The global emergence and spread of the pathogenic, virulent, and highly transmissible fungus Batrachochytrium dendrobatidis, resulting in the disease chytridiomycosis, has caused the decline or extinction of up to about 200 species of frogs. Key postulates for this theory have been completely or partially fulfilled. In the absence of supportive evidence for alternative theories despite decades of research, it is important for the scientific community and conservation agencies to recognize and manage the threat of chytridiomycosis to remaining species of frogs, especially those that are naive to the pathogen. The impact of chytridiomycosis on frogs is the most spectacular loss of vertebrate biodiversity due to disease in recorded history.

/pdf/spread-of-chytridiomycosis-has-caused-the-rapid-global-3258w0sbzd.pdf

Spread of Chytridiomycosis Has Caused the Rapid Global Decline and Extinction of Frogs

Recent results continue to show the general consensus that ozone-related increases in UV-B radiation can negatively influence many aquatic species and aquatic ecosystems (e.g., lakes, rivers, marshes, oceans). Solar UV radiation penetrates to ecological significant depths in aquatic systems and can affect both marine and freshwater systems from major biomass producers (phytoplankton) to consumers (e.g., zooplankton, fish, etc.) higher in the food web. Many factors influence the depth of penetration of radiation into natural waters including dissolved organic compounds whose concentration and chemical composition are likely to be influenced by future climate and UV radiation variability. There is also considerable evidence that aquatic species utilize many mechanisms for photoprotection against excessive radiation. Often, these protective mechanisms pose conflicting selection pressures on species making UV radiation an additional stressor on the organism. It is at the ecosystem level where assessments of anthropogenic climate change and UV-related effects are interrelated and where much recent research has been directed. Several studies suggest that the influence of UV-B at the ecosystem level may be more pronounced on community and trophic level structure, and hence on subsequent biogeochemical cycles, than on biomass levels per se.

/pdf/effects-of-solar-uv-radiation-on-aquatic-ecosystems-and-njcrblgzlq.pdf

Effects of solar UV radiation on aquatic ecosystems and interactions with climate change

The worldwide decline in amphibians has been attributed to several causes, especially habitat loss and disease. We identified a further factor, namely “habitat split”—defined as human-induced disconnection between habitats used by different life history stages of a species—which forces forest-associated amphibians with aquatic larvae to make risky breeding migrations between suitable aquatic and terrestrial habitats. In the Brazilian Atlantic Forest, we found that habitat split negatively affects the richness of species with aquatic larvae but not the richness of species with terrestrial development (the latter can complete their life cycle inside forest remnants). This mechanism helps to explain why species with aquatic larvae have the highest incidence of population decline. These findings reinforce the need for the conservation and restoration of riparian vegetation.

https://science.sciencemag.org/content/sci/318/5857/1775.full.pdf

Habitat split and the global decline of amphibians

The current biodiversity crisis encompasses a sixth mass extinction event affecting the entire class of amphibians. The infectious disease chytridiomycosis is considered one of the major drivers of global amphibian population decline and extinction and is thought to be caused by a single species of aquatic fungus, Batrachochytrium dendrobatidis. However, several amphibian population declines remain unexplained, among them a steep decrease in fire salamander populations (Salamandra salamandra) that has brought this species to the edge of local extinction. Here we isolated and characterized a unique chytrid fungus, Batrachochytrium salamandrivorans sp. nov., from this salamander population. This chytrid causes erosive skin disease and rapid mortality in experimentally infected fire salamanders and was present in skin lesions of salamanders found dead during the decline event. Together with the closely related B. dendrobatidis, this taxon forms a well-supported chytridiomycete clade, adapted to vertebrate hosts and highly pathogenic to amphibians. However, the lower thermal growth preference of B. salamandrivorans, compared with B. dendrobatidis, and resistance of midwife toads (Alytes obstetricans) to experimental infection with B. salamandrivorans suggest differential niche occupation of the two chytrid fungi.

/pdf/batrachochytrium-salamandrivorans-sp-nov-causes-lethal-4yphzzh817.pdf

Batrachochytrium salamandrivorans sp. nov. causes lethal chytridiomycosis in amphibians

Human activities continue to erode the tree of life, requiring us to prioritize research and conservation. Amphibians represent key victims and bellwethers of global change, and the need for action to conserve them is drastically outpacing knowledge. We provide a phylogeny incorporating nearly all extant amphibians (7,238 species). Current amphibian diversity is composed of both older, depauperate lineages and extensive, more recent tropical radiations found in select clades. Frog and salamander diversification increased strongly after the Cretaceous-Palaeogene boundary, preceded by a potential mass-extinction event in salamanders. Diversification rates of subterranean caecilians varied little over time. Biogeographically, the Afro- and Neotropics harbour a particularly high proportion of Gondwanan relicts, comprising species with high evolutionary distinctiveness (ED). These high-ED species represent a large portion of the branches in the present tree: around 28% of all phylogenetic diversity comes from species in the top 10% of ED. The association between ED and imperilment is weak, but many species with high ED are now imperilled or lack formal threat status, suggesting opportunities for integrating evolutionary position and phylogenetic heritage in addressing the current extinction crisis. By providing a phylogenetic estimate for extant amphibians and identifying their threats and ED, we offer a preliminary basis for a quantitatively informed global approach to conserving the amphibian tree of life.

The interplay of past diversification and evolutionary isolation with present imperilment across the amphibian tree of life

Stopping further global losses of amphibian populations and species requires an unprecedented conservation response.

/pdf/confronting-amphibian-declines-and-extinctions-4asdyf4j44.pdf

Confronting Amphibian Declines and Extinctions

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Confronting Amphibian Declines and Extinctions