Growth, Developmental, and Longevity Rhythms in Campanularia flexuosa

Endogenous circannual rhythms in growth, development, and longevityof the marine coelenterate Campanularia flexuosa have persistedfor over 3 years in the absence of periodic signals from theenvironment. The periods for the cycles at three constant ambienttemperatures, 10, 17 and 24 C, approximated 1 year, but werealways more than 365 days. Although uncertainty exists, temperaturewas implicated as a Zeitgeber. The endogenous circannual rhythms were marked by seasons ofluxuriant colony growth that alternated with more sparse growth.During luxuriant growth, development of individual hydranthswas initiated regularly in new positions and as replacementsat regression sites on uprights. Nearly all hydranth developmentwas normal and adult life spans were long. The profuse growthwas interrupted by seasons of sparse growth each summer andpunctuated by recurrent, short periods of sharply curtailedgrowth in mid-winter. During curtailed growth, the rate of hydranthinitiation at all sites was depressed, and abnormal developmentaborted many individuals. Most strikingly, hydranth life spansfell to about half those observed during seasons of luxuriantgrowth. With the spontaneous return to the luxuriant growthhabit, hydranth life spans rose, nearly doubling. The delineation of these endogenous rhythms in C. flexuosa longevitychallenges the generally accepted concept of specific age, anage at death which is characteristic of the species.