NELSON, William; TSUKIMURA, Brian; CSU Fresno; CSU Fresno: Reproductive Inhibition By Methyl Farnesoate in the Tadpole Shrimp Triops longicaudatus

Methyl farnesoate (MF) is believed to play a regulatory role in reproduction in the tadpole shrimp, Triops longicaudatus; a potential model organism based on its short life cycle and high fecundity. MF is structurally similar to insect juvenile hormone III (JHIII), which inhibits reproductive development in juvenile insects, but not in adults. To test the effects of MF, animals were fed pellets that contained MF in two concentrations (0.0001% and 0.001 % by weight). Control pellets contained no MF. Two methods of incorporation were used: MF, incorporated into liposomes, mixed into the feed, and MF sprayed onto pellets using Tween 20 as a binding agent. In trials using the coated pellets, animals were collected after 5 days; weight, length, and number of oocytes were recorded. Both MF concentration groups produced significantly fewer oocytes than controls. To determine the effect of MF on adult tadpole shrimp the low MF coated pellets were administered days 6 -10. No significant difference was found between the delayed exposure group and controls, suggesting MF has no inhibitory effect on reproduction in adults as was hypothesized based on the JHIII model. In trials using the liposome feed, the high MF treatment significantly reduced oocyte number compared to controls. These data suggest MF inhibits ovarian development in juveniles, supporting the contention that MF has juvenilizing activities. We have also begun investigating a possible degradation pathway for MF. We are using radio partition assay (Homola and Chang, 1997), using H3-Methyl Farnesoate, to test germinal and hepatopancreatic tissue homogenates for MF esterase activity. Cal. Ag. & Tech. Inst.-Ag. Research Initiative funded this research.