Abstract
Abstract Background Mandibular organ (MO) in decapods is suggested to play regulatory role in reproduction, in few species; however, MO is considered to control growth. The present study addresses this question by an ultrastructural study on the MO of the field crab, Paratelphusa sp. Our sampling for consecutive years (2008 to 2012) revealed that Paratelphusa sp. devotes July to October for reproduction, judged by the occurrence of growing ovaries and the berried females. From November to the succeeding June, the females are in a state of reproductive arrest (non-reproductive period); ovaries during this season would appear as white bands with no signs of yolk deposition. Results Morphologically, MO of Paratelphusa sp. is positioned posterior to the mandibles and is in close apposition with the distal end of the mandibular apodeme. MO of Paratelphusa sp. exhibited significant levels (t = 8.097, P < 0.0001, N = 10) of season-dependent size variations. Our electron microscopic observations reveal that the MO is highly secretory during the reproductive period, evidenced by the occurrence of sacculated Golgi bodies having dense inclusions, several mitochondria with tubular cristae, and extensive networks of SER and rough endoplasmic reticulum (RER). During the non-reproductive period, however, the MO is least active; RER, the mitochondria, and the Golgi are only sparsely seen. Interestingly, the plasma membrane exhibits a highly convoluted appearance all the way through the non-reproductive period. Conclusions The present study reveals that the secretory activity of MO of Paratelphusa sp. is entrained with reproductive activity. The existence of a high correlation between MO secretory activity and ovarian growth implicates the former’s role in reproduction.
Highlights
Mandibular organ (MO) in decapods is suggested to play regulatory role in reproduction, in few species; MO is considered to control growth
In the 1990s, studies on MO were conducted in the context of changes in the nature of its secretion, a terpenoid compound, farnesoic acid (FA), a pro-hormone that gets methylated by farnesoic acid O-methyl transferase to the active form of the hormone methyl farnesoate (MF) (Gunawardene et al 2002)
Until February and early March, the entire population appeared to be engaged in molting; occurrence of various postmolt and intermolt organisms appear by the end of March
Summary
Mandibular organ (MO) in decapods is suggested to play regulatory role in reproduction, in few species; MO is considered to control growth. The mandibular organ (MO) in crustaceans is a pair of ductless, ectodermally derived gland, first described by Le Roux (1968) in the cephalothorax of the crab Carcinus maenas. Initial studies by several authors suggested the MO to be involved in regulating reproduction (Le Roux 1968, Hinsch 1981), and/or molting (Aoto et al 1974, Byard et al 1975, Yudin et al 1980). While some of the authors are of the view that MF could be stimulating molt (Yudin et al 1980, Tamone and Chang 1993), there have been suggestions that MF could play a crucial role in delaying the onset of molting in larval crustaceans (Borst et al 1987)
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