Variation in Bufadienolide Composition of Parotoid Gland Secretion From Three Taxa of Japanese Toads
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Variation in Bufadienolide Composition of Parotoid Gland Secretion From Three Taxa of Japanese Toads Takato Inoue 1
&
Ryu Nakata 1,2 & Alan H. Savitzky 3 & Naoko Yoshinaga 1 & Akira Mori 4 & Naoki Mori 1
Received: 28 May 2020 / Revised: 14 August 2020 / Accepted: 6 September 2020 / Published online: 30 September 2020 # Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract Toads of the genus Bufo synthesize and accumulate bufadienolides (BDs) in their parotoid glands. BDs are cardiotonic steroids that play an important role in defense against the toads’ predators. Three bufonid taxa occur in mainland Japan, Bufo japonicus formosus, B. j. japonicus, and B. torrenticola. The chemical structures of BDs isolated from B. j. formosus were studied several decades ago, but there is no further information on the toxic components of Japanese toads and their metabolism. In this study, we analyzed BDs of toads from throughout Japan and compared the BD profiles by liquid chromatography/mass spectrometry (LC/ MS) and hierarchical cluster analysis (HCA). We observed BDs in three taxa of Japanese toads, and identified five of the most common BDs by nuclear magnetic resonance (NMR) analyses. Of the five BDs, only bufalin was detected in all individuals. HCA of individual BD profiles divided the three taxa into five primary clusters and several subclusters. This result indicates that BD profiles differ both among and within the taxa. The clustering pattern of BDs is generally concordant with a phylogenetic tree reconstructed from the mitochondrial cytochrome b gene of Japanese toads. Our results suggest that the BDs of Japanese toads have diversified not in response to specific selective pressures, but simply due to population structuring over evolutionary time. Keywords Biotoxin . Bufadienolide . Bufo . Japanese toads . Parotoid gland . Hierarchical cluster analysis . Predator-prey . Chemical defense
Introduction Many vertebrates sequester toxins for defense, including poison frogs, some natricine snakes, and Pitohui birds. Those species acquire toxins from their prey and accumulate them in the skin, internal organs, feathers and muscles (Dumbacher Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10886-020-01217-y) contains supplementary material, which is available to authorized users. * Naoki Mori [email protected] 1
Division of Applied Life Science, Graduate School of Agriculture, Kyoto University, Kitashirakawa, Sakyo, Kyoto, Kyoto 606-8502, Japan
2
Present address: Department of Bioscience and Biotechnology, Kyoto University of Advanced Science, 1-1 Nanjo Otani, Sogabe, Kameoka, Kyoto 621-8555, Japan
3
Department of Biology, Utah State University, Logan, UT 84322-5305, USA
4
Department of Zoology, Graduate School of Science, Kyoto University, Kitashirakwa, Sakyo, Kyoto, Kyoto 606-8502, Japan
et al. 2004; Mori et al. 2012; Takada et al. 2005). On the other hand, toads (Bufonidae) synthesize and store toxins known as bufadienolides (BDs) in c
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