Editorial: From landscape modifications to pathogen infections: are threats to amphibians the same in all biomes?

Joice Ruggeri ^1,2* David Lesbarreres ^3,4

• ¹ CONICET Institute of Subtropical Biology (IBS), Posadas, Argentina
• ² National University of Misiones, Posadas, Misiones, Argentina
• ³ Université d'Angers, Angers, Pays de la Loire, France
• ⁴ Environment and Climate Change Canada, ottawa, Canada

Anthropogenic actions have been altering ecosystems for decades thus impacting biodiversity globally, with a special risk looming on amphibians. Threats range from the direct use of land and habitat modification to the indirect effects of biological invasions and pathogens emergence (Green et al. 2020). Articles published in this Research Topic highlight the consequences of human disturbance on amphibians' health by either reporting the direct cause of harm or mitigation measures aimed at their conservation. Amongst human-induced threats to amphibians, the emergence of infectious diseases caused by novel (or more virulent) pathogens, such as Batrachochytrium dendrobatidis (Bd), B. salamandrivorans (Bsal) and Ranavirus (Rv), is largely associated with amphibian declines worldwide (Teacher et al. 2010;Scheeler et al. 2019). Bd and Rv present a global distribution, whereas Bsal remains restricted geographically due to several efforts to contain its spread (Fisher andGarner 2020, Olson et al. 2024). In the UK, Ball et al. detected patterns of mtDNA haplotypes in populations of the invasive Alpine newt (Ichthyosaura alpestris) compatible with the pet trade, suggesting there is an ongoing release of the species in the territory. Such repeated introductions represent a great danger to native species, as Alpine newts usually remain asymptomatic to infection (Daversa et al. 2018) and could potentially spread disease. Harlequin frogs (Atelopus spp.), for instance, are flagships for those species which have suffered severe population declines due to chytridiomycosis (La Marca et la. 2005). While some species adapted to Bd following outbreaks resulting in a few presumably extinct species reappearing (Jaybes et al. 2022), many others remain declining; thus, reestablishing populations is highly important from a conservation perspective. To this end, Klocke et al. monitored the transition of Atelopus limosus from captivity to sites within the species' historical range in Panama and showed that a 30-day acclimatization is crucial for successful release and survival of captivity-bred individuals.The persistence of Bd in the environment is related to the susceptibility of hosts (Carvalho et al. 2024) and the presence of ideal microclimates for its development (Longcore et al. 1999). Santos et al. detected higher prevalence of Bd in tadpoles from forested sites than agricultural sites in Brazil, likely due to the shading provided by canopy cover (Becker & Zamudio 2011). The authors employed a species-indicator analysis to identify species prone to Bd infection, and used this result to infer which community would likely be Bd-positive. The study confirmed tadpoles of Boana faber as highly susceptible to Bd (Ruggeri et al. 2020), in addition to two species endemic to southern Brazil (Boana curupi and Crossodactylus schmidti), which could be indicator for Bd presence in a community. Presence of Rv, another pathogen posing enormous risks to amphibians globally (Gray and Chinchar 2024), was also investigated on 10 anuran species but not detected. This does not refute the presence of Rv in the area as the infection may be seasonal (Hall et al. 2018) and was previously detected in the region (Ruggeri et al. 2023), indicating it should be continuously investigated. Water pollution has also been associated with Bd (Jacinto-Maldonado et al. 2023) and Jacinto-Maldonado et al. corroborate this by detecting high prevalence on sites with continuous wastewater discharge. Besides, they detected elevated concentrations of chemical elements known to pose risk of bioaccumulation and be transferred through food chain on sites with amphibians coinfected by Bd and the mite.As aforementioned, biological invasions pose a major threat to amphibians not only for disease transmission, but also due to competition and hybridization with native species (Kraus 2015), a point highlighted by Borzée et al. with regards to the Japanese and Chinese giant salamanders. Many invasive amphibians can easily adapt and expand their distribution range rapidly. That is the case for the American bullfrog (Lithobates catesbeianus) worldwide, the cane toad (Rhinella marina) in Australia, and more recently the Lesser Antillean frog (Eleutherodactylus johnstonei) in Brazil (Frost 2024). Melo et al. explored acoustic consequences of invasions on the behaviour of native species, showing that native pond breeder amphibians in Brazil ceased calling in the presence of callings from E. johnstonei. Both and Grant (2012) had shown how calls from invasive bullfrogs caused a shift on calls from a native species in Brazil, suggesting that such acoustic competition could impact the reproductive success of species in the same acoustic niche. Although they highlight that E. johnstonei is a direct-developing frog and such encounter with pond breeders would rarely occur in the wild, the reproductive season of this and most species in Brazil overlap (Bertolucci 1998, Tárano andFuenmayor 2009), and the presence of the invader could indeed cause acoustic interferences, thus impacting native anurans. We learned with this collection that the international movement of live animals and habitat fragmentation resulting from agriculture, urbanization, and waterway obstructions (dams and weirs) can affect amphibians differently, but the result is often the same: populations decline. And while threats may be of different nature or strengths, amphibians are rarely facing only one of them (Green et al. 2020). Therefore, recognizing the main threats to amphibian populations is a primary step towards species conservation. Borzée et al. reviewed the dangers faced by the Japanese giant salamander given the current state of the environment where the population persists, proposing actions to allow the species to thrive. Klocke et al. concluded that a 30-day acclimatization is crucial for successful release and survival of captivity-bred Atelopus limosus in Panama, providing data to potentially improve and refine release methods for other species. Santos et al. identified potential Bd-indicator species in Brazil that would allow researchers to focus on communities composed by such species when screening for Bd, and highlighted forest patches within disturbed habitats as priority areas for conservation. In Mexico, Jacinto-Maldonado et al. showed that species from degraded areas would be highly susceptible to Bd infection and coinfection with parasite/pathogens, and the lowland leopard frog (Lithobates yavapaiensis), a species suffering severe population declines (IUCN 2024), presented the highest Bd loads. We also learned that the pet trade remains playing an important role in introducing alien species in the UK as reported by Ball et al. This practice compromises natural ecosystems and ecological relationships worldwide by causing biological invasions that may lead to acoustic interferences and changes in the behaviour of native species, as exposed by Melo et al. Overall, threats are diverse and complex, and only a comprehensive approach of each ecosystem will help the conservation of amphibians.