Genetic architecture of novel ornamental traits and the establishment of sexual dimorphism: insights from domestic birds

摘要

The evolution of sexually monomorphic ornamental traits is poorly understood and may require a shift in research focus away from strict sexual selection. To properly understand how selection affects such traits, we need to know to what extent they areconstrained by their genetic architecture. Specifically, we need to understand how and in what state (monomorphic or dimorphic) ornamental traits first appear, how they are subsequently rendered sexually dimorphic, or not, and what mechanisms underlie their further elaboration and diversification. Here, I argue that recent developments in the genomic studies of domesticated birds provide insights into these questions. The causal mutations of several ornamental traits have been identified, particularlyin chickens. I briefly review this literature and show that ornamental traits can be caused by a range of different types of mutations, including single-nucleotide polymorphisms and larger structural variations. Novel ornamental traits tend to be sexually monomorphic, suggesting that most cases of sexual dimorphism are the result of additional mutations, although we have no direct evidence for this in domestic birds. Several examples show how existing ornaments can be further elaborated and diversifiedby additional mutations. Ongoing research may also clarify what mutations cause the reversal to sexual monomorphism dull plumage in chickens. I conclude that current cases of sexually monomorphic ornamentation may consist of a mix of traits that are under selection for monomorphism and traits that are constrained to be monomorphic.