page_title: Ruff (bird)
section_title: Biology of variation among males
hierarchical_section_title: Ruff (bird) / Biology of variation among males
caption_attribution_description: English: Philomachus pugnax
context_page_description: The ruff is a medium-sized wading bird that breeds in marshes and wet meadows across northern Eurasia. This highly gregarious sandpiper is migratory and sometimes forms huge flocks in its winter grounds, which include southern and western Europe, Africa, southern Asia and Australia.
  The ruff is a long-necked, pot-bellied bird. This species shows marked sexual dimorphism; the male is much larger than the female, and has a breeding plumage that includes brightly coloured head tufts, bare orange facial skin, extensive black on the breast, and the large collar of ornamental feathers that inspired this bird's English name. The female and the non-breeding male have grey-brown upperparts and mainly white underparts. Three differently plumaged types of male, including a rare form that mimics the female, use a variety of strategies to obtain mating opportunities at a lek, and the colourful head and neck feathers are erected as part of the elaborate main courting display. The female has one brood per year and lays four eggs in a well-hidden ground nest, incubating the eggs and rearing the chicks, which are mobile soon after hatching, on her own.
context_section_description: The ruff has three male forms, which differ in mating behaviour and in appearance: the typical territorial males which have a dark neck ruff, satellite males which have a white neck ruff, and the very rare cryptic males known as "faeders" which have female-like plumage.  The behaviour and appearance of each individual male remain constant through its adult life, and are determined by a simple genetic polymorphism. Territorial behaviour and appearance is recessive to satellite behaviour and appearance,  while preliminary research results suggest that the faeder characteristics are genetically controlled by a single dominant gene.  It was originally thought that the difference between territorial and satellite males was due to a sex-linked genetic factor, but in fact the genetic locus relevant for the mating strategy is located on an autosome, or non-sex chromosome. That means that both sexes can carry the two different forms of the gene, not just males. The female does not normally show evidence of her genetic type, but when females are given testosterone implants, they display the male behaviour corresponding to their genotype. This testosterone-linked behaviour is unusual in birds, where external sexual characteristics are normally determined by the presence or absence of oestrogen.
  In 2016, two studies further pinpointed the responsible region to chromosome 11 and a 4.5-Mb covering chromosomal rearrangement. The scientists were able to show that the first genetic change happened 3.8 million years ago on the resident chromosome, when a part of it broke off and was reintroduced in the wrong direction. This inversion created the faeder allele. About 500,000 years ago another rare recombination event of faeder and resident allele in the very same inverted region led to the satellite allele. The 4.5 Mb inversion covers 90 genes, one of them is the centromere coding gene N- CENPN-, which is located exactly at one of the inversion breakpoints. The inactivation of the gene has severe deleterious effects and pedigree data of a captive ruff colony suggests that the inversion is homozygous lethal. Over the course of the past 3.8 million years, further mutations have accumulated within the inversion i.e. three deletions ranging from 3.3 to 17.6 kb. Two of these deletions remove evolutionary highly conserved elements close to two genes- HSD17B2 and SDR42E1-both holding important roles in metabolism of steroid hormones. Hormone measurements around mating time showed that whereas residents have a sharp increase of testosterone, faeders and satellites only experience higher androstenedione levels, a substance which is considered an intermediate in testosterone biosynthesis. The authors conclude that one or more of the deletions act as a cis-acting regulatory mutation which is altering the expression of one or both genes and eventually contributes to the different male phenotypes and behaviour.
caption: Skeleton of a ruff
exif: {}