Growth, Degrowth, and Irreversible Cell Differentiation in Aurelia aurita

Growth patterns of the Scyphomedusa Aurelia aurita from TomalesBay. California, were examined in the field and in the laboratory.Manipulation of growth patterns demonstrated that degrowth andregrowth are not constrained by initial ievelopmental stage.Although initial degrowth of certain tissues is allometric (e.g.,gonads regress in 5 to 8 days; bell diameter decreases morerapidly at first than do the oral arms), thereafter regressionappears identical to, but reversed from normal growth. Regrowthpatterns are normal. Sexual maturation in the sea does not alwaysalter subsequent capacity for degrowth or regrowth to sexualmaturity in the laboratory, because reproductive and somatictissues do not always degenerate after spawning. Gonadal tissuecan be renewed and maintained in a ripe condition in the laboratoryapparently indefinitely. Sexual maturation is a size-dependentphenomenon, not an agespecific developmental event. Spermatogenesis, once initiated, proceeds irrespective of outsideevents. Labeled spermatogonial cells can continue to differentiateto form sperm even though the gonad containing those cells,and the animal itself, show rapid degrowth. The importance ofthis decoupling of developmental events is discussed. The experimentalimportance of animals with flexible life cycles is emphasized.