The genetic mechanism underlying major differences in mating behaviors between three types of males in a species of wading bird is reported in two papers published online this week in Nature Genetics. The studies illustrate one way in which a single genetic factor can control multiple complex traits.
The ruff (Philomachus pugnax) has three distinctive types, or morphs, of males. Independent males (constituting 80-95% of males) have ornamental plumage of varying colors, and they defend territories to gain access to females. Satellite males (5-20%), which only have white ornamental plumage, are non-territorial and submissive to independents, mating only when independents are otherwise distracted. Faeder males (<1%) resemble females and are thus disguised from aggressive independents. The three male morphs are controlled by a single genetic factor.
To understand how such complex behavioral and visual differences between male morphs could have such a simple genetic basis, two groups, led independently by Leif Andersson and Terry Burke, sequenced the genomes of ruff males. They each found that a region on one chromosome was inverted in satellite and faeder males, relative to that of independents. This region contains over 100 genes, and the inversion can be thought of as a single ‘supergene’ that is inherited in a single block. Andersson, Xin Liu and colleagues estimate that the inversion first occurred about 3.8 million years ago and accumulated mutations over time that led to the differences between satellites and faeders. Burke, David Lank, Mark Blaxter and colleagues identified genes involved in hormone signaling that may contribute to the behavioral differences between the male morphs. Both groups also identified the gene MC1R as potentially responsible for the white ornamental feathers in satellite males.