A new timeline for insects shows that the creatures first evolved 479 million years ago — earlier than previously suspected — and that their appearance coincided with Earth's first land plants.
The revised insect tree of life, also called a phylogeny, is helping scientists answer some of the longstanding questions regarding the origin of these highly diverse and tremendously important arthropods. But constructing the phylogeny was no picnic. Insects are by far the most species-rich group of animals on the planet, and the researchers involved had to use several supercomputers to process all of their genetic data.
Bernard Misof from the Museum Koenig in Bonn, Germany; Xin Zhou from BGI in Shenzen, China; and Karl Kjer from Rutgers University in New Brunswick, New Jersey; along with colleagues from around the world, created a project known as 1KITE to get it done. The group's findings appear in the 7 November issue of Science.
"Very few software programs could even load our data without crashing," said Kjer. "Insects are so abundant that, in terrestrial ecosystems, they consume more in terms of biomass than vertebrates do."
"Actually, insects are so dominant that it's hard to imagine any kind of terrestrial life on Earth that has not been shaped by them," he said. "I'm trying to think of one…Perhaps penguins? They might not need insects in Antarctica, but I think everything else does."
The researchers had to collect fresh DNA samples from all of the major insect orders that exist today. But the 1KITE team was able to accomplish this feat in about a year, allowing researchers to analyze 1,478 different protein-coding genes from insects — as well as a few genes from their close arthropod relatives — and compare their data to the insect fossil record.
"This only worked because we could rely on a network of amateurs and professionals to collect every phylogenetically important species in the project," said Misof.
"Insects did just about everything first. They were the first to form social societies, farm, and sing — just about anything you can imagine."
"The rapid advent of next-generation sequencing technology and informatics also allowed us to produce huge amounts of sequence data that were informative for phylogenetic construction," explained Zhou. "This was not possible in the past, when genes had to be amplified and sequenced one-by-one."
The new timeline reveals that insects likely originated during the Early Ordovician Period, and that their appearance coincided with Earth's first land plants. Thus, the researchers suggest that the diversification of insects played a significant role in shaping the planet's first terrestrial ecosystems — and vice versa.
The 1KITE team also proposes that insect flight emerged approximately 406 million years ago, as terrestrial ecosystems became more complex. They say that the radiation of flowering plants was accompanied by an explosion of diversity among flying insects, such as bees, wasps, and butterflies.
"Wings were a key to insect success," Kjer said. "They turned a two-dimensional environment into a three-dimensional environment."
The researchers' timeline shows that most modern insect species originated about 345 million years ago. Among these modern species, parasitic lice didn't diversify until after avian and mammalian hosts were available, a finding that contradicts the theory that they originated on feathered, non-avian dinosaurs.
The variety of cockroaches and termites that we see today probably evolved in the wake of the Permian mass extinction, the only known mass extinction of insects, which occurred about 252 million years ago.
"However, real insect diversity didn't come about until Holometabola," said Kjer, referring to the subclass of insects that undergo complete metamorphosis, including butterflies and beetles. "Holometabolous insects have very distinct life stages, with larvae that are specialized to feed and hide and adults that are specialized to mate and disperse, meaning that they can custom-design their body forms for what they need when they need it."
"Insects did just about everything first," according to Kjer. "They were the first to form social societies, farm, and sing — just about anything you can imagine."