Gonadulin and Insulin‐Like Growth Factor Involved in <i>Rhipicephalus microplus</i> Reproduction

ABSTRACT Gonadulin and insulin‐like growth factor (IGF) are neuropeptides synthesized by the central nervous system (CNS) of arthropods. In insects, gonadulin is associated with reproduction and vitellogenesis, while IGF is involved in growth and nutrient utilization. In ticks, transcripts for both peptides have been identified in the CNS; however, knowledge about their physiological functions is still scarce. Thus, the present study aimed to evaluate the potential involvement of gonadulin and IGF in the reproductive performance of the tick Rhipicephalus microplus . Molecular assays and immunohistochemistry using anti‐IGF and anti‐gonadulin IgG were performed to detect both neuropeptides in R. microplus ovary and eggs. To analyze their physiological roles, partially engorged female ticks were exposed to anti‐neuropeptide IgG via artificial capillary feeding, or to gonadulin silencing using dsRNA‐mediated RNA interference. The presence of these neuropeptides was observed in tick ovaries, with a changing distribution pattern throughout the tissue maturation process. Immature oocytes exhibited a polarized distribution of the neuropeptides, while mature oocytes (without germinal vesicle) showed ubiquitous dispersion. Despite the presence of these neuropeptides in ovary tissue, no significant differences in reproductive parameters were detected in the artificial feeding and gene silencing assays, suggesting that additional studies may be required to elucidate their physiological functions. The tissue distribution pattern of IGF and gonadulin in tick oocytes is described here for the first time; the data suggest that both neuropeptides are involved in tick reproduction.