Comparison of the abilities of ?-ecdysone and 20-hydroxyecdysone to induce precocious proecdysis and ecdysis in the fiddler crab, Uca pugilator

Abstract

1. The effects of single, double or multiple injections of α-ecdysone and 20-hydroxyecdysone on molting and limb regeneration in the fiddler crab, Uca pugilator, were determined. 2. A single injection of 12 μg of 20-hydroxyecdysone failed to initiate proecdysis in crabs weighing 1.2 to 1.6 g. Administration of 12, 5, and 5 μg of 20-hydroxyecdysone on Days 0, 3, and 6 respectively induced precocious initiation of proecdysis but not precocious ecdysis. However, when two large dosages (20 or 25 μg) of 20-hydroxyecdysone were injected within a period of one or two days all the crabs completed proecdysis and initiated ecdysis precociously but failed to complete the ecdysis and died. 3. Administration of 25 μg of α-ecdysone as a single injection failed to initiate precocious proecdysis. However, when two injections of 25 μg each were given 36% of the crabs completed proecdysis and successfully molted precociously. Injection of larger dosages (80 μg α-ecdysone either as four 20 μg injections or two 40 μg injections) induced precocious proecdysis and ecdysis in 75–86% of the crabs. In contrast to the crabs which died during ecdysis after receiving high dosages of 20-hydroxyecdysone, the recipients of α-ecdysone underwent successful ecdysis and their postecdysial survival was normal. 4. The response of the regenerating limb buds depended on the dosage of the ecdysones administered. Dosages of 20-hydroxyecdysone which failed to initiate proecdysis promoted basal limb growth. Stronger dosages of 20-hydroxyecdysone and α-ecdysone which induced precocious proecdysis and ecdysis accelerated limb growth and caused proecdysial limb growth. The slope of the growth curve obtained for the crabs injected with high dosages of ecdysones was much steeper than that for eyestalkless crabs. 5. The interrelationship between regenerative limb growth and proecdysis and the possible role of ecdysones in the control of proecdysial events in crustaceans are discussed.