Quantifying Anuran Microhabitat Use to Infer the Potential for Parasite Transmission between Invasive Cane Toads and Two Species of Australian Native Frogs

Abstract

Parasites that are carried by invasive species can infect native taxa, with devastating consequences. In Australia, invading cane toads (Rhinella marina) carry lungworm parasites (Rhabdias pseudosphaerocephala) that (based on previous laboratory studies) can infect native treefrogs (Litoria caerulea and L. splendida). To assess the potential of parasite transmission from the invader to the native species (and from one infected native frog to another), we used surveys and radiotelemetry to quantify anuran microhabitat use, and proximity to other anurans, in two sites in tropical Australia. Unsurprisingly, treefrogs spent much of their time off the ground (especially by day, and in undisturbed forests) but terrestrial activity was common at night (especially in anthropogenically modified habitats). Microhabitat overlap between cane toads and frogs was generally low, except at night in disturbed areas, whereas overlap between the two frog species was high. The situations of highest overlap, and hence with the greatest danger of parasite transmission, involve aggregations of frogs within crevices by day, and use of open ground by all three anuran species at night. Overall, microhabitat divergence between toads and frogs should reduce, but not eliminate, the transmission of lungworms from invasive toads to vulnerable native frogs.

Diversity in the genusRhabdias(Nematoda, Rhabdiasidae): Evidence for cryptic speciation

“…There are few opportunities for infection with Rhabdias parasites from bufonids (terrestrial toads) to hylids tree frogs, due to the difference in habitat use. However, Pizzato, Both, and Shine () demonstrated that tree frogs exhibit terrestrial activity, especially at night, increasing the microhabitat overlap with toads and enhancing the potential transmission of lungworms. Hypsiboas raniceps uses terrestrial habitats mainly in the reproductive season when they switch to the ground to breed in lentic environments (Santoro & Brandão, 2014).…”

Invasive cane toad triggers chronic physiological stress and decreased reproductive success in an island endemic

“…The cane toad (Rhinella marina), an anuran amphibian native to Central and South America, was introduced into Australia and several Pacific island nations, for example Fiji Islands, as a bio-control agent (Easteal 1981). In Australia, cane toad invasion dynamics and ecological impacts are well documented (Shine 2010;Pizzatto, Both & Shine 2014). Cane toads possess highly toxic skin secretions that have caused major declines in many na€ ıve Australian predators that die after eating them (Doody et al 2009;Shine 2010).…”

“…Cane toads possess highly toxic skin secretions that have caused major declines in many na€ ıve Australian predators that die after eating them (Doody et al 2009;Shine 2010). More recent evidence highlighting the ecological impact of cane toads on native anurans suggests that in anuran species that share micro-habitat with the cane toad, there is potential for transfer of lethal parasites by the toad, which can have devastating consequences on native species (Pizzatto, Both & Shine 2014). Ecological theory of island invasion suggests that on small islands, invasive cane toads can exploit novel ecological functions that diversify or intensify biodiversity impacts (Sakai et al 2001).…”

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

“…Laboratory studies revealed that R. pseudosphaerocephala is capable of successfully infecting native tree frogs, and is rapidly fatal to one iconic taxon, the magnificent tree frog, Litoria splendida (Pizzatto and Shine 2011). Although habitat differences between cane toads and the vulnerable frog may limit collateral impact (Pizzatto et al 2014), biocontrol using the toad lungworm may confer risks to native anurans (Harris 2012;Hough-Goldstein 2012). In addition, given that toad abundance is often high in populations that are rife with Rhabdias (Pizzatto et al 2013), it is unlikely that the lungworm, on it own, can reduce toad numbers (Pizzatto et al 2013;Pizzatto and Shine 2012b).…”