Image: Oliver Niehuis, ZFMK, Bonn
By Kate Yandell
Using an unprecedented quantity of genetic sequence information from insects, researchers have assembled a new phylogenetic tree showing when these invertebrates evolved and how they are related to each other. The tree suggests that insects evolved approximately 479 million years ago, around the time when plants colonized land, and that insects are most closely related to cave-dwelling crustaceans. The new study, published today (November 6) in Science, also confirms some previously suspected family groupings.
“The results of this work are immense and will be broadly adopted in general and systematic entomology books and textbooks,” Jakub Prokop, an entomologist at Charles University in Prague in the Czech Republic who was not involved in the study, wrote in an e-mail to The Scientist.
David Grimaldi, curator of insects at the American Museum of Natural History in New York, said that the overall pattern of insect relationships in the tree, with a few exceptions, bolsters prevailing views of how insects are related to each other. “It’s pretty amazing to see that after how many gigabases of data they have that we haven’t really changed fundamentally our views about insect relationships,” said Grimaldi, who also did not participate in the research.
The study authors, who are part of an international consortium working on the 1K Insect Transcriptome Evolution (1KITE) project, began their work in 2011 in hopes of using newly available sequencing technology to clarify insect relationships previously only investigated using morphological evidence or smaller molecular datasets. They sequenced transcriptomes from 103 insect species distributed across all living insect orders. They also drew data from previously published whole-genome sequences of 14 arthropod species, as well as from transcriptomes of 27 additional species. They then narrowed down their genetic data to 1,478 protein-coding genes that are present in all of the species analyzed.
By comparing differences and similarities between the sequences of these protein-coding genes, as well as the sequences of amino acids the genes encode, the researchers were able to create a tree showing the relationships between 144 insect genuses. This confirmed many relationships, while also drawing some unexpected conclusions, Grimaldi said. For instance, he said it was surprising but plausible that a blind, wingless order called the Diplura is not lumped with another group of similar primitive invertebrates, the springtails, but rather are their own sister group to insects. Less surprising was the finding that primitive crustaceans called Remipedia are the closest non-extinct relatives to insects.
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