Meeting Abstract

3.6  Wednesday, Jan. 4  Carapace coloration affects body temperature and limits activity in the fiddler crab Uca panacea DARNELL, M.Z.*; FOWLER, K.; MUNGUIA, P.; University of Texas at Austin

Ectotherms can regulate body temperature behaviorally or, in some cases, by changing coloration. Body coloration, however, is also used in communication and camouflage. Organisms using color change for thermoregulation, including fiddler crabs, typically become darker in response to low temperatures or lighter in response to high temperatures which increases the absorption or reflection, respectively, of solar radiation. Often these processes, thermoregulation and communication for example, may be in conflict; therefore the ability to change color becomes habitat- and context-dependent. In the intertidal, organisms such as fiddler crabs are exposed to a wide range of diel and seasonal temperatures. We investigated the effect of coloration on body temperature and activity in the fiddler crab Uca panacea using artificially-applied color. When exposed to a source of radiant heat in the laboratory or exposed to solar radiation, black-painted crabs became significantly warmer than white-painted crabs. Unpainted and clear-painted crabs reached intermediate temperatures. We then placed painted crabs in outdoor mesocosms and monitored activity levels. Activity was greatest in the morning and late evening. Crabs painted white were active more than crabs painted black or control crabs, especially in the unvegetated portion of the mesocosm. Activity during the daytime hours was limited by high temperatures, although this effect was ameliorated in light-colored crabs. These results indicate that carapace coloration and color change are important determinants of body temperature in fiddler crabs and can influence distribution in intertidal habitats. Coupled with previous results on color change and thermoregulation, these results support the hypothesis that carapace coloration plays a role in maintaining optimal body temperatures and may influence crab distribution and activity.