In an arms race between host and parasite, a lungworm's ability to infect a toad is determined by host susceptibility not parasite preference

Abstract

Evolutionary arms races can alter both parasite infectivity and host resistance, and it is difficult to separate the effects of these twin determinants of infection outcomes. We used a co-introduced, invasive host–parasite system (the lungworm Rhabdias pseudosphaerocephala and cane toads Rhinella marina ), where rapid adaptation and dispersal have led to population differences in infection resistance. We quantified behavioural responses of parasite larvae to skin-chemical cues of toads from different invasive populations, and rates at which juvenile hosts became infected following standardized exposure to lungworms. Chemical cues from toad skin altered host-seeking behaviour by parasites, similarly among populations. The number of infection attempts (parasite larvae entering the host's body) also did not differ between populations, but rates of successful infection (establishment of adult worm in host lungs) were higher for range-edge toads than for range-core conspecifics. Thus, lower resistance to parasite infection in range-edge juvenile toads appears to be due to less effective immune defences of the host rather than differential behavioural responses of the parasite. In this ongoing host–parasite arms race, changing outcomes appear to be driven by shifts in host immunocompetence.

Genomic Tools in Biological Invasions: Current State and Future Frontiers

“…For example, microbial symbionts of insects provide essential functions and coevolve with their hosts, and can facilitate invasions by providing detoxification capabilities and/or aiding host range expansion ( Lange et al 2023 ). Similarly, the absence or presence of plant endophytes can determine if a plant becomes invasive ( Kentjens et al 2023 ), and rapid adaptation and dispersal have led to spatial variation in the resistance of the cane toad ( Rhinella marina ) to its native-range lungworm parasite ( Rhabdias pseudosphaerocephala ) ( Eyck et al 2022 ).…”