Luminescent Flash Avoidance in the Nocturnal Crab Portunus Xantusii : I. The Effects of Luminescence and Mechanical Stimulation on Heart Rate

In crabs, the ratio of the heart rate before to that after sensory stimulation (the response ratio) provides a reliable indicator of the effects of sensory stimulation on cardiac activity. The nocturnally active crab Portunus xantusii (Stimpson) exhibits rapid decreases in heart rate in response to the luminescent flashes produced by the sea pansy Renilla kollikeri (Pfeffer) and to mechanical stimulation. Crabs move away from luminescent and mechanical stimuli and this behavior is well correlated with the cardiac responses. Therefore, cardiac response ratios can be used as a reliable bioassay to determine the components of sensory stimuli that are important in eliciting behavioral responses. The similar cardiac responses to both luminescent and mechanical stimuli suggest that a single command pathway may be responsiblefor triggering startle behavior in response to a wide variety of rapid, brief and intense sensory stimuli. Heart rate also varied depending on the body size of the crab and the ambient temperature. Small crabs had faster heart rates than larger crabs, and the relationship between heart rate and body size is described by the equation: fH=794.3x−059222, where fH is heart rate in beats per minute and x is carapace length in millimeters.Heart rate increased with increasing temperature over a range of 10–22 °C, but no further increases occurred at higher temperatures. The Q10 for the range 10–20°C was 1.8.