Cane Toads Challenge the Idea That Evolution Moves Slowly, Study Shows

Scientists studying invasive cane toads in Japan have found that the species is evolving much faster than previously thought, challenging long-held beliefs about the pace of evolutionary change.

Research published in the journal Royal Society Open Science reveals that cane toads in Japan have grown significantly larger than their counterparts in Australia, despite sharing a common origin in Hawaii until the 1930s. Adult toads from Ishigaki Island in southern Japan weigh an average of 190 grams, compared to 135 grams for those in Australia.

Comparison of our samples with cane toads from the native range [French Guiana] and other invasive populations [Hawaii and Australia] reveals substantial shifts in mean body size and shape.

Researchers, Royal Society Open Science

The rapid physical changes observed in the Japanese cane toad population have developed in less than 100 years, a timeframe far shorter than what traditional evolutionary theory would predict for such significant morphological shifts.

Given these populations of toads in Japan and Australia shared a common history in Hawaii until the 1930s, these differences in size and body shape have developed in less than 100 years.

Rick Shine, evolutionary biologist at Macquarie University, Sydney

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, like being translocated to a different habitat.

Rick Shine, evolutionary biologist at Macquarie University, Sydney

Cane toads, native to northeastern South America, have spread to over 40 countries and are considered one of the most studied invasive species globally. Their introduction to Australia decades ago to control beetle populations led to rapid spread and significant ecological damage, as their toxic secretions pose a deadly threat to native predators such as quolls, crocodiles, and snakes.

The findings from Japan add to growing evidence that invasive species can undergo rapid adaptive evolution when faced with new environmental pressures, prompting scientists to reconsider assumptions about the speed at which evolutionary change can occur.