Reproductive Pattern of the Large-Eyed Pit Viper Trimeresurus macrops (Serpentes: Viperidae: Crotalinae) from Bangkok, Thailand

The large-eyed pit viper (Trimeresurus macrops) is a venomous snake found in Bangkok and surrounding areas that frequently bites humans. Very little is known about its reproduction. We monitored the reproductive pattern of T. macrops based on both alterations in annual macroscopic and microscopic morphologies of reproductive organs in relation to annual male testosterone and female estradiol profiles. We collected 45 males and 65 females during a year in Bangkok, central Thailand. Mating was recorded from October to January and vitellogenesis occurs between November and January. Pregnancy was observed between February and April, with parturition during May to July. Additionally, females were able to store sperm throughout the year in both sperm receptacles of the posterior infundibulum and crypts of the non-glandular uterus by means of a uterine muscular twisting. Spermiation within the testis was observed between June to November, coinciding with hypertrophy of sexual segment of the kidney (SSK). Female estradiol showed bimodal peaks: one in September, coincident with copulation, and the second in December associated with vitellogenesis. Male testosterone surged in August, coincident with spermiation and hypertrophy of SSK. Findings concluded that the reproduction of individual T. macrops in Bangkok, Thailand, is a discontinuous cyclical process as evidenced by the ovarian quiescence in adult females and the absence of vitellogenic follicles in pregnant females and fully regressed testes in adult males, while its population displays a seasonally semi-synchronous cycle, with most female individuals showing the peak of vitellogenesis in a season of the year, while the peak of spermiation occurring in two seasons of the year in most male individuals.