Invasive species as drivers of evolutionary change: cane toads in tropical Australia PMC

For example, mammal abundance may vary seasonally and differ among years, depending upon rainfall patterns [35], so that we may have failed to detect small mammals even when they were episodically abundant. The near-extirpation of large varanids induces mesopredator release, with potential impacts on smaller prey [6]. Hence, invasive toads may indirectly depress prey availability for varanids, via trophic cascades–exacerbating the dramatic reduction in prey resources caused by the disappearance of small mammals across most of tropical Australia [2, 61]. Despite logistical advantages (a fragmented invasion front, a significantly higher human population, and infrastructure that facilitates research), the impact of cane toads in southern Australia has been largely ignored. We conducted surveys to quantify the characteristics of native faunal assemblages in adjacent sites that contained versus those that did not contain cane toads to test what impact toads have on fauna assemblages.

Why are we seeing ‘supercharged thunderstorms’ in Australia?

The population includes individuals with a range of personality types that influence behavioural decisions taken in the presence of conspecifics, a pattern that is detectable due to the high densities attained in the area. Perhaps the most surprising and non-intuitive result of our study is to suggest a degree of cryptic sociality in an animal (the cane toad) that we would not have expected to show such disparities in individual responses to social cues. In turn, that result suggests that it will be worth conducting simple experiments to look for similar complexity in other invasive and non-invasive species of ectothermic vertebrates. In addition, differences in morphological traits between juveniles and adults of the invasive cane toad due to ontogenetic allometry could lead to similar morphological niches in juvenile cane toad and adult or juvenile specimens of some Australian species. Thus, this life cycle complexity could result in a niche overlap between cane toad and Australian frogs across different life cycle stages, negatively impacting native species.

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The availability of alternative prey may have been reduced by the decline of small mammals, likely due to feral predators (especially cats), agricultural practices, and modified fire regimes [59]. Also, the latter factors may have affected populations of varanid lizards, independent of the impacts of cane toads. The location and timing of resource availability can greatly impact an animal’s vulnerability to threatening ecological processes [58]. In this case, the invasive (toxic) cane toad may be one of the few large prey items available to yellow-spotted monitors at some times of year–especially, since the decline of small mammals across most of the range of this varanid species [2, 59–61].

Are cane toads harmful to humans, pets? Your questions answered

Both lace monitors and water dragons are widely sympatric with cane toads in Australia (Lever 2001; Wilson and Swan 2013), so the lack of prior reports of toad impact on these taxa is surprising. For east coast sites, each survey consisted of a 15-min active search on foot around focal campsites (areas to which lace monitors are attracted) [16], and a 45-min search along a 5-km transect in a vehicle (paved and unpaved roads were used for transects). Morning surveys commenced sobriety strategies from 0900 to 1200 h, afternoon surveys from 1200 to 1800 h, and nocturnal surveys from 1800 to 0100 h. In tropical Australia, yellow-spotted monitors are most active on relatively cool mornings [33]. Accordingly, at the twenty-four sites in our northern transect, morning surveys consisted of a 1-h active search on foot along a 2 km transect adjacent to focal wetlands, lakes, rivers, creeks, billabongs and floodplains (areas frequented by yellow-spotted monitors) 33.

Carrion removal trials

The largely complete fossil of a roughly 18-year-old Stone Age woman was found in 2015, buried in the fetal position in a limestone cave. DNA extracted from the skull suggests that she shared ancestry with New Guineans and Aboriginal Australians, as well with the extinct Denisovan species of ancient human. The Toalean people, known only from scant archaeological evidence, such as distinctively notched stone tools, were thought to have lived in Sulawesi at around the same time. For librarians and administrators, your personal account also provides access to institutional account management. Here you will find options to view and activate subscriptions, manage institutional settings and access options, access usage statistics, and more. Typically, access is provided across an institutional network to a range of IP addresses.

  1. DNA extracted from the skull suggests that she shared ancestry with New Guineans and Aboriginal Australians, as well with the extinct Denisovan species of ancient human.
  2. That focus may have drawn public attention away from feral species impacts, but it is difficult to understand why scientific efforts were equally scarce.
  3. One grid was placed in bushland adjacent to the focal campground and a second grid established in bushland 2 km away.
  4. As sites differed in extent (see Supporting Information for Table S1), survey effort was standardized (1 h/survey).

The mechanistic explanation for this difference remains to be explored, but our observations suggest that activity levels may be important. They thus emerged from shelters sooner, and seized the first prey item sooner – but before long, began to move about the container apparently attempting to escape. Thus, ‘bold’ toads appeared to rapidly lose interest in feeding, and shift their attention to escaping. In contrast, the more sedentary ‘shy’ toads emerged later, but then settled into feeding without attempting to escape. This pattern may reflect the less active behaviour of shy toads, which allowed them (under our experimental settings) to focus on stimuli from the prey and as a consequence consume more prey.

Mitochondrial (12s and 16s) sequence data were obtained from Rosauer, Laffan, Crisp, Donnellan, and Cook (2009), CJ Hoskin et al. (in prep), JS Keogh, D Moore, PG Byrne, DJ Roberts (in prep), and Pyron (2014), in order to generate a Bayesian phylogenetic tree (Figure S1). Because our goal was not to infer a new phylogeny, we constrained our analyses to ensure the resultant topology did not differ from previously published phylogenetic analyses of the individual families. The phylogeny was highly consistent with Pyron’s (2014) assessment of the phylogenetic history of the World’s amphibians. We evaluated the magnitude of phylogenetic signal in multivariate data in the morphological and environmental variables using Blomberg’s K statistic’s generalization for multivariate data (Kmult; Adams, 2014a) with geomorph (Adams & Otárola‐Castillo, 2013). We performed a phylogenetic ANOVA for both univariate and multivariate data in geomorph (Adams, 2014b), to test whether phylogeny affected morphological traits, environmental variables, and RLLR.

Firstly, monitoring efforts of cane toads’ western and southern advance have increased over the last 30 years, and precise arrival dates were known for 19 of the most recently invaded sites. Based on the known distribution of toads we selected 11 toad-free sites presumed to be beyond the current known invasion distribution, and conducted extensive surveys (both prior to and during our experimental protocol) to confirm toad absence. However, the 15 sites in Queensland with the longest periods of toad occupation pre-date studies of the ecological impact of cane toads in Australia, and the precise timing of toad colonisation was unknown. Human‐mediated introduction of non‐native species to new habitats has occurred for thousands of years (di Castri, Hansen, & Debussche, 1990). Most of the time the introduction fails, but occasionally a species will establish and become invasive.

The work was funded by the Australian Research Council (grant number FF561365), the Mexican National Science and Technology Council (CONACyT) and the University of Sydney. The funders had no role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. Their high tolerance to saline waters (Lever 2001) may have given rise to their specific scientific is it possible to get sober without aa name Rhinella marina and common name of marine toad (Lever 2001). From cuddly companions to realistic native Australian wildlife, the range also includes puppets that move and feel like real animals. Almost half of these species are listed as vulnerable, endangered or critically endangered. We have also demonstrated the promise of our technique for conservation challenges globally.

Remarkably, even anecdotal reports of cane toad impacts are rare in southern Australia, despite the dense human population. Nonchalance among the general public appears to have had flow‐on effects for political and research priorities. Although most taxa were unaffected, toads appear to have caused catastrophic declines in populations of four reptile taxa in temperate Australia. The three lizard species affected have not been studied previously in this respect, but toad‐induced declines in red‐bellied blacksnakes have been reported (Pockley 1965; Rayward 1974), based on anecdotal evidence (but see Seabrook 1993).

Furthermore, a lack of natural predators in the invaded areas (Letnic et al., 2008; Shine, 2010), coupled with a fitness advantage (MacDougall et al., 2009) and their lethal toxicity (Letnic et al., 2008), could dramatically favor invasiveness of the cane toad. In addition, the cane toad is the only member of the bufonid family in Australia and is thus very distantly related to native Australian species. Invasive species that are phylogenetically distant from endemic species will be more successful, due to greater niche differentiation and decreased predation (MacDougall et al., 2009; Strauss, Webb, & Salamin, 2006). Thus, due to this taxonomic discordance, Australia might offer lower resistance to alien invasive species than continental regions, by providing the opportunity to invaders to fill an empty niche (Le Breton, Jourdan, Chazeau, Orivel, & Dejean, 2005; Shea & Chesson, 2002; Simberloff, 1995).

Human Health– The large paratoid glands of Cane Toads contain a milky poison (bufotoxins), and humans can become sick or even die from consuming cane toads or their eggs (Lever 2003). Cane Toad toxicity scales with body size – larger toads are consequently much more toxic than small toads. Larger predators (large lizards, snakes, crocodiles, and mammals that tear apart prey) are therefore at greater risk of poisoning (Shine 2010).

Any predator that tries to eat an adult cane toad is likely to die a quick and painful death. In particular, monitor lizards – once abundant across the Australian tropics – have virtually been wiped out. The parallel effects on invaders and natives of biotic interactions are more clear-cut and may influence establishment success (Strauss et al. 2006b; Tingley et al. 2011) as well as subsequent adaptive shifts (Langkilde 2009). Either or both the invader and the native may be affected by competition, predation, herbivory, toxic ingestion, pathogen transfer, or hybridization between taxa (Fig. 1). The nature of a native taxon’s ecological relationship with the invader will necessarily modify the nature of impact. As Carroll (2008, p. 361) notes, ‘both opportunity and catastrophe generate adaptive responses’.

Accordingly, yellow-spotted monitors now have a listing of ‘Vulnerable’ across some jurisdictions (e.g., Northern Territory). Nonetheless, yellow-spotted monitors are common in some toad-colonised sites close to the areas where toads were first released [21]. No previous studies have quantified patterns of varanid abundance over the long timeframe of toad occupation in Australia, although there are several studies with data on short-term trajectories have a problem with alcohol of varanid abundance after toad invasion [19, 37]. We performed ANOVAs and post hoc pairwise comparisons using Dunnett’s tests as well as for the first two environmental PCs, in order to assess which clades were significantly different to the cane toad. These analyses depicted differences in niche position between Australian frog clades and the cane toad, based on environmental values from the whole geographic distribution of each species.

The consequent explosion of information on evolutionary aspects of biological invasions has attracted several excellent reviews (e.g., Thompson 1998; Mooney and Cleland 2001; Cox 2004; Lambrinos 2004; Strauss et al. 2006b; Sax et al. 2007; Vellend et al. 2007; Buswell et al. 2011; Westley 2011). It is clear that evolutionary change can occur rapidly (Reznick and Ghalambor 2001; Hairston et al. 2005; Carroll et al. 2007; Hendry et al. 2008) and can modify traits both in invaders and in the taxa with which they interact. Understanding such topics may provide a basis for novel approaches to controlling the invader, or mitigating its impact, for example, we may be able to identify and exploit adaptive trade-offs and evolutionary traps to curtail invader numbers (Ward-Fear et al. 2010; Lankau and Strauss 2011). In this review, I will examine ideas and evidence on the evolutionary consequences of biological invasions, with a strong focus on one study system – the invasion of cane toads through tropical Australia.