Sexual Selection on Non-Ornamental Traits Is Underpinned by Evidence of Genetic Constraints on Sex-Biased Expression in Dusky Pipefish.

Species lacking distinct secondary sex characteristics, such as differences in size or morphology, are often thought to experience lower levels of sex-specific selection in comparison to highly sexually dimorphic organisms. However, monomorphism in classic visible traits could be a result of genetic or physiological constraints that prevent the sexes from reaching divergent fitness optima. Additionally, biochemical and molecular work have revealed a variety of less easily observed phenotypes that nonetheless exhibit profound dimorphism.

The roles of sexual selection and sexual conflict in shaping patterns of genome and transcriptome variation.

Sexual dimorphism is one of the most prevalent, and often the most extreme, examples of phenotypic variation within species, and arises primarily from genomic variation that is shared between females and males. Many sexual dimorphisms arise through sex differences in gene expression, and sex-biased expression is one way that a single, shared genome can generate multiple, distinct phenotypes. Although many sexual dimorphisms are expected to result from sexual selection, and many studies have invoked the possible role of sexual selection to explain sex-specific traits, the role of sexual selection in the evolution of sexually dimorphic gene expression remains difficult to differentiate from other forms of sex-specific selection.