Variable Environmental Effects on a Multicomponent Sexually Selected Trait

Abstract

Multicomponent signals are made up of interacting elements that generate a functional signaling unit. The interactions between signal components and their effects on individual fitness are not well understood, and the effect of environment is even less so. It is usually assumed that color patterns appear the same in all light environments and that the effects of each color are additive. Using guppies, Poecilia reticulata, we investigated the effect of water color on the interactions between components of sexually selected male coloration. Through behavioral mate choice trials in four different water colors, we estimated the attractiveness of male color patterns, using multivariate fitness estimates and overall signal contrast. Our results show that females exhibit preferences that favor groups of colors rather than individual colors independently and that each environment favors different color combinations. We found that these effects are consistent with female guppies selecting entire color patterns on the basis of overall visual contrast. This suggests that both individuals and populations inhabiting different light environments will be subject to divergent, multivariate selection. Although the appearance of color patterns changes with light environment, achromatic components change little, suggesting that these could function in species recognition or other aspects of communication that must work across environments. Consequently, we predict different phylogenetic patterns between chromatic and achromatic signals within the same clades.

Male courtship decisions are influenced by light environment and female receptivity

“…We found that males with larger violet patches spent more time in the F55 (lilac) environment and males with larger silver patches spent more time in the clear environment. This is an exciting result that supports other studies that have shown that females prefer combinations of male colour patches that include colours that 'match', and therefore, reflect most intensively, the light environment [7]; the more light a colour patch can reflect, the more conspicuous the patch should be. For example, a violet spot in light containing little short or medium wavelength light (such as F55 and clear) will appear dark because it does not reflect much of the available light.…”

“…Our results suggest that males with more highly contrasting colour patterns that are more attractive [7], court more frequently. This relationship is also stronger in the presence of more receptive females which implies that this is a reaction to positive feedback from females, as has been suggested by previous studies [44,45].…”

“…All eight colour classes [7,21,28] were measured individually (rather than combining them into black, orange, and 'iridescent' as in some published studies) because they are easily distinguishable and combining them into groups may eliminate important phenomena. Analysis was performed 'blind' to fish behaviour or origin and only the right side was analysed because 93% of all males were left -right symmetrical.…”

“…We took reflectance measurements of the eight colour classes from 20 non-experimental males housed in 196 l glass tanks without filters following methods used in [7] (see the electronic supplementary material). The number of colour classes measured per male was dependent on the size of the colour patch and whether the patch overlapped with other colours; not all colour classes could be measured per male.…”

“…Courtship mode also varies with light spectrum and relates to predation risk [20]. Furthermore, light environments directly affect the perceived conspicuousness of male guppy multi-component colour sexual signals [7,21,22]. Male guppies are able to use cues from conspecific females to adapt courtship behaviour, providing a mechanism by which they can receive feedback regarding the attractiveness of their signal [23].…”