Androgenic gland implantation promotes growth and inhibits vitellogenesis in Cherax quadricarinatus females held in individual compartments

Androgenic glands (AGs) were implanted into young female red claw crayfish, Cherax quadricarinatus, with the aim of investigating the role played by the AG in the balance between growth and reproduction under conditions of minimal social interaction (individual compartments). The growth rate of the females with AG implants was significantly higher than that of the control non-implanted females (0.11 ± 0.03 g/day vs. 0.08 ± 0.02 g/day). This difference was attributed to the larger molt increments and slightly shorter molt intervals of the females with implants vs. the control females. At the end of the experiment (538 days), the mean weight of the implanted females was significantly higher than that of the control females (64.58 ± 18.24 g vs. 51.07 ± 12.71 g, respectively), a lead of 26.4% for the implanted females that started 91 days after implantation and became significant at 153 days after implantation. By that time, 55.5% of the implanted females had developed typical male secondary characters, such as the red patch on the propodus. The shift of energy from female reproduction to growth was further demonstrated by the level of expression of the vitellogenin gene in the hepatopancreas: gene expression was high in control females but lower by several orders of magnitude in the AG-implanted females, as shown by real time RT-PCR relative quantification. Confirmation of these findings was provided by an ELISA test, which showed that the level of vitellogenic cross-reactive protein in the hemolymph of AG-implanted females was significantly lower than that in intact females. The significant growth promotion in AG-implanted females was clearly not due to social interaction. It may be attributed to a direct growth factor—like the effect of androgens in vertebrates—in combination with an indirect effect, through the shift of energetic investment from reproduction and vitellogenesis to growth. Since the AG implant had a more marked effect on molt increment than on molt interval, it seems likely that the AG acts as a growth promoter rather than as a molt enhancer