Assessment of Environmental DNA to Determine Presence of Spot-Tailed Earless Lizards in a Controlled, Captive Environment

Spot-tailed Earless Lizards (STEL; Holbrookia lacerata, Plateau, and H. subcaudalis, Tamaulipan) are cryptic, elusive lizards, of which Tamaulipan STEL have been identified as candidates for potential federal threatened status listing. Environmental DNA (eDNA) has been proposed as a method with the potential to quickly assess areas for presence of STEL because eDNA is a non-destructive method that does not require animal capture. Therefore, we assessed the potential of using eDNA as a viable survey technique to assess the presence of STEL. Although development of eDNA could not distinguish Holbrookia at the species level, the designed assay detected the target genus from soil samples in 67% of cases when STEL were known to be present. We found that STEL needed to be in contact with soil substrate for at least 24 h to reliably detect their eDNA. Exposure of soil samples to ultraviolet light and/or high humidity increased the likelihood of obtaining a poor-quality sample that failed endogenous sample integrity checks. Consequently, there was a 77–80% chance of obtaining a false-negative result for STEL eDNA. In addition, locating specific sites where STEL had rested in soil for adequate time was akin to “finding a needle in a haystack.” Lures or pheromones to entice STEL to specific locations away from direct ultaviolet light for eDNA sampling may improve eDNA detection, but such lures have not been identified. Additional research aimed at improving methodology and better understanding of biological and environmental variables in detecting eDNA of terrestrial reptiles is needed. Until then, eDNA is not recommended as a survey technique to assess the presence of STEL.