Role of ecdysone and eyestalk factors in regulating regeneration in larval crustaceans

Megalopae of the mud crab Rhithropanopeus harrisii can regenerate autotomized limbs. Regeneration during the megalopal stage required a significant delay in ecdysis to the first crab. Megalopae that failed to initiate regeneration complete ecdysis significantly faster than do controls. Exposure of intermolt- and premolt-stage megalopae to exogenous ecdysone significantly reduced (greater than or equal to 30%) the number of animals completing regeneration. The regeneration-induced delay in ecdysis was not significantly different in animals exposed to ecdysone. The molt cycle of nonregenerating megalopae exposed to ecdysone was further accelerated. Eyestalk ablation did not significantly reduce the molt cycle duration of regenerating animals. Eyestalkless nonregenerating animals did not display accelerated ecdysis. It is hypothesized that two additional hormonal factors are involved in "fine tuning" the molt cycle of regenerating animals. One located outside the eyestalks extends the molt cycle to accommodate regeneration. The second factor accelerates ecdysis in nonregenerating animals and appears to be produced in the eyestalks.

Ecdysteroid levels during the larval development of the spider crab Hyas araneus

Ecdysteroid levels were determined by radioimmunoassay during the larval development of the spider crab Hyas araneus L. In each of the three larval instars (zoea I, zoea II, megalopa) a minimum in ecdysteroid levels was found during early postmoult and a maximum during premoult. The amounts of ecdysteroids increased during development and reached maxima of 93, 137, and 165 pg ecdysone equivalents per larva in zoea I, zoea II, and megalopa, respectively. Ecdysteroid concentrations per unit of body dry weight or carbon increased during each moulting cycle, but the average values showed decreasing tendency from the first to the last instar. The main ecdysteroid in all larval instars and during the moulting cycle was 20-OH-ecdysone, and practically no ecdysone could be detected by HPLC-RIA.