Host-Parasite Relationships During a Biologic Invasion: 75 Years Postinvasion, Cane Toads and Sympatric Australian Frogs Retain Separate Lungworm Faunas

Abstract

ABSTRACT:Invasive species may carry with them parasites from their native range, differing from parasite taxa found in the invaded range. Host switching by parasites (either from the invader to native fauna or from native fauna to the invader) may have important consequences for the viability of either type of host (e.g., their survivorship, fecundity, dispersal ability, or geographic distribution). Rhabdias pseudosphaerocephala (Nematoda) is a common parasite of cane toads (Rhinella marina) in the toad's native range (South and Central America) and also in its introduced Australian range. This lungworm can depress host viability and is capable of infecting Australian frogs in laboratory trials. Despite syntopy between toads and frogs for up to 75 yr, our analyses, based on DNA sequence data of lungworms from 80 frogs and 56 toads, collected from 2008 to 2011, did not reveal any cases of host switching in nature: toads and native frogs retain entirely different lungworm faunas. All lungworms in cane toads were the South and Central American species Rhabdias pseudosphaerocephala, whereas Australian frogs contained at least four taxa (mostly undescribed and currently lumped under the name Rhabdias cf. hylae). General patterns of prevalence and intensity, based on the dissection of 1,315 frogs collected between 1989 and 2011 across the toads' Australian range, show that these Australian endemic Rhabdias spp. are widely distributed geographically and across host taxa but are more common in some frog species (especially, large-bodied species) than they are in others.

Immune Response Varies with Rate of Dispersal in Invasive Cane Toads (Rhinella marina)

“…Surveys of parasites and diseases in Australian cane toads provide some indication of the pathogen pressure faced by invading toads. At least one of the 100 toads brought to Australia from Hawaii in 1935 harbored a nematode lungworm native to South America [49] and this parasite is now common in Australian toad populations [50], though it lags behind the frontline of the toad invasion, where host density is too low for transmission [35]. Aside from harboring and outrunning a lungworm with which they have a long association, toads in Australia are also exposed to and can become infected with a suite of native pathogens [51]–[53], including pentastomids [37], myxosporea [54], and native nematode lungworms (GPB unpublished data).…”

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

“…Toads have invaded the region occupied by Litoria splendida only within the last three years, and examination of 31 Green Treefrogs collected over that period showed no parasitism by toad lungworms [18]. Dissections of seven L. caerulea at two sites where toads have been present for 6 years and >30 years, respectively, also did not reveal any infected frogs [18], and toad lungworms have not caused mortality in experimentally infected adult Green Treefrogs [54]. Broadly, then, our results are encouraging.…”

“…One of these species (the Green Treefrog, Litoria caerulea ) shows no overt ill effects from the infections whereas the other (Magnificent Treefrog, L. splendida ) exhibits high levels of mortality [17]. Thus, an absence of records of the toad lungworm in Australian native frogs from surveys [18] might reflect either a lack of transmission, or high mortality of infected frogs. The cane toad invasion has already spread through large areas containing L. caerulea , and has now reached areas containing L. splendida .…”

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

“…Also, both laboratory and field studies showed that lungworm infection reduces the growth rates of adult toads by twofold (Kelehear et al 2011a). Field surveys of anuran parasites suggested that the toad's lungworm has not spread to any Australian frogs (Dubey and Shine 2008;Pizzatto et al 2012). Earlier studies on other bufonid-Rhabdias interactions also have reported detrimental effects of the parasite on growth, locomotor performance, and survival of the host (Goater and Ward 1992;Goater et al 1993;Moretti et al 2014).…”