Supergenes can determine behaviour
How genes can control complex courting behaviours has been revealed this week by UK researchers.
The choices we make are often down to past experience and circumstances, including picking partners. However, for a bird called the ruff, the way it picks up ladies is determined genetically.
The ruff, Philomachus pugnax, is a wading bird that breeds on coastal marshes across Northern Eurasia. They have what's known as a lek-based breeding system where females choose between displaying males.
Writing in Nature Genetics, an international team of scientists studying ruff behaviour and genetics have identified a supergene that determines which of three personality types the males exhibit during the breeding season. "We showed how it is that different male morphs can evolve and how they can be maintained," explains Jon Slate, a co-author from the University of Sheffield.
Some ruffs are territorial and impress using dramatic, coloured neck feathers. Less common are the satellites or girlfriend stealers who display on the edge of territories and attempt to lure females away. Finally, the rarest and most difficult to identify, female mimics or cross dressers sneak into the territories and pounce on females.
By comparing the genome sequence of different males in a large captive population of Ruffs the scientists were able to pin down a region of DNA containing many genes that are responsible for these differing courting strategies.
This supergene - a region containing several hundred genes next to each other - codes for a whole set of genes that work together to define the appearance and behaviour of each male. The three personalities are recognisable and distinct because there are only three possible combinations of these many genes.
A DNA rearrangement several million years ago, known as an inversion, has prevented the genes responsible from being jumbled up with the genes of the other parent when passed on to offspring.
"Rather than inheriting just one gene from parent to offspring, in the case of a supergene you get a whole string together," says Slate. "By having lots of genes that are co-inherited, i.e. passed from parent to offspring all as one, then it's easier for complex behaviour to evolve."
"The idea of supergenes has been first hypothesised many, many years ago but until recently there weren't many examples."
The discovery of the supergene gives scientists an insight into how small genetic changes can lead to dramatic differences in the appearance and behaviour of birds.
This mechanism for developing an alternative strategy may be how separate species have evolved in the past and going further back in evolution may even have allowed the evolution of separate sexes.