How to disinfect anuran eggs? Sensitivity of anuran embryos to chemicals widely used for the disinfection of larval and post‐metamorphic amphibians

Emerging infectious diseases are major drivers of global and local amphibian biodiversity loss. Developing effective disinfection methods to manage the impact of diseases in wild and captive ‘ark’ populations is therefore an important goal in amphibian conservation. While chemical disinfectants have been used safely and effectively in larval and adult amphibians infected with pathogenic microbes, their applicability to amphibian egg masses has remained untested. To bridge this gap, we experimentally exposed embryos of the common toad (Bufo bufo) and agile frog (Rana dalmatina) to three widely used disinfectants: voriconazole, chloramphenicol and chlorogen-sesquihydrate. For three days we exposed portions of egg masses to these disinfectants at 1×, 2×, 5× and 10× of the concentration recommended for the disinfection of tadpoles and adults. Subsequently, we recorded embryonic and larval survival, as well as larval body mass and the incidence of abnormalities twelve days after hatching. Application of voriconazole had species and concentration-dependent negative impacts on survival and body mass and caused marked malformations in the viscerocranial structure of B. bufo tadpoles. Exposure to chlorogen-sesquihydrate also resulted in significant mortality in B. bufo embryos and negatively affected body mass of R. dalmatina larvae. Chloramphenicol had little negative effects on embryos or larvae in either species. Based on these results, the application of voriconazole and chlorogen-sesquihydrate cannot be recommended for the disinfection of amphibian eggs, whereas treatment with chloramphenicol appears to be a safe method for eliminating potential pathogens from anuran egg masses and their immediate aquatic environment

Azol gombaölő hatóanyagok teratológiai kockázata kétéltűekre

A növénytermesztésben nagy mennyiségben használt, a növényvédelmi technológiák nagy részében meghatározó azol hatóanyagú gombaölő szerek természetes vizekbe kerülve károsíthatnak bizonyos nem-célszervezeteket, így a világszerte egyed- és fajszámukban visszaszorulóban lévő kétéltűeket. Több tanulmány bizonyítja, hogy az azol hatóanyagok a gerincesek embrióin rendellenes fejformát okozhatnak, ami súlyos esetben az egyed pusztulásával járhat. A kétéltűek félig áteresztő bőrük miatt különösen érzékenyek a környezetbe kerülő mesterséges kémiai anyagokra. Védelmük nem egyszerűen természetvédelmi feladat, hanem a kétéltűek állományainak megtartásába és ezen keresztül a környezetünk fenntartásába fektetett közérdekű erőfeszítés, amelynek pozitív mezőgazdasági és humán egészségügyi vonatkozásai lehetnek. Szeretnénk felhívni a figyelmet, hogy amennyiben a kétéltűek tavaszi szaporodási időszaka idején (március–április) a gazdálkodó az azol hatóanyagú gombaölő szerek használatakor a puffer zónákat fokozottan betartja, illetve a szaporodó helyeket, azaz a felszíni vizek környékét lehetőség szerint nem kezeli, azzal nagymértékben hozzájárul a kétéltűek védelméhez. Megfontolandó lehet más hatásmechanizmusú gombaölő készítmények kockázatának felmérése és alkalmazása ebben az időszakban, amikor a vizekben, a partok mentén köbméterenként akár több ezer kétéltűembrió is fejlődhet

Host–multiparasite interactions in amphibians: a review

Parasites, including viruses, bacteria, fungi, protists, helminths, and arthropods, are ubiquitous in the animal kingdom. Consequently, hosts are frequently infected with more than one parasite species simultaneously. The assessment of such co-infections is of fundamental importance for disease ecology, but relevant studies involving non-domesticated animals have remained scarce. Many amphibians are in decline, and they generally have a highly diverse parasitic fauna. Here we review the literature reporting on field surveys, veterinary case studies, and laboratory experiments on co-infections in amphibians, and we summarize what is known about within-host interactions among parasites, which environmental and intrinsic factors influence the outcomes of these interactions, and what effects co-infections have on hosts. The available literature is piecemeal, and patterns are highly diverse, so that identifying general trends that would fit most host–multiparasite systems in amphibians is difficult. Several examples of additive, antagonistic, neutral, and synergistic effects among different parasites are known, but whether members of some higher taxa usually outcompete and override the effects of others remains unclear. The arrival order of different parasites and the time lag between exposures appear in many cases to fundamentally shape competition and disease progression. The first parasite to arrive can gain a marked reproductive advantage or induce cross-reaction immunity, but by disrupting the skin and associated defences (i.e., skin secretions, skin microbiome) and by immunosuppression, it can also pave the way for subsequent infections. Although there are exceptions, detrimental effects to the host are generally aggravated with increasing numbers of co-infecting parasite species. Finally, because amphibians are ectothermic animals, temperature appears to be the most critical environmental factor that affects co-infections, partly via its influence on amphibian immune function, partly due to its direct effect on the survival and growth of parasites. Besides their importance for our understanding of ecological patterns and processes, detailed knowledge about co-infections is also crucial for the design and implementation of effective wildlife disease management, so that studies concentrating on the identified gaps in our understanding represent rewarding research avenues. [Image: see text

Mitigating Disease Impacts in Amphibian Populations: Capitalizing on the Thermal Optimum Mismatch Between a Pathogen and Its Host

Understanding how animal behavior can influence the susceptibility of endangered hosts to emerging pathogens and using this knowledge to ameliorate negative effects of infectious wildlife diseases is a promising avenue in conservation biology. Chytridiomycosis, an emerging infectious disease caused by the fungal pathogen Batrachochytrium dendrobatidis (Bd) in amphibians has led to the most spectacular disease-borne loss of vertebrate biodiversity ever recorded in history. Unfortunately, the methods of mitigation that are available today are only practical in captive populations, and an effective method that could be applied in natural habitats without inflicting vast collateral damage is lacking. We suggest here that the thermal tolerance mismatch between Bd and its ectothermic hosts coupled with the thermoregulatory behavior of amphibians could be exploited in mitigation interventions combating Bd infection in situ. If microhabitats with elevated temperatures are made available in their natural environment, individuals taking advantage of the possibility to reach their preferred body temperature could critically lower their infection intensity or even clear the pathogen. We provide a basis for studying this approach by reviewing the evidence that supports the idea, describing how technical difficulties may be overcome, pointing out gaps in our knowledge that need to be filled by future studies, and listing presumable bene fits and probable limitations of localized heating. The proposed approach has good potential to become an effective in situ mitigation method that can be easily employed in a wide taxonomic range of amphibians, especially in species that are warm-adapted, while causing less collateral damage than any other method that is currently available. If so, it may quickly become a widely applicable tool of biodiversity conservation and may contribute to saving many amphibian populations and species from extinction in the next few decades

A klímaváltozás hatása kétéltűek ivari fejlődésére: Eltűnnek a békalányok?

A kétéltűeket világszerte veszélyeztető egyik legfontosabb tényező a klímaváltozás. Az emelkedő átlaghőmérséklet és az egyre gyakrabban előforduló szélsőséges időjárási jelenségek olyan mértékű hőstressznek tehetik ki ezeket az állatokat, hogy az többek között megzavarhatja az ivari fejlődésüket, ami kiegyensúlyozatlan ivararányokhoz és akár teljes populációk összeomlásához vezethet. Arról azonban, hogy a kétéltűek esetében milyen magas hőmérséklet vezet ivarváltáshoz, vagyis a genetikailag meghatározott nemmel ellentétes nem kialakulásához, meglepően keveset tudunk

Metabolites of Xenorhabdus bacteria are potent candidates for mitigating amphibian chytridiomycosis

Chytridiomycosis, caused by the chytrid fungus Batrachochytrium dendrobatidis (Bd), has caused extreme losses in amphibian biodiversity. Finding bacteria that produce metabolites with antifungal properties may turn out to be invaluable in the fight against this devastating disease. The entomopathogenic bacteria, Xenorhabdus szentirmaii and X. budapestensis produce secondary metabolites that are effective against a wide range of fungal plant pathogens. To assess whether they may also be effective against Bd, we extracted cell-free culture media (CFCM) from liquid cultures of X. szentirmaii and X. budapestensis and tested their ability to inhibit Bd growth in vitro. As a second step, using juvenile common toads (Bufo bufo) experimentally infected with Bd we also tested the in vivo antifungal efficacy of X. szentirmaii CFCM diluted to 2 and 10% (v/v), while also assessing possible malign side effects on amphibians. Results of the in vitro experiment documented highly effective growth inhibition by CFCMs of both Xenorhabdus species. The in vivo experiment showed that treatment with CFCM of X. szentirmaii applied at a dilution of 10% resulted in infection intensities reduced by ca. 73% compared to controls and to juvenile toads treated with CFCM applied at a dilution of 2%. At the same time, we detected no negative side effects of treatment with CFCM on toad survival and development. Our results clearly support the idea that metabolites of X. szentirmaii, and perhaps of several other Xenorhabdus species as well, may prove highly useful for the treatment of Bd infected amphibians

Chytridiomycosis and climate change: exposure to Batrachochytrium dendrobatidis and mild winter conditions do not increase mortality in juvenile agile frogs during hibernation

Hibernation is often associated with high mortality, especially during early life stages, and losses can be exacerbated by unusual winter conditions or if animals enter hibernation carrying a disease. Here, we examined how overwintering amphibians may be affected by the combined effects of mild winters, which are projected to increase in frequency due to climate change, and of chytridiomycosis, a disease that has contributed to the decline of hundreds of species worldwide. We exposed juvenile agile frogs Rana dalmatina to Batrachochytrium dendrobatidis (Bd), the causative agent of chytridiomycosis, and subsequently subjected them to either a long, cold winter (1.5°C for 91 days) or a short, mild winter (4.5°C for 61 days) under laboratory conditions. Agile frogs proved to be highly resistant to Bd as only 37% of Bd-exposed individuals became infected as determined before hibernation, and prevalence further decreased to 8% by the end of hibernation, with individuals showing very low infection intensity values. We observed lack of mortality in control and Bd-exposed groups also, in both types of winter. The two types of winter we simulated did not result in differing body mass loss either alone or in combination with experimental infection. In the Bd-exposed group, the two types of winter also did not cause differences in prevalence and infection intensity. However, among Bd-exposed frogs, individuals that were Bd negative when entering hibernation lost more body mass than their conspecifics that carried the fungus at the onset of overwintering. Based on our results, warming winter climate conditions, with or without Bd infection, do not decrease body mass and survival rate of hibernating agile frogs, and do not increase susceptibility of individuals to chytridiomycosis. It remains to be seen to what extent the relatively weak effects of milder winters can be generalized to other amphibians of the temperate climate zone