Spatial and Temporal Instability of Local Biotic Community Mediate a Form of Aposematic Defense in Newts, Consisting of Carotenoid-Based Coloration and Tetrodotoxin
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.
- Cortesi F, Cheney KL (2010) Conspicuousness is correlated with toxicity in marine opisthobranchs. J Evol Ecol 23:1509–1518Google Scholar
- Digiovanni M, Brodie ED Jr (1981) Effects of skin glands in protecting the salamanders Ambystoma opacum from repeated attacks by the shrew Blarina brevicauda. Herpetologica 37:234–237Google Scholar
- Matsui K, Takaichi S, Nakamura M (2003) Morphological and biochemical changes in carotenoid granules in the ventral skin during growth of the Japanese newt, Cynops pyrrhogaster. Zool Sci 20:436–440Google Scholar
- Matsuo K (1989) Amphibians and reptiles of Nagasaki prefecture. Biology of Nagasaki prefecture, Biological Society of Nagasaki Prefecture, Nagsaki, pp 103–110Google Scholar
- Tsuruda K (2001) Studies on the toxicity of a Japanese newts Cynops pyrrhogaster. Japan (in Japaneses)Google Scholar
- Tsuruda K, Arakawa O, Noguchi T (2001) Toxicity and toxin profiles of the newt, Cynops pyrrhogaster from Western Japan. J Nat Toxin 10:79–89Google Scholar