ABSTRACT
Cardiac responses of Portunus xantusii (Stimpson) (Crustacea: Decapoda) to simulated luminescent flashes were similar to responses to real flashes produced by the sea pansy Renilla kollikeri (Pfeffer). Tethering the crabs did not significantly affect cardiac responses to light flashes and allowed for more control over stimulus presentation. Crabs were maximally responsive to wavelengths from 500 to 510 nm (175 nm width at half-maximum response). The wavelength of maximal sensitivity based on the electroretinogram was 510nm. The critical fusion frequency for P. xantusii was 25·6 Hz. Pulse rate and train duration of light flashes were the most important features of the stimulus for eliciting maximal cardiac responses, with pulse duration and inter-pulse interval having minor effects on flash effectiveness. Pulse rates of 4–5 Hz within a train elicited the largest cardiac responses. Increases in train duration from 1 to 5 s resulted in a linear increase in heart response, but stimuli with train durations longer than 5 s did not elicit concomitant increases in heart response. Habituation to pairs of stimulus trains occurred if inter-train intervals were less than 8–10 min. The characteristics of the luminescent signals produced by benthic invertebrates are well matched to the characteristics of light stimuli that are most effective at eliciting physiological and behavioral responses from Portunus xantusii.
