Effect of UV-reflecting markings on female mate-choice decisions in Cosmophasis umbratica, a jumping spider from Singapore

Earlier studies have shown that Cosmophasis umbratica, a jumping spider from Singapore, is sexually dimorphic in the reflectance of ultraviolet (UV) (males, but not females, have UV-reflecting markings). Here we present the first experimental evidence that the male's UV markings influence mate choice of C. umbratica females. When presented with males whose appearance was manipulated by the use of a UV-blocking filter, females spent more time watching UV+ males (i.e., males with UV present) and less time watching UV− males (UV absent). We also manipulated the levels of male brightness by using 2 UV-transmitting neutral density filters and showed that UV reflectance was used specifically for hue discrimination instead of being used for detecting differences in brightness alone. This is not only the first strong evidence of UV influence on female mate-choice decisions for a spider but also the best experimental demonstration of color vision, whatever the wavelength.