The flashier a male is, a study has revealed, the more attractive a mate he is.
"Females typically use carotenoid colours to assess the quality of a potential mate, with more colourful males generally being regarded as the most attractive," said Dr Tom Pike of the University of Exeter.
Pike conducted the study using a stickback fish model.
"The major difference between stickleback vision and our own is that they can see ultraviolet light, which is invisible to humans. This may be important because carotenoids reflect ultraviolet light as well as the red, oranges and yellows that we can see," Pike said.
"The model tells us how much of the light reflected from a carotenoid signal is actually detected by a female and how this information might be processed by her brain, and so gives us exciting new insights into how females may use colour to choose the best mates," he added.
The model reveals that sticklebacks' visual system and coloration are extremely well co-adapted, and that females are surprisingly good at assessing the quantity of carotenoids a male is able to put in his signal.
The results will help ecologists get a better understanding of why carotenoid-based signals evolved in the first place, and provides insights into why males use the specific carotenoids they do.
"There are many carotenoids in the sticklebacks' diet, but males use only two of them for signalling; because the visual system evolved long before male coloration in this species, it suggests that males 'chose' to use those two carotenoids to make the most of what the female fish sees."