The Induction And Mechanism Of Metamorphosis In Larvae Of Bivalvia

Metamorphosis is an important stage from larva to juvenile in bivalvia. Studying the metamorphosis process and mechanism of bivalvia is important for us to determine their population variation and increase the economic efficiency of bivalvia cultivation industries. In this paper, apart from the induction of metamorphosis by chemical matter in bivalvia (Argopecten irradians, Argopecten irradians concentricus and Mercenaria mercenaria), we study the metamoiphosis mechanism of bivalvial larvae at molecular biology and neurobiology levels, which through determining the hormone and neurotransmitter content and the second messenger cAMP content in bay scallop Argopecten irradians larvae. The main results are as follows. 1. The advancement in researching on settlement and metamorphosis of marine invertebrate larvae are reviewed in detail according to a lot of references. There are many factors that affecting these processes, including biotic and abiotic factors. Biotic factors involve larval behavior, abiotic factors involve physical and chemical factors. Last decade many achievements about mechanism of settlement and metamorphosis of marine invertebrate larvae have been achieved, at neurology and molecular biology levels. So far there are three models for explaining the settlement and metamorphosis mechanism of marine invertebrate larvae: the two control pathyways model for Pacific oyster (Crassostrea gigas) larvae, the up-regulation model for red abalone (Haliotis rufescens) larvae and the free fatty acid control model for polychaete Phragmatopoma california larvae. Some inductive matters such as GABA, epinephrine, norepinephrine have been successfully applied to economical molluscan seed-production. The delayed ? The Induction and Mechanism of Metamorphosis in Larvae of Bivalvia: ABSTRACT metamorphosis of marine invertebrate larvae is also reviewed, including the cause occurring delayed metamorphosis and effects of delayed metamorphosis on metamorphosis, growth and mortality. 2. Bay scallop A.irradians larvae are treated with Ach Cl, ATP and CaC12 to test the ability to induce metamorphosis during 3? April, 2000. Ach Cl and ATP are found ineffective exception at special concentrations and exposure time tested. CaC12 has been identified as active inducer of metamorphosis. Exposure to lOX I O~?0 X 1 03M CaCl2 for 1 2?4h is sufficient to promote >10% metamorphosis. The inductive effect is dose- dependent with a maxima under 40 X 1 03M and 24h, at which the percentage metamorphosis increment is 23.18%. All the three chemical matters affect the morality of bay scallop larvae. The effect is dose- and time-dependent, the higher the concentration and the longer the exposure time, the higher the mortality. 3. The induction of metamorphosis of larvae of the southern bay scallop Argopecaen irradians concentricus Say by KC1, epinephrine (EPI), norepinephrine (NE) and choline chloride have studied. The results suggest that KC1, EPI, NE and choline chloride are all the active inducers of metamorphosis. KCI can increase metamorphosis at all concentrations (6.71 X 103?3.56X 103M) and exposure time (12桝Sh). When exposure to 13.42 X 1 03M and 20.13 X 1 03M KC1 for 1 2~?8h, the average percentage metamorphosis increment arc all >10%. The better inductive effect of EPI and NE are all archived at 1.0 X 104M?0 X 104M when exposure to lh?2h, the av...