Seasonal and sexual variations in plasma concentrations of testosterone, 17β-estradiol, and progesterone in the endangered Beale’s Eyed Turtle, Sacalia bealei , in captivity

Seasonally breeding species exhibit annual gonadal hormone fluctuations that synchronize with reproductive activity and ecology. However, the reproductive physiology of the Beale’s Eyed Turtle ( Sacalia bealei ), a critically endangered turtle species endemic to southeastern China, remains profoundly undocumented—a knowledge gap that is imperative for its recovery. Herein, we measured plasma concentrations of testosterone (T), 17β-estradiol (E2), and progesterone (P4) in captive S. bealei over a one-year period using enzyme-linked immunosorbent assay. Both male and female S. bealei display distinct seasonal reproductive cycles. Males showed a bimodal T profile (peaks in August and May), likely associated with spermatogenesis and mating in early autumn and mating in spring, suggesting a dissociated strategy with postnuptial spermatogenesis. A small rise in E2 and P4 levels in August may regulate male spermiogenesis. Females exhibited a single E2 peak in April, associated with Type I vitellogenesis and a single annual clutch, with T peaks in April and August, likely corresponding to ovarian growth and recrudescence, respectively, and P4 peaks in June linked to ovulation. Positive correlations between hormones suggest synergistic regulation. The data from this study provide a reference for future research regarding the reproductive cycle of this turtle and also allow reproductive management while in captivity.