Of poisons and parasites: the defensive role of tetrodotoxin against infections in newts

1. Classical research on animal toxicity has focused on the role of toxins in protection against predators, but recent studies suggest these same compounds can offer a powerful defense against parasites and infectious diseases. 2. Newts in the genus Taricha are brightly colored and contain the potent neurotoxin, tetrodotoxin (TTX), which is hypothesized to have evolved as a defense against vertebrate predators such as garter snakes. However, newt populations often vary dramatically in toxicity, which is only partially explained by predation pressure. 3. The primary aim of this study was to evaluate the relationships between individual-level TTX concentration and infection by parasites. By systematically assessing micro- and macroparasite infections among 345 adult newts (sympatric populations of Taricha granulosa and T. torosa), we detected 18 unique taxa of helminths, fungi, viruses, and protozoans. 4. For both newt species, per-host concentrations of TTX, which varied from undetectabl...