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Une nouvelle espèce pour la fonge d'Alsace : découverte de Batrachochytrium dendrobatidis Longcore, Pessier & Nichols, 1999 (Fungi: Rhizophydiales), champignon parasite des Amphibiens

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... Si l'on ne connaît pas pour l'instant de cas de chytridiomycose chez le Sonneur à ventre jaune, l'espèce est cependant porteuse saine de Bd dans certaines localités européennes (DEJEAN et al., 2010). En Alsace, Bd a été trouvé sur des sonneurs dans la forêt de l'Illwald à Sélestat (VACHER et al., 2013), ainsi que sur la bande rhénane au nord du Haut-Rhin (VACHER, inédit). Jusqu'à présent, nous n'avons pas observé de mortalité attribuée à la chytridiomycose en Alsace. ...
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EN ALSACE : STATUT, MENACES ET PLAN RÉGIONAL DʼACTIONS par Jean-Pierre VACHER Résumé : Bien qu'il soit encore relativement répandu, le Sonneur à ventre jaune est une espèce en déclin en France. Sa population globale a en effet fortement régressé au cours du XX e siècle, particulièrement dans la frange occidentale de son aire. En Alsace, cette espèce montre une répartition en taches. Dans cette région, il se rencontre principalement dans les forêts de plaine, mais quelques populations se trouvent dans des zones de collines comme le piémont vosgien, le Sundgau et les Vosges du Nord. Le long de la bande rhénane, un hiatus de distribution s'observe entre l'île de Rhinau et la confluence de la Moder avec le Rhin. Bien qu'il n'existe pas de suivi précis de l'espèce, certaines populations semblent assez importantes en termes d'effectifs, comme par exemple dans la forêt d'Epfig en Centre Alsace, dans le secteur de Marckolsheim le long de la bande rhénane, dans le massif de Haguenau et dans certains secteurs du Sundgau. Cette espèce se rencontre dans plusieurs aires protégées ou gérées, comme des réserves naturelles ou encore des sites Natura 2000. On la trouve également dans plusieurs carrières, dont certaines encore en activité. Un plan régional d'actions a été lancé en 2012 pour une durée de cinq ans. Ce plan dresse une liste des actions qui doivent permettre de maintenir le statut actuel de l'espèce dans la région. Les principales thématiques abordées sont la conservation et l'interconnexion des habitats, le recueil de données scientifiques concernant la génétique des populations et la tendance d'évolution des populations à une large échelle par le biais de modèles d'occupation de sites.
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Chytridiomycosis, caused by the fungus Batrachochytrium dendrobatidis, contributes to amphibian declines worldwide. Recently, the fungus has shown to be widely distributed in Belgium and the Netherlands, although no clinical cases of the disease have been diagnosed yet. This case report describes the first case of mortality due to chytridiomycosis in Belgium in a wild population of midwife toads (Alytes obstetricans). The presence of clinical chytridiomycosis, combined with the relatively high prevalence of the fungus in Belgium, emphasizes the urgent need for a thorough study on the impact of infection on the native amphibian populations in Belgium.
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Captive and wild frogs from North and Central America and Australia recently have died with epidermal infections by chytridiomycete fungi. We isolated a chytridiomycete into pure culture from a captive, blue poison dart frog that died at the National Zoological Park in Washington, D.C. Using this isolate, we photographed developmental stages on nutrient agar, examined zoospores with transmission electron microscopy, and inoculated test frogs. This inoperculate chytrid develops either monocentrically or colonially and has thread-like rhizoids that arise from single or multiple areas on the developing zoosporangium. The taxonomically important features of the kinetosomal region of the zoospore indicate that this chytrid is a member of the Chytridiales but differs from other chytrids studied with transmission electron microscopy. Its microtubule root, which begins at kinetosome triplets 9-1 and extends parallel to the kinetosome into the aggregation of ribosomes, is distinctive. Histologic examination of test frogs revealed that the pure culture infected the skin of test frogs, whereas the skin of control frogs remained free of infection. The fungus is described as Batrachochytrium dendrobatidis gen. et sp. nov.
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Epidermal changes caused by a chytridiomycete fungus (Chytridiomycota; Chytridiales) were found in sick and dead adult anurans collected from montane rain forests in Queensland (Australia) and Panama during mass mortality events associated with significant population declines. We also have found this new disease associated with morbidity and mortality in wild and captive anurans from additional locations in Australia and Central America. This is the first report of parasitism of a vertebrate by a member of the phylum Chytridiomycota. Experimental data support the conclusion that cutaneous chytridiomycosis is a fatal disease of anurans, and we hypothesize that it is the proximate cause of these recent amphibian declines.
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A l’échelle mondiale, les amphibiens subissent d’importants déclins de populations dûs à la Chytridiomycose, une maladie émergente provoquée par le champignon Batrachochytrium dendrobatidis (noté par la suite Bd). Des déclins catastrophiques ont été observés en Australie, Amérique du Nord, Amérique centrale, Amérique du Sud et dans les Caraïbes. En Europe, des mortalités massives associées à Bd ont été observées en Espagne et en France, mais nos connaissances sur la prévalence de Bd en Europe ne sont encore que fragmentaires. Les causes exactes de l’émergence récente de la Chytridiomycose sont encore mal connues. Néanmoins, les scientifiques s’accordent aujourd’hui à penser que ce champignon aurait été récemment disséminé à travers le monde par l’intermédiaire de matériel ayant été au contact avec Bd, d’eau contenant des zoospores ou d’amphibiens infectés (notamment lors de l’introduction d’espèces exotiques). Les activités humaines, dans ou à proximité de sites aquatiques, participent donc fortement à la dissémination du champignon et représentent un risque majeur pour les populations d’amphibiens. Si un individu infecté peut être efficacement traité avec un fongicide, le champignon ne peut pas être contrôlé, à ce jour, dans le milieu naturel. Néanmoins, quelques procédures simples de désinfection permettent de décontaminer les équipements, ce qui réduit notablement le risque que le champignon soit passivement transféré lors des déplacements. L’objectif de ce document est de fournir aux personnes travaillant sur les amphibiens, ou plus largement en milieu aquatique, un ensemble de mesures de précaution à mettre en oeuvre lors de leurs campagnes de terrain. Bien que ciblées sur la Chytridiomycose, ces précautions permettront également de limiter la dissémination d’autres maladies ou d’espèces végétales ou animales envahissantes. Certaines de ces procédures peuvent être appliquées dans les laboratoires et élevages, mais il est nécessaire que les personnels impliqués se confèrent à la réglementation vétérinaire. Les mesures de biosécurité pour les amphibiens captifs pourraient différer de celles proposées pour le terrain.
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We surveyed the population status of the Neotropical toad genus Atelopus, and document recent catastrophic declines that are more severe than previously reported for any amphibian genus. Of 113 species that have been described or are candidates for description, data indicate that in 42 species, population sizes have been reduced by at least half and only ten species have stable populations. The status of the remaining taxa is unknown. At least 30 species have been missing from all known localities for at least 8 yr and are feared extinct. Most of these species were last seen between 1984 and 1996. All species restricted to elevations of above 1000 m have declined and 75 percent have disappeared, while 58 percent of lowland species have declined and 38 percent have disappeared. Habitat loss was not related to declines once we controlled for the effects of elevation. In fact, 22 species that occur in protected areas have disappeared. The fungal disease Batrachochytrium dendrobatidis has been documented from nine species that have declined, and may explain declines in higher elevation species that occur in undisturbed habitats. Climate change may also play a role, but other potential factors such as environmental contamination, trade, and introduced species are unlikely to have affected more than a handful of species. Widespread declines and extinctions in Atelopus may reflect population changes in other Neotropical amphibians that are more difficult to survey, and the loss of this trophic group may have cascading effects on other species in tropical ecosystems.
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During the summers of 1997, 1998 and 1999 mass mortality episodes of post-metamorphic common midwife toads (Alytes obstetricans) occurred in a protected area in central Spain. The population suffered a sharp decline, disappearing from 86% of the ponds where they were known to reproduce some years ago. Scanning electron microscopy and histological techniques revealed the presence of a chytridiomycosis infection in the skin of the toads. This evidence supports chytridiomycosis as the most plausible cause of the decline of the species in the area. This is the first report of an apparent chytridium-caused amphibian decline in Europe.
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Batrachochytrium dendrobatidis (Bd) is a globally ubiquitous fungal infection that has emerged to become a primary driver of amphibian biodiversity loss. Despite widespread effort to understand the emergence of this panzootic, the origins of the infection, its patterns of global spread, and principle mode of evolution remain largely unknown. Using comparative population genomics, we discovered three deeply diverged lineages of Bd associated with amphibians. Two of these lineages were found in multiple continents and are associated with known introductions by the amphibian trade. We found that isolates belonging to one clade, the global panzootic lineage (BdGPL) have emerged across at least five continents during the 20th century and are associated with the onset of epizootics in North America, Central America, the Caribbean, Australia, and Europe. The two newly identified divergent lineages, Cape lineage (BdCAPE) and Swiss lineage (BdCH), were found to differ in morphological traits when compared against one another and BdGPL, and we show that BdGPL is hypervirulent. BdGPL uniquely bears the hallmarks of genomic recombination, manifested as extensive intergenomic phylogenetic conflict and patchily distributed heterozygosity. We postulate that contact between previously genetically isolated allopatric populations of Bd may have allowed recombination to occur, resulting in the generation, spread, and invasion of the hypervirulent BdGPL leading to contemporary disease-driven losses in amphibian biodiversity.
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Infectious diseases are increasingly recognized as the cause of mass mortality events, population declines, and the local extirpation of wildlife species. In a number of cases, it has been hypothesized that pathogens have caused species extinctions in wildlife. However, there is only one definitively proven case of extinction by infection, and this was in a remnant captive population of a Polynesian tree snail. In this article, we review the potential involvement of infectious disease in the recent extinction of the sharp-snouted day frog Taudactylus acutirostris. Our review of available evidence suggests that a virulent pathogen of amphibians, Batrachochytrium dendrobatidis, caused a rapid, catastrophic decline of this species, from which it did not recover. We propose that this is the first case of extinction by infection of a free-ranging wildlife species where disease acted as both the proximate and ultimate cause of extinction. This highlights a probable underreporting of infectious disease as a cause of biodiversity loss historically and currently. Yes Yes
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Declining of amphibian populations is a worldwide phenomenon. A cutaneous mycosis as a cause of death in free-living amphibians as well as in captive ones due to an chytrid fungus (Batrachochytrium dendrobatidis) was reported at first in 1998. This infections were reported hitherto from Australia, North, Central and South America. This is the first report on chytrid infections in captive anurans from Europe. Dendrobates auratus and D. pumilo imported from Costa Rica and P. vittatus imported from French Guayana died with chytridiomycosis within a week after arrival in Europe. Batrachocytrium was also found on captive bred frogs in Germany and Belgium. Clinical signs, diagnosis and conclusions for protecting free-living amphibian populations and captive frogs are discussed.
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The first global assessment of amphibians provides new context for the well-publicized phenomenon of amphibian declines. Amphibians are more threatened and are declining more rapidly than either birds or mammals. Although many declines are due to habitat loss and overutilization, other, unidentified processes threaten 48% of rapidly declining species and are driving species most quickly to extinction. Declines are nonrandom in terms of species' ecological preferences, geographic ranges, and taxonomic associations and are most prevalent among Neotropical montane, stream-associated species. The lack of conservation remedies for these poorly understood declines means that hundreds of amphibian species now face extinction.
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Batrachochytrium dendrobatidis is the chytridiomycete fungus which has been implicated in global amphibian declines and numerous species extinctions. Here, we show that introduced North American bullfrogs (Rana catesbeiana) consistently carry this emerging pathogenic fungus. We detected infections by this fungus on introduced bullfrogs from seven of eight countries using both PCR and microscopic techniques. Only native bullfrogs from eastern Canada and introduced bullfrogs from Japan showed no sign of infection. The bullfrog is the most commonly farmed amphibian, and escapes and subsequent establishment of feral populations regularly occur. These factors taken together with our study suggest that the global threat of B. dendrobatidis disease transmission posed by bullfrogs is significant.
Un champignon menace les amphibiens. Qu'avons-nous appris de la Chytridiomycose ? Le Courrier de la
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La chytridiomycose : une maladie émergente des amphibiens
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