Where Does All the Poison Go? Investigating Toxicokinetics of Newt (Taricha) Tetrodotoxin (TTX) in Garter Snakes (Thamnophis).

Animals that consume toxic diets provide models for understanding the molecular and physiological adaptations to ecological challenges. Garter snakes (Thamnophis) in western North America prey on Pacific newts (Taricha), which employ tetrodotoxin (TTX) as an antipredator defense. These snakes possess mutations in voltage-gated sodium channels (Nav), the molecular targets of TTX, that decrease the binding ability of TTX to sodium channels (target-site resistance). However, genetic variation at these loci that cannot explain all the phenotypic variation in TTX resistance in Thamnophis. We explored a separate means of resistance, toxin metabolism, to determine if TTX-resistant snakes either rapidly remove TTX or sequester TTX. We examined the metabolism and distribution of TTX in the body (toxicokinetics), to determine differences between TTX-resistant and TTX-sensitive snakes in the rates at which TTX is eliminated from organs and the whole body (using TTX half-life as our metric). We assayed TTX half-life in snakes from TTX-resistant and TTX-sensitive populations of three garter snake species with a coevolutionary history with newts (T. atratus, T. couchii, T. sirtalis), as well as two non-resistant "outgroup" species (T. elegans, Pituophis catenifer) that seldom (if ever) engage newts. We found TTX half-life varied across species, populations, and tissues. Interestingly, TTX half-life was shortest in T. elegans and P. catenifer compared to all other snakes. Furthermore, TTX-resistant populations of T. couchii and T. sirtalis eliminated TTX faster (shorter TTX half-life) than their TTX-sensitive counterparts, while populations of TTX-resistant and TTX-sensitive T. atratus showed no difference rates of TTX removal (same TTX half-life). The ability to rapidly eliminate TTX may have permitted increased prey consumption, which may have promoted the evolution of additional resistance mechanisms. Finally, snakes still retain substantial amounts of TTX, and we projected that snakes could be dangerous to their own predators days to weeks following the ingestion of a single newt. Thus, aspects of toxin metabolism may have been key in driving predator-prey relationships, and important in determining other ecological interactions.

DO Toxic Invasive Prey Become a Toxin Source for Native Consumers?

Toxic organisms can become food that potentially harms consumers. When these organisms become invasive species, the harm often turns to a serious threat that disrupts native ecosystems. On the other hand, there are consumers that can exploit toxic organisms for food and sequester intact toxins from them for the consumers' own chemical defense. Therefore, it can be expected that toxic invasive prey can become a toxin source for native consumers. Here, we focused on the relationship between toads, which are one of the major toxic invasive organisms and possess bufadienolides (BDs), and Rhabdophis snakes, which sequester BDs from toads. On Sado Island, Japan, R. tigrinus is native, but no toads had inhabited this island until Bufo japonicus formosus was introduced as a domestic invasive species in 1963 and 1964. At present, invasive toads are distributed only in the southwestern part of the island. We collected a total of 25 and 24 R. tigrinus from areas allopatric and sympatric with toads, respectively. Then, we investigated the possession of BDs and the BD profile of these snakes. We found that only R. tigrinus sympatric with toads possessed BDs, whereas all snakes allopatric with toads lacked BDs. Based on the characteristics of the BD profile, the toxin source was identified as B. j. formosus. Our findings show that a new case of impact caused by toxic invasive species, i.e., "toxin supply to native consumers from invasive prey", could occur.

Using community science to identify predators of spotted lanternfly, Lycorma delicatula (Hemiptera: Fulgoridae), in North America.

Spotted lanternfly, Lycorma delicatula (Hemiptera: Fulgoridae), is an invasive insect that was first detected in the United States in 2014 and feeds on a wide variety of plants, with economic impacts on the agricultural, ornamental, and timber industries. Part of what likely contributes to the success of L. delicatula in its invaded range is that it appears to be chemically defended by sequestering toxins from its host plant(s), which may deter predators in the introduced range. To determine the identity and behavior of North American predators that feed on spotted lanternfly, we performed a community science study in which we asked members of the public to contribute reports of animals feeding on spotted lanternfly through a Facebook page. The largest group of reported predators was arthropods followed by birds. Araneae was the arthropod order with the most reports and Phasianidae was the most frequently reported bird family. Using Pearson's χ2 tests, we also identified significant relationships between predator behavior and (1) taxonomic group of the predator, (2) L. delicatula life stage, and (3) host plant L. delicatula was observed on. These results can help to guide future research on predator host shifting to spotted lanternfly and potential for biocontrol as a management tactic.

Inorganic catalase-powered nanomotors with hyaluronic acid coating for pneumonia therapy.

Clinical therapy for widespread infections caused by Streptococcus pneumoniae (S. pneumoniae), such as community-acquired pneumonia, is highly challenging. As an important bacterial toxin, hydrogen peroxide (H2O2) secreted by S. pneumoniae can suppress the host's immune system and cause more severe disease. To address this problem, a hyaluronic acid (HA)-coated inorganic catalase-driven Janus nanomotor was developed, which can cleverly utilize and decompose H2O2 to reduce the burden of bacterial infection, and have excellent drug loading capacity. HA coating prevents rapid leakage of loaded antibiotics and improves the biocompatibility of the nanomaterials. The Janus nanomotor converted H2O2 into oxygen (O2), gave itself the capacity to move actively, and encouraged widespread dispersion in the lesion site. Encouragingly, animal experiments demonstrated that the capability of the nanomotors to degrade H2O2 contributes to diminishing the proliferation of S. pneumoniae and lung tissue damage. This self-propelled drug delivery platform provides a new therapeutic strategy for infections with toxin-secreting bacteria.

Passive accumulation of alkaloids in non-toxic frogs challenges paradigms of the origins of acquired chemical defenses.

Understanding the origins of novel, complex phenotypes is a major goal in evolutionary biology. Poison frogs of the family Dendrobatidae have evolved the novel ability to acquire alkaloids from their diet for chemical defense at least three times. However, taxon sampling for alkaloids has been biased towards colorful species, without similar attention paid to inconspicuous ones that are often assumed to be undefended. As a result, our understanding of how chemical defense evolved in this group is incomplete. Here we provide new data showing that, in contrast to previous studies, species from each undefended poison frog clade have measurable yet low amounts of alkaloids. We confirm that undefended dendrobatids regularly consume mites and ants, which are known sources of alkaloids. Further, we confirm the presence of alkaloids in two putatively non-toxic frogs from other families. Our data suggest the existence of a phenotypic intermediate between toxin consumption and sequestration-passive accumulation-that differs from active sequestration in that it involves no derived forms of transport and storage mechanisms yet results in low levels of toxin accumulation. We discuss the concept of passive accumulation and its potential role in the origin of chemical defenses in poison frogs and other toxin-sequestering organisms.

Chemical defense of an Asian snake reflects local availability of toxic prey and hatchling diet.

Species that sequester toxins from prey for their own defense against predators may exhibit population-level variation in their chemical arsenal that reflects the availability of chemically defended prey in their habitat. Rhabdophis tigrinus is an Asian snake that possesses defensive glands in the skin of its neck ('nuchal glands'), which typically contain toxic bufadienolide steroids that the snakes sequester from consumed toads. In this study, we compared the chemistry of the nuchal gland fluid of R. tigrinus from toad-rich and toad-free islands in Japan and determined the effect of diet on the nuchal gland constituents. Our findings demonstrate that captive-hatched juveniles from toad-rich Ishima Island that had not been fed toads possess defensive bufadienolides in their nuchal glands, presumably due to maternal provisioning of these sequestered compounds. Wild-caught juveniles from Ishima possess large quantities of bufadienolides, which could result from a combination of maternal provisioning and sequestration of these defensive compounds from consumed toads. Interestingly, juvenile females from Ishima possess larger quantities of bufadienolides than do juvenile males, whereas a small sample of field-collected snakes suggests that adult males contain larger quantities of bufadienolides than do adult females. Captive-born hatchlings from Kinkasan Island lack bufadienolides in their nuchal glands, reflecting the absence of toads on that island, but they can sequester bufadienolides by feeding on toads (Bufo japonicus) in captivity. The presence of large quantities of bufadienolides in the nuchal glands of R. tigrinus from Ishima may reduce the risk of predation by providing an effective chemical defense, whereas snakes on Kinkasan may experience increased predation due to the lack of defensive compounds in their nuchal glands.

Do predators prefer toxic animals? A case of chemical discrimination by an Asian snake that sequesters firefly toxins.

Several Asian natricine snakes of the genus Rhabdophis feed on toads and sequester steroidal cardiac toxins known as bufadienolides (BDs) from them. A recent study revealed that species of the Rhabdophis nuchalis Group ingest lampyrine fireflies to sequester BDs. Although several species of fireflies are distributed in the habitat of the R. nuchalis Group, only lampyrine fireflies, which have BDs, are included in the diet of these snakes. Thus, we hypothesized that the R. nuchalis Group chemically distinguishes fireflies that have BDs from those that do not have BDs. We also predicted that the R. nuchalis Group detects BDs as the chemical cue of toxin source. To test these predictions, we conducted 3 behavioral experiments using Rhabdophis chiwen, which belongs to the R. nuchalis Group. In the first experiment, R. chiwen showed a moderate tongue flicking response to cinobufagin, a compound of BDs. On the other hand, the snake showed a higher response to the chemical stimuli of lampyrine fireflies (BD fireflies) than those of lucioline fireflies (non-BD fireflies). In the second experiment, in which we provided live BD and non-BD fireflies, the snake voluntarily consumed only the former. In the third, a Y-maze experiment, the snake tended to select the chemical trail of BD fireflies more frequently than that of non-BD fireflies. These results demonstrated that R. chiwen discriminates BD fireflies from non-BD fireflies, but the prediction that BDs are involved in this discrimination was not fully supported. To identify the proximate mechanisms of the recognition of novel toxic prey in the R. nuchalis Group, further investigation is necessary.

Nano-metal-organic-frameworks for treating H2O2-Secreting bacteria alleviate pulmonary injury and prevent systemic sepsis.

As a vital bacteria-secreted toxin, hydrogen peroxide (H2O2) can destroy infected tissues and increase vascular permeability, leading to life-threatening systemic bacteremia or sepsis. No strategy that can alleviate H2O2-induced injury and prevent systemic sepsis has been reported. Herein, as a proof of concept, we demonstrate the use of H2O2-reactive metal-organic framework nanosystems (MOFs) for treating H2O2-secreting bacteria. In mice infected with Streptococcus pneumoniae (S. pneumoniae) isolated from patients, MOFs efficiently accumulate in the lungs after systemic administration due to infection-induced alveolar-capillary barrier dysfunction. Moreover, MOFs sequester pneumococcal H2O2, reduce endothelial DNA damage, and prevent systemic dissemination of bacteria. In addition, this nanosystem exhibits excellent chemodynamic bactericidal effects against drug-resistant bacteria. Through synergistic therapy with the antibiotic ampicillin, MOFs eliminate over 98% of invading S. pneumoniae, resulting in a survival rate of greater than 90% in mice infected with a lethal dose of S. pneumoniae. This work opens up new paths for the clinical treatment of toxin-secreting bacteria.

Response Mechanisms of Invertebrates to Bacillus thuringiensis and Its Pesticidal Proteins.

Extensive use of chemical insecticides adversely affects both environment and human health. One of the most popular biological pest control alternatives is bioinsecticides based on Bacillus thuringiensis This entomopathogenic bacterium produces different protein types which are toxic to several insect, mite, and nematode species. Currently, insecticidal proteins belonging to the Cry and Vip3 groups are widely used to control insect pests both in formulated sprays and in transgenic crops. However, the benefits of B. thuringiensis-based products are threatened by insect resistance evolution. Numerous studies have highlighted that mutations in genes coding for surrogate receptors are responsible for conferring resistance to B. thuringiensis Nevertheless, other mechanisms may also contribute to the reduction of the effectiveness of B. thuringiensis-based products for managing insect pests and even to the acquisition of resistance. Here, we review the relevant literature reporting how invertebrates (mainly insects and Caenorhabditis elegans) respond to exposure to B. thuringiensis as either whole bacteria, spores, and/or its pesticidal proteins.

The secret social lives of African crested rats, Lophiomys imhausi.

The crested rat, Lophiomys imhausi, is the only mammal known to sequester plant toxins. Found in eastern Africa, this large rodent is thought to defend against predation by coating specialized hairs along its sides with cardenolide toxins from the poison arrow tree, Acokanthera schimperi. To better understand the ecology of this unusual poisonous mammal, we used camera traps, livetrapping, and captive behavioral observations, to study L. imhausi in central Kenya. Although crested rats were rarely detected with camera traps, 25 individuals were caught in live traps, with estimated densities of up to 15 rats/km2 at one of nine trapping sites. Trapping records and behavioral observations suggest that L. imhausi live in male-female pairs, with juveniles that might exhibit delayed dispersal. We observed chewing of A. schimperi and/or anointing in 10 of 22 individuals, confirming the previous poison sequestration observation. We monitored crested rat activity using cameras and found that chewing on A. schimperi and cardenolide exposure had no effect on feeding, movement, or total activity. One crested rat also fed on milkweed (Gomphocarpus physocarpus; Gentaniales: Apocynaceae), but did not anoint with this cardenolide containing plant. This observation, combined with L. imhausi's selective use of A. schimperi, suggests the potential for use of alternative poison sources. This research provides novel insight into the ecology of L. imhausi, while also suggesting that more field observations, feeding trials, and chemical analyses are needed to understand their behavior and physiology. Furthermore, their complex social interactions, slow life history, and fragmented populations suggest that L. imhausi could be at risk of decline.

Polymer antidotes for toxin sequestration.

Toxins delivered by envenomation, secreted by microorganisms, or unintentionally ingested can pose an immediate threat to life. Rapid intervention coupled with the appropriate antidote is required to mitigate the threat. Many antidotes are biological products and their cost, methods of production, potential for eliciting immunogenic responses, the time needed to generate them, and stability issues contribute to their limited availability and effectiveness. These factors exacerbate a world-wide challenge for providing treatment. In this review we evaluate a number of polymer constructs that may serve as alternative antidotes. The range of toxins investigated includes those from sources such as plants, animals and bacteria. The development of polymeric heavy metal sequestrants for use as antidotes to heavy metal poisoning faces similar challenges, thus recent findings in this area have also been included. Two general strategies have emerged for the development of polymeric antidotes. In one, the polymer acts as a scaffold for the presentation of ligands with a known affinity for the toxin. A second strategy is to generate polymers with an intrinsic affinity, and in some cases selectivity, to a range of toxins. Importantly, in vivo efficacy has been demonstrated for each of these strategies, which suggests that these approaches hold promise as an alternative to biological or small molecule based treatments.