Reptile toxicology: Challenges and opportunities on the last frontier in vertebrate ecotoxicology

In the wake of a changing global environment, reptile populations, like those of other vertebrates, appear to be declining [1]. The Partners in Amphibian and Reptile Conservation recently identified six major threats to reptile populations, most of which were anthropogenic in nature [1]. Environmental pollutants were among the threats identified, but little empirical evidence currently exists to document the frequency and severity of their contamination. Although reptiles surely face a multitude of challenges when exposed to chemicals in the environment, they have remained poorly studied in ecotoxicology. Therefore, the purpose of this letter is to identify reptiles as grossly underexamined vertebrate taxa that deserve immediate attention from ecotoxicologists. In addition, this letter will discuss the biological traits that make reptiles excellent study organisms for certain ecotoxicological investigations and future research priorities and challenges in reptile toxicology. Reptiles are the least studied group of vertebrates (mammals, birds, fish, amphibians, and reptiles) with regard to environmental contaminants. Over the last 10 years of Environmental Toxicology and Chemistry (ET&C), 933 studies published (36% of total papers in ET&C) addressed contaminant effects on vertebrate species. However, only 12 studies on reptiles (0.4% of total papers, 1.3% of vertebrate studies) were published in ET&C during the same time period (Table 1). If reviews of wildlife toxicology (three published in 1998) that mention reptiles are excluded, the number of reptile studies expressed as a percentage of vertebrate studies decreases to less than 1%. Previous comprehensive reviews of reptile toxicology corroborate the problem identified in the limited literature survey presented here [2–4] and also reveal that previous reptile toxicological research has primarily focused on American alligators (Alligator mississippiensis) and snapping turtles (Chelydra serpentina). Moreover, ecotoxicological studies on reptiles often document tissue concentrations of contaminants but seldom provide adequate insight into the biological significance of the tissue burdens observed [5]. Even though amphibians and reptiles are sometimes considered collectively in broad toxicological discussions, amphibian ecotoxicological studies outnumber reptile studies by a factor of 5 (Table 1). The increasing number of amphibian studies published during the latter portion of the decade undoubtedly, and justifiably, arises from recent concern over their susceptibility to contaminants and the status of global amphibian populations. Fortunately, the past 2 years have brought increased awareness, often from amphibian toxicologists, that reptile toxicology desperately needs attention. However, because of the paucity of data on reptile toxicology and the recent focus on amphibians, reptiles remain underrepresented in forums that consider the two vertebrate classes collectively. For example, only two papers (20%) presented at the 1998 SETAC symposium on amphibian and reptile toxicology included original research on reptiles. Clearly, it is critical to identify reptiles as vertebrates that deserve attention by ecotoxicologists without riding the coattails of amphibian issues [1]. Understanding the unique features of reptiles is key to overcoming the tendency to group amphibians and reptiles and critical for shaping appropriate research protocols in the future. Amphibians and reptiles each exhibit distinct biological traits and therefore have very different requirements for study within an ecotoxicological framework. The complex life cycles and permeable integument of amphibians have provided much of the impetus for recent amphibian ecotoxicological investigations. Reptiles do not share these traits, but exhibit a suite of other life-history and biological characteristics that make them vulnerable to contaminants.