Application of gamma-irradiation to sterilize nonnative Swinhoe's tree lizards in Miyazaki Prefecture, Japan.
Sterilization using radiation has been widely employed to control insect pests. The effectiveness of the method relies on preventing the production of viable offspring after copulation. In this study, we attempted to produce sterile male lizards using this method. Swinhoe's tree lizards (Diploderma swinhonis) are native to Taiwan and are regarded as an invasive alien species in Japan. We irradiated male lizards captured in Miyazaki Prefecture, Japan, with γ-rays and examined whether irradiation induced permanent sterility. The lizards were irradiated with 5, 10, and 15 Gy as air-absorbed doses and were dissected one month after irradiation. Two additional groups were prepared; one group was dissected at three months after a single dose of 10 Gy, and the other group was dissected at four months following two doses of 10 Gy. All lizards were euthanized and their testes were removed to evaluate the histological change of testes. Testicular atrophy and damage to spermatogenic epithelium were observed in all lizards at one month after irradiation. However, the regeneration of spermatogenic epithelium was observed in lizards that were kept for more than three months, and permanent sterility could not be induced. The mortality rate for lizards irradiated with 15 Gy was high, suggesting high-dose irradiation is unsuitable for sterilizing this species. Compared to lizards that were irradiated once, the spermatogenic epithelium of lizards that were irradiated twice did not regenerate, indicating that repeated irradiation is effective for inducing permanent sterility in this species.