Invasion and the evolution of speed in toads

Cane toads seem to have honed their dispersal ability to devastating effect over the generations. Raising cane The introduction of the cane toad into Australia 70 years ago has been a disaster. Initially meant to control insect pests in fields of sugar-cane, they rapidly became pests themselves. Both the tadpole and adult are toxic to predators, so native ecosystems are transformed when they arrive. Insight into their alarming rate of spread, which has increased fivefold since their arrival, is presented this week, and the news is bad. It seems that toads at the invasion front have developed longer legs over the generations, adapting to accelerate their expansion into new areas. Cane toads ( Bufo marinus ) are large anurans (weighing up to 2 kg) that were introduced to Australia 70 years ago to control insect pests in sugar-cane fields. But the result has been disastrous because the toads are toxic and highly invasive. Here we show that the annual rate of progress of the toad invasion front has increased about fivefold since the toads first arrived; we find that toads with longer legs can not only move faster and are the first to arrive in new areas, but also that those at the front have longer legs than toads in older (long-established) populations. The disaster looks set to turn into an ecological nightmare because of the negative effects invasive species can have on native ecosystems 1 , 2 ; over many generations, rates of invasion will be accelerated owing to rapid adaptive change in the invader 3 , with continual ‘spatial selection’ at the expanding front favouring traits that increase the toads' dispersal 4 , 5 .