VISION IN THE CTENID SPIDER CUPIENNIUS-SALEI - SPECTRAL RANGE AND ABSOLUTE SENSITIVITY

Electroretinograms were recorded from all eyes of the wandering spider Cupiennius salei (Ctenidae) and were found to be simple cornea-negati ve potential differences with amplitudes of up to 10 mV. In both the p rincipal eyes and all of the secondary eyes, the spectral response cur ves show a prominent green peak at 520 or 540 nm and a shoulder in the ultraviolet between 340 and 3 80 nm. The largest response in the ultr aviolet measures between 65 % and 80 % of the green peak. Selective ch romatic adaptation to either green or ultraviolet monochromatic light does not change these relative response levels and fails to indicate t he presence of more than one spectral type of receptor. In the range 4 50-500 nm, however, the Dartnall curve clearly deviates from the spect ral sensitivity (SS) curve. Since the SS curves of all eyes have a sma ll shoulder in the blue at 480 nm, the existence of two or even three visual pigments is a possibility. Intensity curves were determined wit h white and monochromatic light. For white light, absolute corneal ill uminance thresholds were clearly below 0.01 lx. For monochromatic ligh t stimuli, a corneal illuminance of approximately 3 x 10(12) photons c m-2 st-1 is needed to elicit a half-maximal response. At threshold, th e equivalent value is 3 x 10(9) photons cm-2 st-1, which corresponds t o a retinal illuminance of 5.9 x 10(9) photons cm-2 st-1. Consequently , Cupiennius salei should be able to use its visual sense not only sho rtly after sundown but also under much poorer light conditions, such a s those provided by moonlight. The log-linear response range of all ey es covers a stimulus intensity range of 4 log units. The sensitivity o f the principal eyes increases by up to 0.81 log units at night as com pared with daytime. The chromophore of the visual pigment of all eyes is 11-cis retinal. nearly abolished by aerial hyperoxia. These results also indicate that Amia calva respond to changes in intravascular P(O 2); however, externally facing chemoreceptors that stimulate air-breat hing in aquatic hypoxia cannot be discounted. Type II air-breaths, whi ch occurred in aerial hyperoxia, despite aquatic hypoxia, appear to be stimulated by reductions of V(B), suggesting that type II breaths are controlled by volume-sensitive gas bladder stretch receptors. Type II breaths are likely to have a buoyancy-regulating function.