By analyzing a locust swarm of data —1,478 genes from each of 144 kinds of insects and their relatives —a worldwide research team has reconstructed the tale of how insects arose and took over the Earth.
The first insects may have appeared as early as 479 million years ago, 101 members of the 1KITE (1,000 Insect Transcriptome Evolution) collaboration report in the Nov. 7 Science.
Insects eventually became the first animals to fly, taking off about 406 million years ago, the researchers calculate. Since then, branching and twigging of the genealogical tree of the six-legged creatures has produced today’s wild diversity of form and lifestyle among 32 major groups, or orders: silverfish, beetles, termites, butterflies, glacier-prowling predators called ice crawlers, the enigmatic order called “twisted wing parasites” and so on.
1KITE focused on getting the most possible genetic information out of representative insects from each order. Researchers captured as much as they could of the genetic templates (made from RNA) that genes produce for creating proteins. By working back from all these templates, researchers inferred what the genes were like, and then analyzed the subset of 1,478 genes that all the insects in the study share.
Previous evolutionary studies used at most a couple of hundred genes, and no other study with this technique has covered such a broad group of organisms, says study coauthor Bernhard Misof of the Zoological Research Museum Alexander Koenig in Bonn, Germany. The international project started when the Chinese federal-private science institute called BGI authorized funds for the genetic lab work, says coauthor Karl Kjer of Rutgers University in New Brunswick, N.J.
The arrangement of branches of the new genealogical family tree is reassuring, says Niels Kristensen of the University of Copenhagen, who was not part of the study. The new data confirm much of what earlier research concluded about the basic pattern of the tree. “Overall it fits my ideas about how things are,” he says.
Details have changed, though. Among the tweaks, the collaboration shifted the dragonfly order and the mayflies beloved by fly fishermen into one ancient lineage. It’s a controversial pairing because, among other differences, mayflies molt as adults but dragonflies don’t, says David Grimaldi of the American Museum of Natural History in New York. It’s an idea that “entomologists have been volleying back and forth … for decades,” he says. Even the new data-rich paper, he notes, calls for more research on the topic.
The new work also changess the timing for some landmark insect events. The analysis concludes that modern parasitic lice diverged onto their own evolutionary path about 53 million years ago. That contradicts the scenario of lice going parasitic early enough to vex dinosaurs, as described by Vincent Smith of the Natural History Museum in London and his colleagues.
Smith sees a lot of uncertainty still in louse history. Admittedly the lousy-dino idea came from a study with far less genetic information, but it had many more kinds of lice and more detailed timing calibration than did the 1KITE study.
Grimaldi takes issue with dates assigned to several of the branches in the new tree, in large part because 1KITE used only 37 fossils to refine their genetics-based timing. “I can say with confidence that the molecular estimates are excessive in places,” he says, particularly with the very old events. Fossils from so far in the past can be tricky to assign as ancestors of modern organisms, but Grimaldi urges that the effort be made.
NEW INSECT TIMELINE
The earliest insects may have arisen as long ago as 479 million years, says a new study. Insects first took flight about 406 million years ago, as plants developed their vascular plumbing and expanded into the air too. Silhouettes show when ancestors of some major living orders of insects likely first started on their distinctive evolutionary paths. (From earliest, on left: springtails; jumping bristletails; silverfish; dragonflies and damselflies; crickets and katydids; bugs, cicadas and plant lice; snakeflies; beetles; sawflies, wasps bees and ants; moths and butterflies; true flies; caddisflies; cockroaches; and scorpionflies.)