Defining the current distribution of the imperiled Black-spotted Newt across south Texas, USA

Abstract

The Black-spotted Newt ( Notophthalmus meridionalis ) is a chronically understudied salamander species, with many aspects of its natural history, ecology, and distribution poorly known. Previous studies using traditional methodologies have had limited success documenting N. meridionalis on the landscape, detecting individuals at 6% (7 of 114) and 1% (2 of 221) of sites surveyed. A novel environmental DNA (eDNA) assay was designed and implemented with the goals of assessing the current distribution of N. meridionalis across south Texas, USA, and better understanding the conditions for positive eDNA detections. We conducted eDNA sampling and traditional surveys at 80 sites throughout south Texas. Notophthalmus meridionalis was detected at 12 localities in total: four localities using eDNA surveys, four localities using traditional methods, and four localities with both methodologies. eDNA detections were obtained from five counties, including one where N. meridionalis has never been reported and another where N. meridionalis has not been observed since the 1930s. eDNA detections were obtained in all four seasons, generally following moderate to heavy rainfall events. Our results support the increased use of eDNA surveys to detect rare and cryptic amphibians and to better understand the current distribution of this imperiled species. • Notophthalmus meridionalis is an understudied salamander that is difficult to survey for using traditional methodologies. • An eDNA assay was designed and used with traditional methods to survey for Notophthalmus meridionalis . • Notophthalmus meridionalis was detected at eight localities via eDNA, including three that were previously undocumented. • eDNA detections were obtained year-round, primarily within 8 d following moderate rainfall, but also >14 d after heavy rainfall. • The distribution of Notophthalmus meridionalis is described using historic locality data and results from this study.