Changes in Toxin Quantities Following Experimental Manipulation of Toxin Reserves in Bufo bufo Tadpoles

Abstract

Possessing toxins can contribute to an efficient defence against various threats in nature. However, we generally know little about the energy- and time-demands of developing toxicity in animals, which determines the efficiency of chemical defence and its trade-off with other risk-induced phenotypic responses. In this study we examined how immersion into norepinephrine solution inducing the release of stored toxins, administration of mild stress mimicking predator attack or simple handling during experimental procedure affected the quantity and number of toxin compounds present in common toad ( Bufo bufo ) tadpoles as compared to undisturbed control individuals, and investigated how fast toxin reserves were restored. We found that total bufadienolide quantity (TBQ) significantly decreased only in the norepinephrine treatment group immediately after treatment compared to the control, but this difference disappeared after 12 h; there were no consistent differences in TBQ between treatments at later samplings. Interestingly, in the norepinephrine treatment approximately half of the compounds characterized by >700 m/z values showed the same changes in time as TBQ, but several bufadienolides characterized by <600 m/z values showed the opposite pattern: they were present in higher quantities immediately after treatment. The number of bufadienolide compounds was not affected by any treatments, but was positively related to TBQ. Our study represents the first experimental evidence that toxin quantities returned to the original level following induced toxin release within a very short period of time in common toad tadpoles and provide additional insights into the physiological background of chemical defence in this model vertebrate species. Electronic supplementary material The online version of this article (10.1007/s10886-019-01045-9) contains supplementary material, which is available to authorized users.

The impact of multiple climatic and geographic factors on the chemical defences of Asian toads (Bufo gargarizans Cantor)

“…The composition and proportions of defensive chemicals can markedly affect deterrent effects 20 . This study investigated the geospatial distribution characteristics of the GB/CBG, TBG/CBG, BFL/CBG, CFL/CBG, BL/CBG and RBG/CBG ratios, as shown in Fig.…”

“…These toxins are important defences against predators and microorganisms 17–19 . Many reports have confirmed that the main component of these toxin cocktails is bufadienolide, cardiotoxic steroids that inhibit Na + /K + -ATPases 20,21 . Bufadienolide compounds are usually classified into two types: free-type bufogenins and conjugated-type bufotoxins 22 .…”

“…These compounds are considered major contributors to the role of toxins in defence 27 . Despite similar chemical structures, the different bufagenins may exhibit functional differences in the potency and selectivity of their toxicity to different types of predators 20,28 . For example, many arthropod Na + /K + -ATPases lack the binding site for certain bufagenins, whereas certain vertebrate Na + /K + -ATPases have high affinity for the same bufagenins 29,30 .…”

“…For example, many arthropod Na + /K + -ATPases lack the binding site for certain bufagenins, whereas certain vertebrate Na + /K + -ATPases have high affinity for the same bufagenins 29,30 . Therefore, the concentrations and composition of such highly toxic components in the toxin blend are more relevant to the deterrent efficiency of the chemical defence than the amount of toxin 20 .

Figure 1Chemical structures of seven bufogenins.

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Predator‐induced changes in the chemical defence of a vertebrate

“…This approach yields only a rough estimate of TBQ, but due to the unavailability of standards for the majority of bufadienolides, there is currently no better alternative for toxin quantification. This method has been successfully applied in similar studies (Benard & Fordyce, ; Bókony et al, , , , ; Hagman et al, ; Tóth, Kurali, Móricz, & Hettyey, ; Üveges et al, ). We calculated mass‐corrected total bufadienolide quantities (mcTBQ) by dividing TBQ values by tadpole dry mass.…”