Differentiation of the female reproductive body in the colonial hydroidCampanularia flexuosa

Abstract

A comparison of two genetic stocks ofCampanularia flexuosa revealed consistent differences with respect to (1) the number of eggs present in the maturefemale reproductive body (gonangium), (2) the level on each upright stem at which the first gonangium forms, and (3) their preference for the formation of reproductive versusvegetative (side-branch) structures.Alterations in food intake established the optimum feeding level for maximal production of structurally normal gonangia and also showed differences between stocks in the effects of reduced food intake on gonangial versus vegetative growth.A staging series for gonangiogenesis was developed from observations of filling of the gonangium with primordial egg cells (PEC), gonangial elongation, funnel maturation and oogenesis.When upright segments bearing immature gonangia are isolated from the stolon the gonangia frequently resorb, transform into vegetative outgrowths, or form structurally abnormal gonangia bearing fewer germ cells than normal. These responses, and the observed accumulation of PEC at sites of presumptive gonangial outgrowth, support a stolonic origin hypothesis for PEC and implicate PEC and oocytes in the initiation, maintenance and maturation of structurally normal gonangia. In addition, continued differentiation of the gonangial structure appears to be necessary for oocyte maturation.Possible mechanisms for somatic and gametic cell recruitment, and the theoretical importance of cellular proliferation, aging, cell-shape changes, cell movement and cellular interactions in normal gonangial differentiation are discussed.