169-180.
Christy, J. H. 1978. Adaptive significance of reproductive cycles in the fiddler crab Uca pugilator: a hypothesis. Science 199:453-455.