Endokrinologische und genetische Untersuchungen an einer proterandrischen Population des Polychaeten Ophryotrocha labronica

Decerebrate, sexually immature juveniles of Ophryotrocha labronica develop into males and females, although the normal ratio observed in intact worms is not attained. Even without the prostomium, primary males split into secondary females and stable males. Stable males and females do not show any reaction after decerebration as far as sexual differentiation is concerned. The females proliferate new sets of oocytes and the males continue spermatogenesis. In a great number of cases, decerebrate secondary females resume spermatogenesis. Amputation of the prostomium induces the development of the k-jaw. Even in small individuals below the size at which the k-jaw normally appears, the change to the k-jaw is induced. Heterospecific transplantations of prostomia from female O. labronica donors to decerebrate O. puerilis hosts revealed that the prostomia of female O. labronica produce and release a substance which completely compensates the lack of the host's own prostomium. Obviously, this ootropic substance is not necessary in all cases for gaining and/or maintaining female differentiation in O. labronica. Although it is produced both in stable females and secondary females, only a portion of the secondary females requires this substance for female differentiation. It is, therefore, presumed that the strength or stability of female differentiation expresses itself by hormone-dependent or independent oogenesis. In crosses with a gonochoristic population of O. labronica, protandric hermaphroditism is restricted to a few descendants. Crossing experiments within the protandric population of O. labronica seem to indicate a genetic component in the degree of protandry and in sex determination.