Inhibition of ovarian development by methyl farnesoate in the tadpole shrimp, Triops longicaudatus

Methyl farnesoate (MF), a putative crustacean hormone, is the immediate precursor of insect juvenile hormone III (JHIII) in the biosynthetic pathway. We examined whether MF, shown to inhibit adult metamorphosis in several crustacean species, is a juvenilizing factor in the tadpole shrimp, Triops longicaudatus. Oocyte production was chosen as a parameter for measuring reproductive development. MF was administered to juveniles by ingestion via biological vector (Artemia nauplii), MF-coated food pellets, and MF liposome food pellets. Artemia were incubated in 30 μl of 5 μg/ml MF. The MF-coated and MF liposome pellets were prepared with MF concentrations ranging between 0.1 μg/g and 10 μg/g MF by weight. Groups of tadpole shrimp were treated with these vectors from the time of hatching for 5 or 10 days in laboratory and field studies. The treatment groups of all the MF vectors showed reductions in oocyte production. Lower concentrations of MF (0.75 μg/g–3.8 μg/g MF) appeared to have a physiological effect on fecundity, but higher concentrations (10 μg/g MF) reduced somatic growth. MF-coated pellets (1 μg/g MF) administered to adults (after 5 days) caused no difference in oocyte production. The observed reductions of fecundity and the disparity of results between MF treatment on juveniles and adults suggest that MF may regulate ovarian development.