Reproductive cycle and maturation of Swinhoe’s tree lizard (Diploderma swinhonis (Günther, 1864)) in Hyuga City, Miyazaki Prefecture, Japan

Swinhoe’s tree lizard (Diploderma swinhonis) is an arboreal agamid that is native to Taiwan. The species has been introduced to some areas of Japan and is regarded as an invasive alien species. In 2016, a nonnative population of D. swinhonis was discovered in Hyuga City, Miyazaki Prefecture, Japan, but little information was available on the ecology of the population at the time. The main purpose of this study was therefore to investigate the reproductive cycle and maturation of this population. Field research was conducted from 2017 to 2019, and 764 lizards were collected. Euthanized lizards were dissected and the reproductive organs were examined to determine the reproductive period, clutch size, clutch frequency and size at sexual maturity. Females with oviductal eggs or vitellogenic ovarian follicles were observed from May to October. Clutch size ranged from 2 to 8, and clutch frequency was more than twice a year. In males, spermiogenesis started in early May and testicular regression was observed in September. Males with spermatozoa in the epididymides were found from May to November. Minimum snout-vent length at sexual maturity was 50.2 mm in females and 53.0 mm in males. Comparisons of the findings of this study and reports from Taiwan suggest that the nonnative population of D. swinhonis in Hyuga City has a higher fecundity than populations in Taiwan. It is therefore considered necessary to exterminate the population in Hyuga City before this species colonizes other areas.