Typhoid Mary in the frogpond: Can we use native frogs to disseminate a lungworm biocontrol for invasive cane toads?

Abstract

Invasive cane toads Rhinella marina have had severe ecological impacts in Australia. The toads brought with them a native-range (New World) parasitic lungworm Rhabdias pseudosphaerocephala that can kill metamorph toads, stunt the growth and reduce the stamina of both metamorph and adult toads. No cases of natural transfer to native frogs have been reported, but experimental studies have shown that metamorphs of one native anuran (the green tree frog Litoria caerulea) are capable of maintaining lungworm infections, without reducing frog survivorship. Thus, we might be able to increase the distribution of the lungworm, and its prevalence in toads, by deliberately infecting green tree frogs. In laboratory studies, we found that the toad lungworm had no detectable effects on growth or survival of adult green tree frogs. Worms that developed in the lungs of the frogs, passed out in the frog's faeces, and were able to infect toads, reducing their stamina. Synthesis and applications: Our results are encouraging for the possibility of using the green tree frog as a Typhoid Mary (to carry parasites to invasive toads without itself suffering any ill effects due to the parasite's presence), but this management approach raises significant issues of statistical power (we can never be sure that lungworms have absolutely no effect on frog viability) and animal welfare (are we justified in infecting the native species to help control the invasive species?). Animal Conservation © 2012 The Authors. Animal Conservation © 2012 The Zoological Society of London.