Three strikingly different alternative male mating morphs (aggressive “Independents”, semi-cooperative “Satellites” and female mimic “Faeders”) coexist as a balanced polymorphism in the ruff, Philomachus pugnax, a lek-breeding wading bird1,2,3. Major differences in body size, ornamentation, and aggressive and mating behaviour are inherited as an autosomal polymorphism4,5. We show that development into Satellites and Faeders is determined by a supergene6,7,8 consisting of divergent alternative, dominant, non-recombining haplotypes of an inversion on chromosome 11, which contains 125 predicted genes. Independents are homozygous for the ancestral sequence. One breakpoint of the inversion disrupts the essential Centromere protein N (CENP-N) gene, and pedigree analysis confirms lethality of inversion homozygotes. We describe novel behavioural, testes size, and steroid metabolic differences among morphs, and identify polymorphic genes within the inversion that are likely to contribute to the differences among morphs in reproductive traits.

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The display of lekking Great Snipe males is an energetically demanding activity and therefore, access to the rich feeding sites in the proximity of their leks is essential. During the breeding season, Great Snipes mostly prey on earthworms, whose availability is affected by moisture and penetrability of the soil. In this study, we investigated the relation between the body condition of displaying Great Snipe males and the water level of the river flowing through their breeding grounds, which can affect soil characteristics. We found that the body condition of males decreased over the course of the lekking period in May, showing the great energetic expenditure of their advertising display in courtship. The high water level in the river resulted in the increase in body condition of birds, probably due to improved prey availability, as earthworms moved closer to the ground surface in search of optimal conditions. Further rise in the water level caused flooding of the meadow and a decrease in the body condition of lekking Great Snipes, possibly because of the deterioration of feeding condition, as earthworms tend to leave flooded areas. Moreover, as the flooded area enlarged, the floodplain became inaccessible for foraging Great Snipes, due to their relatively short legs restricting them from wading in deep water. Our results show that for the lowland leks of the Great Snipe to be preserved it is advisable to allow for the natural water level fluctuations in the river shaping the hydrological conditions of the floodplains.