Sex ratio represents a unique context for selection on attractive traits: Consequences for the evolution of sexual dimorphism

We explored the idea that sex ratio represents a unique context for selecti on on attractive traits by manipulating sex ratio and pollinator abundance in experimental populations of a gender-dimorphic wild strawberry Fragaria virginiana. We found that increasing the frequency of functional males (the pollen- bearing morph) increased the frequency of pollen- collecting syrph id flies in the pollinator assemblage, decreased pollinator visitation to l ess preferred morph (females), and decreased the degree of pollen limitatio n of females. Moreover, sex ratio influenced the strength of selection on p etal size through female fitness but did not alter the strength of selectio n through male fitness components, suggesting that sex ratio can alter the gender bias of selection on an attractive trait. This study of context- dep endent selection has important implications for the evolution of sexual dim orphism in attractive traits. First, it suggests that only certain conditio ns generate male- biased selection and, thus, could lead to selection- driv en male- biased petal size dimorphism. Second, it suggests that flexible po llinator foraging may be an important mechanism by which sex ratio influenc es selection on attractive traits. Finally, it implies that variation in se x ratio could limit the evolution of sexual dimorphism and/ or could mainta in genetic variation in attractive traits.