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Here’s what you’ll learn when you read this story:
- Zorapterans, an insect group that includes angel insects, or ground lice, has defied phylogenetic categorization for decades.
- The big question was whether Zorapterans and Dermapterans (earwigs) were together the first to branch off from Polyneopterans (known as Haplocercata-first hypothesis) or if Zorapterans alone were first.
- A new study by scientists in China concluded that Zorapterans-first was the correct theory, and also developed a new strategy for solving similar evolutionary conundrums.
Placing certain animals on the phylogenetic Tree of Life is relatively straightforward. We all can surmise what feline species fill the group felidae, after all. And while some mammalian species can initially confound us—we once thought cetaceans were fish, for example—sorting out the insects, which scientists estimate contain up to 20 million total species, is much harder.
One of the more well-known conundrums of insect classification involves the order Zoraptera, which contains angel insects, also known as ground lice. The name, first given by Italian entomologist Filippo Silvestri in 1913, means “pure wingless,” which reflects a misunderstanding of the species, since many of the 41 members of Zoraptera—the third-smallest order of insects—have wings. This error, as it turns out, would only be the beginning of a century of misinformation surrounding these insects, as scientists had no idea where Zoraptera fit in the Tree of Life.
According to Phys.org, Zorapterans have many physical characteristics that don’t closely align with other orders, although they look superficially like termites. This small group may not seem important, but they sit at a potentially monumental moment in the evolution of winged insects—the arrival of the Polyneoptera, a major cohort of winged insects (Pterygota) that accounts for 98 percent of all hexapod species, the largest and most diverse group of animals on Earth. Knowing where this small group of insects belonged became known as the Zoraptera problem, or the “Hundred-Year Conundrum.”
Now, a new study led by researchers at the Chinese Academy of Sciences solved the mystery by creating new genome data for groups closely related to Zorapterans and using analytical tools to study it. The results of the research were published in the journal Proceedings of the Royal Society B.
“Since their discovery in 1913, the phylogenetic position of zorapterans has represented one of the most persistent problems in reconstructing the insect Tree of Life,” the authors write. “The Zoraptera problem results, at least in part, from the insects’ unusual biology and associated morphological specializations.”
While the authors note that the insects have been placed in a “bewildering number of positions,” molecular data eventually discerned that the group belonged to the major group of winged insects Polyneoptera, but where exactly in that group was up for debate. Over the decades, two rival theories emerged. Either Zorapterans are part of the Haplocercata-first hypothesis, which states that Zorapterans along with Dermapterans (earwigs) were together the earliest branch of the group Polyneoptera,, or Zorapterans alone were the first to diverge, which is known as the Zoraptera-first hypothesis.
“The core inspiration for our paper came from persistent contradictions across decades of research,” two of the paper’s authors, Yehao Wang and Chenyang Cai, told Phys.org. “We suspected that this result was a statistical artifact caused by uncorrected molecular biases…prior work also suffered from limited Zorapteran genomic data and unbalanced taxon sampling, leaving the debate unresolved.”
By building a far larger dataset than previous studies while running various models to separate evolutionary data from statistical noise, the team could confidently say that the Zoraptera-first hypothesis is the correct one. While solving this mystery will help piece together the evolutionary puzzle of insects, the authors say this technique can be used to solve other mysteries found throughout the phylogenetic Tree of Life.
“Our results underscore the significance of both proper modeling and the integration of both molecular and morphological evidence for resolving contentious issues in insect phylogeny,” the authors conclude.
With a more accurate evolutionary roadmap, scientists can now start to discern exactly when Zorapterans branched off from Polyneoptera and develop a better understanding of how certain insect morphologies and behaviors came to be.
