Abstract

Understanding turtle reproduction is crucial for gaining insights into its life history, particularly of endangered species as the Atrato River Slider, Trachemys medemi, for which this aspect is unknown. We estimated the timing of mating, spermatogenesis, vitellogenesis, nesting, and the quiescence of T. medemi in relation to serum sexual hormone levels, the local precipitation and temperature, and field observations. We captured 29 wild adult individuals between January 2022 and February 2023, including 25 unique females with 1 recapture (5 were gravid and 20 nongravid) and 4 unique males. We estimated that mating and nesting occur from December to March during the dry season when river beaches are available. During this time, gravid females (n = 5) had higher estradiol and progesterone, nongravid females had generally higher testosterone, and males exhibited basal hormones. The quiescent period was difficult to assess because of lack of hormonal data from April to July, and from September to November, but we infer that in females it occurs during the wet season when hormones were low (August), and in males from February or March when testosterone was basal to some time before August when testosterone increased 5.7×, suggesting the beginning of the spermiogenesis period in males. In conclusion, T. medemi follows an annual reproductive cycle with a prenuptial pattern and a single nesting season.