Index >> Determination of Sex >> Environmentally Controlled Sex Determining Mechanism

An excellent example of environmental determination of sexual phenotype is afforded by Bonellia viridis, a marine echiuroid worm studied extensively by F. Baltzer, (1935). The adult female is about an inch long and has fairly complex anatomical organization. The male is of the size of large Protozoa and has rudimentary organs. The males live as endoparasites in the uterus of the females. All larvae that are reared in isolation become females. The larvae that are released in water containing mature female can have one of two fates. Some larvae settle in mud and grow up into mature females, while some other free swimming larvae may come in contact with the females, they attach with the proboscis of females and develop into males. The males eventually migrate to the female reproductive tract, where they take up their parasitic existence. It has been demonstrated that female proboscis produces a hormone like substance that influences the larvae toward maleness. This implies, that the male producing substance inhibits the actions of female developing genes of the larvae, while permitting its male developing genes to function.

There must correspondingly be some mechanism, which may be unknown to us, for inhibiting the action of some genes, while permitting others to function.