Ultraviolet reflectance patterns of male guppies enhance their attractiveness to females

In many groups of fish male colour patterns reflect in the ultraviolet, but little is known about female preferences for these components of male ornaments. We studied UV-reflective colour patterns in male guppies, Poecilia reticulata, and their importance in female choice. Using photographs taken with a filter transmitting only short wavelengths, we found that 4–24% of the area of a male's colour pattern reflects in the UV. We measured female visual responses to paired males placed, alternately, behind UV-blocking and UV-transmitting Plexiglas partitions. When pairs were matched for carotenoid (red), structural (white) and UV-reflective colour patterns, females spent significantly greater amounts of time inspecting a male when he was behind the UV-transmitting partition. These results show that UV-reflective components of male colour patterns enhance their attractiveness to females. To determine whether level of predation affects female response to UV-reflective colour patterns, we tested females from two populations differing in predation pressure. Females from both populations preferred males viewed through the UV-transmitting partition. When females were presented with male pairs that differed in the area of UV reflectance but were matched for carotenoids and structural pigments, difference in the time spent with the males was positively correlated with difference in the area of UV reflectance. Our results indicate that UV-reflective colour patterns enhance male attractiveness to females and thus may be elaborated through sexual selection.