Contrary to the Australian system, invasion has been accompanied by a reduction rather than increase in rates of cannibalism under standard laboratory conditions. To explore the generality of such changes, we examined cannibalism in Japanese common toads ( Bufo japonicus ) on the islands of Honshu (native range) and Hokkaido (invasive range). In their invasive range in Australia but not in their native range in South America, cane toads ( Rhinella marina ) exhibit high rates of cannibalism of embryos (eggs and hatchlings) by tadpoles. 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.īy imposing novel evolutionary pressures, biological invasions can favour rapid changes in intraspecific competitive mechanisms such as cannibalism. Cardenolide aglycones (e.g., digitoxigenin) were active attractors, whereas C-3 glycosides (e.g., digoxin, oubain) were far less effective. 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. 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). To clarify the molecular basis of this attraction response, we presented captive tadpoles with components present in toad eggs. 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.

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