Getting caned

The invasion of the cane toad (Rhinella marina) in tropical Australia has come at a great cost to native species and domestic pets since their introduction. The toads were introduced in 1935 in a spectacularly unsuccessful attempt to control cane beetles, which were destroying sugar cane crops. About 3,000 cane toads were initially introduced and the number is now reported to exceed 200 million.

The cane toad has poison glands, and the tadpoles are highly toxic to most animals if ingested. There have been numerous ineffective government strategies to eradicate this “pest”.

A group of scientists in Australia believe that they have found a solution to the problem.² Richard Shine of the University of Sydney, Australia, told The Column: “The study arose from a serendipitous observation. We discovered that many tadpoles of native frog species were killed by eating toad eggs, so we put out funnel-traps with these eggs in a local pond to see if the tadpoles of some species of frogs were especially likely to be attracted to those eggs (and thus, at most risk).”

“Instead, we found that the traps filled up with toad tadpoles. That unexpected observation suggested that toad tadpoles were attracted to some chemical produced by toad eggs, so we fractionated chemical cues from water around toad egg masses and tested the responses of toad tadpoles to each fraction. After two years of trials, we finally hit upon the answer … the critical chemical that attracts toad tadpoles is one or more of the distinctive poisons that toads produce to discourage predators from eating them or their eggs.”

Laboratory results showed that tadpoles find the eggs by searching for the bufadienolide toxins (in particular, bufogenins) that toads use to deter predators. By turning the tables on the invading species they believe that the species can be contained. Using those toxins as bait, funnel-traps were placed in two natural waterbodies. The team found that near-complete eradication of cane toad tadpoles with minimal collateral damage (as most native (non‑target) species were repelled by the toads’ toxins) was achieved.

Shine added: “We are continuing to collaborate with Rob Capon and his team, with the aim of developing a simpler, safer and more powerful attractant — one more suitable for use by the general public. Within another year or two, I am confident that we will have a really effective weapon against this devastating invader.”

1. Jonathan Pearlman, The Telegraph, 13 June 2012 (http://bit.ly/Kmt9zT).

2. Richard Shine et al., Proc Biol Sci. 279(1742), 3436–42 (2012).

This story originally appeared in The Column. Click here to view that issue.