Question

Describe and define the glands and hormones involved in crustacean molt. Include in your answer the phases or stages in the molt process

Answer 1

The process of shedding parts of body at specific time of life cycle of an organism which is regulated by hormones is called molting. The crustaceans molting process is under the endocrine regulation that consist of nuerosecretory system peptidergic neurons clustered in the medulla terminalis X-organ. It releases a number of peptide hormones directly into the haemolymph. The different hormones that regulate the molting process comprised of molt-inhibiting hormone from X-organ or sinus gland, Ecdysteroids from a pair of Y organs (YOs), Crustacean hyperglycemic hormone (CHH), Mandibular organ inhibiting hormone (MOIH), Methyl farnesoate (MF), Gonadal inhibiting hormone (GIH) or vitellogenin inhibiting hormone (VIH).

Role of Ecdysteroids- It is secreted by a pair of Y organs (YOs) located in the cephalothorax. The different ecdysteroids associated are ecdysone, 20-hydroxyecdysone (20-OH-E), PonasteroneA (PoA), etc and this are varies through different molt stages. At the premolt stage the level of ecdysone is high as compared to other ecdysteroids; at the late premolt stage, the haemolymph show lower level of ponasteroneA. During post molt and intermolt stages the levels of 20-OH-E and PoA increases, and PoA is an active molting hormone present in the three stages in addition to ecdysone. These hormones serves as the link between neurological signaling and steroidal control of molting and embryo development.

Role of molt inhibiting hormone (MIH)- It is a type II peptide hormone secreted by the neurosecretory cells located in medulla terminalis X-organ, specific XO sinus gland present in eyestalk. This actually supppress or inhibit ecdysteroid synthesis by YO. MIH increases the levels of cAMP and cGMP which then activates protein kinase in YOs and inhibits ecdysteroids synthesis by binding to the receptors of guanylyl cyclase. The level of MIH is low in premolt and rises gradually in post and intermolt stages.

Role of crustacean hyperglycemic hormone (CHH)- It belongs to the class of inhibitory neuropeptide hormone which increases the glucose levels in haemolymph. It inhibit molting in response to environmental stress and has multifunctional aspects like elevating glucose, lipid metabolism tregulation, inhibition of methyl farnesoate synthesis, vitellogenin and ovarian maturation, etc.

Role of methyl farnesoate (MF)-It is structurally similar to juvenile hormone of insects. It is the secretory product from the mandibular organ and it is under the negative control of MOIH peptide hormone. MF has a significant role in metamorphosis, gonads development and maturation and molting. It generally checks the appearance of adult charachters. Its level rises in premolt stage and declines in postmolt stage.

Role of Vitellogenesis or Gonad inhibiting hormone (GIH)- It has a inhibitory role in vitellogenesis i.e the formation of mature ova in females during gonadial maturation. Its presence is also observed in males which provides additional role in regulating molting process.