Sexual selection drives the evolution of male wing interference patterns

Abstract

The seemingly transparent wings of many insects have recently been found to display unexpected structural coloration. These structural colours (wing interference patterns: WIPs) may be involved in species recognition and mate choice, yet little is known about the evolutionary processes that shape them. Furthermore, to date investigations of WIPs have not fully considered how they are actually perceived by the viewers' colour vision. Here, we use multispectral digital imaging and a model of Drosophila vision to compare WIPs of male and female Drosophila simulans from replicate populations forced to evolve with or without sexual selection for 68 generations. We show that WIPs modelled in Drosophila vision evolve in response to sexual selection and provide evidence that WIPs correlate with male sexual attractiveness. These findings add a new element to the otherwise well-described Drosophila courtship display and confirm that wing colours evolve through sexual selection.

Keywords: Drosophila; courtship; evolution; sensory ecology; sexual selection.

Figure 1.

Examples of Drosophila simulans wing interference patterns (WIPS) photographed for this study using a customized multispectral photography system. Like many insects, Drosophila can see into the ultraviolet range, but not the human ‘red’ range of the spectrum. The images in the left-hand column show ‘false colour’ Drosophila vision (created from cone-catch image stacks using the ‘Make Presentation image’ in the micaToolbox [5]), where the red, green and blue values correspond to normalized Rh6, Rh5 and Rh4 cone-catch quanta, respectively. Images in the right-hand column show the same wings in ‘normal’ human-vision colours. (Online version in colour.)

Figure 2.

Mean luminance of WIPs as measured by average stimulation of the broadband Rh1 photoreceptor in the Drosophila visual system. Boxes represent the interquartile range, black bars are medians, white diamonds are means. SS+ = flies from populations evolving with sexual selection, SS− = flies from populations evolving without sexual selection. Differences in letter annotation denote significance at p < 0.05. (Online version in colour.)

Figure 3.

Luminance contrast of WIPs as measured by the standard deviation of the average stimulation of the broadband Rh1 photoreceptor in the Drosophila visual system. Boxes represent the interquartile range, black bars are medians, white diamonds are means. SS+ = flies from populations evolving with sexual selection, SS− = flies from populations evolving without sexual selection. Differences in letter annotation denote significance at p < 0.01. (Online version in colour.)

Figure 4.

Principal components (PC1) explaining variation in the opponent channels Rh5–Rh3, Rh6–Rh4, Rh6–Rh1 and Rh4–Rh1 for both mean hue (a) and colour contrast (b). SS+ = flies from populations evolving with sexual selection, SS− = flies from populations evolving without sexual selection. Differences in letter annotation denote significance at p < 0.05 for mean hue (a), and significance at p < 0.01 for colour contrast (b). Boxes represent the interquartile range, black bars are medians, white diamonds are means.