Reproductive biology of the fossorial snake apostolepis gaboi (Elapomorphini): a threatened and poorly known species from the caatinga region

Abstract

Knowledge of reproductive biology is essential to understand the intrinsic traits of any species and to elaborate effective conservation strategies, particularly for threatened species. Despite recent advances, knowledge on the reproductive biology of snakes remains deficient for most species, especially for tropical fossorial taxa. Apostolepis gaboi is a psammophilous, fossorial, and threatened snake endemic of the Quaternary Sand Dunes of the São Francisco River, Caatinga domain. Here, we present information on its reproductive biology based on macroscopic and microscopic data obtained from the examination of all specimens preserved in Brazilian museums. Specifically, we addressed sexual maturity, sexual dimorphism, clutch size, timing of gametogenesis, activity of the sexual segment of the kidney (SSK), and female sperm storage. Apostolepis gaboi is one of the smallest species of the genus. Females attain sexual maturity at larger body sizes and grow larger than males. However, adult females have relatively shorter tails than males. We found no sexual dimorphism in body circumference and head size. Clutch size is small and averages 4.5 eggs. All males from the wet season showed testes in spermiogenesis, ductus deferentia packed of sperm, and SSK hypertrophied and secretory. Secondary vitellogenesis also occurs in the wet season. Moreover, females in early vitellogenesis from the wet season showed sperm stored in the posterior infundibulum. Mating occurs in the second half of the wet season, as suggested by the finding of aggregations of sperm in the uterine lumen of a female in early secondary vitellogenesis. Mating is associated with gonadal activity in males. Sperm storage confers flexibility for females to ovulate at the most suitable time in an unpredictable habitat such as the Caatinga. Apostolepis gaboi exhibits similarities (association between mating and spermiogenesis, small clutch) and differences (absence of sexual dimorphism in head size and stoutness) compared with another Elapomorphini species. Lastly, we argue that some of the intrinsic traits of A. gaboi (small clutch and small body size) may increase its vulnerability to extinction, raising additional concerns to its conservation.