The gut bacteria of an invasive amphibian respond to the dual challenges of range-expansion and parasite attack

Gut bacterial communities influence, and are influenced by, the behaviour and ecology of their hosts. Those interactions have been studied primarily in humans and model organisms, but we need field research to understand the relationship between an organism’s gut bacteria and its ecological challenges, such as those imposed by rapid range expansion (as in invasive species) and the presence of host-manipulating parasites. Cane toads (Rhinella marina) provide an excellent model system in this respect, because the species’ ongoing colonization of Australia has enforced major changes in phenotypic traits (including behaviour), and lungworm parasites (Rhabdias pseudosphaerocephala) modify host gut function in ways that enhance the viability of lungworm larvae. We collected female toads from across the species’ invasive range and studied their morphology, behaviour, parasite infection status and gut bacterial community. Range-core versus range-edge toads differed in morphology, behaviour, gut bacterial composition and predicted gut bacterial function but did not differ in the occurrence of parasite infection nor in the intensity of infection. Toads infected with lungworms differed from uninfected conspecifics in gut bacterial composition and diversity. Our study demonstrates strong associations between gut bacterial community and host ecology and behaviour.