TUBERTY, S. R.; GLAS, P.S.; Appalachian State University, Boone, NC; The Citadel, Charleston, SC: Free Ecdysteroid Levels in Grass Shrimp Embryos Relate to Embryonic Envelope Elevation

Ecdysteroids, the hormones responsible for stimulating arthropod molting, are secreted by Y-organs in eyestalks of adult crustaceans. Ecdysteroids have been identified in crab (Okazaki and Chang, 1991) lobster (Goudeau, et al., 1990) and shrimp embryos (Spindler, et al.,1987) in studies which characterized and quantified ecdysteroid titers, but overlooked the timing of the production and/or release of the ecdysteroids as it relates to the development of the individual embryonic envelopes. During embryonic development, the grass shrimp elevates 4 embryonic envelopes (EE) over a period of 10 to 12 days to form the protective embryonic coat (EC). In preliminary studies using Palaemonetes pugio embryos, increases in ecdysteroid levels correlate with the timing of the synthesis and elevation of the individual EE. Peaks of ecdysteroids are small during early development, possibly due to limited maternal ecdysteroid investment via the egg yolk, followed by larger peaks in ecdysteroids at a time concomitant with eyestalk development. Two large peaks at 48-60 hours pre-hatch can be associated with formation of the innermost embryonic envelope, EE4, and the advent of embryonic cuticle production. The relevance of a peak within 6-12 hours of hatching is uncertain, but may signal the breakdown of the EC prior to hatching. Ecdysteroid levels fall sharply within hours of these peaks and are low in newly hatched zoeal larvae. This hormone cycle may signal the individual elevation events for the embryonic envelopes as each morphologically unique envelope forms and elevates from the egg surface. The increases in ecdysteroid production at later development may also indicate a switch from maternal or stored precursors to production of ecdysteroids by the embryonic eyestalk.