Hemolymph ecdysteroids during the last three molt cycles of the blue crab, Callinectes sapidus: quantitative and qualitative analyses and regulation

Jun 27, 2009Archives of insect biochemistry and physiology

Levels and types of molting hormones in the blood of blue crabs during their last three molts and how they are controlled

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Abstract

Circulating ecdysteroid concentrations in juvenile blue crabs range between 210-330 ng/ml hemolymph during molt cycles.

Ecdysteroid profiles showed consistent patterns across three molt cycles.
Six types of ecdysteroids were identified, with ponasterone A and 20-OH ecdysone as the major forms.
Bilateral eyestalk ablation reduced peak ecdysteroid levels compared to intact crabs.
Daily injections of crustacean hyperglycemic hormone and molt-inhibiting hormone maintained low ecdysteroid levels in ablated animals.
The dominant ecdysteroid in ablated crabs was 20-OH ecdysone, rather than ponasterone A.

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The profiles of circulating ecdysteroids during the three molt cycles prior to adulthood were monitored from the juvenile blue crab, Callinectes sapidus. Ecdysteroid patterns are remarkably similar in terms of peak concentrations ranging between 210-330 ng/ml hemolymph. Analysis of hemolymph at late premolt stage revealed six different types of ecdysteroids with ponasterone A (PoA) and 20-OH ecdysone (20-OH E) as the major forms. This ecdysteroid profile was consistent in all three molt cycles. Bilateral eyestalk ablation (EA) is a procedure that removes inhibitory neurohormones including crustacean hyperglycemic hormone (CHH) and molt-inhibiting hormone (MIH) and often results in precocious molting in crustaceans. However, the inhibitory roles of these neuropeptides in vivo have not yet been tested in C. sapidus. We determined the regulatory roles of CHH and MIH in the circulating ecdysteroid from ablated animals through daily injection. A daily administration of purified native CHH and MIH at physiological concentration maintained intermolt levels of ecdysteroids in the EA animals. This suggests that Y organs (YO) require a brief exposure to CHH and MIH in order to maintain the low level of ecdysteroids. Compared to intact animals, the EA crabs did not exhibit the level of peak ecdysteroids, and the major ecdysteroid turned out to be 20-OH E, not PoA. These results further underscore the important actions of MIH and CHH in ecdysteroidogenesis, as they not only inhibit, but also control the composition of output of the YO activity.

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