JCU scientists say cane toads are becoming less poisonous in urban areas

Cane toads are becoming less poisonous as they rapidly adapt to life in Australia’s urban areas, according to scientists at James Cook University.

Cane toads which live in urban areas are becoming less poisonous

Cane toads are becoming less poisonous as they rapidly adapt to life in Australia’s urban areas, according to scientists at James Cook University.

A research team collected over 400 toads from three different areas in north Queensland and found that the parotoid glands, which contain the poison that are the toad’s major defence against predators, are smaller in the toads from urban areas compared to rural areas.

Lin Schwarzkopf, JCU’s head of zoology and ecology who was part of the research team, said there may be fewer predators of toads in urban environments, which made producing toxins less important for these toads.

“Fewer predators may mean urban toads have decreased their energy investment in anti-predator defences. If so, this change has occurred rapidly, within the past 85 years, as toads were introduced to north Queensland in 1935,” Professor Schwarzkopf said.

However while it is known that there are fewer bird predators of toads in urban areas, more work on predation rates is needed to confirm the hypothesis.

Another difference was found in the length of toads’ legs. Male toads from urban areas had longer legs (due to a longer tibiofibular bone), while urban females had shorter legs compared to their rural cousins.

Professor Schwarzkopf said a longer tibiofibular bone may allow toads to move faster and cover more distance, and it was likely that urban toads needed to travel further than rural toads to overcome barriers such as roads and buildings.

“Given that male toads tend to move more often than females, males with longer tibiofibulas, and therefore better movement ability, may be favoured in urban environments. However, more sedentary females may not experience a similar benefit,” she said,

The team believes more research is needed on the differences in leg length to clearly determine what is driving the change.

Professor Schwarzkopf said that the rapid growth of urban areas is causing drastic environmental change but scientists are only just beginning to understand urbanisation as an evolutionary force.

“Natural habitats, such as parks and gardens, are often isolated from each other by artificial barriers like buildings and roads and this isolation can make evolution quicker,” she said.