Effect of Rhabdias pseudosphaerocephala on prey consumption of free-ranging cane toads (Rhinella marina) during Australian tropical wet seasons

AbstractInvasions often accelerate through time, as dispersal-enhancing traits accumulate at the expanding range edge. How does the dispersal behaviour of individual organisms shift to increase rates of population spread? We collate data from 44 radio-tracking studies (in total, of 650 animals) of cane toads (Rhinella marina) to quantify distances moved per day, and the frequency of displacement in their native range (French Guiana) and two invaded areas (Hawai’i and Australia). We show that toads in their native-range, Hawai’i and eastern Australia are relatively sedentary, while toads dispersing across tropical Australia increased their daily distances travelled from 20 to 200 m per day. That increase reflects an increasing propensity to change diurnal retreat sites every day, as well as to move further during each nocturnal displacement. Daily changes in retreat site evolved earlier than did changes in distances moved per night, indicating a breakdown in philopatry before other movement behaviours were optimised to maximise dispersal.

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Ecological immunization: in situ training of free-ranging predatory lizards reduces their vulnerability to invasive toxic prey

Biology Letters ◽

10.1098/rsbl.2015.0863 ◽

2016 ◽

Vol 12 (1) ◽

pp. 20150863 ◽

Cited By ~ 24

Author(s):

G. Ward-Fear ◽

D. J. Pearson ◽

G. P. Brown ◽

Balanggarra Rangers ◽

R. Shine

Keyword(s):

Taste Aversion ◽

Conditioned Taste Aversion ◽

Population Declines ◽

Apex Predators ◽

Rhinella Marina ◽

Invasion Front ◽

In Situ Training ◽

Free Ranging ◽

The Impact

In Australia, large native predators are fatally poisoned when they ingest invasive cane toads ( Rhinella marina ). As a result, the spread of cane toads has caused catastrophic population declines in these predators. Immediately prior to the arrival of toads at a floodplain in the Kimberley region, we induced conditioned taste aversion in free-ranging varanid lizards ( Varanus panoptes ), by offering them small cane toads. By the end of the 18-month study, only one of 31 untrained lizards had survived longer than 110 days, compared to more than half (nine of 16) of trained lizards; the maximum known survival of a trained lizard in the presence of toads was 482 days. In situ aversion training (releasing small toads in advance of the main invasion front) offers a logistically simple and feasible way to buffer the impact of invasive toads on apex predators.

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The cost of chemical defence: the impact of toxin depletion on growth and behaviour of cane toads ( Rhinella marina )

Proceedings of The Royal Society B Biological Sciences ◽

10.1098/rspb.2019.0867 ◽

2019 ◽

Vol 286 (1902) ◽

pp. 20190867 ◽

Cited By ~ 6

Author(s):

Ryann A. Blennerhassett ◽

Kim Bell-Anderson ◽

Richard Shine ◽

Gregory P. Brown

Keyword(s):

Chemical Defence ◽

Toxin Production ◽

Substantial Cost ◽

Rhinella Marina ◽

Chemical Defences ◽

Trade Offs ◽

The Cost ◽

Rates Of Growth ◽

Free Ranging ◽

The Impact

Many animals capable of deploying chemical defences are reluctant to use them, suggesting that synthesis of toxins imposes a substantial cost. Typically, such costs have been quantified by measuring the elevation in metabolic rate induced by toxin depletion (i.e. during replenishment of toxin stores). More generally, we might expect that toxin depletion will induce shifts in a broad suite of fitness-relevant traits. In cane toads ( Rhinella marina ), toxic compounds that protect against predators and pathogens are stored in large parotoid (shoulder) glands. We used correlational and experimental approaches in field and laboratory settings to investigate impacts of toxin depletion on growth rate and behaviour in cane toads. In free-ranging toads, larger toxin stores were associated with smaller gonads and livers, suggesting energetic trade-offs between toxin production and both reproduction and energy metabolism. Experimental removal of toxin (by manually squeezing parotoid glands) reduced rates of growth in body mass in both captive and free-ranging toads. Radio tracking demonstrated that de-toxined toads dispersed more slowly than did control toads. Given that toxin stores in cane toads take several months to fully replenish, deploying toxin to repel a predator may impose a substantial cost, explaining why toads use toxin only as a final line of defence.

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Wildfires modify the parasite loads of invasive cane toads

Biology Letters ◽

10.1098/rsbl.2021.0470 ◽

2021 ◽

Vol 17 (12) ◽

Author(s):

Shannon W. Kaiser ◽

Matthew J. Greenlees ◽

Richard Shine

Keyword(s):

Body Size ◽

Parasite Load ◽

Free Living ◽

Rhinella Marina ◽

Burned Areas ◽

Host Parasite Interactions ◽

Eastern Australia ◽

Anthropogenic Modifications ◽

Host Parasite ◽

Rhabdias Pseudosphaerocephala

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.

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URINARY CORTICOSTERONE CONCENTRATIONS IN FREE-RANGING AND MANAGED CANE TOADS (RHINELLA MARINA)

Journal of Zoo and Wildlife Medicine ◽

10.1638/2020-0221 ◽

2021 ◽

Vol 52 (4) ◽

Author(s):

Tarra Freel ◽

Elizabeth Koutsos ◽

Larry J. Minter ◽

Troy N. Tollefson ◽

Frank Ridgley ◽

...

Keyword(s):

Rhinella Marina ◽

Free Ranging

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Predators learning to avoid toxic invasive prey: a study on individual variation among free-ranging lizards

Behaviour ◽

10.1163/1568539x-bja10040 ◽

2020 ◽

Vol 157 (14-15) ◽

pp. 1153-1172 ◽

Cited By ~ 1

Author(s):

Georgia Ward-Fear ◽

Gregory P. Brown ◽

Richard Shine

Keyword(s):

Taste Aversion ◽

Individual Variation ◽

Opportunity To Learn ◽

Population Persistence ◽

Wild Populations ◽

Rhinella Marina ◽

Behavioural Responses ◽

Invasive Prey ◽

Threatening Processes ◽

Free Ranging

Abstract Within all wild populations, individuals vary in ways that affect their vulnerability to threatening processes. Understanding that variation may clarify mechanisms of population persistence and/or evolution. In Australia, Yellow-spotted Monitors (Varanus panoptes), decline by >90% when toxic Cane Toads (Rhinella marina) invade an area. Taste-aversion training (exposing animals to non-lethal toads) can buffer impacts; but does pre-existing behavioural variation also influence survival? An individual’s fate can be predicted from its behaviour during aversion-training trials. Lizards presented with small toads either consumed them, rejected them, or fled. When Cane Toads invaded our study site, mortality was lower in lizards that ‘consumed’ (aversion-trained) than in those that ‘fled’ (untrained), but even lower in lizards that ‘rejected’ toads outright. Thus, animals reluctant to consume toads in trials survived despite never being aversion-trained. In this system, lizard vulnerability is driven by boldness, behavioural responses to novel prey types, and the opportunity to learn aversion.

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Spatial ecology of cane toads (Rhinella marina) in their native range: a radiotelemetric study from French Guiana

Scientific Reports ◽

10.1038/s41598-021-91262-8 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Jayna L. DeVore ◽

Richard Shine ◽

Simon Ducatez

Keyword(s):

Invasive Species ◽

Body Condition ◽

Spatial Ecology ◽

French Guiana ◽

Source Region ◽

Behavioural Flexibility ◽

Native Range ◽

Environmental Niche ◽

Rhinella Marina ◽

Free Ranging

AbstractLike most invasive species, cane toads have attracted less research in their native range than in invaded areas. We radio-tracked 34 free-ranging toads in French Guiana, a source region for most invasive populations, across two coastal and two rainforest sites. Coastal toads generally sheltered in pools of fresh or brackish water but nocturnally foraged on beaches, whereas rainforest toads sheltered in forested habitats, moving into open areas at night. Over five days of monitoring, native toads frequently re-used shelters and moved little between days (means = 10–63 m/site) compared to invasion-front toads from Australia (~ 250 m). Larger toads moved less between days, but displaced in more consistent directions. At night, foraging toads travelled up to 200 m before returning to shelters. Foraging distance was related to body condition at coastal sites, with toads in poorer body condition travelling farther. Rain increased the probability of coastal toads sheltering in the dry habitats where they foraged. Dispersal and rainfall were lower at coastal sites, and the strategies utilized by coastal toads to minimize water loss resembled those of invasive toads in semi-desert habitats. This global invader already exhibits a broad environmental niche and substantial behavioural flexibility within its native range.

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