Hemolymph Ecdysteroid Titers in a Brachyuran Crab Uca triangularis that Concomitantly Undergoes Molting and Reproduction

Investigations conducted thus far suggest that premolt growth and ovarian growth are antagonistic events in brachyuran crabs, arguably implying that yolk deposition does not occur during premolt when the ecdysteroid titer is very high. The present paper examines ecdysteroid levels in a brachyuran crab Uca triangularis that exhibits simultaneous programming of premolt growth and reproduction during certain seasons of the year. The species exhibits 2 patterns of breeding cycles, 1 (premolt breeding cycle) synchronous with the premolt cycle during Feb.-May, and the other (intermolt breeding cycle) taking place only during intermolt (Aug.-Jan.); no breeding activity occurs during June-July. Results depicted in the present paper are also expected to help us evaluate the possible role of ecdysteroids in reproduction in crustaceans, a matter of active discussion during the past few years. Yolk deposition in the intermolt breeding cycle occurs under a very low ecdysteroid titer (3-6 ng/ml hemolymph), but it takes place at a perceptibly higher ecdysteroid titer (12-36 ng/ml hemolymph) in the premolt breeding cycle; a positive correlation exists between the ecdysteroid titer and oocyte diameter during the premolt breeding cycle. These results on the 1 hand indicate that yolk deposition can occur at a high ecdysteroid titer (premolt titer) in a natural population of U. triangularis; on the other hand, it reveals that a high ecdysteroid titer (as high as the premolt titer) is not mandatory for successful ovarian growth in the species. The study also suggests that molting and reproduction in the species are not mutually dependent events, as normal yolk deposition can occur irrespective of the molt stage.