Ecology of the large South American snake, Hydrodynastes gigas (Serpentes: Dipsadidae)

Abstract

We analyzed the ecology of Hydrodynastes gigas, one of the largest snakes of South America, studying 342specimens obtained during 21 years of field sampling including road sampling, intensive searches and opportunisticencounter methods. Females attained sexual maturity at larger relative body size than males, and were largest, hadbiggest heads and more ventral scales. Males had larger tails and more subcaudal scales than females. This sexualdimorphism, common among snakes, would be related to an increment in its reproductive potential. The females’reproductive cycle was seasonal and annual; while in males it was continuous and annual. The reproductive potentialwas high, 16.3 eggs/female/year, with a clear tendency to be higher in larger females. Hydrodynastes gigas is adiurnal snake and preys on all kinds of common vertebrates in wetlands habitats, including amphibians, reptiles,fish, mammals and birds, in order of importance. Individuals were active throughout the year, being one of the 4most abundant species of snakes in the floodplains of large South American rivers. Due to its abundance, generalistdiet, higher size and reproductive potential, we suggest that this species is an important predator in South America’saquatic ecosystems.