Know thine anemone

Natural History, Oct, 2005 by Nick W. Atkinson

Sea anemones don't come across as particularly complicated social creatures. Who would have guessed they organize themselves into armies, with tentacled soldiers at the front fighting violent underwater battles? Yet that's the conclusion reached by David Ayre, an evolutionary biologist at the University of Wollongong, Australia, and Richard Grosberg, an evolutionary biologist at the University of California, Davis, from their study of the sea anemone Anthopleura elegantissima.

The species lives in groups of hundreds to thousands of genetically identical individuals, known collectively as a clone. Within a clone, individual polyps fall into one of several classes, or castes--rather like the castes of social insects such as ants or bees. A polyp's caste may be determined by its location within the clone and by cues it receives from other polyps. Where a clone borders another clone, "warriors"--small, heavily armed polyps, bristling with stinging tentacles--square off against their counterparts in the neighboring clone. Some warriors act as "scouts" that try to infiltrate enemy lines, but often they're forced to retreat to the safety of their own clone. Far from the lines of battle another class of polyp--the large, relatively unarmed, and sexually mature "reproductive"--safely dwells in the center of the clone.

Battlefronts are marked by persistent polyp-free zones, a kind of "no anemone's land." In spite of warriors' struggles to defend and acquire more territory, these borders are stable, and competing clones can remain deadlocked for years. (Animal Behaviour 70:97-110, 2005)