Newt
Newts, as with salamanders in general and other amphibians, serve as bioindicators because of their thin, sensitive skin and evidence of their presence (or absence) can serve as an indicator of the health of the environment. Most species are highly sensitive to subtle changes in the pH level of the streams and lakes where they live. Because their skin is permeable to water, they absorb oxygen and other substances they need through their skin. Scientists study the stability of the amphibian population when studying the water quality of a particular body of water.
Rough-skinned newt
Newts are not immune to their own toxin; they only have a heightened resistance. The toxin in newts consists of a tradeoff. Each time they release the toxin, they inject themselves with a few milligrams. The TTX becomes concentrated in certain parts of the tissue after passing through cell membranes. As a result of tissue exposure to the toxin, newts have evolved a protection mechanism via a single amino acid substitution to the voltage-gated sodium channel normally affected by TTX. Puffer fishes show a similar amino acid sequence that allows them to survive from their own toxin exposure.