Comparative Studies of Circadian Locomotory Rhythms in Four Species of Terrestrial Crabs

Abstract

Spontaneous locomotor behavior of four species (Gecarcinus lateralis, Cardisoma guanhumi, Ocypode quadrata, Coenobita clypeatus) of land crabs was studied in the field and in controlled conditions in the laboratory. All were found to be predominantly nightactive, and these locomotor rhythms persisted in constant temperature and in both constant darkness or constant illumination of various intensities for periods of over 3 months. No difference in the circadian period length of the rhythm could be distinguished at constant light intensities between 5 and 50 ft-c. The rhythms could be rephased by subjecting the crabs to artificial light cycles offered out of phase with the natural one. The effect of various constant temperatures (all within the ecological range) on the period lengths of rhythms in two species of crabs was tested; the rhythms were found to be essentially independent of temperature. The great edible land crab reacted differently to increases in temperature in that the length of its period increased slightly, producing a Ql0 of 0.996. I