Sex-specific UV and fluorescence signals in jumping spiders

The paper describes the courtship of an ornate species of jumping spider (Cosmophasis umbriata) in which both sexes exploit ultraviolet coloration during displays, but in quite different ways. The males have UV reflective patches of scales on the face and body, which are lacking in females, and the females have palps that display a bright green fluorescence, excited by UV light, that is absent in males. We show that occluding the UV component of sunlight greatly reduces the courtship behavior of both sexes. This is not because UV has a direct effect on the courting spider itself. If only one of a pair (male or female) is lit by UV-deficient light, and the other with full-spectrum light, then the UV-deficient partner is ignored by the other. Thus it is the absence of UV reflectance or induced fluorescence that depresses courtship.

This is the first time that UV light has been shown to have different sex-specific effects in courtship in any animal. The only other report of UV- induced fluorescence as a possible courtship signal was in a budgerigar, but there the effect merely boosted to a limited degree the brightness of the yellow body color, and its behavioral relevance has been questioned. Neither the UV reflectance nor the fluorescence was sex specific.

In addition, budgerigars are known to have four single cones classes with four separate peak spectral sensitivities, while jumping spiders are known to possess receptors with only two peak sensitivities (UV and green). UV-induced fluorescent colorations may excite more than one cone class in budgerigars, but only the green photoreceptors in jumping spiders are sensitive to this fluorescence, indicating that jumping spiders are more sensitive to the presence and absence of fluorescence signals compared to budgerigars. The evidence from our behavioral experiments strongly substantiates this point: very few males court females that lack fluorescence.

Coverage from all over..

Video Clip