Protection against anuran lungworm infection may be mediated by innate defenses rather than their microbiome

Host-associated microbiomes provide protection against disease in diverse systems, through both direct and indirect interactions with invaders, although these interactions are less understood in the context of non-gut helminth infections in wildlife. Here, we used a widespread, invasive host-parasite system to better understand helminth-amphibian-microbiome dynamics. We focus on cane toads and their lungworm parasites, which invade the host through the skin, to study the interactions between lungworm infection abundance and skin and gut (colon) bacterial microbiomes. Through two experiments, first reducing skin bacterial loads, and second reducing bacterial diversity, we found no evidence of protection by skin bacteria against infection. We also did not find divergent gut communities dependent on lungworm infection, signifying little to no immune modulation from infection causing changes to gut communities, at least in the first month after initial parasite exposure. In light of previous work in the system, these results underscore the contribution of toads' innate susceptibility (including possible protection provided by skin secretions) rather than skin microbes in determining the chance of infection by these macroparasites.