Role of ecdysteroids and methyl farnesoate in morphogenesis and terminal moult in polymorphic males of the spider crab Libinia emarginata
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Here we examine morphogenesis and terminal anecdysis in male morphotypes of the spider crab Libinia emarginata through eyestalk removal (ablation). Methyl farnesoate (MF), an unepoxidated form of juvenile hormone (JH III) and hydroxyecdysone, a moulting hormone, were measured in attempt to understand these processes and to determine the physiological characteristics of each morphotype, to he able to induce maturation by hormonal treatment and improve crustacean culture. Following arrival at the laboratory, ablated small-claw unabraded small-carapace males (SUM) moulted within 30 days to a juvenile and control SUM moulted within 75 days to a mature morphotype with large claws. Following eyestalk removal small-carapace abraded males (SAM), large-carapace unabraded large-claw (LUL) and large-carapace abraded large-claw (LAL) males never moulted even after 60 days, while the other ablated morphs moulted in 25-35 days. Significant increase of MF levels was observed in SUM, SAM and LUL de-stalked animals compared to intact control group, while no differences were observed in LAL individuals. in fact, LAL crabs presented the highest level of MF up to 2.23 ng/ml. Ten days prior to moulting MF increased 4-fold, and the ecdysteroids increased 15-fold in the haemolymph of ablated SUM and 25% in their testes. Ecdysteroid levels in the haemolymph of the SAM, LUL and LAL morphotypes remained low (around 5 ng/ml), and none of these animals moulted. The results strongly suggest that: (1) SUM an able to moult, and represent the juvenile stage, (2) SAM, LUL and LAL are terminally moulted and may represent the reproductive population, (3) circulating ecdysteroids induce moulting in juveniles, (4) high levels of ecdysteroids in the testes of SAM, LUL and LAL suggest a gonadal function, and (5) circulating MF controls morphogenesis of juveniles (SUM) and seems to stimulate gonads in adults. (C) 2000 Elsevier Science B.V. All rights reserved.