Thursday, February 9, 2012

Cane toads lose their killer touch in east Australia (via Herp Digest)

Invasive weeds may save Australia's blue-tongue lizards from cane toad poison.

Since the cane toad was introduced to Australia in 1935, it has killed swathes of Australia's native animals including quolls, crocodiles and blue-tongue lizards (Tiliqua scincoides).

Native species that prey on the alien amphibians die because the toads produce a lethal toxin called bufadienolide.

Some blue-tongue lizards in eastern Australia can dine on the cane toads and live, though. Oddly enough, they might owe their immunity to another invasive species.

An ornamental plant native to Madagascar called mother-of-millions (Bryophyllum delagoense) is common in eastern Australia, and has also become part of the lizards' diet. The plants' flowers contain a poison similar to bufadienolide. Rick Shine at the University of Sydney, Australia, suspected that lizards which have already gained immunity to this toxin might be in a better position to withstand the toad toxin too.

His team caught 75 lizards that lived in areas containing either the toad and the ornamental plant, just one of the two, or neither of the toxic invaders. Shine injected toad poison into the lizards, administering a dose high enough to provoke a reaction, but not enough to kill the animal. His team then timed how fast the lizards could swim 50 centimetres.

Blue-tongue lizards from areas containing mother-of-millions were affected to a lesser degree than any others. This was true even for lizards that lived in regions of eastern Australia that contain no cane toads.

"Eastern blue-tongue lizards are able to defend themselves well against cane toads even though they've never actually met one," says Shine.

Mother-of-millions has been recorded in Australia for 70 years or so, suggesting that the lizards have gained tolerance to its toxin rapidly. Blue-tongue lizards create a new generation every two to four years, says study co-author Gregory Brown, also at the University of Sydney.

"It is extremely surprising that one of the lizard populations should genetically change over such a relatively short period of time," says Michael Tyler, an evolutionary biologist at the University of Adelaide, South Australia, who was not involved in the work. "But I am convinced. There is no other explanation I can find."

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