The costs of parasite infection: Effects of removing lungworms on performance, growth and survival of free-ranging cane toads

Most research on the effects of parasites on their hosts has focused on the parasites of mammals or birds (especially, domesticated taxa) rather than systems in which the hosts are ectothermic wildlife species. We used experimental methods (antihelminthic drugs) to quantify the effects of lungworms (Rhabdias pseudosphaerocephala) on their anuran hosts, the invasive cane toad (Rhinella marina). In captivity, eradicating lungworms enhanced toad activity (measures of boldness and level of spontaneous activity), performance (locomotor speed, climbing ability) and foraging success (feeding rate). In free‐ranging toads (n = 123) at a site in tropical Australia, eradicating lungworm infection increased rates of host survival by 8%, movement by 20%, growth by 28% and elaboration of male secondary sexual characteristics by 30%. The presence of the lungworm thus has a substantial negative effect on fitness‐related traits of the host. Given their long shared evolutionary history and the mild inflammatory and immune response elicited by the parasite in the host, the magnitude of the effects of parasite removal were surprising. Parasites may impose hidden costs, related to modification of host behaviour or metabolism. Experimental removal of parasites can be a useful means of quantifying costs of infection. A plain language summary is available for this article. Plain Language Summary