ChangingToads · Invasion driven evolution of spatial behavior and brain structure in the cane toad

Invasive species threaten ecosystems around the world. In fighting to protect local flora and fauna, scientists typically focus on research about preventative measures. However, cognitive functions that aid invaders in exploiting novel environments, such as spatial memory, mostly go unstudied. Spatial behaviors are of special interest to understanding how invasive species disperse, as movement and navigation affect the area that species can exploit and determine the range they ultimately occupy. To fill this gap, I will take an integrative approach that combines behavioral observations generated through cutting-edge biologging (use of wearable devices to record information about movement) with state-of-the-art lab-based characterizations of neural function and structure. I will study how invasion has affected the evolution of a well-known invasive amphibian in Australia, the cane toad (Rhinella marina). Specifically, I will: (a) investigate how navigation abilities differ between toads from the vanguard (invasion-front) as compared to those that have been longer established (invasion core) using translocation-homing experiments in the wild; (b) compare whole-brain activity between navigating, exploring, and dispersing toads to understand how brain regions support spatial cognition using whole-mount immunolabeling and 3D imaging; and (c) determine if selective pressures from invasion have caused shifts in brain structure by using microCT scans and isotropic fractionation to characterize regional volume and neuron density across toad populations. This project will be the first to investigate how selection has shaped cognitive traits that facilitate invasion, including neural substrates that underlie invasion success, leveraging the massive unplanned “natural experiment” created by cane toad invasion. In addition, this work will fill in a major blind spot in the understanding of vertebrate spatial cognition created by lack of knowledge of amphibian neural function.