Argentina is the country with the most geographically extended biological invasion of the American bullfrog (Lithobates catesbeianus) in South America after Brazil. Here, we used a maximum entropy ecological niche modeling algorithm (using records of the native range of American bullfrog) to project the model onto the whole of Argentina. We determined the most suitable habitats for this invasive alien species and where we consider urgent measures should be taken. Our projections showed good agreement with known feral populations of American bullfrog in Argentina.

The ability to develop reversible dermal extensions on the lower jaw in some South American characiform fishes has been proposed as a way to optimize the performance of aquatic surface respiration (ASR) during hypoxic conditions. These structures are formed by edema of the hypodermal tissues and can develop in a large proportion of individuals inhabiting a lake within a few hours following daily changes in dissolved oxygen. Our study report the development of dermal lip protuberances in eleven species of characiform fishes associated with periods of strong environmental hypoxia in floodplain lakes of Salado River, Argentina. Protuberances occurred in different basic forms in fishes with divergent head morphology (genera Astyanax, Ctenobrycon, Aphyocharax, Brycon, Mylossoma, Triportheus, Oligosarcus and Acestrorhynchus). The discovery of dermal projections on the anterior border of maxillary bone extends the known range of structures affected by lip protuberances. Dermal structures began to develop simultaneously in both jaws below dissolved oxygen (DO) concentrations of 1.20-1.75 mgl −1 and rose in a steep manner as oxygen level decreased. The degree of morphological plasticity differed among traits and species. The shape of response of morphology to DO was similar to that previously reported on ASR, providing additional evidence about the functional link between these traits. Our results suggests that dermal lip protuberances are widely spread among characiform fishes, affecting several mouth structures. The different types of protuberances would make up for the limitations imposed by body size and mouth shape and position on the performance of ASR in fishes with divergent morphology.

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Within the last two decades Batrachochytrium dendrobatidis (B.d.), the causative agent of chytridiomycosis, seems to have become a pandemic parasite, and is proposed as one of the more important causes of amphibian declines worldwide. In Argentina, the first report was in 2002 in Leptodactylus ocellatus. Since then, the fungus has expanded through different environments and species. In this study, we predict B.d. distribution in Argentina applying niche modelling based on reports of infected amphibians and environmental variables. The distribution hypothesis showed regions with highest suitability for B.d. including habitat types with (1) the most diverse amphibian fauna in Argentina such as the Paraná River Basin, (2) endangered species, such as north Patagonia and northwest Andean highlands, and (3) wide range of optimum precipitation and temperatures allowing development of B.d.

We present the first data on age structure, growth pattern, and lines of arrested growth (LAG) forLeptodactylus latransin temperate wetlands. Based on these data, we estimate LAG periodicity, age, size at sexual maturity and longevity for this species. We also tested for differences of these parameters between sexes. The age was determined through skeletochronology. Female maturity was determined by presence of differentiated ova, while male maturity was assessed through histological analysis to evaluate spermatozoid production. To establish whether this species marks one LAG per year, eight individuals were kept one year in captivity. For each specimen, LAG was compared for different phalanges of the same toe clipped at start and end of captivity.Leptodactylus latransmarked one LAG per year, indicating a growth rhythm adjusted to a seasonal environment and mainly driven by genetic factors. Longevity was five years for both sexes and frogs reached sexual maturity during the first year, exhibiting a reproductive lifespan of four years. Sexual maturity was related to a minimal size of 60 mm or a body mass of around 33 g. There was no difference in either size or growth pattern between sexes. The von Bertalanffy growth model showed thatL. latransgrows fast after metamorphosis and their growth rate strongly decreases at about three years, probably due to the increased allocation of energy to reproduction. The high growth rates and early sexual maturation ofL. latranswould allow an elevated rate of population renewal.

Some South American freshwater fishes can improve their capability of aquatic surface respiration (ASR) by developing dermal lip protuberances in the lower jaw. This adaptation was thought to be limited to omnivorous or herbivorous fishes. The present work provides the first evidence that juveniles of a piscivorous characid, Salminus brasiliensis, develop dermal lip protuberances during periods of hypoxia in floodplain ponds of the Salado River, in Argentina. The protuberance of S. brasiliensis involves dermal portions of both jaws exhibiting lateral lobes on the sides of the mouth arranged in the vertical plane. Water dissolved oxygen concentrations less than or equal to 1.05 mgl -1 were associated with a remarkable increase in lip protuberance. The lateral lobes of the protuberance in this species may limit the access of water to the anterior portion of the mouth which is positioned nearer to the oxygenated surface water during ASR. Finally, ASR, complemented with the development of dermal lip protuberances, can be considered a valuable strategy to survive in hypoxic environments, even for carnivorous fishes with elevated oxygen requirements.Alguns peixes de água doce da América do Sul podem melhorar o desempenho da respiração aquática superficial (RAS) desenvolvendo protuberâncias dérmicas labiais na mandíbula. Considerava-se que essa adaptação era limitada aos peixes onívoros ou herbívoros. Este trabalho apresenta os primeiros indícios de que juvenis de um caracídeo piscívoro, Salminus brasiliensis, desenvolvem protuberâncias dérmicas labiais durante períodos de hipoxia em lagoas de várzea do rio Salado, Argentina. As protuberâncias de S. brasiliensis envolvem porções dérmicas das duas mandíbulas e exibem lóbulos laterais ao lado da boca dispostas no plano vertical. Concentrações de oxigênio dissolvido na água, inferiores ou iguais a 1,05 mgl -1 , foram associadas a um aumento notável no desenvolvimento das protuberâncias labiais. Nesta espécie os lóbulos laterais da protuberância podem limitar o acesso de água à porção anterior da boca, que está posicionada mais perto da superfície da água oxigenada durante a RAS. Finalmente, a RAS, complementada com o desenvolvimento de protuberâncias dérmicas labiais, pode ser considerada uma valiosa estratégia para a sobrevivência em ambientes hipóxicos, mesmo para peixes carnívoros com elevada demanda de oxigênio.

Chytridiomycosis, a disease caused by the chytrid fungus Batrachochytrium dendrobatidis (B.d.), is recognized as one of the major factors of amphibian decline. Global trade of amphibians has been identified as one of the causes of B.d. spread, involving hundreds of species world wide. In this work we detected the presence of B.d. through histological examination on 5 out of 9 analyzed specimens of bullfrogs (Lithobates catesbeianus) from a farm in Santa Fe City (Argentina), deposited since 1993 in the herpetological collection of the Provincial Museum of Natural Sciences "Florentino Ameghino". Our finding represents the oldest record of B.d. for Argentina and the first case of the chytrid fungus infecting the exotic bullfrog in this country. We emphasize the importance of determining and monitoring the distribution and spread of B.d in Argentina, particularly in areas where feral bullfrog populations have already been identified.

Water moulds are pathogens of amphibian eggs and embryos. However, little is known about oxidant or antioxidant status of amphibians in response to stress caused by water moulds. We exposed embryo stages of Two-colored Oval Frogs (Elachistocleis bicolor (Guérin-Méneville, 1838)) to a Saprolegnia-like species of water mould to explore homeostatic adjustments by the shifting of oxidative stress markers. We also tested whether water mould infection affected survivorship, hatching time, and morphology of hatching embryos. We found that the Saprolegnia-like species is a genuine stressor and substantially altered the physiological state of E. bicolor embryos. Among antioxidant defences, superoxide dismutase (SOD) and glutathione S-transferase (GST) activities increased in embryos exposed to the Saprolegnia-like species. However, no difference in lipid peroxidation levels was found between treatments, which might indicate that SOD and GST activations could be enough to prevent oxidative damage. Finally, we found higher mortality and number of malformations in the water mould treatment. We showed the stressful effect of water moulds on amphibian embryos, evidenced by the activation of their antioxidant system, and reveal the importance of considering physiological stress markers as key information when studying the potential consequences of disease outbreaks in the ecology and conservation of amphibians.