Amphibians face significant dehydration challenges due to their permeable skin and weak water retention mechanisms, especially under ongoing global warming that predicts increasing land dryness. This makes the identification of physiological stress indicators crucial to assessing hydric risk in amphibian populations. This study examines iris darkening as a response to dehydration in the neotropical tree frog (Boana punctata) under controlled conditions. Twenty-five adult frogs were collected in the province of Chaco, Argentina, and subjected to sequential dehydration treatments (10, 20, and 30 min) using two methods (constant airflow of 0.2 m/s or desiccant rice), followed by 2-h rehydration. Linear mixed‑effects models revealed a strong negative relationship between hydration level and iris darkening, increasing about 1.5% in dark area for each 1% loss in hydration level, consistent across dehydration methods and with similar sensitivity across body sizes and individuals, although larger frogs showed lower baseline darkening. Iris darkening showed partial reversal post-rehydration. This validates iris darkening as a robust, non-invasive biomarker for hydric stress in wild amphibian populations facing climate-driven aridity.

Urbanization influences responses of organisms differently compared to non-urbanized environments, but the patterns of these responses across different geographic contexts remain poorly understood. In this study, we employed a geographically replicated design across 32 sites in two countries—Argentina and Uruguay—to examine how the morphology of the common toad, Rhinella arenarum, varies in relation to spatial predictors, environmental factors, and urbanization. We characterized each sampling site using a composite urbanization index and collected 16 morphometric traits from 360 adult toads (255 males, 105 females). We used Random Forests to identify sex-discriminant traits, linear mixed models to assess the influence of urbanization, and variance partitioning to clarify the contributions of environmental, spatial, and urban components to morphological traits. We found a marked difference between the sexes in spatial patterns: male morphology was significantly spatially structured, whereas female morphology was not. Results revealed that environmental gradients, particularly water availability, were the primary correlates of morphological variation. Urbanization acted as a significant secondary correlate, exhibiting sex-specific and context-dependent influences. Males showed nonlinear changes in both snout-vent length and body weight along the urbanization gradient, whereas females did not. Both sexes, however, exhibited distinct changes in head morphology and limb dimensions. Despite geographic heterogeneity in morphological responses, male foot length and female tibia–fibula length showed consistent and parallel responses among cities. We suggest that urbanization does not override broad-scale ecological patterns but interacts with them, producing both context-dependent and parallel morphological responses. This interplay highlights the role of phenotypic plasticity in facilitating the persistence of R. arenarum in urban ecosystems.

.-Variations in environment can lead to differences in life-history traits across anuran species. Increased environmental stress can result in increased age at sexual maturity, slower growth, longer longevity, and larger body size, among others. Sexual size dimorphism (SSD) refers to how multiple selective forces drive evolution of sex-specific body size. Our aims were to study sexual size dimorphism (SSD) in Pleurodema nebulosum, and to understand demographic life-history traits such as age structure, age at maturity, and longevity. Chronological formation of lines of arrested growth was analyzed in relation to reproductive activity and SSD. We observed sexual dimorphism in body size, with females reaching a significantly larger size than males. According to our skeletochronology results, P. nebulosum females reach sexual maturity at a later age than males. Therefore, females grow more slowly and delay sexual maturity, giving them more time to allocate energy to growth. On the other hand, males were on average younger than females. This pattern may be due to higher predation rates during the reproductive period, due to vulnerability from calling behavior.

Leptodactylidae es una de las familias de anuros más diversas del mundo (239 especies) y posee una amplia distribución en el continente américano. Sus hábitos de alimentación reflejan esta diversidad mostrando múltiples estrategias. El canibalismo en esta familia ha sido reportado en diferentes momentos del ciclo de vida, y es evidente entre los adultos. Nosotros reportamos un caso de canibalismo en Leptodactylus bufonius (Anura: Leptodactylidae) evidenciado luego de una regurgitación por parte de un individuo adulto durante el período de aclimatación en un estudio de balance hídrico. Este reporte contribuye a la evidencia de la dieta generalista del género Leptodactylus y es el primer reporte de canibalismo para esta especie.

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We studied the thermal tolerances of Odontophrynus occidentalis during the dry and wet seasons of the Monte Desert in San Juan Province, Argentina. This toad had differences in CTmax between dry and wet seasons, with CTmax values being greater in the wet season (Austral summer). Operative temperature, body temperature, and environmental maximal temperature were related to CTmax suggesting seasonal acclimatization in O. occidentalis. Additionally, the CTmax recorded for O. occidentalis was 36.1ºC, and the maximum ambient temperature measured during the toads’ activity time was 37ºC. The CTmin of O. occidentalis was 4.1ºC while the minimum environmental temperature recorded was 7.2 ºC. The wide tolerance range observed and the relationship between tolerance limits and the environmental extremes indicate that seasonal acclimatization is an effective mechanism by which toads can raise their thermal tolerance. This is a highly relevant adaptation allowing them to survive in the challenging conditions of the Monte Desert.

Locomotion is a fundamental aspect in the life cycle of any organism, and plays a crucial role in survival, feeding, escaping from predators, territoriality, and reproduction. Locomotion in amphibian anurans includes swimming, walking, jumping, climbing, and gliding. Amphibians living in arid regions face a constant compromise between hydration balance and locomotor performance. We studied the effects of water stress on the locomotion of the frog Pleurodema nebulosum, a specialist from the Monte Desert. Locomotor performance was measured through different physical variables during the jump. The locomotor performance of P. nebulosum showed a significant decrease in the magnitudes associated with a decrease in body hydration. Our study demonstrated how a desert-adapted frog (P. nebulosum) showed changes in locomotion related to the loss of body water. Additionally, we observed an abrupt drop in locomotion with 15% desiccation, followed by a plateau where the evaluated parameters remained stable. Pleuroderma nebulosum showed a clear adaptation to extreme desiccation. The frogs are rarely found in optimal hydration conditions as the environment in which they develop is extremely stressful from a water perspective. The data evaluated here are the beginning of a deeper exploration of the desert adaptations of South American desert frogs.

One of the main causes of contamination of aquatic environments, which affects biotic communities, is the use of pesticides in agricultural regions. Amphibians are considered good bio-indicators of aquatic pollution, because they are one of the most susceptible groups to pollution. Several studies suggest that both pollution and climate change produce synergistic effects in amphibians which amplify the toxicity afecting survival, and malformations with an increase in temperature. We studied the sensitivity of sublethal concentrations of dimethoate in Rhinella arenarum tadpoles on two fitness related thermal traits including locomotor swimming performance and thermal tolerance limits (CTmax = critical thermal maximum and CTmin = critical thermal minimum). The locomotor performance of R. arenarum tadpoles decreased with increasing sublethal dimethoate concentrations up to similar to 60 % at intermediates dimethoate concentration. The tadpoles showed a tendency to decrease their tolerance to high temperatures (CTmax) with increasing dimethoate concentration around similar to 0.5 degrees C, however no significant differences were found among treatments. Similarly, tadpoles showed decreases in their cold resistance (CTmin) with dimethoate concentrations, around 1 degrees C the high concentrations of dimethoate. The increase of atypical climatic events, such as heat waves may put R. arenarum tadpoles at greater risk when exposed to dimethoate. Our results show that the sublethal concentrations of the dimethoate pesticide may affect the fitness and survival of the larvae of R. arenarum in natural, and seminatural enviroments.

The intensive use of agrochemicals and the rapid increase of global temperatures have modified the thermal conditions of aquatic environments, thus increasing amphibians ' vulnerability to global warming and positioning them at great risk. Commercial formulations of chlorpyrifos (COM) are the pesticides most widely used in agricultural activities, with a high toxic potential on amphibians. However, little is known about the separate effects of the active ingredient (CPF) and adjuvants (AD). We studied the thermal sensitivity at different concentrations and pesticide fractions in Rhinella arenarum tadpoles, on thermal tolerance limits (CT max = Critical thermal maximum and CT min = Critical thermal minimum), swimming speed (S s ), Optimum temperature (T o p ), and Thermal breadth 50 (B 50 ). Our results demonstrate that the pesticide active ingredient, the adjuvants, and the commercial formulation of chlorpyrifos differentially impair the thermal sensitivity of R. arenarum tadpoles. The pesticide fractions affected the heat and the cold tolerance (CT max and CT min ), depending on the concentrations they were exposed to. The locomotor performance (S s , T op , and B 50 ) of tadpoles also varied among fractions, treatments, and environmental temperatures. In the context of climate change, the outcomes presented are particularly relevant, as mean temperatures are increasing at unprecedented rates, which suggests that tadpoles inhabiting warming and polluted ponds are currently experiencing deleterious conditions. Considering that larval stages of amphibians are the most susceptible to changing environmental conditions and the alarming predictions about environmental temperatures in the future, it is likely that the synergism between high temperatures and pesticide exposure raise the threat of population deletions in the coming years.

Testosterone, the primary sex hormone in male lizards, is closely linked to Leydig cell activity (the cells where steroidogenesis occurs) throughout the reproductive cycle, but testosterone action is related to androgen receptors (ARs) distribution in the seminiferous epithelium. In temperate zones, environmental factors detected through the hypothalamic-pituitary-gonadal axis, downregulate plasma testosterone, resulting in a seasonal reproductive cycle. The aim of this work is to study plasma testosterone in adult male lizards of Liolaemus cuyanus, an oviparous species, throughout its reproductive cycle and its relationship with Leydig cell histology, TotalLeydigCell/ActiveLeydigCell (TLC/ALC) ratio, environmental factors (temperature, relative humidity and solar irradiation) and ARs distribution in seminiferous epithelium. Specimens (N = 27) were captured (October to March) in a semi-arid zone (Valle de Matagusanos, San Juan, Argentina) and grouped into three relevant reproductive periods: pre-reproductive (PrR), reproductive (R), and post-reproductive (PsR). Significant differences in plasma testosterone were found among these periods, highest during R than in PsR. A significant positive correlation between plasma testosterone and TLC/ALC ratio was also observed. Plasma testosterone has a significant positive correlation only with solar irradiation, but not with the other variables. In PrR and R, ARs distribution was cytoplasmic and nuclear, shifting to only cytoplasmic in PsR. These results highlight the close correspondence between plasma testosterone, Leydig cell histology and activity, environmental factors, and ARs distribution, resulting in a synchronization that allows males of L. cuyanus to coordinate their reproductive cycle with the most favorable environmental conditions, probably for mating and birth of offspring.

Male reproductive cycles in lizards can be continuous or seasonal depending on the environmental conditions and female availability. The aim of this study is to investigate whether adult males of the psammophilus lizard Liolaemus cuyanus present seasonal changes of reproductive traits throughout the reproductive cycle. In order to carry out this task, sampling of specimens (N = 27) was carried out monthly from October to March in Valle de Matagusanos, Ullúm, San Juan, Argentina (31°06′46.08′’ S, 68°38′03.84′’ W; altitude: 945 m), a semi-arid zone. The animals captured in different months were grouped based on reproductive criteria according to three relevant periods: pre-reproductive (PrR), reproductive (R) and post-reproductive (PsR). In order to identify and characterize these periods, several male reproductive traits were obtained, like morphometric parameters (body mass, snout-vent length, testes and abdominal fat body mass), tubular surface and estimation of the interstitial tissue coverage, combined with histological and cell seminiferous tubule observations (germ cells types, histological and ultrastructural details) and presence of sperm in the cauda epididymis. During the PrR period, which occurred during spring, well-developed testes with free tubular sperm cells were present, but these were less frequent than during the R period. On the other hand, luminal sperm cells were evident at the seminiferous tubules from the beginning of the R period, in conjunction with the maximum testes mass and seminiferous tubular surfaces. This was also coincident with a higher abundance of sperm cells in the cauda epididymal lumen. At the end of this period, the initial regression of the seminiferous epithelium was corroborated by organelle regression which was observed in the ultrastructure of spermatogenic cells. At the beginning of the PsR period, before autumn, a marked decrease in male reproductive traits above described was detected. Instead, an increase in abdominal fat body mass could be observed indicating the onset of the lethargy period. The results obtained suggest that this population of L. cuyanus has a seasonal reproductive cycle, with its reproductive activity occurring during the spring-summer months (PrR-R periods) and finishing in late summer (PsR).

El campo magnético de la Tierra (EMF) es una de las fuentes de información direccional más uniformes y accesibles que los animales pueden usar en los movimientos de comportamiento. El presente estudio tuvo como objetivo determinar la capacidad de Rhinella arenarum para percibir los campos electromagnéticos. Para evaluar la influencia de los campos electromagnéticos en los anuros in situ, recolectamos cuarenta y cuatro especímenes adultos de R. arenarum durante la temporada de reproducción. Registramos el movimiento de cada sapo desde el centro hasta la periferia de un arenero circular utilizando una cámara de visión nocturna. Repetimos el experimento después de cinco minutos, con un campo magnético inducido adicional (IMF), que fue creado empleando dos bobinas de aire Helmholtz. Los movimientos de los sapos bajo la presencia de EMF y IMF fueron significativamente diferentes. Concluimos que R. arenarum podría usar el EMF como mecanismo de navegación y sistema de ubicación, para viajar largas distancias hasta los estanques de desove año tras año.

The competitive effects among tadpoles make the bullfrog a possible agent of native amphibian population declines at its introduction sites. Our aim was to analyze the dietary composition of an invasive population of Lithobates catesbeianus tadpoles and to evaluate the degree of dietary changes among activity months. We hypothesized that bullfrog tadpoles would exhibit temporal changes in diet, consistent with the variation of tadpole size and availability of resources. We collected 94 bullfrog tadpoles and identified 50 taxa in their digestive tracts. The items most frequently consumed were microalgae of the genera Navicula (frequency of occurrence [Fo] = 19) and Cymbella (Fo = 17). The trophic niche breadth was 8.13, which is considered moderate-high. The trophic habits of L. catesbeianus larvae changed seasonally, with the diets during October and December being numerically similar (Morisita's quantitative index = 0.86). The composition of the diet had a similarity of 63% (Jaccard's qualitative index) between August and October. The larvae of L. catesbeianus collected during the different months showed significant differences in their stages of development and body mass. On average, individuals were larger and more developed in the month of December, which was to be expected given that the abundance of prey items is greatest during the summer season. Our results show that L. catesbeianus tadpoles have a wide trophic niche with a diet that is not strongly selective; thus, the aquatic life-history stages play an important role in the structuring of invaded anuran larval communities.

Current assessments of organismal vulnerability to global warming are focusing on physiological trait-based indices that may allow biologically sounding estimates of heating risk at the local scale. However, intraspecific variability in both exposure and physiological performance may determine large heterogeneity in the distribution of heating risks through the overall species range compromising whole species risk assessments. We examine intra- and interspecific variability in two vulnerability indexes: warming tolerances (WT), or the extent that maximum temperatures (T (max)) reaching upper thermal tolerances (CTmax); and thermal safety margin (TSM), or the magnitude that average environmental temperatures (T (mean)) exceeding the selected or preferred temperatures (T (sel)), in a subtropical warm amphibian tadpole community, at the Monte Desert ecoregion, Argentina. Tadpole populations breeds in temporary ponds and permanent streams that exhibit high thermal heterogeneity. Those populations and species living in hot water bodies, although exhibiting higher CTmax, have lower WT and are more prone to suffer acute heat impacts, thus confirming the prediction of higher thermal risk in ectotherms exposed to higher temperatures. However, these hot pond breeders, although living closer to their CTmax, also preferred high temperatures, showing higher TSMs and being actually exposed to a lower proportion of stressful temperatures than cool selecting populations. Both WT and TSM indexes have significant interpopulational variation. Thus, our findings suggest that attempts to build mechanistic models to forecast species vulnerability to heat stress due to climate change have to include physiological variation among populations.

We studied the thermophilic response to feeding of a typical desert adapted anuran from the Monte Desert. Our aim was to evaluate thermal changes in the selected body temperature of adult frogs of Pleurodema nebulosum, and measure the intestinal passage time, and food digestion. Our results show that after feeding, they selected higher micro-environmental temperatures ~ + 2 °C than frogs that remained starved. Pleurodema nebulosum would present a postprandial thermophilic response. The time of retention of food in the digestive tract was thermo-dependent, being lower in those individuals who were incubated at high temperatures (25 °C) compared to those subjected to lower temperatures (20 °C). Although we did not detect effects of temperature on digestive efficiency, the mass of faecal material indicates an increase at temperatures closer to the selected ones, suggesting that the defecation rate is influenced by temperature. Laiuoperinae frogs are characterized by explosive breeding behavior and fast growing rate. The digestive efficiency is essential for acquiring energy necessary for growth, reproduction and refuge-seeking, among others. In this framework, the differential selection of temperatures between moments of fasting and feeding allows the frogs to maintain a high digestive efficiency, maximizing the absorption of nutrients.

The temperature of anuran activity from arid regions have been poorly studied. In recent years, the emphasis was placed on predicting the impacts of global warming on the fauna of ectotherms in general. Many times future impacts are predicted based on global thermal information (macroscale) but not on an individual scale. We used literature data about body temperature in anurans that inhabit the desert region of the Northwest of Argentina to analyze the role of the elevation, eco-region and substrate temperature on the individual scale. Also, we evaluated the predictive capacity that global environmental variables obtained from WorldClim for this region, and compared them with those of local scale. Our results showed that the activity body temperature of the toads in the arid region of western Argentina strongly influenced by elevation and the substrate temperature on the individual scale. We observed that data of the global scale (WorldClim) can predict the body temperature of the studied amphibians, but with a deviation, not less than 8 °C. According to our results, it is evident that to making reliable predictions of how global warming impacts on amphibians in the region, the environmental temperature data need to be recorded at the local scale (operative temperatures).

Objective: This study reports the presence of a copepod, affecting adults of the torrent catfish in a tributary of the San Juan River in the southern part of South America. Materials and Methods: The fish (48.1-54.1 mm standard length) were collected in Los Bretes, San Juan province, Argentina. They were anesthetized, fixed in formalin, preserved in ethanol and deposited in the Ichthyological Collection of the FACEN. Results: Three torrent catfish (Trichomycterus corduvensis) examined were infested with nine copepod parasites (Lernaea cyprinacea), which were attached to the gill, urogenital opening, and base pectoral fin. Conclusion: According to our results, this is the first record of parasitism of Lernaea on the torrent catfish (T. corduvensis) and a new locality from the Andean Mountains of Argentina.

Few studies have characterized the reproductive cycles of desert anurans, particularly species from South America. This has hampered efforts to identify broad patterns in anuran reproduction, which are known to vary both phylogenetically and throughout climatic gradients. We studied the reproductive cycle of male Odontophrynus barrioi, a small (similar to 20 g) terrestrial toad from the Monte Desert of San Juan, Argentina. The main goal of this work was to determine spermatogenic activity, plasma testosterone concentrations, and reproductive parameters during prereproductive (preR), reproductive (R), and postreproductive (postR) periods. We determined the plasma testosterone concentrations in male toads by radioimmunoassay (RIA). We performed histological analyses of the testes of males with the use of the hematoxylin and eosin method, and also examined the testes with a light microscope. During the preR and R periods, spermatogenesis in O. barrioi showed substantial development of the late stages (sperm bundles), coincident with high sperm percentage (spermiation) in the seminiferous tubules. Spermiation occurred when testosterone levels were high. This species exhibits a continuous spermatogenic cycle, with maximum levels of testosterone during the dry season. Therefore, O. barrioi is a desert-adapted anuran exhibiting an "associated'' reproductive strategy given its association between breeding season and high plasma testosterone concentrations. This reproductive strategy likely evolved to coordinate the reproductive cycle with brief rains in summer as an adaptation to the challenging climate imposed by the desert environment, as well as Monte Desert.

Rhinella spinulosa is distributed from Peru to Argentina (from 1200 to 5000 m elevation), inhabiting arid mountain valleys of the Andes, characterized by salty soils. The variations in soil salinity, caused by high evapotranspiration of water, can create an osmotic constraint and high thermal oscillations for metamorphsed Andean toad (R. spinulosa), affecting their thermoregulation and extreme thermal tolerances. We investigated the changes in thermal tolerance parameters (critical thermal maximum and crystallization temperature) of a population of metamorphosed R. spinulosa from the Monte Desert of San Juan, Argentina, under different substrate salinity conditions. Our results suggest that the locomotor performance of metamorphs of R. spinulosa is affected by increasing salinity concentrations in the environment where they develop. On the other hand, the thermal extremes of metamorphs of R. spinulosa also showed changes associated with different salinity conditions. According to other studies on different organisms, the increase of the osmolarity of the internal medium may increase the thermal tolerance of this species. More studies are needed to understand the thermo-osmolar adjustments of the metamorphs of toads to environmental variability.