In many places in the animal kingdom, we see extreme traits – the antlers of elk or the tails of a peacock, for example. Traits such as these can often be attributed to sexual selection, an evolutionary process that is due to competition for and attraction of mates. Yet, not all extreme traits in animals are due to forces within a species – inter-species interactions can be important too! This is the case for the California newt (Taricha torosa) – an endemic (meaning it lives nowhere else in the world) California amphibian species that boasts an incredibly strong toxin that is excreted from its skin. These newts live in two bands in California – one coastal and one in the Sierra Nevadas [1]. While once considered one species, they have now been broken up into two species.

One of the most striking things about the California newt is the fact that it is poisonous (poison is absorbed, venom is injected) – something it shares with several other members of its genus Taricha. Just 1/2500 of a teaspoon of the skin containing the poison of the closely related rough-skinned newt is enough to kill a mouse in 10 minutes [2]. This level of poison is certainly more than sufficient to kill any would-be predators of the newt. So, why produce such potent toxin? To answer that question, we have to look at one of the predators of the newt: the common garter snake (Thamnophis sirtalis). These snakes have evolved the ability to resist the poison of the newt [3]. What likely started as a change in one snake’s DNA lead this snake to be able exploit an ample food resource, and as a result, they survived and produced more offspring. Overtime, all snakes had the ability to resist the poison. And the newts? Well, the newts that survived the best were those that already had highly potent poison. Overtime, the newts get more and more poisonous, and the snakes counter with more and more resistance. This is a classic example of an evolutionary arms race. Such arms races can create extreme traits – such as extreme poison and resistances.

If California newts are so poisonous, they must be doing great in the wild, right? Unfortunately, wrong. Crayfish are known to harass adults during mating season in the shallow streams/ponds where they live. This can decrease the amount of mating and thus the number of offspring that can be produced [4]. Invasive species, like many areas of the world, are also a problem for the California newt. Invasive mosquitofish (Gambusia affinis) prey on newt larvae and egg masses [5], also decreasing the reproductive output of any adult. These problems have made the California newt a California Special Concern species.

So the next time you are hiking in the Sierras or visiting marshy areas near the California coast, keep an eye out for California newts. Remember though to never touch these amphibians for fear of a reaction to the incredible poison on their skin.

[By Meredith Lutz]

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[1] Tan, A., & Wake, D. (1995). MtDNA Phylogeography of the California Newt, Taricha torosa, (Caudata, Salamandridae). Molecular, Phylogenetics, and Evolution, 4, 383-394.

[2] Brodie, E. (1968). Investigations on the skin toxin of the adult rough-skinned newt Taricha granulosa. Copeia, 2, 307-313.

[3] Williams, B., Brodie, E., & Brodie, E. (2004). A resistant predator and its toxic prey: Persistence of newt toxin leads to poisonous (not venomous) snakes. Journal of Chemical Ecology, 30, 1901-1919.

[4] Gamradt, S., Kats, L., & Anzalone, C. (1997). Aggression by non-native crayfish deters breeding in California newts. Conservation Biology, 11, 793-796.

[5] Gamradt, S., & Kats, L. (1996). Effect of introduced crayfish and mosquitofish on California newts. Conservation Biology, 10, 1155-1162.

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