Stable isotope analysis suggests that tetrodotoxin-resistant Common Gartersnakes (Thamnophis sirtalis) rarely feed on newts in the wild

Abstract

Toxin-resistant predators may suffer costs from eating chemically-defended prey and do not feed exclusively on toxic prey. Common Gartersnakes (Thamnophis sirtalis) (Linnaeus, 1758) have been considered the drivers of an evolutionary arms race with highly toxic newts (Taricha spp.), which they consume with few or no deleterious effects. However, how frequently newts are consumed in nature is less clear. To address this question, we investigated the diets of T. sirtalis at a site in central Oregon where snakes have high levels of resistance and newts have high levels of tetrodotoxin in the skin. Because snake diets are difficult to quantify using traditional means, we used stable isotopes to estimate the proportion of T. sirtalis diets made up of newts. Our estimate for the proportion of T. sirtalis diet made up of T. granulosa at this site is 3.2%. Ambystoma salamanders were predicted to be the most important prey, followed by slugs, chorus frogs, and mice, with a very minor role for earthworms. Our results demonstrate that even though T. sirtalis are physiologically capable of consuming toxic prey, they do not often do so. Generalist predators can be exposed to very strong selection from, and exert reciprocal selection on even rarely eaten, chemically-defended prey.

Snakes on the plains: The impacts of habitat structure on snake communities in Illinois grasslands

“…For example, garter snake occupancy was negatively related to grass cover, though this estimate was less precise. Unlike black kingsnakes, small mammals comprise only a small proportion of the diet of common garter snakes (Durso et al 2021, and citations therein), so they may not necessarily respond to any increases in vole abundance that might result from greater grass cover.…”

Are Pacific Chorus Frogs (Pseudacris regilla) Resistant to Tetrodotoxin (TTX)? Characterizing Potential TTX Exposure and Resistance in an Ecological Associate of Pacific Newts (Taricha)

“…In cases where environmental selective regimes are not predictable, more plastic responses like upregulation of detoxifying enzymes may be the primary way animals deal with toxin exposure (Zanger and Schwab, 2013). Nevertheless, even occasional exposure to TTX can result in maintenance of target-site insensitivity (Durso et al, 2021).…”

“…Although both of these assumptions may be violated by changes in climate and species distributions over time, evidence from the evolutionary arms race between garter snakes and TTX-bearing newts suggest that TTX potency and the degree of TTX resistance can change over a short period of time (Brodie et al, 2002), which aligns with our study that examines approximately the past 50 years. Occasional exposure to TTX may also be sufficient to select for target-site insensitivity (Durso et al, 2021). We aimed to test whether the sympatry of Taricha newts with Pseudacris regilla has selected for target-site insensitivity in the skeletal muscle voltage-gated sodium channel of P. regilla.…”

Phenotypic outcomes of predator–prey coevolution are predicted by landscape variation in climate and community composition

“…California may increase activity and movement and increase the likelihood a snake encounters a toxic newt. In some places, newts comprise a small proportion of a garter snakes' diet (Durso et al, 2021) so snakes that are more active are likely to opportunistically encounter newts more than snakes that are less active.…”