Variability of tetrodotoxin and of its analogues in the red-spotted newt, Notophthalmus viridescens (Amphibia: Urodela: Salamandridae)

► We present the first thorough analysis of the toxin content of newt populations. ► The phylogenetic relationship of the populations was analyzed for the first time. ► We demonstrate lack of genetic evidence for the endogenous toxin production. ► We present evidence for ecological factors causing the presence of toxins in newts.