Chasing Cane Toads: Assessing Locomotory Differences in Toads from Core and Edge Populations in Florida

Cane Toads (Rhinella marina) are an invasive species introduced to southern Florida, USA, and populations have spread northward through the state. Populations established near expanding edges of their distributions are predicted to have greater endurance, an indicator of dispersal capability, than longer established populations. To assess endurance, we collected Cane Toads from a northern (edge) and southern (core) population in Florida, placed them into a track, and prodded them to hop. The number of prods (taps), hops, and time spent hopping were recorded, along with the total distance each toad moved on the track. Edge population toads were less willing to move and did not travel as far in the track as those from the core population. To further evaluate endurance, we placed an additional set of toads inside a treadmill, where movement was required to maintain equilibrium. Toads moved on the treadmill until reaching exhaustion. We measured blood lactate levels from each toad upon exhaustion and during a 3-h recovery period. After the treadmill trials, there was no population effect on the distances traveled by toads. There was also no population effect on lactate levels of toads when reaching exhaustion or during recovery. Overall, Cane Toads from our sampled northern edge population showed no differences in endurance compared to those sampled from the southern population in this study. This finding may indicate that further dispersal is limited in the northernmost populations of the Cane Toad range in Florida. Furthermore, the reluctance of Cane Toads to move in the track trials may indicate that selective pressures differ for edge populations in Florida.