Quantitation of female newt tetrodotoxin concentrations and their impact in the newt-garter snake evolutionary arms race

Waves Cafeteria

Taricha newts possess tetrodotoxin (TTX), a potent neurotoxin, which is sequestered in poison glands on the surface of their skin and can be quantified via HPLC-FD. It is known TTX functions as a form of defense, greatly limiting the amount of possible predators for Taricha. The main predator of Taricha is the common garter snake, Thamnophis sirtalis, and it has long been thought there is a coevolutionary arms race between snake resistance and newt toxicity. Previous results from other labs studying phenotypic mismatches between these two species led to the conclusion that snakes have won this arms race and newts cannot become toxic enough to overcome snake resistance. In our study of phenotypic mismatches between Thamnophis and Taricha at nine locations across California and Oregon that correlate to geographic locations in previous studies, five sites had newts with higher toxicity than snake resistance, one had matched resistance and toxicity at extreme levels, and three sites had snakes at higher resistance than newt toxicity. Whereas previously at these same nine sites, four sites had higher snake resistance, four sites had tied snake resistance and newt toxicity, and one site had newts with higher toxicity than snake resistance. After our previous study establishing sexual dimorphism in TTX concentrations between males and all females, we believe a lack of studies including female newt data skewed phenotypic mismatches towards higher snake resistance, because female newts on average contain higher concentrations of TTX. Prior studies almost exclusively focused on male newts, ignoring the chemical ecological contribution of female newts. Utilizing sampling and ion-pair HPLC methods developed in our laboratory we suggest newt populations are capable of overcoming high snake resistance but this phenomena can only be seen when both male and female TTX concentrations are studied.