Colour blindness of the movement-detecting system of the spider Cupiennius salei

Abstract

SUMMARYThe nocturnal wandering spider Cupiennius salei has one pair of principal eyes and three pairs of secondary eyes located on the prosoma, which differ in both morphology and function. Their spectral sensitivity, measured with intracellular recordings, is due to three different types of photoreceptors with absorbance maxima in the mid-range of the spectrum, at 480nm and 520nm and in the UV at 360nm. Based on these physiological data colour vision might be possible. In the present study, the ability to discriminate coloured moving stimuli from grey backgrounds was tested. The perception of moving coloured stripes in front of backgrounds with 29 different grey levels was measured by using extracellular recordings from the anterior median eye muscles as a monitoring system. Each of these eyes has two muscles, which increase their activity when moving stimuli are presented in front of a secondary eye. This variation in eye muscle activity can be recorded extracellulary in a living spider using a single channel telemetry device. If colour perception exists, the animal should be able to detect a moving coloured stripe in front of any grey level. Blue, green and red stripes were used as moving stimuli, in front of all 29 grey backgrounds. The results indicate that C. salei is not able to discriminate the coloured stimuli from distinct shades of grey. It is therefore evident that the movementdetecting system in this spider appears to be colour blind.

Brightness discrimination in the day- and night-adapted hunting spider Cupiennius salei

“…This device, adapted for the spider Fenk and Schmid, 2011;Neuhofer et al, 2009;Orlando and Schmid, 2011) from one used previously with locusts (Kutsch et al, 1993), comprises an amplifier, an oscillator, a transmitter and a small battery. The recording electrode (a coated Manganin wire, diameter 30 μm) was inserted into the muscle; the reference electrode (a silver wire, diameter 250 μm) was inserted laterally into the prosoma.…”

“…They differ from the principal eyes morphologically and functionally: they lack muscles and are involved in detecting targets and motion (Neuhofer et al, 2009;Schmid, 1998). Behavioral experiments show that the secondary eyes are color blind (Orlando and Schmid, 2011). Moreover, the eyes of C. salei are extremely sensitive: vision is possible up to a threshold of 0.0001 to 0.001 lx (Barth et al, 1993;Fenk and Schmid, 2011), and the spider's spectral sensitivity ranges from 365 to 695 nm as a result of three different types of photoreceptors (Walla et al, 1996;Zopf et al, 2013).…”

“…The dorsal muscles of the principal eyes of this spider are spontaneously active (frequency of 12±1 Hz) (Kaps and Schmid, 1996). This frequency increases after stimulus detection, which can either be mechanical (Kaps and Schmid, 1996) or visual Fenk and Schmid, 2011;Neuhofer et al, 2009;Orlando and Schmid, 2011), in order to move the gaze of the principal eyes towards the stimulus. A flickering stimulus whose luminance is perceived as different from that of the background can be detected by the secondary eyes of C. salei.…”

“…This increases the muscle activity of the principal eyes. The activity of a dorsal principal eye muscle can be recorded extracellularly through a single-channel telemetric transmitter device Fenk and Schmid, 2011;Kaps and Schmid, 1996;Neuhofer et al, 2009;Orlando and Schmid, 2011). This approach enables investigation of the brightness discrimination ability of C. salei.…”

Flicker-induced eye movements and the behavioural temporal cut-off frequency in a nocturnal spider

“…Thus, the secondary eyes seem to be responsible for movement detection whereas the principal eyes are necessary for object discrimination (Neuhofer et al, 2009). The motion-detecting system was very recently shown to be colour blind (Orlando and Schmid, 2011). The field of view of the AME is shifted during locomotion; the spiders enhance eye muscle activity in the ipsilateral eye before turning and thus look in the subsequent walking direction (Schmid and Trischler, 2011).…”