A single gene drives big differences in male behaviour

Scientists are closer to understanding the evolution of a peculiar bird which has three different ways to attract attention from females.

The ruff sandpiper is a highly social, medium-sized wading bird that breed in leks. A lek is an aggregation of males gathered to engage in competitive displays and courtship rituals, known as lekking, to entice visiting females which are surveying prospective partners.

Different morphs of ruffs in a lek.
Illustration of a ruff lek by Johann Friedrich Naumann

Males fall into one of three types (or ‘morphs’) that differ in looks and behaviour.

“Independent” males sport elaborate plumage and aggressively defend their display territories.

“Satellite” males are less ornate and less aggressive, displaying alongside independent birds to opportunistically attract mates.

“Faeder” males resemble females, allowing them to blend in and mate covertly.

A female ruff, which resembles the faeder male morph.
A female ruff. Credit: Wikimedia Commons / DickDaniels

Previous research found that these birds have different blood levels of testosterone – the primary male sex hormone. Independent males have high testosterone while non-aggressive satellite and faeder males have low levels.

Testosterone is a hormone produced in the gonads and then carried into the bloodstream, which delivers it to the rest of the body, including the brain.

Studies showed that the gonads of all three morphs produce the same amount of testosterone, so this does not explain why the morphs have different blood levels of this hormone.

Two breeding male birds, one with large black feathers around its neck and the other with white feathers. These represent two breeding morphs.
Two male ruffs. Credit: Wikimedia Commons / Arjan Haverkamp CC BY

The research team led by Jasmine Loveland of the Max Plank Institute, discovered that the different testosterone levels could be explained by a single gene, called HSD17B2.

HSD17B2 produces a protein that inactivates testosterone. Experiments showed that the version of HSD17B2 in the two non-aggressive morphs inactivated testosterone more efficiently than the version in the aggressive morph.

The researchers found evidence of this protein in the blood of non-aggressive morphs as well as other areas of the body where it could counteract the effects of testosterone.

For example, the non-aggressive morphs had high levels of HSD17B2 in six regions of the brain, which could explain why these morphs have different behaviours.

“These findings change what we know about how hormone levels can be controlled and how hormone-mediated traits evolve,” writes Kimberley Rosvall of Indiana University in a related Perspectives piece in Science.

The research is published in the journal, Science.

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