Invasive cane toads in Japan are growing larger and evolving more rapidly than long-held evolutionary theories suggest, a new study has found. Researchers discovered that toads on the subtropical Ishigaki island weigh an average of 190g, compared to 135g for their Australian counterparts.
The study, published in Royal Society Open Science, compared cane toads from Japan, Australia, Hawaii and the species' native range in French Guiana. It found substantial shifts in mean body size and shape within less than 100 years, since the Japanese and Australian populations shared a common history in Hawaii until the 1930s.
“The idea that evolutionary change happens at a glacially slow pace is being challenged by recent evidence showing rapid changes in species confronted with novel challenges,” said Rick Shine, an evolutionary biologist at Macquarie University, Sydney, and co-author of the study.
Researchers are unsure what drives the changes, but suspect favourable climatic conditions, especially year-round rainfall on Ishigaki, and lower predation pressure may be factors. The cane toad, native to northeastern South America, has spread to over 40 countries and is considered one of the world's most studied invasive species.
