Evolution's new line

Evolution's new line

By Dr David Whitehouse
BBC News Online science editor

The tree of life has a new branch. Genetic studies show that the group from which insects were thought to come, the Collembola, turns out not to be closely related to insects after all.

Springtail: A different story to insects

Instead, the creatures, known as wingless hexapods but more commonly called springtails, belong to a separate evolutionary line that predates even the separation of insects and crustaceans.

"Based on the similarities in their body organisation, their six legs, and other morphological characteristics, it has been generally accepted that the Collembolans were the basal stock from which insects arose," says Jeffrey Boore, a biologist at the Lawrence Berkeley National Laboratory in the US.

"But our study shows that they evolved separately from insects and independently adapted to life on land.

"The Collembolan appear to branch off the evolutionary line leading to the insects at a much earlier stage than previously thought - earlier than some if not all of the crustaceans," adds Francesco Nardi of the University of Sienna, Italy.

"In fact, the few crustaceans that we've analysed so far using mitochondrial genomics appear to be more closely related to the true insects than are the Collembolans."

Different DNA

The discovery was made after studying mitochondrial DNA. Mitochondria are found in living cells and play an important part in vital life processes such as metabolism.

They are believed to have once been free-living organisms that long ago evolved into a symbiotic relationship with the nuclei of cells.

They have a tiny genome that is separate from the genome of the host cell. It can serve as a powerful tool for the study of evolution.

Insects have been thought to be the dominant group of Hexapoda, also thought to include the Collembola and a few other wingless groups.

Together these groups have been included as part of the phylum Arthropoda (meaning "jointed feet"), which constitutes nearly 85% of all known species of animal life.

It was believed that all Hexapoda are descended from a single ancestor. However, the new mitochondrial research shows that Collembola should not be included within Hexapoda.

"We can say that Collembolans should be separated so that they constitute a separate evolutionary line," says Nardi.