Unifying Concepts Learned from Methyl Farnesoate for Invertebrate Reproduction and Post-Embryonic Development

Since the discovery that methyl farnesoate (MF), the unepoxidatedform of the insect juvenile hormone (JHIII), is produced bymandibular organs of numerous crustaceans, extensive evidencehas accumulated that this compound appears to perform similarfunctions in the Crustacea as JH performs in insects. A majorfunction of MF appears to be in enhancing reproductive maturation.This was first shown by indirect experimentation with eyestalkablation, which augmented MF production. Subsequently, directtreatments of several species of crustacea with MF showed thatreproductive maturation was enhanced. A second function of MF, similar to that of the JH of insects,is in the maintenance of juvenile morphology. This is especiallytrue in the late larval transformations into juveniles, whereMF plays an inhibitory role, as well as during the transformationof juveniles into adults. These results were inferred from eyestalkremoval experiments. In the case of the larval-juvenile transition,inhibitory results were also obtained with MF by direct hormonetreatments. However, the transition from very early larval stages,such as one nauplius stage proceeding to the next, which inmany cases also involves morphogenetic changes, may be occurringin the presence of MF. Indeed, MF appears to be stimulatoryto early postembryonic larval stages of Crustacea. Again, thisfunction of MF in Crustacea appears to be similar to functionsof JH in early postembryonic insects. However, it should bepointed out that there are many more "early" stages in Crustaceathan there are in insects, and very few of these cases havebeen investigated. When considering the animal kingdom and larval metamorphosis,the question may be raised whether there are other members ofthe JH family regulating metamorphosis and reproduction. Oneplausible example appears to be among certain annelids. Thetrochophores of Capitella respond to various juvenoids, butare most responsive, within one hour, to MF and eicosatrienoicacid. This latter compound is present also in adult annelids,where it has been named "Sperm Maturation Factor," since itseems to function in the maturation of sperm in Arenicola. Therefore,eicosanoids perform in annelids two functions performed in insectsby JHs. In conclusion, it seems that there are morphogenesis promotingresponses to JHs in early larval development in crustaceans,annelids, and possibly other forms, which differ from thoseMF effects in later larvae of Crustacea where MF retards morphogenesis.Such early responses as noted here have recently also been describedfor insects. Furthermore, it is clear that the polyunsaturated8,11,14-eicosatrienoic and aracidonic acids seem to be juvenoids,and appear to function as such in annelids, and may also befunctionally active in insects and crustaceans. It seems reasonableto conclude therefore that new and novel juvenoids exist, whileothers still await discovery.