Bufo Marinus Research Articles

Is developmental plasticity triggered by DNA methylation changes in the invasive cane toad (Rhinella marina)?

Many organisms can adjust their development according to environmental conditions, including the presence of conspecifics. Although this developmental plasticity is common in amphibians, its underlying molecular mechanisms remain largely unknown. Exposure during development to either 'cannibal cues' from older conspecifics, or 'alarm cues' from injured conspecifics, causes reduced growth and survival in cane toad (Rhinella marina) tadpoles. Epigenetic modifications, such as changes in DNA methylation patterns, are a plausible mechanism underlying these developmental plastic responses. Here we tested this hypothesis, and asked whether cannibal cues and alarm cues trigger the same DNA methylation changes in developing cane toads. We found that exposure to both cannibal cues and alarm cues was associated with local changes in DNA methylation patterns. These DNA methylation changes affected genes putatively involved in developmental processes, but in different genomic regions for different conspecific-derived cues. Genetic background explains most of the epigenetic variation among individuals. Overall, the molecular mechanisms triggered by exposure to cannibal cues seem to differ from those triggered by alarm cues. Studies linking epigenetic modifications to transcriptional activity are needed to clarify the proximate mechanisms that regulate developmental plasticity in cane toads.

Whole-mitogenome analysis unveils previously undescribed genetic diversity in cane toads across their invasion trajectory.

Invasive species offer insights into rapid adaptation to novel environments. The iconic cane toad (Rhinella marina) is an excellent model for studying rapid adaptation during invasion. Previous research using the mitochondrial NADH dehydrogenase 3 (ND3) gene in Hawai'ian and Australian invasive populations found a single haplotype, indicating an extreme genetic bottleneck following introduction. Nuclear genetic diversity also exhibited reductions across the genome in these two populations. Here, we investigated the mitochondrial genomics of cane toads across this invasion trajectory. We created the first reference mitochondrial genome for this species using long-read sequence data. We combined whole-genome resequencing data of 15 toads with published transcriptomic data of 125 individuals to construct nearly complete mitochondrial genomes from the native (French Guiana) and introduced (Hawai'i and Australia) ranges for population genomic analyses. In agreement with previous investigations of these populations, we identified genetic bottlenecks in both Hawai'ian and Australian introduced populations, alongside evidence of population expansion in the invasive ranges. Although mitochondrial genetic diversity in introduced populations was reduced, our results revealed that it had been underestimated: we identified 45 mitochondrial haplotypes in Hawai'ian and Australian samples, none of which were found in the native range. Additionally, we identified two distinct groups of haplotypes from the native range, separated by a minimum of 110 base pairs (0.6%). These findings enhance our understanding of how invasion has shaped the genetic landscape of this species.

Cryptic diversity in toads of the Rhinella marina species group (Anura, Bufonidae) with a subjectively beautiful new species from Western Ecuador

Abstract The mainly Mesoamerican cane toad, Rhinella horribilis, is the northernmost species in the Rhinella marina species group of giant or cane toads, occupying an extensive range west of the Andean Cordillera from Ecuador north to southern Texas. However, a thorough assessment of geographic variation among R. horribilis populations, and of the phylogenetic relationships of the R. marina species complex, indicates previously unsuspected diversity within this species as currently recognized. Specifically, we evaluated whether toad populations from western Ecuador represent an evolutionary lineage distinct from the rest of R. horribilis based on extensive specimen collections and the combined evidence of mtDNA sequence variation, morphological, bioacoustics, and environmental information. Our results revealed that populations west of the Ecuadorian Andes constitute a well-supported, monophyletic clade that is distinctly different genetically, morphologically, acoustically, and ecologically from a sister taxon composed of R. horribilis populations from Central America and from populations ascribable to R. marina s.s. from the Amazon Basin of Ecuador and other countries. The weight of evidence confirms a new species (R. bella sp. nov.), described here, adding to our understanding of biogeographic relationships in this widespread clade of Neotropical toads. The new species name means ‘beautiful’ in Latin, in contrast to its sister species, ‘horribilis’. In addition, we designate a lectotype for Bufo marinus var. fluminensis to avoid ambiguity in the applicability of that name.

A biological invasion modifies the dynamics of a host-parasite arms race.

By imposing novel selection pressures on both participants, biological invasions can modify evolutionary 'arms races' between hosts and parasites. A spatially replicated cross-infection experiment reveals strong spatial divergence in the ability of lungworms (Rhabdias pseudosphaerocephala) to infect invasive cane toads (Rhinella marina) in Australia. In areas colonized for longer than 20 years, toads are more resistant to infection by local strains of parasites than by allopatric strains. The situation reverses at the invasion front, where super-infective parasites have evolved. Invasion-induced shifts in genetic diversity and selective pressures may explain why hosts gain advantage over parasites in long-colonized areas, whereas parasites gain advantage at the invasion front.

Mechanisms, costs, and carry-over effects of cannibal-induced developmental plasticity in invasive cane toads.

Inducible defences can improve survival in variable environments by allowing individuals to produce defences if they detect predators. These defences are often expressed as inter-related developmental, morphological, and behavioural changes. However, producing defences can incur costs, which may be expressed immediately and/or during subsequent life stages. In Australia, waterborne cues of potentially cannibalistic conspecific tadpoles induce hatchlings of invasive cane toads to accelerate their developmental rate, thereby reducing their window of vulnerability. However, the mechanisms and costs of such accelerated development are poorly understood, and whether cane toad embryos show cannibal-induced plasticity in other traits is unknown. Here, we found no evidence of altered time of hatching for embryos exposed to non-feeding conspecific cannibal tadpole cues. Additionally, hatchling dispersal behaviours were not affected by exposure to these cues. However, developmental acceleration of hatchlings induced by exposure to tadpole cues was accompanied by reduced hatchling growth, indicating a trade-off between these processes. At the conclusion of the hatchling stage, cannibal-exposed individuals were smaller and morphologically distinct from control siblings. This size reduction affected performance during the subsequent tadpole stage: smaller cannibal-exposed individuals were more likely to die, and initial size tended to be positively associated with subsequent tadpole growth and development across treatments (respectively, p = .07 and p = .06). However, even accounting for variation in initial size, there was an additional negative effect of cannibal exposure on tadpole growth and development, demonstrating that the fitness costs associated with developmental acceleration are not entirely attributable to size reductions.

Unlocking the biosynthesis of psychedelic-inspired indolethylamines

A recent report by Chen et al. describes the discovery of RmNMT, a highly active and promiscuous tryptamine N-methyltransferase from the cane toad, Rhinella marina. N,N-dimethyltryptamine derivatives produced by this enzyme were then evaluated for their potential to serve as next-generation treatments for mental health disorders.

The reduction in arterial pH with increased temperature is not affected by hyperoxia in toads (Rhinella marina) and pythons (Python molurus).

It is well established that arterial pH decreases with increased temperature in amphibians and reptiles through an elevation of arterial PCO2, but the underlying regulation remains controversial. The alphastat hypothesis ascribes the pH fall to a ventilatory regulation of protein ionisation, but the pH reduction with temperature is lower than predicted by the pKa change of the imidazole group on histidine. We hypothesised that arterial pH decreases at high, but not at low, temperatures when toads (Rhinella marina) and snakes (Python molurus) are exposed to hyperoxia. In toads, hyperoxia caused similar elevations of arterial PCO2at 20 and 30°C, indicative of a temperature-independent oxygen-mediated drive to breathing, whereas PCO2was unaffected by hyperoxia in snakes at 25 and 35°C. These findings do not support our hypothesis of an increased oxygen-mediated drive to breathing as body temperature increases.

Parasitic helminths of alien invasive anurans in Butuan City, Northeastern Mindanao, Philippines.

This study aimed to identify the helminth parasites of invasive anuran species in selected barangays in Butuan City, Philippines. In urbanized areas, invasive species dominate anuran diversity, and one of the primary threats they pose to native wildlife is the transmission of diseases and parasites. Out of the 91 collected individuals of invasive anuran species, Rhinella marina was the most abundant (88 %), followed by Hoplobatrachus rugulosus (12 %) and Kaloula pulchra (3 %). The study identified five species of parasites, with Spirometra sp. being the most prevalent (17.58 %), followed by Echinostoma sp. (16.5 %), Rhabdias bufonis (14.3 %), Cosmocerca sp. (6.6 %), and Strongyloides stercoralis (3.30 %), respectively. Spirometra sp. also had the highest intensity (7.67), followed by Cosmocerca sp. (5), Strongyloides stercoralis (3.33), Rhabdias bufonis (3.30), and Echinostoma sp. (2.73). This parasitological survey revealed that H. rugulosus had the highest prevalence and infection of parasites, and residential areas had the highest parasite prevalence among the habitat types. Adult hosts were found to harbor a higher prevalence and intensity, and male hosts had a higher prevalence. The results highlight the high risk of parasite transmission from anurans to other animals and emphasize the need for the community to control the population of invasive anuran species for the safety of native anurans and to prevent zoonotic transmission to other animals and humans.

A Comprehensive Update on Helminth Parasite Biodiversity and Richness in Peruvian Amphibians

This study aimed to comprehensively update and expand the knowledge on the diversity and richness of helminth parasites found in Peruvian amphibians. A systematic search was conducted across primary databases, encompassing both indexed and non-indexed articles, to compile the most recent data. As of the present study, a total of 83 distinct helminth taxa have been documented in association with 78 anuran species of the order Anura, marking a 176.7% increase from previously recorded figures. Nematodes exhibited the highest species richness, totalling 52 taxa (62.65%), followed by trematodes (21 taxa, 25.3%), acanthocephalans and cestodes (4 taxa each, 4.8%), and monogeneans (2 taxa, 2.4%). The overwhelming majority (85.5%) of the collected parasites (71 taxa) were identified as mature helminths, with the remaining 14.5% (12 taxa) in their larval stages. Notably, Cosmocerca brasiliense Travassos, 1925 (Cosmocercidae), and Physaloptera sp. (Physalopteridae) were the most prevalent nematodes, having infected the broadest range of host species. Rhinella marina Linnaeus, 1758 (Bufonidae), emerged as the anuran host with the highest diversity, harboring 17 distinct helminth species. These findings underscore the crucial role of helminth parasites in shaping amphibian ecosystems and their significance as bioindicators of environmental health. Protecting both amphibian hosts and their associated helminth parasites is paramount, as it is intrinsically linked to the preservation of ecological equilibrium within these ecosystems.

Intraspecific interference retards growth and development of cane toad tadpoles, but those effects disappear by the time of metamorphosis.

Competition among larval anurans can occur via interference as well as via a reduction in per-capita food supply. Previous research on intraspecific interference competition in cane toad (Rhinella marina) tadpoles found conflicting results, with one study detecting strong effects on tadpoles and another detecting no effects on metamorphs. A capacity to recover from competitive suppression by the time of metamorphosis might explain those contrasting impacts. In a laboratory experiment, we found that nine days of exposure to intraspecific interference competition strongly reduced tadpole growth and development, especially when the competing tadpoles were young (early-stage) individuals. Those competitive effects disappeared by the time of metamorphosis, with no significant effect of competition on metamorph body condition, size, larval period or survival. Temporal changes in the impact of competition were not related to tadpole density or to variation in water quality. The ability of larval cane toads to recover from intraspecific interference competition may enhance the invasive success of this species, because size at metamorphosis is a significant predictor of future fitness. Our study also demonstrates a cautionary tale: conclusions about the existence and strength of competitive interactions among anuran larvae may depend on which developmental stages are measured.

Thimet oligopeptidase (THOP 1) distribution in cane toad (Bufo Marinus, Linnaeus, 1758) brain

Thimet oligopeptides (THOP 1) is a metal-dependent peptidase involved in the metabolism of neuropeptides and the presentation of peptides via MHC-1. It has been shown to play a role in the regulation of protein-protein interactions and the metabolism of intracellular peptides. THOP 1 is associated with important biological processes such as metabolism and neurodegenerative diseases, among others. The objective of this study is to elucidate the distribution of THOP 1 in the Bufo marinus brain. The analysis of THOP 1 amino acid sequences indicates that they have been conserved throughout evolution, with significant homology observed across various phyla. When comparing amphibians with other species, more than 70% identity can be identified. Immunohistochemistry analysis of the toad's brain has demonstrated that the enzyme has a ubiquitous distribution, consistent with previous findings in mammals. THOP 1 can be found in important areas of the brain, such as bulb, thalamic nuclei, striatum, hypothalamus, and among others. Nonetheless, THOP 1 is consistently localized within the nucleus, a pattern also observed in the rat brain. Therefore, based on these results, the toad appears to be an excellent model for studying the general biology of THOP 1, given the substantial homology of this enzyme with mammals and its similarity in distribution within the brain.

Levels of persistent organic pollutants in cane toads (Rhinella marina) differ among sites with varying industrial and agricultural activities

In this study, we captured cane toads (Rhinella marina) in four sites located in different regions affected by anthropogenic activities in Mexico. Subsequently we analyzed liver tissue for the presence of organochlorine pesticides (OCs) and polychlorinated biphenyls (PCBs) The levels of these POPs in the toads’ livers ranged from 863.2 to 3109.6 ng/g of lipid weight across all sites. A multivariate statistical analysis highlighted two sites with the highest POPs levels, with the most polluted site displaying a high level of PCBs, suggesting influence of industrial activities. The second most polluted site displayed significant amounts of OCs, linking this location to agricultural activity. Additionally, we found pesticide metabolites and isomers that allowed us to distinguish past and recent exposure events. Our observations indicate that R. marina is suitable bioindicator of sites impacted by anthropogenic activities.

A new approach to contactless probing of vital signs

Vital sign detection is used across ubiquitous scenarios in medical and health settings and contact and wearable sensors have been widely deployed. Contactless detection can be achieved using camera imaging, but it is susceptible to ambient light conditions along with privacy concerns. This brief report appraises a photonic radar for non-contact vital sign detection. The high resolution of the radar system enables accurate respiratory detection from breathing simulators and a cane toad as a human proxy. This could cater for contactless and high-resolution vital sign detection to meet the increasing demands of future medical and healthcare applications.

Faunal Diet of Adult Cane Toads, Rhinella marina, in the Urban Landscape of Southwest Florida.

We investigated the diet of cane toads (Rhinella marina) inhabiting urbanized areas in southwest Florida to provide high taxonomic resolution of prey items, contrast toad diets between sampling seasons and sexes, and assess this invasive species' ecological role in the urban landscape. A pest control agency collected cane toads from two golf course communities in Naples, Florida, USA during November-December 2018 (early dry season) and June-July 2019 (early wet season), and faunal stomach contents were quantified from a random subsample of 240 adult toads (30 males and 30 females from each community and season). Yellow-banded millipedes (Anadenobolus monilicornis), big-headed ants (Pheidole spp.), and hunting billbugs (Sphenophorus venatus vestitus) were the most frequently consumed prey items and had the highest total numbers and/or volume with corresponding highest indices of relative importance. There was considerable overlap in the seasonal prey importance values for each golf course community and little if any difference in the importance values between toad sexes in each community. Nonetheless, big-headed ants were the most important prey in both communities during the wet season, while yellow-banded millipedes were the most important dry season prey in one community and hunting billbugs the most important in the other. Despite limited spatiotemporal sampling effort, our results indicated that cane toad was consuming arthropod taxa considered pests in the urban ecosystem. Further studies are needed to investigate the potential effects of human activities and environmental variability on the cane toad diet and to determine whether cane toads act as a biological control for pest populations.

A cane toad (Rhinella marina) N-methyltransferase converts primary indolethylamines to tertiary psychedelic amines

Psychedelic indolethylamines have emerged as potential medicines to treat several psychiatric pathologies. Natural sources of these compounds include 'magic mushrooms' (Psilocybe spp.), plants used to prepare ayahuasca, and toads. The skin and parotid glands of certain toads accumulate a variety of specialized metabolites including toxic guanidine alkaloids, lipophilic alkaloids, poisonous steroids, and hallucinogenic indolethylamines such as DMT, 5-methoxy-DMT, and bufotenin. The occurrence of psychedelics has contributed to the ceremonial use of toads, particularly among Mesoamerican peoples. Yet, the biosynthesis of psychedelic alkaloids has not been elucidated. Herein, we report a novel indolethylamine N-methyltransferase (RmNMT) from cane toad (Rhinella marina). The RmNMT sequence was used to identify a related NMT from the common toad, Bufo bufo. Close homologs from various frog species were inactive, suggesting a role for psychedelic indolethylamine biosynthesis in toads. Enzyme kinetic analyses and comparison with functionally similar enzymes showed that recombinant RmNMT was an effective catalyst and not product inhibited. The substrate promiscuity of RmNMT enabled the bioproduction of a variety of substituted indolethylamines at levels sufficient for purification, pharmacological screening, and metabolic stability assays. Since the therapeutic potential of psychedelics has been linked to activity at serotonergic receptors, we evaluated binding of derivatives at 5-HT1A and 5-HT2A receptors. Primary amines exhibited enhanced affinity at the 5-HT1A receptor compared with tertiary amines. With the exception of 6-substituted derivatives, N,N-dimethylation also protected against catabolism by liver microsomes.

Predation record of Rhinella marina (Linnaeus, 1758) (Anura: Bufonidae) by Cerdocyon thous (Carnivora: Canidae) using camera trap in Vale do Paraíso, Rondonia, Brazil

The crab-eating fox (Cerdocyon thous) is a Neotropical canid with a generalist and opportunistic diet that includes a wide variety of food items. On this note, we report the first record of predation on Rhinella marina by Cerdocyon thous in the state of Rondonia, Brazil, based on camera trap footage. For the state of Rondonia, there is no study reporting the prey of C. thous. Therefore, this report approaches important ecological knowledge of the crab-eating fox, portraying behaviors and diet of the species.

Ecophysiological observations on the body temperatures of the anurans Dendropsophus bifurcus, Rhinella marina, and Scinax ruber from upper basin Amazon in northeastern Ecuador

Ectothermic inhabitants of tropical forests are subjected to constant environmental temperatures, which determine their passive thermoregulatory strategies. We observe these trends during the summer of 2017, in the anurans Dendropsophus bifurcus, Rhinella marina, and Scinax ruber, in a tropical rainforest from the Upper Amazon Basin of Ecuador. D. bifurcus and S. ruber showed a tendency to tigmothermy, whereas R. marina presented tendencies towards heliothermy. Body temperatures (Tbs) did not differ between D. bifurcus and R. marina, but S. ruber presented a lower Tb. Our results suggest that thermal environment is influencing different thermoregulatory strategies as tigmothermy and heliothermy of frogs and toads distributed in tropical environments at low elevation.

Uncommon Diet of the Toad Rhinella marina (Anura: Bufonidae) in a Rural Zone of the Amazon Forest in Brazil

Uncommon Diet of the Toad Rhinella marina (Anura: Bufonidae) in a Rural Zone of the Amazon Forest in Brazil

Long term monitoring reveals the importance of large, long unburnt areas and smaller fires in moderating mammal declines in fire‐prone Savanna of northern Australia

Abstract Biodiversity loss is often attributable to multiple interacting pressures that are moderated across environmental gradients. These processes contribute to complex responses that are challenging to interpret and understand. Well‐designed and well‐implemented monitoring can play a vital role in this but is rarely undertaken. Mounting evidence suggests that current fire regimes across Savanna ecosystems have contributed to the decline of a range of biota. Hence, contemporary fire regimes are at odds with conservation goals. Using an extensive spatiotemporal monitoring dataset from three large National Parks in northern Australia, we applied generalised linear mixed models to examine: (1) trends in mammal richness and abundance through time and variation across environmental gradients such as productivity or landscape position (e.g. terrain ruggedness); and (2) how fire, a potential driver, is moderated by environmental gradients. Across 24 years, major declines in mammal richness and abundance were observed with greater reductions in less rugged and less mesic habitats. Patterns of decline were related to multiple aspects of fire regimes, but not changes in vegetation structure and composition, or cane toads, Rhinella marina, arrival and concomitant poisoning of predatory animals during consumption. More pronounced declines occurred in sites that were exposed to larger fires, had less long unburnt (>5 years without fire) vegetation and were more distant from large, long unburnt patches. Relationships between mammal persistence and fire varied among vegetation communities, with the strongest fire effects observed in lowland woodland—drier with few barriers to fire spread—where the availability of long unburnt areas moderated declines more than in other vegetation communities. Synthesis and applications. Current fire regimes are contributing to mammal declines in northern Australian Savanna. Collectively, our results highlight: (1) the value of long term monitoring, and importance of considering landscape position when assessing faunal responses to landscape‐level perturbations like fire; (2) that significant improvements in fire regimes are required to ameliorate mammal declines; and (3) the need to shift management focus from retaining small, short‐lived unburnt patches toward preserving relatively large contiguous areas of long unburnt habitat, particularly in less rugged lowland and sandstone woodlands.

New species of Foleyellides (Nematoda: Onchocercidae: Waltonellinae), parasite of Lithobates brownorum (Amphibia: Ranidae) from South-eastern Mexico and genetic barcodes of the Mexican species of the genus.

Specimens of Foleyellides were collected from the body cavity of frogs in different regions of Mexico; Lithobates brownorum from Yucatán, Quintana Roo and Campeche; L. megapoda from Jalisco and Rhinella marina, from Guerrero. Foleyellides calakmulesis n. sp. is described based on specimens found parasitizing L. brownorum. The new species is distinguished from the other members of the genus by the combination of the following male characters: four pairs of caudal papillae different in size and the presence of a preanal plaque. Partial DNA sequences of the mitochondrial Cytochrome Oxidase C, subunit I of the four known Mexican species of Foleyellides and two potentially new species collected in this study were generated and compared, validating the erection of the new species.