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Expansion of global commerce has facilitated pathogen pollution via the transportation and translocation of invasive species and their associated parasites and pathogens. In Florida, imported cane toads ( Rhinella horribilis ) were accidentally and intentionally released on multiple occasions. Early populations were found to be infested with the invasive tick, Amblyomma rotundatum , yet it is unknown if these ticks dispersed with their hosts as cane toads spread throughout much of the state. The objectives of our investigation were to (1) determine if there are fewer tick infestations on toads at the periphery than at the core of their distribution as predicted by founder effect events, and (2) identify if ticks were infected with exotic pathogens. We captured toads from 10 populations across Florida. We collected ticks, vent tissue, and tick attachment site tissue from each toad, then tested samples for bacteria in the genus, Rickettsia . We found that 3/10 populations had toads that were infested with A. rotundatum , and infested individuals were in the earliest introduced populations at the core of their distribution. Pathogen testing confirmed Rickettisa bellii in ticks, but not in toad tissues. Haplotype networks could not clearly distinguish if R. bellii in Florida was more closely related to North or South American strains, but host-tick associations suggest that the pathogen was exotic to Florida. Our investigation demonstrated that an invasive species facilitated the introduction of parasites and pathogens into Florida, yet the invasive tick species encountered limitations to dispersal on this host species.

In response to novel environments, invasive populations often evolve rapidly. Standing genetic variation is an important predictor of evolutionary response but epigenetic variation may also play a role. Here, we use an iconic invader, the cane toad ( Rhinella marina ), to investigate how manipulating epigenetic status affects phenotypic traits. We collected wild toads from across Australia, bred them, and experimentally manipulated DNA methylation of the subsequent two generations (G1, G2) through exposure to the DNA methylation inhibitor zebularine and/or conspecific tadpole alarm cues. Direct exposure to alarm cues (an indicator of predation risk) increased the potency of G2 tadpole chemical cues, but this was accompanied by reductions in survival. Exposure to alarm cues during G1 also increased the potency of G2 tadpole cues, indicating intergenerational plasticity in this inducible defence. In addition, the negative effects of alarm cues on tadpole viability (i.e. the costs of producing the inducible defence) were minimized in the second generation. Exposure to zebularine during G1 induced similar intergenerational effects, suggesting a role for alteration in DNA methylation. Accordingly, we identified intergenerational shifts in DNA methylation at some loci in response to alarm cue exposure. Substantial demethylation occurred within the sodium channel epithelial 1 subunit gamma gene ( SCNN1G ) in alarm cue exposed individuals and their offspring. This gene is a key to the regulation of sodium in epithelial cells and may help to maintain the protective epidermal barrier. These data suggest that early life experiences of tadpoles induce intergenerational effects through epigenetic mechanisms, which enhance larval fitness. This article is part of the theme issue ‘How does epigenetics influence the course of evolution?’

Accurate forecasts of biological invasions are crucial for managing invasion risk but are hampered by niche shifts resulting from evolved environmental tolerances (fundamental niche shifts) or the presence of novel biotic and abiotic conditions in the invaded range (realized niche shifts). Distinguishing between these kinds of niche shifts is impossible with traditional, correlative approaches to invasion forecasts, which exclusively consider the realized niche. Here we overcome this challenge by combining a physiologically mechanistic model of the fundamental niche with correlative models based on the realized niche to study the global invasion of the cane toad Rhinella marina . We find strong evidence that the success of R . marina in Australia reflects a shift in the species’ realized niche, as opposed to evolutionary shifts in range-limiting traits. Our results demonstrate that R. marina does not fill its fundamental niche in its native South American range and that areas of niche unfilling coincide with the presence of a closely related species with which R. marina hybridizes. Conversely, in Australia, where coevolved taxa are absent, R. marina largely fills its fundamental niche in areas behind the invasion front. The general approach taken here of contrasting fundamental and realized niche models provides key insights into the role of biotic interactions in shaping range limits and can inform effective management strategies not only for invasive species but also for assisted colonization under climate change.

The process of rapid range expansion (as seen in many invasive species, and in taxa responding to climate change) may substantially disrupt host–parasite dynamics. Parasites and pathogens can have strong regulatory effects on their host population and, in doing so, exert selection pressure on host life history. We construct a simple individual‐based model of host–parasite dynamics during range expansion. This model shows that the parasites and pathogens of a range‐expanding host are likely to be absent from the host's invasion front, because stochastic events (serial founder events) in low‐density frontal populations result in local extinctions or transmission failure of the parasite/pathogen and, hence, a preponderance of uninfected hosts in the invasion vanguard. This pattern is true for both density‐dependent and density‐independent transmission rates, although it is exacerbated in the case of density‐dependent transmission because, in this case, transmission rates also decline on the front. Data from field surveys on the prevalence of lungworms (Rhabdias pseudosphaerocephala) in invasive cane toads (Bufo marinus) support these predictions, in showing that toads in newly invaded areas of tropical Australia lack the parasite, which only arrives 1–3 years after the toads themselves. The resultant “honeymoon phase” immediately post‐invasion, when individuals in the invasion‐front population are virtually pathogen‐free, may lead to altered host population dynamics on the invasion front, causing, for example, high densities in invasion‐front populations, followed by a decline in numbers as parasites and pathogens arrive and begin to reduce host viability. The honeymoon phase may ultimately impact the evolution of life‐history investment strategies in both host and parasite on the invasion vanguard, as hosts are released from immune challenges and parasites continuously expand into a favorable and unoccupied niche.

Background Amphibian defence against predators and microorganisms is directly related to cutaneous glands that produce a huge number of different toxins. These glands are distributed throughout the body but can form accumulations in specific regions. When grouped in low numbers, poison glands form structures similar to warts, quite common in the dorsal skin of bufonids (toads). When accumulated in large numbers, the glands constitute protuberant structures known as macroglands, among which the parotoids are the most common ones. This work aimed at the morphological and biochemical characterization of the poison glands composing different glandular accumulations in four species of toads belonging to group Rhinella marina ( R. icterica , R. marina , R. schneideri and R. jimi ). These species constitute a good model since they possess other glandular accumulations together with the dorsal warts and the parotoids and inhabit environments with different degrees of water availability. Results We have observed that the toads skin has three types of poison glands that can be differentiated from each other through the morphology and the chemical content of their secretion product. The distribution of these different glands throughout the body is peculiar to each toad species, except for the parotoids and the other macroglands, which are composed of an exclusive gland type that is usually different from that composing the dorsal warts. Each type of poison gland presents histochemical and biochemical peculiarities, mainly regarding protein components. Conclusions The distribution, morphology and chemical composition of the different types of poison glands, indicate that they may have different defensive functions in each toad species.

A new semiarboreal species of the group is described from montane forests of the Cordillera Azul National Park between 1245 and 1280 m a.s.l. in the Cordillera Oriental, San Martín region, northern Peru. The new species is morphologically and genetically compared with members of the group (former genus ) and members of the group. The new species is characterized by its large size (female SVL 47.1-58.3 mm, n = 4), eight presacral vertebrae, fusion of the sacrum and coccyx, long protuberant snout, snout directed slightly anteroventral in lateral view, cranial crests moderately developed, absence of occipital crest, presence of tympanic membrane, dorsolateral rows of small conical tubercles extending from parotoid gland to groin, hands and feet with long digits, fingers basally webbed and toes moderately webbed. Phylogenetically it is a member of the group which is most closely related to and from Peru. Morphologically the new species shares similarities with and , members of the group from Colombia.

Invasions 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.

Anthropogenic activities may generate significant changes in the integrity of aquatic ecosystems, so long-term monitoring of populations that inhabit them is crucial. Counting micronucleated erythrocytes (MN) and erythrocytic nuclear abnormalities (ENA) in peripheral blood is a widely used method for detecting chromosomal damage due to chemical agents in the water. We analyzed MN and ENA frequency in blood obtained from the common toad Rhinella arenarum populations in sites with different degrees of environmental degradation. The results of this study indicate that there is an association between the frequency of micronuclei and nuclear abnormalities and the degree of environmental alteration recorded for the sites studied.

In invasive species, geographically variable evolutionary and ecological pressures can cause the rapid evolution of divergent behavioural phenotypes. Studies on invasive cane toads (Rhinella marina) in tropical Australia have revealed strong (and heritable) shifts in physiological traits related to dispersal rate. Behavioural phenotypes may have evolved in similar ways. We used standardised arena trials to test field-collected adult female toads from three populations: a range-core area in Queensland (ca.76 years post-colonisation), a range-front population in Western Australia (<5 years post-colonisation) and an intermediate Northern Territory population (11 years postcolonisation). As predicted, toads from the range-front population were more exploratory and more likely to take risks in a novel arena environment than were conspecifics from the range-core population. We suggest that differential selection on behavioural responses to novel conditions in range-core versus range-front populations has produced a distinctive behavioural phenotype at the range-front that retains a high propensity for exploration and risk-taking (enhancing the ability of range-front toads to locate food and shelter) even when faced with novel environments. In contrast, at the range core where the locations of resources are known, a decrease in exploration and risktaking in response to a novel environment may be favoured as it assists toads in evading threats.

Our best hope of developing innovative methods to combat invasive species is likely to come from the study of high-profile invaders that have attracted intensive research not only into control, but also basic biology. Here we illustrate that point by reviewing current thinking about novel ways to control one of the world’s most well-studied invasions: that of the cane toad in Australia. Recently developed methods for population suppression include more effective traps based on the toad’s acoustic and pheromonal biology. New tools for containing spread include surveillance technologies (e.g., eDNA sampling and automated call detectors), as well as landscape-level barriers that exploit the toad’s vulnerability to desiccation— a strategy that could be significantly enhanced through the introduction of sedentary, rangecore genotypes ahead of the invasion front. New methods to reduce the ecological impacts of toads include conditioned taste aversion in free-ranging predators, gene banking, and targeted gene flow. Lastly, recent advances in gene editing and gene drive technology hold the promise of modifying toad phenotypes in ways that may facilitate control or buffer impact. Synergies between these approaches hold great promise for novel and more effective means to combat the toad invasion and its consequent impacts on biodiversity.