Coordinated behavior in pelagic animal colonies: Siphonophores, salps, and Pyrosoma

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George Mackie, Ph.D.
University of Victoria

Wednesday, October 14, 1998
3:00 p.m.—Pacific Forum

"Colonial" animals are so named because they are composed of asexually budded, modular units (zooids) that resemble the "individual" members of related, non-colonial groups but which stay physically attached instead of separating and living freely. In some cases the zooids undergo specialization into several morphologically and functionally distinct types, but even where the zooids remain monomorphic, in almost all cases at least some activities are organized on a colony-wide basis. Thus, functionally speaking, a new "colonial individuality" tends to emerge, transcending the primary individuality of the component zooids. Protective and defensive responses, including escape locomotion, are the most commonly seen activities in which the colony behaves as a single unit, but the mechanisms whereby the zooids intercommunicate vary considerably. In siphonophores the zooids are directly interconnected by nerves. Salps use a combination of nerves and excitable epithelia. Pyrosoma, a bioluminescent organism, uses photic signalling to spread ciliary arrest responses from zooid to zooid, both within and between colonies.

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