Donna Maney, Clemens Küpper

At the birth of supergenes, the genomic landscape is dramatically re-organized leading to pronounced differences in phenotypes and increased intrasexual diversity. Two of the best- studied supergenes in vertebrates are arguably the inversion polymorphisms on chromosomes 2 and 11 in the white-throated sparrow (Zonotrichia albicollis) and the ruff (Calidris pugnax), respectively. In both species, regions of suppressed recombination determine plumage coloration and social behavioral phenotypes. Despite the apparent lack of gene overlap between these two supergenes, in both cases the alternative phenotypes seem to be driven largely by alterations in steroid hormone pathways. Here, we explore the interplay between genomic architecture and steroid-related genes. Due to the highly pleiotropic effects of steroid- related genes and their universal involvement in social behavior and transcriptomic regulation, processes favoring their linkage are likely to have substantial effects on the evolution of behavioral phenotypes, individual fitness, and life history strategies. We propose that inversion- related differentiation and regulatory changes in steroid-related genes lie at the core of phenotypic differentiation in both of these interesting species.