Wildfires modify the parasite loads of invasive cane toads.

Shannon W Kaiser,Richard Shine,Matthew J Greenlees

doi:10.1098/rsbl.2021.0470

Abstract

The frequency and severity of wildfires are increasing due to anthropogenic modifications to habitats and to climate. Post-fire landscapes may advantage invasive species via multiple mechanisms, including changes to host–parasite interactions. We surveyed the incidence of endoparasitic lungworms (Rhabdias pseudosphaerocephala) in invasive cane toads (Rhinella marina) in near-coastal sites of eastern Australia, a year after extensive fires in this region. Both the prevalence of infection and number of worms in infected toads increased with toad body size in unburned areas. By contrast, parasite load decreased with toad body size in burned areas. By killing moisture-dependent free-living lungworm larvae, the intense fires may have liberated adult cane toads from a parasite that can substantially reduce the viability of its host. Smaller toads, which are restricted to moist environments, did not receive this benefit from fires.

Highlights

Over recent decades, changes to temperature and rainfall patterns are causing more extreme events such as bushfire, flood and drought [1,2]
The parasite loads of small toads were unaffected by fire, whereas those of large toads were lower in burned areas
The pattern for parasite load to increase with toad body size, as seen in our unburned sites, mirrors the results of an earlier study in tropical Australia [14], whereas a broader-scale sampling study reported that parasite loads were highest in toads of intermediate body sizes [28]

Summary

Introduction

Changes to temperature and rainfall patterns are causing more extreme events such as bushfire, flood and drought [1,2]. Intense fire may reduce the incidence of parasitic lungworms that are widespread in Australian cane toads [14] and can enforce major reductions in host viability [15]. To test this idea, we compared parasite loads in cane toads from adjacent sites that differed in whether or not they had been burned during the 2019–2020 bushfires. A mixed model with negative binomial link distribution and log link In both cases, we included fire condition (burned versus unburned) as a factor, and toad body size (SUL) as a covariate, plus the interaction between these two variables. To explore possible shifts through time, we added ‘number of months since fire’ as an additional covariate in the analyses above

Results

Findings

Discussion