Rhabdias pseudosphaerocephala infection in Bufo marinus: Lung nematodes reduce viability of metamorph cane toads

School of Biological Sciences A08, University of Sydney, NSW 2006, Australia.
Parasitology (Impact Factor: 2.35). 07/2009; 136(8):919-27. DOI: 10.1017/S0031182009006325
Source: PubMed

ABSTRACT Cane toads (Bufo marinus) were introduced to Australia in 1935 and have since spread widely over the continent, generating concern regarding ecological impacts on native predators. Most Australian cane toad populations are infected with lung nematodes Rhabdias pseudosphaerocephala, a parasite endemic to New World (native-range) cane toad populations; presumably introduced to Australia with its toad host. Considering the high intensities and prevalence reached by this parasite in Australian toad populations, and public ardour for developing a control plan for the invasive host species, the lack of experimental studies on this host-parasite system is surprising. To investigate the extent to which this lungworm influences cane toad viability, we experimentally infected metamorph toads (the smallest and presumably most vulnerable terrestrial phase of the anuran life cycle) with the helminth. Infected toads exhibited reduced survival and growth rates, impaired locomotor performance (both speed and endurance), and reduced prey intake. In summary, R. pseudosphaerocephala can substantially reduce the viability of metamorph cane toads.

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Available from: Crystal Kelehear, Aug 16, 2015
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    • "To stimulate oviposition and fertilization, we injected adult cane toads (from the northeastern NSW study area) with 0.4 mL (males) or 0.8 mL (females) of Leuprorelin acetate (0.5 mg/mL; Lucrin, Abbott Australasia, Botany, NSW) diluted at 1∶20 with saline (see Kelehear et al. 2009 for details). Following deposition of eggs into water of pH 7, viable eggs containing early embryos (Gosner stage 10–13, 100 per container; Gosner 1960) were placed into 15-L solutions of the five pH treatments, with six replicates per treatment (randomly arranged in the experimental area). "
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    ABSTRACT: Invasive cane toads are colonizing southeastern Australia via a narrow coastal strip sandwiched between unsuitable areas (Pacific Ocean to the east, mountains to the west). Many of the available spawning sites exhibit abiotic conditions (e.g., temperature, salinity, and pH) more extreme than those encountered elsewhere in the toad’s native or already invaded range. Will that challenge impede toad expansion? To answer that question, we measured pH in 35 ponds in northeastern New South Wales and 8 ponds in the Sydney region, in both areas where toads occur (and breed) and adjacent areas where toads are likely to invade, and conducted laboratory experiments to quantify effects of pH on the survival and development of toad eggs and larvae. Our field surveys revealed wide variation in pH (3.9-9.8) among natural water bodies. In the laboratory, the hatching success of eggs was increased at low pH (down to pH 4), whereas the survival, growth, and developmental rates of tadpoles were enhanced by higher pH levels. We found that pH influenced metamorph size and shape (relative head width, relative leg length) but not locomotor performance. The broad tolerance range of these early life-history stages suggests that pH conditions in ponds will not significantly slow the toad’s expansion southward. Indeed, toads may benefit from transiently low pH conditions, and habitat where pH in wetlands is consistently low (such as coastal heath) may enhance rather than reduce toad reproductive success. A broad physiological tolerance during embryonic and larval life has contributed significantly to the cane toad’s success as a widespread colonizer.
    Physiological and Biochemical Zoology 04/2015; 88(4):000-000. DOI:10.1086/681263 · 2.05 Impact Factor
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    • "\1 % survival of eggs and hatchlings in the presence of cannibalistic conspecific tadpoles: Alford et al. 1995). In addition, parasitism, cannibalism and predation by ants can reduce survival of metamorph toads (Pizzatto and Shine 2008; Kelehear et al. 2009; Ward-Fear et al. 2010). Predation by vertebrates on this invasive species remains poorly studied (but see, for example, Hamley and Georges 1985; Letnic et al. 2008; Ujvari and Madsen 2009). "
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    ABSTRACT: The success of an invasive species can be reduced by biotic resistance from the native fauna. For example, an invader that is eaten by native predators is less likely to thrive than one that is invulnerable. The ability of invasive cane toads (Rhinella marina) to spread through Australia has been attributed to the toad’s potent defensive chemicals that can be fatal if ingested by native snakes, lizards, marsupials and crocodiles. However, several taxa of native insects and birds are resistant to cane toad toxins. If native rodents are also capable of eating toads (as suggested by anecdotal reports), these large, abundant and voracious predators might reduce toad numbers. Our field observations and laboratory trials confirm that native rodents (Melomys burtoni, Rattus colletti and Rattus tunneyi) readily kill and consume cane toads (especially small toads), and are not overtly affected by toad toxins. Captive rodents did not decrease their consumption of toads over successive trials, and ate toads even when alternative food types were available. In combination with anecdotal reports, our data suggest that rodents (both native and invasive) are predators of cane toads in Australia. Despite concerns about the decline of rodents following the invasion of toads, our data suggest that the species we studied are not threatened by toads as toxic prey, and no specific conservation actions are required to ensure their persistence.
    Journal of Pest Science 03/2014; 88(1). DOI:10.1007/s10340-014-0586-2 · 2.66 Impact Factor
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    • "When infected with R. pseudosphaerocephala, these invasive anurans can experience a reduction in endurance and sprint speed (Kelehear et al., 2009; Pizzatto and Shine, 2011a,b), altered cardio-respiratory function (Pizzatto and Shine, 2012), and reduced growth rates (Kelehear et al., 2009, 2011a) and survivorship (Kelehear et al., 2009). These effects suggest that the lungworms may suppress cane toad viability sufficiently to influence toad populations and may even warrant consideration for biocontrol (Kelehear et al., 2009, 2011a). Accordingly , we need to understand the interactions between the invasive toad and its lungworm parasite. "
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    ABSTRACT: The impact of parasites on host populations depend upon parasite prevalence and intensity. Understanding how infection dynamics change through time following a host population's initial exposure to the parasite is fundamental to host-parasite biology. We studied an invasive host (the cane toad, Rhinella marina) currently undergoing range expansion - a process through which this host's range is expanding faster than that of its lung parasites (the nematode, Rhabdias pseudosphaerocephala), such that hosts at the expanding range edge remain parasite-free for several years. It was predicted that parasite intensity and prevalence would be affected by host characteristics (e.g., size, sex), environmental conditions (e.g., seasons, habitat type), and time since parasite arrival in the newly established invading host population. Over 2,400 cane toads were sampled at 10 sites in recently established toad populations in the highly seasonal monsoonal tropics of northern Australia. The sampling spanned 14 consecutive 3 month seasons commencing in the early stages of lungworm establishment in those toad populations. Both parasite prevalence and intensity increased with host body size but were unaffected by host sex. Prevalence and intensity were highest during drier times of year and in drier habitats (i.e., sites lacking permanent waterbodies). These changes in parasite prevalence may reflect a trend for saturated soil to reduce parasite survival during the free-living infective stage, and to allow anuran hosts to disperse widely (thus reducing the transfer of directly transmitted parasites between hosts). Conversely, dry conditions induce toads to aggregate in moist dry-season refugia where conditions may be more conducive to direct transmission of infective parasitic larvae between hosts.
    International journal for parasitology 06/2013; DOI:10.1016/j.ijpara.2013.05.002 · 3.40 Impact Factor
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