Stimulus discrimination and wave source localization in fishing spiders (Dolomedes triton and D. okefinokensis)

We have studied the behavioral responses of fishing spiders (Dolomedes triton and Dolomedes okefinokensis) to water surface wave stimuli. D.okefinokensis responded to click-like wave stimuli (Fig. 3C) in less than 15% of the cases. Responsiveness did not increase if up to 20 clicks were elicited in quick succession from the same spot (Fig. 5). If longer lasting concentric stimuli were offered, the spiders determined the direction (Fig. 6) and the distance (Fig. 8) to the wave source. This was true for monofrequency stimuli and for narrow-band and broadband noise stimuli. If concentric multifrequency surface waves were offered, even a fivefold decrease in stimulus amplitude did not significantly change the mean running distance of D.triton. However, if multifrequency wave stimuli with a flat wave front were presented, the spiders (D.triton) no longer determined the source distance precisely (Figs. 11, 12). Our results indicate that fishing spiders of the genus Dolomedes mainly use the curvature of a concentric wave stimulus for distance determination.