First author

Evolutionary biologists would like to map the origin and early diversification of animals. So far, researchers have targeted sponge and sea anemone genomes for clues. The seeming simplicity of a microscopic soft-bodied marine organism called Trichoplax adhaerens made it a top candidate for a descendent of the earliest animal branch of the evolutionary tree. Mansi Srivastava, a PhD student at the University of California, Berkeley, was part of the team that decoded the Trichoplax genome (see page 955). She tells Nature about Trichoplax's surprising complexity.

Did Trichoplax turn out to be an evolutionary goldmine?

More than we expected. It has only four or five cell types, yet we found an extensive repertoire of factors that are involved in specifying additional cell types in other animals. We even found genes for neural functions, even though Trichoplax has no neurons. Maybe most strikingly, co-author Nicholas Putnam found that some genes that are present together on human chromosomes are also present together on Trichoplax chromosomes — despite their having diverged perhaps 650 million years ago.

Is Trichoplax a blueprint for modern animals?

It's tempting to assume that. Unfortunately it's impossible to say without a fossil record of Trichoplax or its ancestors. But we can safely say that the Trichoplax genome has retained a lot of primitive features relative to other living animals.

Why is so little known about this organism?

Because of its small size, it is hard to observe Trichoplax in its native marine environment. In the lab, it only grows asexually, but sexual activity has recently been inferred on the basis of genetics. Unfortunately, no one has yet observed its entire life cycle. Its genes will tell us what Trichoplax is capable of.

Do you expect Trichoplax 's evolutionary significance to be debated?

Yes. Mitochondrial gene sequences suggest that it belongs to the earliest branch of animal evolution, but our data conflict with that hypothesis. We suggest that Trichoplax and its relatives diverged from other animals after sponges but before the diversification of all other animals. Decoding the genome of a comb jelly, or ctenophore, will help to illuminate early evolutionary events because recent studies suggest this was the earliest animal group to evolve.

Has this work shaped your aspirations?

Yes. Working on this exciting and contentious project has given me a taste for work with far-reaching implications for animal evolution.