No signs of Na+/K+-ATPase adaptations to an invasive exotic toxic prey in native squamate predators
Invasions by exotic toxic prey, like the release of the South American cane toad (Bufo (Rhinella) marinus) to the toad-free Australian continent in 1935, have been shown to result in massive declines in native predator numbers. Due to minor nucleotide mutations of the Na + /K + -ATPase gene most Australian squamate predators are highly susceptible to cane toad toxin. However, in spite of this, predators like yellow-spotted goannas (Varanus panoptes) and red-bellied black snakes (Pseudechis porhyriacus) still persist in parts of Queensland where they, in some areas, have co-existed with cane toads for more than 70 years. Here, we show that the amino acids of the Na + /K + -ATPase enzyme in the two species do not provide toad toxin resistance, and hence the two Queensland predators are still highly susceptible to cane toad toxin. Both yellow-spotted goannas and lace monitors (Varanus varius) have, however, been recorded avoiding feeding on cane toads in areas where they co-exist with this toxic amphibian. Moreover, both varanids have also been shown to learn to avoid feeding on toads when first subjected to conditioned taste aversion. Such behavioural shifts may therefore explain why yellow-spotted goannas and red-bellied black snakes still exist in cane toad infested areas of Queensland. The process appears, however, to be unable to rapidly restore varanid populations to pre-toad population numbers as even after 10 years of co-existence with cane toads in the Northern Territory, we see no signs of an increase in yellow-spotted goanna numbers.