The impact of lungworm parasites on rates of dispersal of their anuran host, the invasive cane toad

Abstract

Translocation of native-range parasites to control invasive species is effective only if the parasite substantially impairs either the viability or dispersal rate of the invasive host. Lungworms (Rhabdias pseudosphaerocephala) of cane toads (Rhinella marina) were introduced to Australia from the toad's native range, along with the toads, and have been suggested as a potential biocontrol of invasive toads due to various negative impacts on toad viability. We conducted two radio-telemetry studies on a tropical floodplain to specifically assess the parasite's impact on toad dispersal. First, a retrospective correlative analysis of data from field-collected animals showed that toads infected with lungworms moved farther, not less, than uninfected conspecifics. Second, an experimental study (comparing movements of experimentally infected toads vs. uninfected controls) showed that lungworms did not modify rates of toad dispersal. In addition, experimental infection with lungworms did not elicit an immune response substantial enough to influence dispersal behaviour. Thus, we conclude that increasing lungworm densities at the invasion front as an attempt at biocontrol would not slow down the spread of cane toads.

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

“…The effects we documented seem likely to influence toad fitness in an evolutionary sense, with infected toads growing slower, dying sooner, and investing less into the elaboration of sexually dimorphic traits, which in turn influence male mating success (Bowcock, Brown, & Shine, ; Narayan, Christi, Morley, & Trevenen, ). Thus, this parasite‐host relationship may have ecological importance, influencing broad demographic features of toad populations, potentially reducing toad abundance and/or rates of dispersal (Brown et al., ; Ebert, Lipsitch, & Mangin, ; Hudson, Dobson, & Newborn, ; Phillips et al., ). Given the destructive effect of the invasive cane toad on native Australian fauna, and the toad's still‐advancing invasion front (Shine, ), our data demonstrating a negative influence of parasite infection in free‐ranging hosts are encouraging for the potential use of R. pseudosphaerocephala as a component of a biological control approach for toads in Australia (Tingley et al., ).…”

“…The inflammation and immune reaction elicited by Rhabdias in their toad hosts are relatively mild (Brown et al., ; Pizzatto et al., ; Santos et al., ), and presumably shaped by their long co‐evolutionary history. Thus, the dramatic effects of removing the parasites are surprising.…”

“…These findings indicate a stronger and more consistent negative effect of lungworm infection on host growth and performance than has been shown by earlier studies on this system and on similar amphibian host-parasite interactions. Although the effects of R. pseudosphaerocephala on the performance of cane toads have attracted considerable research, different methodologies and life stages have made it difficult to form a clear consensus on the strength of impact (Brown, Kelehear, Pizzatto, & Shine, 2016;Kelehear et al, 2009;Pizzatto & Shine, 2012a). Other research on the influence of Rhabdias lungworms on bufonid anurans have similarly documented significant but variable effects (Goater, Semlitsch, & Bernasconi, 1993;Goater & Ward, 1992).…”

A review of the role of parasites in the ecology of reptiles and amphibians

“…However, infection did not affect dispersal behaviour of adult toads (Brown et al . ). A bacteria (Ochrobactrum anthropi) was also explored as a causative agent of spinal arthropathy in cane toads ( R. marina ; Brown et al .…”

Ticks on snakes: The ecological correlates of ectoparasite infection in free‐ranging snakes in tropical Australia

“…Parasites can also indirectly affect host fitness by altering host behaviour and spatial ecology (Main & Bull ; Fenner & Bull ; Brown et al . ). In many cases, however, it is difficult to disentangle whether correlations between parasite loads and host fitness and/or behaviour are a direct impact of parasitism, or reflect the fact that a host's ecological or behavioural traits affect its susceptibility to parasites (Finnerty et al .…”