First Centipede Genome Sequenced but Scientists Still Grappling with Multiple Legs Mystery

The genome of a species of centipede with no eyes or regulating body clock has been sequenced for the first time by 100 scientists from 15 countries.

Strigamia maritime, a venomous and carnivorous centipede species that can be found on the coast of the Moray Firth in Scotland, has provided scientists with an insight into the evolution of myriapods (a subphylum of arthropods that includes centipedes and millipedes), a group that first evolved over half a billion years ago.

Published in the journal PLOS One, the international team of researchers were looking at arthropods because they are seen as one of Earth's greatest success stories. However, little is known about their genetic make-up and how they diversified.

Despite their lengthy history, the relationship between the different groups of arthropods is little understood.

"We have good sampling of insects but this is the first time a centipede, one of the more simple arthropods - simple in terms of body plan, no wings, simple repetitive segments, etc, - has been sequenced," said Ariel Chipman, of the Hebrew University of Jerusalem.

"This is a more conservative genome, not necessarily ancient or primitive, but one that has retained ancient features more than other groups."

Researchers discovered that the Strigamia maritime species of myriapods lost their eyes at least 200 million years ago, having no genes related to vision. They also found the creatures have no genes relating to the circadian clock, which governs how an animal regulates sleep.

"Strigamia (centipedes) live underground and have no eyes, so it is not surprising that many of the genes for light receptors are missing, but they behave as if they are hiding from the light. They must have some alternative way of detecting when they are exposed," Michael Akam, from the University of Cambridge said.

"It's curious, too, that this creature appears to have no body clock - or if it does, it must use a system very different to other animals."

Arthropod mysteries remain

Stephen Richards, assistant professor in the Human Genome Sequencing Center at Baylor College of Medicine, said: "Arthropods are particularly interesting for scientific study because they diverged into more species than any other animal group as they adapted in many ways to conquer the planet. The genome of the myriapod in comparison with previously completed genomes of the other arthropod classes gives us an important view of the evolutionary changes of these exciting species."

Speaking to IBTimes UK, Richards said how and if the centipede sleeps is still a mystery: "They don't have the circadian clock because there's no light input. The circadian clock relies on light input to tell the creature if its day or night.

"Now, I'm not sure what happens when things don't sleep - I'm presuming they do sleep - and if you look at other arthropods like fruit flies, if you stop them sleeping they go kind of weird. I would love to know what's going on there but that will have to wait for another time."

Explaining why it was important to sequence the centipede genome, he said: "Arthropods are things with shells and jointed legs – that's your crustaceans in the sea, the myriapods, spiders and mites, and insects, crustaceans that came to land and learned how to fly.

"We had this large group of the arthropods that hadn't been sampled – and we've been trying to understand this great diversity of different arthropods and how they have so many different shapes and sizes and how they've adapted to life on the entire planet. To miss this large group - it was really important to get this first sample.

"In the future we'll have more of the samples in more and more detail, for example, how does a centipede differ from a millipede?"

However, one thing the researchers failed to learn about the centipede was how it came to have so many legs: "I'm frustrated we didn't get to look at that as much," Richards said.

"The reason is that if you look at these centipedes, the number of legs vary. From the genetic point of view it's interesting because it varies depending on the environment. I wanted to go ahead and sequence centipedes that have lots of legs and ones that have fewer legs from this one species, but actually it's an environmental change, so it's not clear we would've learned a lot from the genetics there."