Nerodia sipedon

Northern water snake, Nerodia sipedon

Snakes, though often maligned by humans, play important roles in many temperate and tropical ecosystems.  They are high trophic level predators and, as ectotherms, frequently occur at densities far greater than comparable mammalian and avian carnivores.  However, as top predators, they are also particularly susceptible to the negative effects of bioaccumulative contaminants, such as mercury (Hg).  Although effects of mercury on wildlife have received considerable attention, few studies have focused on reptiles. Moreover, recent research has demonstrated that female organisms inhabiting contaminated habitats can maternally transfer Hg, resulting in negative effects on their offspring. However, no studies have evaluated the effects of maternally-transferred Hg on offspring fitness in snakes. North American watersnakes (Nerodia) provide an ideal model for investigating effects of maternal Hg transfer in snakes. Streams and rivers are among habitats most frequently degraded by Hg contamination and watersnakes are often abundant predators within these habitats. Our current research aims to examine mercury accumulation and maternal transfer in watersnakes inhabiting contaminated aquatic habitats and the effects of Hg on female reproductive characteristics and offspring fitness.

Research Approach

  1. We will collect pregnant female northern watersnakes (Nerodia sipedon) representing a broad range of Hg exposure along an Hg contamination gradient present at a historically contaminated site.
  2. We will return females to the laboratory where they will be held until they give birth in the late summer.
  3. We will quantify tissue Hg concentrations in females using non-destructive sampling techniques and evaluate maternal transfer by comparing these values to Hg concentrations in neonates.
  4. We will examine litter characteristics (litter size, neonate body size, and frequency of malformations) in relation to maternal Hg concentrations and use several measures of performance to assess sublethal effects of maternally-transferred Hg on neonates. Specifically, we will quantify neonate swimming and crawling speed and endurance, and measure foraging performance using laboratory feeding trails.

Expected Results

Because they are high-level predators and forage extensively on contaminated aquatic prey, we expect that female watersnakes will accumulate high levels of Hg and transfer Hg to their offspring in a tissue residue-dependent manner. Additionally, due to the known negative effects of Hg on development and neurological function, we expect that exposure to Hg through maternal transfer will have negative sublethal effects in neonatal watersnakes. Of the performance endpoints we will examine, we predict that foraging performance will be most severely impaired, because foraging is a highly integrated activity, requiring high levels of neuromuscular and sensory coordination.