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First published online February 15, 2008
Journal of Experimental Biology 211, 731-740 (2008)
Published by The Company of Biologists 2008
doi: 10.1242/jeb.011148

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Physiological characterization of stolon regression in a colonial hydroid

Kimberly S. Cherry Vogt, Gabrielle C. Geddes, Lori S. Bross and Neil W. Blackstone^*

Department of Biological Sciences, Northern Illinois University, DeKalb, IL 60115, USA

^* Author for correspondence (e-mail: neilb{at}niu.edu)

Accepted 24 December 2007

As with many colonial animals, hydractiniid hydroids display a range of morphological variation. Sheet-like forms exhibit feeding polyps close together with short connecting stolons, whereas runner-like forms have more distant polyps and longer connecting stolons. These morphological patterns are thought to derive from rates of stolon growth and polyp formation. Here, stolon regression is identified and characterized as a potential process underlying this variation. Typically, regression can be observed in a few stolons of a normally growing colony. For detailed studies, many stolons of a colony can be induced to regress by pharmacological manipulations of reactive oxygen species (e.g. hydrogen peroxide) or reactive nitrogen species (e.g. nitric oxide). The regression process begins with a cessation of gastrovascular flow to the distal part of the stolon. High levels of endogenous H₂O₂ and NO then accumulate in the regressing stolon. Remarkably, exogenous treatments with either H₂O₂ or an NO donor equivalently trigger endogenous formation of both H₂O₂ and NO. Cell death during regression is suggested by both morphological features, detected by transmission electron microscopy, and DNA fragmentation, detected by TUNEL. Stolon regression may occur when colonies detect environmental signals that favor continued growth in the same location rather than outward growth.

Key words: cell death, clonal organism, cnidarian, evolution and development, evolutionary morphology, hydroid, Podocoryna, Podocoryne, reactive oxygen species, reactive nitrogen species