Showing papers on "Uca pugilator published in 1998"

Retinal location is the key to identifying predators in fiddler crabs (Uca pugilator).

Abstract: Fiddler crabs (Uca pugilator Bosc; Crustacea, Decapoda) feed and court in open, flat spaces. Their visual system has several putative adaptations to their flat habitat, including the tendency to keep the vertical axis of their eyes perpendicular to the plane of the substratum. It is hypothesized that one of the functions of this behavior is to distinguish accurately predators from conspecifics by aligning the region of the eye sensitive to predators with the region in space in which predators occur. To test this hypothesis, a crab was placed in a glass dish, and a moving stimulus was presented between 20 degrees above and below eye level (horizontal). Stimuli below the crab's horizon hardly ever evoked escape responses, while identical stimuli above the horizon produced escape responses whose frequency varied with the angular size, not the absolute size, of the stimulus. Experiments with artificial horizons showed that it is the position of the stimulus relative to the eye that is important, rather than its position relative to external cues such as the visible horizon, the vertical light gradient or the gravitational horizon. It is concluded that a crab responds to stimuli according to their position relative to its retinal equator. This conclusion is discussed in light of the crabs' natural behavior with respect to supra-horizontal stimuli.

Effects of Temperature and Water Loss on Terrestrial Locomotor Performance in Land Crabs: Integrating Laboratory and Field Studies'

Abstract: SYNOPSIS. Terrestrial and semi-terrestrial crustaceans are exposed to fluctuations in ambient temperature and conditions that favor evaporative water loss. These environmental stresses alter performance limits in the laboratory and behavior in the field. The maximal rate of oxygen consumption, maximum aerobic speed, and endurance capacity are greater at a body temperature (Tb) of 24°C than at 15°C or 30°C in the ghost crab, Ocypode quadrata . The total metabolic cost to move at the same relative speed is greater at a Tb of 24°C than at 15°C. Slower aerobic kinetics at 15°C result in a smaller relative contribution of oxidative metabolism to total metabolic cost. However, the relative contributions from accelerated glycolysis are similar at both temperatures. When locomotion is intermittent, the total distance traveled before fatigue can be similar at Tbs of 15 and 24°C but result from different movement and pause durations at these temperatures. Performance limits of the ghost crab are negatively affected by dehydration and are sensitive to rates of water loss. In the laboratory, endurance capacity of the fiddler crab, Uca pugilator, is greater at a Tb of 30°C than at 25°C. In the field, freely moving fiddler crabs with a Tb of 30°C travel at faster mean preferred speeds, as determined by motion analysis, than crabs at 25°C. Data for land crabs support and advance general ectothermic models for the effects of temperature and dehydration on locomotor performance.