Invasive cane toads on a small Japanese island have evolved larger bodies and heavier weights than their Australian ancestors in less than a century, according to a study published in the journal Ecology and Evolution on April 28, 2026.
Researchers from Kyoto University and the University of the Ryukyus measured toads on Hahajima, part of the Ogasawara Islands, where the amphibians were introduced in the 1930s to control agricultural pests. They found that female toads now average 15% longer and 30% heavier than those in Australia, while males are 10% longer and 20% heavier.
Lead author Dr. Yuki Kobayashi said the rapid change likely resulted from a combination of island gigantism—where large body size is favored due to fewer predators—and the toads' high reproductive output. The study notes that the toads have also developed longer legs, possibly to aid movement through dense island vegetation.
The findings challenge the assumption that significant evolutionary changes require thousands of years, demonstrating that invasive species can adapt quickly to new environments. The toads have become a major pest on Hahajima, preying on native insects and competing with local frogs.
