‘Dark DNA’ may help explain peacock spiders’ extraordinary diversity, researchers say

Researchers studying Australia’s peacock spiders say a mysterious component of the animals’ genomes known as “dark DNA” could help explain why more than 100 distinct peacock spider species have evolved, far more than the handful of species typical for many animal groups.

The international team, led in part by scientists at the Wellcome Sanger Institute, combined detailed behavioural and acoustic measurements of each described peacock spider species with genetic analyses to search for genomic features that might underlie differences in colour, dance and courtship song. The researchers report that peacock spiders carry substantially more non-coding or so-called dark DNA than humans — roughly three times as much — and they are investigating whether variation in these regions helps the spiders adapt and form new species more rapidly.

Peacock spiders are tiny — each about the size of a pinhead — and the males are known for bright, iridescent abdominal patterns displayed during elaborate courtship dances. Males also produce rhythmic foot-drumming sounds as part of their mating rituals. Researchers catalogued fine-scale differences in appearance, movement and acoustic signals across the species they collected, then cross-referenced those observations with genomic data to look for genes or other DNA elements associated with particular traits.

"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. 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."

The term dark DNA refers to stretches of the genome that do not code for proteins and whose functions are poorly understood. While classical genetics has focused on genes that directly determine traits such as height or eye colour, researchers now suspect that regulatory and non-coding regions can influence how, when and where genes are expressed — potentially altering development, behaviour and morphology without changing protein-coding sequences.

The work on peacock spiders is part of a broader push to map the genomes of Earth’s eukaryotic life. Dr. Jonana Meier, a co-leader on the project, has already helped decode DNA from about 1,000 species of butterflies and moths. Those efforts feed into the Earth BioGenome Project, an international initiative that has decoded genomes from roughly 3,000 species so far and aims to sequence 10,000 species next year, with a long-term objective of cataloguing the DNA of some 1.8 million living species within the next decade.

"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."

The Sanger-led team said the peacock spider project remains a work in progress. By gathering complete genomes and detailed phenotypic data across an unusually diverse group, researchers hope to identify whether changes in non-coding regions correlate with shifts in courtship behaviour, colouration and other traits that could drive reproductive isolation and speciation.

Scientists caution that the hypothesis linking dark DNA directly to rapid speciation is preliminary. Confirming causal links will require further sequencing, functional studies and comparisons across additional taxa. Still, researchers say peacock spiders provide an extreme example of biodiversity that may reveal general principles about how genomes — both genes and the large stretches of non-coding DNA between them — shape the evolution of form and behaviour.

If non-coding regions are found to play a decisive role in the development of novel traits, the findings could reshape understanding of how genetic variation is translated into the wide variety of life forms on Earth. For now, the team continues to expand its catalogues of behaviour and genomes, with the aim of pinpointing genomic features associated with the dazzling diversity of the peacock spiders.