The three-spine stickleback (Gasterosteus aculeatus) has been the focus of numerous studies exploring its response to changing environments. Phenotypic changes have been linked to its adjustments to diverse habitats. We specifically study two populations thriving in marine and acidic freshwater environments. The dominant marine phenotype possesses three dorsal spines and a fully developed pelvic girdle formed by pelvic spines, pelvic processes, and pelvic plates. In contrast, the most frequent acidic freshwater phenotype exhibits merely two dorsal spines and lacks pelvic structures. Our study's primary aim is to discern the loci accountable for these dual phenotypic traits and unravel the underlying developmental mechanisms.
To achieve this, we execute a genome-wide association study to pinpoint the most distinct genomic regions in spined versus spineless fish. Our investigation uncovers two profoundly dissimilar regions: chromosome VI governing dorsal spines and chromosome XIV overseeing pelvic spines. Employing whole-mount skeletal and cartilage staining, we identify the developmental stages where the ontogeny of these two phenotypes diverges. Building on this knowledge, we analyse the RNA expression profiles of the regions of interest. As we refine our understanding of the causative loci and the developmental stages at which the divergence in the ontogeny of the distinct phenotypes occurs, we intend to conduct in-situ hybridisation experiments. Additionally, we will endeavour to induce changes using CRISPR-Cas9 to corroborate our findings within the framework of established protocols.