Neural bases for behavioral differences in male Ruffs

Birds have evolved a wide diversity of courtship tactics, with mesmerizing feather arrangements, color patterns and behaviors, to attract potential mates. Understanding the role of genetics in the development of neural circuits underlying such behaviors and their evolvability is at the heart of our project. Here, we will study how genetics and hormones shape the brain and mating behaviors of a fascinating shorebird: the Ruff. In Ruffs, breeding plumage colors, hormone profiles and alternative mating strategies are linked to a unique genetic feature called a chromosome inversion. Inversions occur when a fragment of DNA containing several genes becomes flipped from its original orientation. Interestingly in the history of the Ruff, an inversion captured genes important for hormone production and allowed three distinct morphs to evolve: Independents, Satellites and Faeders. Only Satellites and Faeders carry the inversion and these males have both extremely low levels of testosterone and a loss of aggression during the breeding season, compared to Independent males. Independent and Satellite males have a flashy appearance during the breeding season with long ruff feathers in different colors - Independents are dark and Satellites are usually light colored or white. These two morphs form an alliance and perform courtship displays together, this is known as cooperative courtship. Males of the third morph, Faeders, are considered `female-mimics` because they are small, lack long ruff feathers and even show some typically female behaviors. In this project, at the behavioral level, we will develop tools to study Ruff courtship using customized video software analyses. In the scope of male neuroendocrinology, we will measure gene expression across the entire genome using RNA-seq, in the brain and hormone-producing organs. For sex and morph differences in brain organization, we will analyze the brains of males and females with a focus on cell types that are usually known to be different between males and females. This allows us to further question the role of sex, and how the presence of the inversion along with low testosterone levels impacts key nodes of neural circuits for courtship and aggression. This study has important implications for understanding the biology of sex differences in neural development. Our research will explore how adult mating behaviors are shaped by a complex interaction between life-history differences in sex hormone levels, gonadal sex and gene expression.