Is there more than one way to skin a newt? Convergent toxin resistance in snakes is not due to a common genetic mechanism.

This corrects the article DOI: 10.1038/hdy.2015.73.

Is there more than one way to skin a newt? Convergent toxin resistance in snakes is not due to a common genetic mechanism.

Convergent evolution of tetrodotoxin (TTX) resistance, at both the phenotypic and genetic levels, characterizes coevolutionary arms races between amphibians and their snake predators around the world, and reveals remarkable predictability in the process of adaptation. Here we examine the repeatability of the evolution of TTX resistance in an undescribed predator-prey relationship between TTX-bearing Eastern Newts (Notophthalmus viridescens) and Eastern Hog-nosed Snakes (Heterodon platirhinos). We found that that local newts contain levels of TTX dangerous enough to dissuade most predators, and that Eastern Hog-nosed Snakes within newt range are highly resistant to TTX. In fact, these populations of Eastern Hog-nosed Snakes are so resistant to TTX that the potential for current reciprocal selection might be limited. Unlike all other cases of TTX resistance in vertebrates, H. platirhinos lacks the adaptive amino acid substitutions in the skeletal muscle sodium channel that reduce TTX binding, suggesting that physiological resistance in Eastern Hog-nosed Snakes is conferred by an alternate genetic mechanism. Thus, phenotypic convergence in this case is not due to parallel molecular evolution, indicating that there may be more than one way for this adaptation to arise, even among closely related species.

Thresholds and escalation of antipredator responses in the Chinese salamander Cynops cyanurus: inter- and intra-individual variation.

Aspects of the control of antipredator behavior, including short- and long-term response modifications, were examined for the Chinese salamander Cynops cyanurus. Salamanders were tested for their antipredator behavior following repeated contact with the flicking tongue of a predatory snake. In a given trial, a salamander was contacted ten times by the snake and within-trial escalation or reduction in response was monitored. For each salamander, trials were repeated 6 times at 21-day intervals to test for long-term changes in response threshold and extent of escalation, and to identify consistent differences in behavior among individuals. The salamanders were found to escalate their antipredator responses over the ten stimuli within trials. They were significantly more responsive to tongue contacts late in a given trial than to the initial stimuli. They also showed long-term, among-trial decreases in the threshold to initial response and increases in the mean responses to the first tongue contacts. However, there was no significant long-term change in maximum response threshold or in the mean responses to the final tongue contacts. Variation among individuals in thresholds and responses was considerable and was consistent over trials.