Spatial and Temporal Instability of Local Biotic Community Mediate a Form of Aposematic Defense in Newts, Consisting of Carotenoid-Based Coloration and Tetrodotoxin
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Most animals advertise their unprofitability to potential predators via conspicuous signals. Whether the strength of this aposematic signal indicates the quality and quantity of chemical defenses in animals is controversial. Here, we investigated the relationship between the conspicuousness of an aposematic signal and toxicity, which likely depends, at least in part, on dietary sources, in the newt Cynops pyrrhogaster. Our results indicate that the magnitude of the aposematic signal was not correlated with the amount of tetrodotoxin (TTX) and 6-epi TTX of wild individuals among populations. Using atoxic newts, reared from eggs, we compared the ability to accumulate TTX from diets between mainland and island populations. Newts of a mainland population that exhibited a less conspicuous signal accumulated more TTX than did equivalent newts of an insular population that displayed a more conspicuous signal; this was unrelated to variation in the toxicity of wild individuals of these two populations. We also found toxicity of wild newts changed over approximately one generation (10 years) in both populations. These results indirectly suggest that environmental variance, such as fluctuations in TTX resources in nature, may obscure differences in the ability of wild newts to accumulate TTX, and that this variation may be responsible for a lack of correlation between the strength of a newt’s signal and its toxicity in the wild. These results imply that toxicity of wild individuals likely is a phenotypic trait largely dependent on environmental conditions.
KeywordsTTX Carotenoids Aposematism Honest signal Cynops pyrrhogaster
We thank K. Arakawa, K. Matsui, and A. Mori for early discussion, K. Matsuo for collecting animals, T. Kurita for illustrating figures, and two anonymous reviewers for their constructive comments that improved the manuscript. This work was financially supported in part by a JSPS Research Fellowship for Young Scientists and a Grant-in-Aid for Research Activity Start-up (228700159) to KM.
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