Featured White Evolutionary Lab researcher: Hugh tests the limits of toad invasion in Australia

Hugh and an experimental cane toad

Invasive cane toads are well-known for their deleterious effects on wildlife in Australia: most native animals that consume cane toads die as a result of the cane toad toxin, and the cane toads themselves consume many species of small native animals. This is especially a concern for some of Australia's more endangered animals, such as the carnivorous spotted-tail quoll, and consequently, any means of predicting where the toads are going, and how fast they are heading there, is important for conservation scientists.

The locomotion test involves swimming in fast-flowing water

Portrait of an experimental cane toad - they have beautiful eyes!

Cane toads (Chaunus [Bufo] marinus) were first introduced into Australia in 1935-1937 along a 1200 km stretch of north east Australia. Now, these animals cover up to 1.2 million square km of north east Australia (Urban et al., 2007). This rapid spread over such a wide area, however, has only occurred in the warmer (tropical) parts of Australia: to the south, cane toads only extend as far as the upper regions of New South Wales.

Previous research suggested that cane toads were physiologically limited in their ability to invade the more temperate regions of Australia (such as New South Wales and further south), because the colder temperatures presented a physiological barrier to cane toad invasion. There is now evidence, however, of a slow but gradual creep of the southern cane toad invasion front headed further south.

This poses an interesting, two-part question, and one that Hugh in the White Evolutionary lab of The University of Queensland is researching:

1. Is this southern invasion slower because cane toads are reaching limitations on their tolerance of colder temperatures, and as such the physiological barrier to cane toads will be upheld? 
2. Is this a sign of cane toads physiologically adapting to colder temperatures, and the colder regions of Australia no longer present a barrier to the invasion front?

Hugh is in the final stages of his Honours research that asks these questions. What his research entails is looking for whether there are differences in the energetic costs (metabolic rate) associated with locomotion (as a proxy for physiological performance) in cold and warm conditions between a northern population of adult toads (from Cairns), and a southern population of adult toads (from Ballina and Yamba in New South Wales).

Hugh's research will shed some light in determining whether cane toad physiology in the southern population is better suited to cold temperatures, and ultimately, are toads evolving to tolerate colder temperatures and are thus shifting the invasion front progressively more south. Let's hope for Australia's wildlife that Hugh finds the answer is no!