Abstract
Chemical cues produced by late-stage embryos of the cane toad (Rhinella marina) attract older conspecific larvae, which are highly cannibalistic and can consume an entire clutch. To clarify the molecular basis of this attraction response, we presented captive tadpoles with components present in toad eggs. As previously reported, attractivity arises from the distinctive toxins (bufadienolides) produced by cane toads, with some toxins (e.g., bufagenins) much stronger attractants than others (e.g., bufotoxins). Extracts of frozen toad parotoid glands (rich in bufagenins) were more attractive than were fresh MeOH extracts of the parotoid secretion (rich in bufotoxins), and purified marinobufagin was more effective than marinobufotoxin. Cardenolide aglycones (e.g., digitoxigenin) were active attractors, whereas C-3 glycosides (e.g., digoxin, oubain) were far less effective. A structure–activity relationship study revealed that tadpole attractant potency strongly correlated with Na+/K+ ATPase inhibitory activity, suggesting that tadpoles monitor and rapidly react to perturbations to Na+/K+ ATPase activity.
Highlights
Chemical cues produced by late-stage embryos of the cane toad (Rhinella marina) attract older conspecific larvae, which are highly cannibalistic and can consume an entire clutch
We have shown that the chemical basis for attraction of toad larvae to developing eggs involves the distinctive toxins produced by this s pecies6
The extract of fresh parotoid secretion showed a very different chemical profile to those obtained from eggs, tadpoles and frozen parotoid glands, with marinobufotoxin [6] as the major component and a mixture of bufotoxins 7–10 and marinobufagin [1] as minor components (Fig. 1e)
Summary
Chemical cues produced by late-stage embryos of the cane toad (Rhinella marina) attract older conspecific larvae, which are highly cannibalistic and can consume an entire clutch. The present study extends our work on this system to further clarify the chemical basis of the attractant cue and the mechanisms by which it operates To achieve this aim we conducted laboratory trials in which we exposed captive larvae to a range of concentrations of several chemicals that were judged likely to elicit the attractant response. We exposed the larvae to extracts obtained from different life stages of cane toads (eggs, early-development and late-development tadpoles), from frozen parotoid glands and from fresh parotoid secretion, to compare attractant responses to the types of compounds present in each extract
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