Does environmental enrichment really matter? A case study using the eastern fence lizard, Sceloporus undulatus

Institutional and federal ethics committees regulate research on live vertebrate animals. Current regulations require researchers to provide environmental enrichment for laboratory animals. The intention is that such enrichment reduces stress and prevents atypical behavior of captive animals, enhancing the ethical treatment of these individuals, as well as providing more robust scientific results. Enrichment can take various forms but most frequently mimics aspects of the animal's natural environment, such as the inclusion of plant life, shelters, conspecifics, or providing challenges to keep the animals occupied. These approaches have proven effective for mammals and birds; however, we know little about the effectiveness of environmental enrichment for other common research taxa, such as reptiles and amphibians. These taxa are more phylogenetically distant from humans, making intuition an unreliable guide upon which to base decisions about ethics best practice, including the benefits of environmental enrichment. The eastern fence lizard, Sceloporus undulatus, spends much of its time off the ground. Therefore, we provided climbing enrichment to captive fence lizards to allow them the opportunity to carry out this common natural behavior in captivity, and tested its effect on a range of ecologic- and scientifically relevant physiological and behavioral parameters. The provision of environmental enrichment, in the form of raised basking platforms, did not affect survival (P=. 0.25), baseline levels of plasma corticosterone (an indicator of physiological stress; P=. 0.81), activity (P=. 0.19), basking behavior (P=. 0.89), time spent hiding (P=. 0.59), growth (mass: P=. 0.44; snout-vent length: P=. 0.47), or overall body condition of these lizards (P=. 0.61). This lack of an effect highlights the need for researchers to objectively test the effectiveness of enrichment, rather than relying on subjectivity and anthropomorphism when making decisions about their use.