Hormonal Control of Molting and Reproduction in Ticks

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Abstract
SYNOPSIS. Among ticks there are two developmental and three reproductive patterns that correlate with taxonomic groupings (Argasidae, prostriate and metastriate Ixodidae). Feeding is a prerequisite for molting; feeding and mating are necessary for reproduction in all except a few parthenogenetic species. Growth and development in ticks and other chelicerates appear to be controlled by molting hormones (ecdysteroids), as they are in insects and crustaceans. Ecdysone and 20-hydroxyecdysone appear to be present in most or all of the major chelicerate taxa. Epidermis is the site of ecdysone production and fat body the site of 20-hydroxylation in the argasid Ornithodoros parkeri, as is probably the case in all ticks. Ecdysteroids influence early stages of spermatogenesis by stimulation of DNA synthesis in spermatocytes, but controls for later stages of meiosis are unknown. A polypeptide (12,000 daltons) from male genital accessory glands stimulates capacitation (maturation) of spermatids into sperm at the time of spermatid transfer to females. Knowledge of control of egg development and oviposition is incomplete. Stimuli from the synganglion are necessary for completion of oogenesis and two synganglial factors have been proposed. An Egg Development Stimulation Factor (EDSF) in O. parkeri is synthesized and/or released three to six days after feeding. Vitellogenesis Inducing Factor (VIF) in O. moubata is synthesized and/ or released within one hour after feeding. The VIF is hypothesized to impact an unidentified tissue which in turn produces a Fat Body Stimulation Factor (FSF) that stimulates fat body to synthesize vitellogenin (Vg). Roles of ecdysteroids and juvenile hormones during egg development and oviposition are unclear.

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