Adaptive Coloration in Invertebrates
Five species of fiddler crabs occupy a variety of intertidal niches along the Texas coast. Each Uca is adapted to a specific array of physical factors in the environment. Some aspects of their adaptations are reflected by body color. Interspecific differences in morphological coloration are correlated with camouflage and substrate characteristics. Intraspecific color variation is expressed through neurosecretion-mediated physiological change in cellular pigment distribution. Adaptation to a dark or light colored background reveals different "secondary" chromomotor capabilities for each species. In addition, pigments in melanophores, leucophores and erythrophores exhibit circadian rhythms of dispersion and aggregation.
During a "primary" chromomotor response to light or temperature, chromatophores act as independent effectors without endocrine mediation. Generally, logarithmic changes in luminosity from 12- to ,000-foot candles disperse chromatophore pigments in species from the Minuca subgenus but not member of the Celuca subgenus. In the very terrestrial Celuca, U. subcylindrica, erythophores and melanophores were observed to aggregate. Since this does not occur in eyestalk-less crabs the response is augmented by light activating a visual-neurosecretory reflex. Changing temperature stimulated thermoregulatory chromomotor activity in the Celuca, U. panacea and U. subcylindrica, but not the Minuca. In Celuca , the carapace darkens as temperature decreases and lightens as it increases. Based on these chromatophore studies, the pigmentary systems of the subgenus Celuca appear to be predisposed for better short-term thermoregulaiton than those in the subgenus Minuca.
Department of Biology
Original Publication Date
UNI ScholarWorks, University of Northern Iowa, Rod Library
©1990 Carl L. Thurman
Thurman, Carl L., "Adaptive Coloration in Texas Fiddler Crabs (Uca)" (1990). Biology Faculty Publications. 17.