An international team of scientists led by researchers at Virginia Tech has completed the millipede family tree for the first time.
Millipedes are among the earliest colonizers of land on Earth, but the full story of their evolution has remained incomplete.
This is because specimens from two orders, Siphoniulida and Siphonocryptida, are so rare that they’ve eluded researchers for decades. “These last two were kind of like our white whales,” said Paul Marek, the study's lead investigator and associate professor at Virginia Tech's Department of Entomology, in a press release.
To find members of the two missing orders, the scientists traveled to Los Tuxtlas, Mexico, and La Palma in Spain's Canary Islands.
One of the specimens took the team more than a week to track down and isolate. "Finding them in the field was hard because we were just seeing this little white nematode. We didn't know for sure it was a millipede until we looked under the microscope," says first author Luisa 'Fernanda' Vasquez-Valverde.
Then they sequenced the DNA of these two mysterious groups and compared hundreds of genes across 82 distinct living millipede species. They processed terabytes of this genetic data alongside morphological evidence from 29 distinct fossil specimens.
Siphoniulida was placed appropriately among its close relatives in the millipede family tree, and Siphonocryptida turned out to be a member of an already existing lineage of millipedes rather than a distinct order on its own.
Millipedes are some of the planet's hardest-working detritivores, quietly breaking down dead and decomposing organic matter and recycling nutrients back into soil and water; all while remaining one of the most understudied groups in entomology.
"Millipedes in general are severely understudied, yet they play a very important role in our ecosystems,” Vasquez-Valverde said to Refractor. “Without them, all that leaf litter in the forest would just accumulate, and nutrients like nitrogen and many other chemicals wouldn't decay fast enough for them to be reabsorbed and recycled into the ecosystem."
The team’s completed evolutionary timeline showed that millipedes were present on Earth much earlier than we had previously assumed. “Millipedes beat vertebrates onto land by more than 80 million years,” said Paul Marek.
The findings bolster the case for millipedes as among Earth’s first terrestrial animals, with some evidence pushing their first presence on land back to the Ordovician.
"This gives us a picture of how life in special terrestrial ecosystems started and evolved," said Vasquez-Valverde.
Back then, the Earth was very different from what it is now. There were no trees, no leaves, seeds, or flowering plants. Millipedes played a foundational role in colonizing this Earth ahead of other animals, including vertebrates, by consuming decaying slime, moss, and other materials.
Their revised timeline also let scientists pin down when the millipede’s signature survival trait, their defensive chemical secretions, first evolved. The most potent of these chemical defenses, complex terpenoid alkaloids, evolved in these creatures about 261 million years ago.
Millipedes are evolving daily. About 14,232 species have been discovered worldwide, and at least as many are believed to remain undiscovered. "Studying millipedes in general is very important because, not only are they important detritivores in our world, they are a vastly diverse group, and there is still so much we don't yet know about them," Vasquez-Valverde said.
This work provides a genetically unified framework for researchers to use to properly identify and classify new millipede species.
The research was published in Current Biology.
Source: EurekAlert
Fact-checked by Mike McRae
