Sex-specific adaptation in the world’s most fashionable fish

The prevalence of sexual dimorphism, spanning morphology, physiology, behaviour, and life history, is a testament to the role of sexual selection in shaping animal phenotypes. However, unlike species-level adaptation, sexual selection can act in opposing directions in males and females while operating on a genome they largely share. This creates a fundamental tension: how does sexual selection produce strikingly different phenotypes from the same genetic material? I will present recent work from my lab using guppies (Poecilia reticulata) to address this question with insights from quantitative genetics, genomics, and machine-learning-based phenotyping. We have shown that male colour pattern diversity, one of the most striking examples of intraspecific phenotypic variation in vertebrates, is shaped by a combination of autosomal and sex-linked loci, with transposable elements playing an unexpected role in trafficking ornament genes onto the Y chromosome. We also demonstrated that sex differences in behaviour can evolve with surprising speed despite complex genetic architectures. Together, this work shows not only how sexual selection shapes phenotypes, but how it reshapes the genome itself, altering gene content, chromosomal architecture, and the distribution of heritable variation in ways that both enable and constrain future evolution.