Two phase regulation of tick vitellogenesis by blood feeding and mating in the soft tick Ornithodoros moubata (Acari: Argasidae)

Blood feeding arthropods require a blood meal to produce eggs. Synthesis of the yolk protein precursor vitellogenin (Vg) is initiated after blood feeding and under hormonal regulation. Viable egg production requires both engorgement and mating, but the distinct roles of these two stimuli are not understood. The soft tick Ornithodoros moubata provides an excellent model to study the separate roles of feeding and mating because both virgin and mated females engorge but only mated females produce viable eggs. Our previous studies showed ecdysteroid titers significantly increased in only mated females and remained low in virgin females. In addition, both mated and virgin females showed up-regulation of EcR and RXR hormonal receptors immediately after engorgement. In this study, we compared Vg expression in mated and virgin females after engorgement. Both mated and virgin females showed Vg expression during an early phase (3 to 10 days) after engorgement, whereas only mated females showed increased Vg expression during the late phase (12 to 20 days). Whole mount in situ hybridization revealed the main site of Vg expression is the midgut during the early phase while the fat body enlarges and shows strong Vg expression during the late phase in only mated females. Therefore, feeding stimulates Vg expression in both virgin and mated females while mating is required for Vg up-regulation in the late phase. Furthermore, mating appears to induce secretion of ecdysteroids after engorgement and high titers of ecdysteroids up-regulate Vg expression in mated females leading to mature egg production. This two phase regulation of vitellogenesis in O. moubata reveals the importance of investigating the separate roles of nutrition and mating in arthropod reproduction.