Australia's Invasive Cane Toads Show Signs Of Cannibalism

Australia, you've done it again! A study published this month studied the behaviors of invasive populations of cane toads in Australia. These toads, it would seem, have evolved to target not only competition in other species, but in their own. Scientists have shown that these toads – in their tadpole stage – have evolved "both a strong behavioral attraction to the vulnerable hatchling stage and an increased propensity to cannibalize these younger conspecifics."

When we speak, here, about cannibal toads, it's not that we're talking about toads eating other toads. It's more like toad tadpoles – before they become full-fledged hopping-around toads – are eating the even earlier stages of their kin. Researchers Jayna L. DeVore, et. al. have shown that there is now an "evolutionary arms race" between stages of toad in invaded habitats.

The rise of the cannibalistic tadpole in populations of cane toad in invaded habitats have put pressure on the lesser stages of this same species. Egg and hatchling stages are changing, and the species is "reducing the duration of the vulnerable period" to avoid being eaten.

Observations of these populations of invasive toads showed that vulnerable stages have grown "stronger constitutive defenses and greater cannibal-induced plastic responses" than their counterparts without cannibalistic pressure. When these sorts of changes appear, said individuals have "performance reductions" in later stages of life.

Researchers suggest that these findings show "the importance of intraspecific conflict in driving rapid evolution" and how evolutionary processes can product "mechanisms that regulate invasive populations."

Have you noticed any mechanisms in humans that might act to regulate us as we've acted as the most successful invasive species of animal on the planet Earth?

To learn more about the study, take a peek at "The evolution of targeted cannibalism and cannibal-induced defenses in invasive populations of cane toads". This paper can be found with code DOI:10.1073/pnas.2100765118 as authored by Jayna L. DeVore, Michael R. Crossland, Richard Shine, and Simon Ducatez for publication in PNAS August 31, 2021 118 (35) e2100765118.