Searching for intralocus sexual conflicts in the three-spined stickleback (Gasterosteus aculeatus) genome

Differences between sexes in trait fitness optima can generate intra-locus sexual conflicts that have the potential to maintain genetic diversity through balancing selection. However, these differences are unlikely to be associated with string selective coefficients and as a result are challenging to detect. Additionally, recent studies have highlighted that duplication on sexual chromosomes can create artefactual signals of inter-sex differentiation and increased genetic diversity. Thus, testing the relationship between intra-locus sexual conflicts and balancing selection requires a high-quality reference genome, stringent filtering of potentially duplicated regions, and dedicated methods to detect loci with low levels of inter-sex differentiation. In this study, we investigate intra-locus sexual conflicts in the three-spined stickleback using whole genome sequencing (mean coverage = 12X) of 50 females and 49 males from an anadromous population in the St. Lawrence River, Québec, Canada. After stringent filtering of duplications from the sex chromosomes, we compared three methods to detect intra-locus sexual conflicts. This allowed us to detect various levels of inter-sex differentiation, from stronger single locus effects to small cumulative or multivariate signals. Overall, we found only four genomic regions associated with confidence to intra-locus sexual conflict that displayed associations with long-term balancing selection maintaining genetic diversity. Altogether, this suggests that most intra-locus sexual conflicts do not drive long-term balancing selection and are most likely transient. However, they might still play a role in maintaining genetic diversity over shorter time scales by locally reducing the effects of purifying selection and the rates of genetic diversity erosion.