Thermoregulation as an Alternate Function of the Sexually Dimorphic Fiddler Crab Claw

Abstract

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. abstract: Fiddler crabs are highly sexually dimorphic. Males possess one small (minor) feeding claw and one greatly enlarged (major) claw; females possess two small claws. The major claw is used to attract mates and for burrow defense, but it is costly for the male to possess. We tested the hypothesis that the major claw also functions as a thermoregulatory structure, a function that would allow males to spend a greater amount of time at the surface, foraging and attracting potential mates. Fiddler crabs Uca panacea were exposed to a source of radiant heat and body temperatures were monitored.Four groups of crabs were tested: intact males, males with the minor claw removed, males with the major claw removed, and females. The body temperatures of males without the major claw increased more rapidly and reached higher values than did those of males with the major claw intact, but the results from these animals were similar to those of females. These results support the hypothesized thermoregulatory function of the major claw. The major claw may function as a heat sink, transferring heat away from the body and dissipating it into the air. Enhanced thermoregulatory ability provided by the major claw may partially ameliorate the energetic costs of possessing such a large claw.

Size-dependent temperature and desiccation constraints on performance capacity: Implications for sexual selection in a fiddler crab

“…Under similar environmental conditions, small crabs experienced greater water loss and presumably associated desiccation stress compared with large crabs. Darnell and Munguia (2011) reported a similar pattern of increasing dehydration rate with decreasing body size for the closely-related fiddler crab U. panacea. Studies of terrestrial locomotion in ghost crabs (Ocypode quadrata), crayfish (Orconectes rusticus), and isopods (Porcellio laevis) have found that locomotion is significantly reduced or even ceases when water loss approaches 10% (Claussen et al, 2000;Dailey et al, 2009;Weinstein et al, 1994).…”

Survival and arm abscission are linked to regional heterothermy in an intertidal sea star

“…The Journal of Experimental Biology 216 (12) An intriguing hypothesis to explain the temperature deviation between body regions is that the arms might function as heat sinks, as proposed for the major claw in fiddler crabs (Darnell and Munguia, 2011). Such a mechanism implies a capacity to transfer heat between the central disc and the arms, where the heat can be exchanged more easily with the environment due to the comparatively higher surface area to volume ratio.…”

“…The heat sink function of appendages is relatively frequent in vertebrates such as the enlarged ears of jackrabbits (Hill et al, 1980) and elephants (Weissenböck et al, 2010), or the bill of some birds (Tattersall et al, 2009), but this phenomenon remains understudied for most ectotherms (e.g. Darnell and Munguia, 2011).…”

“…Overall, however, regional heterothermy is likely to result from an association of both passive and active processes for most ectotherms. Recently, for example, the major claw of the fiddler crab was suggested to serve as a heat emitter, collecting the heat (active way) from the body exposed to solar radiation, and releasing it (passive way) to the environment via convection (Darnell and Munguia, 2011).…”

Thermal games in crayfish depend on establishment of social hierarchies

“…Indeed, Wilson and colleagues Wilson et al, 2009) have shown that in adult crayfish, although chela size is a dishonest signal of strength, it is a reliable predictor of resource holding potential and contest outcome. As swimming speed is inversely related to chela size, chela size may represent a trade-off (via the handicap principle), signaling greater resource holding potential based not on force production, but on other parameters that cannot be readily detected, such as thermoregulation (Darnell and Munguia, 2011). Because of the risks of injury, however, accurate signaling between conspecifics may still be important in minimising the escalation of contests.…”