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 jumpingspider from Singapore, is sexually dimorphic in the reflectanceof ultraviolet (UV) (males, but not females, have UV-reflectingmarkings). Here we present the first experimental evidence thatthe male's UV markings influence mate choice of C. umbraticafemales. When presented with males whose appearance was manipulatedby the use of a UV-blocking filter, females spent more timewatching UV+ males (i.e., males with UV present) and less timewatching UV– males (UV absent). We also manipulated thelevels of male brightness by using 2 UV-transmitting neutraldensity filters and showed that UV reflectance was used specificallyfor hue discrimination instead of being used for detecting differencesin brightness alone. This is not only the first strong evidenceof UV influence on female mate-choice decisions for a spiderbut also the best experimental demonstration of color vision,whatever the wavelength.