Anemone Armies Battle To A Standoff

The sea anemone Anthopleuraelegantissima lives in large colonies of genetically identical cloneson boulders around the tide line. Where two colonies meet they form adistinct boundary zone. Anemones that contact an animal from anothercolony will fight, hitting each other with special tentacles that leavepatches of stinging cells stuck to their opponent.

David J. Ayrefrom the University of Wollongong, Australia, and Rick Grosberg from UCDavis have previously taken individual anemone polyps from separatecolonies and studied fighting strategies one-on-one. But that's liketrying to understand two armies by taking a single soldier from eachside, Grosberg said.

Now, the researchers have been able to study two entire colonies as they clash.

Whenthe tide is out, the polyps are contracted and quiet. As the tidecovers the colonies, "scouts" move out into the border to look forempty space to occupy. Larger, well-armed "warriors" inflate theirstinging arms and swing them around. Towards the center of the colony,poorly armed "reproductive" anemones stay out of the fray and conductthe clone's business of breeding.

When anemones from opposingcolonies come in contact, they usually fight. But after about 20 or 30minutes of battle the clones settle down to a truce until the next hightide.

It's not just polyps along the border between two clonesthat clash. Polyps three or four rows away from the front will reachover their comrades to engage in fights, Grosberg said.

Differentiationinto warriors seems to depend on a combination of signals from enemystings and the genetics of the colony. Different colonies reactdifferently to similar signals, explaining why different clones areorganized into so many different kinds of armies. But borders betweencolonies can remain stable for years, even though the two coloniesorganize their armies in different ways.

The study shows thatvery complex, sophisticated, and coordinated behaviors can emerge atthe level of the group, even when the group members are very simpleorganisms with nothing resembling a brain, Grosberg said. The researchwas published in the June issue of the journal Animal Behaviour.