‘Dark DNA’ may explain dancing spiders’ extraordinary diversity

It’s not just the dazzling colours and slick moves of Australia’s dancing spiders that make them special.

There are more than 100 different species of the peacock spider, whereas most animals have only five or ten.

Researchers believe that’s partly down to the spider’s ‘dark DNA’ – a mysterious part of the animal’s genetic code, and they are studying it to find out more.

They think that this dark DNA might enable it to adapt rapidly to changing environmental circumstances by developing into new species.

What the scientists find out, they say, might help to explain why there is so much variation in the natural world.

“We are interested in how the spiders evolve to become that diverse,” Jonah Walker, of the Sanger Institute told BBC News.

“When you go outside you see so much variation in species of plants and animals,” he said.

“Peacock spiders are at the extreme end of that. And so, by studying them, we can use that extreme case to try to understand what processes produce variation in general.”

Peacock spiders are found across Australia and each one is the size of a pin head. It is so-named because of the brilliant colours males have on their abdomen, which they show off in a beguiling mating ritual.

They create a drumming sound with their feet, a spider song of sorts, and move rhythmically while displaying their dazzlingly patterned features. What is remarkable about these creatures is how varied they are in their appearance, songs and dance moves.

Mr Walker used to be scared of spiders, but he overcame his phobia because he was so drawn to the science behind the spiders and took the project on as part of his PhD research.

“When I told friends and family that I was going to study spiders in Australia I got some worried looks and I was obviously apprehensive myself. But just a few seconds of watching them dance was enough for any fears to be washed away.”

Mr Walker worked with his group leader, Dr Joana Meier and an international team to collect each and every one of the species discovered so far.

They then painstakingly categorised precise details about each one’s behaviour, movement and songs. The final piece of the jigsaw was to cross-reference all this information with the DNA of each species.

By comparing the results of each species, they hope to find out which genes are responsible for each trait and ultimately why there are so many different types of peacock spider.

The research is a work in progress but the team already has a strong scientific lead to investigate further.

“It is early days, but one of the tantalising things we have discovered is that it may not only be the genes that are responsible for the diversity, but the bits in between, the so-called ‘dark DNA’, that may influence how spiders evolve,” says Mr Walker.

DNA consists of a long string of molecules. Some parts of them are involved in deciding specific traits. In the case of humans they can decide height or eye colour. These sections are called genes.

But the bulk of the sections of DNA are not genes, and no one really knows what they do. The Sanger researchers think that this so-called dark DNA may be responsible for peacock spiders’ diversity.

They have three times more dark DNA than humans.

Some butterflies and moths also have an exceptionally large number of species. Dr Meier has already decoded the DNA of a thousand species of butterflies and moths.

But spiders, butterflies and moths are just the start of one of the most ambitious genetic projects ever undertaken. The plan is to decipher the genetic code of every single plant, animal and fungus on the planet in the next 10 years.

“Just like all plants, animals and fungus we have very similar DNA,” Dr Meier told BBC News.

“By understanding the DNA of all the different organisms, we learn about the general principles of how genes work and what the function of dark DNA is, and so it also helps us find out a lot about ourselves”

Researchers have decoded the DNA of 3,000 different species so far as part of the Earth BioGenome Project.

The aim is to decode 10,000 next year and complete all 1.8 million living species in the next decade. The knowledge gained, scientists hope, will enable them to gain an unprecedented insight into how all living things evolved and the intricate interrelationships between them.