Caves are, by definition, subterranean spaces that range from canaliculi only a few millimeters wide to caverns large enough for human entry and transit. Compared with the surface, their characteristics are strikingly peculiar. Light is permanently absent, which means little or no primary productivity. Humidity tends toward saturation. Temperatures remain mild and stable. Energy resources are largely allochthonous, arriving from outside rather than being generated within. These conditions arise because caves form in the most varied types of rock, mainly through mechanical and chemical action of water on the matrix rock in landscapes known as karst. Water also acts as the great transporter of trophic resources into the subterranean realm, carrying organic material from the entire recharge area, and it can remain stored in caves for prolonged periods due to underground water dynamics. That stability attracts organisms seeking an environment that is less disturbed than the surface.

For amphibians, whose permeable skin makes them exquisitely vulnerable to desiccation, the cave environment offers an almost ideal combination. High relative humidity and low incidence of sunlight prevent the skin from drying out, a factor that has long been recognized as decisive for frog shelter. But the subterranean realm also provides conditions for other fundamental activities in the anuran life cycle. Feeding is possible because caves support a wide diversity and abundance of invertebrates. Reproduction is feasible because water bodies are frequently present inside caves. Moreover, the cave environment reduces exposure to predators. Taken together, these features suggest that caves could function as true habitats rather than mere rocky refuges, yet the scientific literature has treated frog presence underground with skepticism.

The skepticism has a history. Frogs have traditionally been considered accidental animals in the subterranean environment, meaning they eventually enter a cave and do not stay there, leaving within a short period, or failing to find their way out and dying inside. This assumption has shaped decades of research priorities, and it shows. Studies on reptiles and amphibians linked to speleology in South America remain scarce. The works focused on this type of habitat occupation have recorded only about 6 percent of the 1,144 Brazilian frog species inside caves. The scarcity of data is itself a product of the accidental-fauna assumption, creating a circular problem: because frogs are presumed accidental, few studies document them, and because few studies document them, the presumption goes unchallenged.

The new paper challenges that presumption directly. Drawing on the authors’ own records and those of research partners in biospeleology, the study compiles evidence of numerous frog species found in caves of four different lithologies, distributed from north to south of Brazil across the Amazon, Atlantic Forest, Caatinga, Cerrado and areas near the Pantanal. The records span sites in Parauapebas in Pará, Natividade and Arraias in Tocantins, Ourolândia in Bahia, Caverna da Ponte de Pedra in Goiás, Caverna das Pitangueiras in Mato Grosso do Sul, Serra da Piedade and Belo Horizonte in Minas Gerais, Ribeirão Bonito and Caverna do Cafezal in São Paulo, and Caverna do Zé in Paraná. Among the species documented are Adelphobates galactonotus, Rhaebo guttatus, Rhinella diptycha, Scinax x-signatus, Leptodactylus labyrinthicus, Bokermannohyla species, Scinax fuscovarius, Ischnocnema verrucosa, Physalaemus cuvieri, Bokermannohyla martinsi, Crossodactylus caramaschii, Cycloramphus eleutherodactylus, Aplastodiscus albosignatus and Boana bischoffi. This geographic and taxonomic breadth suggests that cave use by frogs is neither rare nor restricted to a single geological setting.

Based on this evidence, the authors argue that several species can be classified as trogloxenes, following the Schiner-Racovitza classification as adapted by Sket in 2008. Trogloxenes are animals that can inhabit the cave environment for reproduction, food or shelter. In the case of anurans, this resembles the group with cryptozoic habits, hiding in galleries or small cavities in the ground or ravines, and rheophilic tendencies, occupying rocks located next to or beside small streams or rapids. Preliminary studies already show signs that anurans are inhabitants better suited to being classed as trogloxenes rather than accidents, and they are already treated this way in other parts of the world, including studies in Mexico and Thailand. The Brazilian evidence now adds a continental-scale dimension to that global picture.

Yet the authors are careful to frame their argument as a discussion rather than a definitive conclusion, and they identify several important questions for future biospeleological research. Are frogs able to complete their entire life cycle inside caves? Can they maintain a diet without nutritional deficit in this environment? Are they preyed upon, and if so, by whom? How does the use of cave habitat differ from the use of the rocky environment? Answering these questions systematically is difficult because it is nearly impossible to follow the life cycle of an anuran in this hard-to-access environment. The authors propose that studies in controlled laboratory environments could bring new evidence to fill the knowledge gap, and that an increase in long-term population studies with frogs in caves would help improve the ecological understanding of the taxon.

The conservation implications of the accidental-fauna assumption are substantial. When all anurans are considered accidental fauna, there is no legal support for these species in the environmental legislation for subterranean environments currently in force in Brazil. There is no legal obligation to collect and register anurans in caves, and companies responsible for projects are optional in registering these species in studies of relevance, impacts and environmental monitoring. Anurans thus go against the grain of other groups such as Chiroptera and invertebrates, which served as the basis for studies that leveraged subterranean biology research from Decree 6640 in 2008. For those groups, there has since been a significant increase in descriptions of cave invertebrates, research of paramount importance for bats, and the description of hotspots of subterranean fauna in various regions of Brazil. Despite these advances, the herpetofauna remains completely neglected.

The stakes are high because the cave environment is one of the most threatened habitats in the face of mineral exploration and urban development, even though it is classified as Brazilian cultural, biological and geological heritage. Today, Brazilian caves are under high pressure for licensing, including those classified as of maximum relevance, which have hitherto been prevented from being impacted. The diversification of ecological and conservation studies expanded to other groups, such as herpetofauna, could bring new insights into subterranean environments and increasingly consolidate the paths for recognition of their ecological importance. Whether caves are true habitats for anurans or merely a favorable rocky environment is more than an academic question. It determines whether frogs count when the fate of a cave is decided.

Subject of Research: Are caves true habitats for anurans or more a favorable rocky environment? A discussion of habitat occupation by frogs in Neotropical caves

Article Title: Are caves true habitats for anurans or more a favorable rocky environment? A discussion of habitat occupation by frogs in Neotropical caves

Article References: Sperandei, V. D. F., Alvarenga, D. D. A., Araújo, M. S. D., & Pereira, C. C. (2023). Are caves true habitats for anurans or more a favorable rocky environment? A discussion of habitat occupation by frogs in Neotropical caves. Neotropical Biology and Conservation, 18(3), 131-137. https://doi.org/10.3897/neotropical.18.e100778

Image Credits: AI Generated

DOI: 10.3897/neotropical.18.e100778

Keywords: caves, true, habitats, anurans, favorable, rocky, environment, discussion, habitat, occupation, frogs, Neotropical

The research team, led by scientists from Brazilian and Argentine institutions, applied a combination of classical cytogenetic techniques and modern molecular mapping methods to five species within the P. gracilis group. Their goal was ambitious: to test a long-standing hypothesis about chromosome homology across these closely related frogs, and to determine whether the nucleolus organizer regions (NORs)—the chromosomal sites where ribosomal RNA genes cluster—occupy the same evolutionary position in different species, or whether they have shifted over time through structural rearrangements. The answer, as it turns out, is more nuanced than anyone expected.

Physalaemus evangelistai proved to have a diploid number of 22 chromosomes and a fundamental number of 44, which is entirely consistent with the karyotypic configuration seen across the entire genus. Chromosome pairs 1, 5, 6, and 10 were metacentric, while pairs 2 through 4 and 7 through 11 were submetacentric. C-banding revealed small blocks of constitutive heterochromatin in the centromeric regions of all chromosomes, a pattern that is remarkably conserved across the group. But the real surprise came when the researchers examined chromosome 8 in detail.

In every specimen analyzed, chromosome 8 carried an interstitial NOR on its long arm, coinciding with a secondary constriction visible under standard Giemsa staining. Yet the NOR was not uniform in size across individuals. The team identified two distinct morphotypes: chromosome 8a, bearing a small NOR, and chromosome 8b, carrying a much larger one. Three of the four males examined were heterozygous for this trait, while both females analyzed were homozygous for the smaller variant. More intriguingly, both females carried an additional NOR on one homologue of chromosome pair 9—a feature entirely absent from all four males and from every other karyotyped species in the group.

This sex-specific pattern immediately raised the possibility that P. evangelistai possesses a ZZ/ZW sex determination system, with the NOR serving as a cytogenetic marker distinguishing the sex chromosomes. Such a mechanism has been documented in other anuran species, including Physalaemus ephippifer, Gastrotheca riobambae, Buergeria buergeri, and Hyla femoralis, where NORs have been identified as the sole cytogenetic difference between sex chromosomes. However, the researchers are careful to note that NOR polymorphisms are relatively common among frogs in general, and the limited sample size—particularly the small number of females—prevents any definitive conclusion. Whether this heteromorphism is truly sex-linked or represents an autosomal polymorphism remains an open question that will require larger sampling efforts to resolve.

Beyond the novel karyotype description, the study made a significant contribution to the ongoing debate about chromosome homology within the P. gracilis group. Four of the six species had been karyotyped previously, and their NORs occupy seemingly different positions: interstitial on chromosome 8 in P. carrizorum and P. lisei, terminal on chromosome 8 in P. gracilis, and terminal on chromosome 10 in P. barrioi. Because chromosomes 8 through 11 in these karyotypes are very similar in size and morphology, determining whether the NOR-bearing chromosome of P. barrioi is truly homologous to chromosome 8 of the other species has been extremely challenging. The new study found a subtle but consistent clue: an interstitial DAPI-positive C-band on the short arm of the NOR-bearing chromosomes in P. evangelistai, P. carrizorum from Palmas, and P. barrioi. This shared heterochromatic feature, though faint and easily missed in some metaphase preparations, provides the first independent cytogenetic evidence supporting the hypothesis that these chromosomes are indeed homologous across the group.

The researchers also mapped two repetitive DNA sequences—PcP190 satellite DNA and the U2 small nuclear RNA gene—across the karyotypes of the analyzed species. PcP190 is a satellite DNA family widely distributed among hyloid anurans, having been reported in seven families to date. In the P. gracilis group, it produces a small number of chromosomal clusters arranged in apparently species-specific patterns. The new mapping revealed that P. carrizorum from Palmas, Paraná, carries PcP190 clusters on chromosomes 1 and 3, while P. evangelistai has a cluster only on chromosome 1, and P. barrioi shares the chromosome 1 and 3 pattern. This distribution is phylogenetically informative: the species carrying the chromosome 1 cluster (P. evangelistai, P. carrizorum, and P. barrioi) form one clade, while P. lisei and P. gracilis, which lack it, form another. The most parsimonious explanation is that the chromosome 1 cluster was present in the ancestor of the group and subsequently lost in the lineage leading to P. lisei and P. gracilis.

Perhaps the most striking finding of the entire study concerns P. carrizorum itself. Specimens from Palmas in Paraná, Brazil, differ markedly from those previously described from Misiones, Argentina—localities separated by approximately 242 kilometers. The Palmas population shows a terminal NOR on chromosome 8 and PcP190 clusters on chromosomes 1 and 3, whereas the Misiones population has an interstitial/pericentromeric NOR on chromosome 8 and only a single PcP190 cluster on chromosome 3. Additional differences in heterochromatin distribution further distinguish the two populations. These cytogenetic divergences could reflect intraspecific variation, but they could equally signal the presence of cryptic species hidden within what is currently recognized as a single taxon. The authors emphasize that further taxonomic analyses, integrating morphological, molecular, and bioacoustic data, will be essential to determine which explanation is correct.

The U2 snRNA gene mapping provided a contrasting picture of evolutionary stasis. In all four analyzed species of the P. gracilis group, U2 snRNA gene clusters are restricted to the terminal region of the short arm of chromosome 6. This same condition has been observed in other species of Physalaemus and in the related genus Leptodactylus, supporting the hypothesis that chromosome 6 is homologous across these lineages. While the authors caution that mapping this sequence in additional leptodactylid genera is needed before drawing definitive conclusions, the consistency of this marker across such a broad taxonomic range makes it one of the most reliable chromosomal landmarks available for comparative cytogenetics in the family.

Taken together, these findings paint a picture of a frog group whose genomes are simultaneously conserved and dynamic. The fundamental karyotype—22 chromosomes with a fundamental number of 44—has remained stable across the genus, yet the positions of NORs, the distribution of satellite DNA clusters, and even the number of heterochromatic bands vary considerably between species and even between populations of the same species. This combination of stability and lability makes the P. gracilis group an excellent natural laboratory for studying how chromosomal rearrangements contribute to speciation, particularly in a lineage already known for its high frequency of cryptic diversity. As the authors note, much work remains to be done, but the characterization of P. evangelistai‘s karyotype and the identification of shared heterochromatic markers on NOR-bearing chromosomes represent important steps toward resolving the evolutionary history of this enigmatic group of Neotropical frogs.

Subject of Research: Comparative cytogenetics and karyotype characterization of frog species in the Physalaemus gracilis group

Article Title: Comparative cytogenetics of the Physalaemus gracilis group ( Anura , Leptodactylidae ) with characterization of the karyotype of Physalaemus evangelistai Bokermann, 1967

Article References: Mosquini, P. H. P., Souza, L. H. B., Ferro, J. M., & Lourenço, L. B. (2025). Comparative cytogenetics of the Physalaemus gracilis group (Anura, Leptodactylidae) with characterization of the karyotype of Physalaemus evangelistai Bokermann, 1967. Comparative Cytogenetics, 19, 171-188. https://doi.org/10.3897/compcytogen.19.171637

Image Credits: AI Generated

DOI: 10.3897/compcytogen.19.171637

Keywords: Physalaemus, cytogenetics, karyotype, NOR, satellite DNA, FISH, anurans, chromosome evolution, Leptodactylidae, heterochromatin, cryptic species, U2 snRNA

Anurans, the order that includes frogs and toads, are famously sensitive vertebrates. Their permeable skin demands moisture, their life cycles are tightly coupled to both aquatic and terrestrial conditions, and their distributions are strongly shaped by environmental stability. Yet these same vulnerabilities make caves attractive. Natural subterranean environments offer high and relatively stable humidity, reduced temperature fluctuations, and near-total darkness, conditions that shield amphibians from desiccation and from visually oriented predators. Caves frequently host abundant invertebrate prey and often contain watercourses suitable for reproduction, making them potential all-purpose shelters for animals that are predominantly nocturnal to begin with.

To understand which anurans actually exploit these environments, the researchers compiled 177 occurrence records covering 54 species from the scientific literature, drawing on Google Scholar, Scopus, and the Web of Science following PRISMA guidelines for systematic searches. Only records with complete species-level identification were retained, and nomenclature was verified against the authoritative Amphibian Species of the World database. Each species was then characterized by its conservation status under both the IUCN Red List and the Brazilian Ministry of the Environment, its geographic distribution, endemism, and a suite of life-history traits including activity period, body size, habitat, and breeding site.

The statistical centerpiece of the study was a redundancy analysis, a multivariate technique that relates a matrix of explanatory variables to a matrix of response variables. Before running the model, the team checked for multicollinearity among predictors using variance inflation factors, keeping all variables below the conventional threshold of 10.0. The analysis revealed that three variables tied to conservation status and geography, namely IUCN status, distribution area, and endemism, best explain which anurans turn up in Brazilian caves. These three predictors accounted for 27.0 percent of the total variance explained by the model, with the first two ordination axes capturing 31.1 percent of the variance, and the overall model was statistically significant at p = 0.001.

The dominance of Least Concern species was striking. Of all occurrence records compiled, 94.3 percent corresponded to species classified as Least Concern under both the IUCN and the Brazilian national list. Threatened categories were marginal by comparison: Vulnerable species made up 3.5 percent of IUCN-classified records and Endangered species 1.5 percent, while the national classification included Near Threatened at 3.5 percent and Endangered at 1.5 percent, with 0.7 percent of records not evaluated. Eight species were strongly associated with the conservation-status variable, including the poison frog Adelphobates galactonotus, the rocket frog Allobates marchesianus, the striped poison frog Ameerega flavopicta, several hylid tree frogs of the genera Boana and Bokermannohyla, and the cycloramphid Cycloramphus eleutherodactylus. Only one species, Bokermannohyla martinsi, carried a Vulnerable designation.

Why would common, wide-ranging species dominate cave records? The authors argue that broad geographic distributions signal low niche specificity. Species capable of occupying heterogeneous environments, from leaf litter to stream margins to rock crevices, possess the ecological plasticity to treat caves as one more available microhabitat. Ameerega flavopicta, Cycloramphus eleutherodactylus, and Boana boans, for example, already use rock crevices, holes in slopes, tree trunks, and bromeliad rosettes, microhabitats whose microclimatic conditions resemble those inside caves. Such surface habits provide indirect evidence that these animals can tolerate, and potentially exploit, subterranean conditions when the need arises.

Geographic distribution and endemism carved the species into three distinct biogeographic patterns. Scinax ruber and Scinax x-signatus are non-endemic and widely distributed, hylid tree frogs that thrive in everything from anthropized open areas to preserved forest interiors, a versatility that favors opportunistic cave occupation as temporary shelter. Thoropa miliaris and Thoropa taophora are endemic but relatively widespread within their regions, often associated with disturbed or heterogeneous environments, and may enter caves seasonally during periods of surface water or thermal stress. Finally, Thoropa megatympanum stands apart as endemic with a restricted range, confined to the rupestrian landscapes of the Serra do Espinhaço in Minas Gerais. Its presence in caves appears less tied to generalism and more to the availability of humid rocky microhabitats, since the genus deposits eggs on wet surfaces and its tadpoles are adapted to water films on rock, demanding high humidity stability.

Perhaps the most counterintuitive finding was what did not matter. Life-history variables, including activity period, body size, habitat, habits, and breeding site, contributed little to the model’s explained variance and were not selected as determinants of cave presence. The authors suggest this reflects both ecological reality and methodological limitations: life-history traits for many Neotropical anurans are incompletely or inconsistently reported, weakening their statistical power. The result implies that cave occupation depends less on physiological or behavioral specialization and more on the geographic and ecological context of each species, reinforcing the interpretation of caves as complementary microhabitats open to a broad range of ecologically distinct species.

The study also exposes a regulatory blind spot. Under Brazilian environmental legislation governing subterranean environments, anurans are classified as accidental fauna, a category for animals that wander into caves without the capacity to sustain themselves there. Because of this designation, there is no legal obligation to record or collect anurans during cave studies, in contrast to bats, fish, and invertebrates, which are explicitly covered and have driven much subterranean research since Federal Decree 6640 in 2008. This legal gap has left herpetofauna marginal in biospeleological research, producing sporadic records and regional sampling biases that the authors caution should temper interpretation of macroecological patterns drawn from published data.

The implications for conservation are concrete. The researchers recommend systematically incorporating anuran surveys into environmental licensing procedures and speleological inventories, since these animals are currently overlooked in many cave monitoring programs. They also point to emerging tools, acoustic monitoring, environmental DNA detection, and genetic comparisons between cave and surface populations, as promising avenues for clarifying habitat use, detectability, and population connectivity in subterranean ecosystems. For now, the message is clear: Brazilian caves are not frog fortresses of rare endemics but flexible refuges serving the generalists, and protecting them means recognizing that even common species depend on the stability these dark chambers provide.

Subject of Research: Macroecology of anuran habitat use in Brazilian caves

Article Title: Opportunistic habitat use: widespread and non-threatened anurans in Brazilian caves

Article References: Sperandei, V. D. F., Vaz-Silva, W., Pereira, C. C., & Tejerina-Garro, F. L. (2026). Opportunistic habitat use: widespread and non-threatened anurans in Brazilian caves. Neotropical Biology and Conservation, 21(1), 31-48. https://doi.org/10.3897/neotropical.21.e184592

Image Credits: AI Generated

DOI: 10.3897/neotropical.21.e184592

Keywords: anurans, Brazilian caves, cave ecology, amphibians, redundancy analysis, IUCN conservation status, endemism, ecological plasticity, Neotropical biodiversity, subterranean habitats, trogloxenes, systematic review

The research team, led by Ivy Miranda Amaral-Alves of the Federal University of Bahia and Luisa Maria Diele-Viegas, worked across two major mountain chains: the Serra da Mantiqueira, sampled in Itatiaia National Park, and the Serra do Mar, sampled in Serra dos Órgãos National Park. At Itatiaia, they focused on high-altitude zones between 2,100 and 2,450 meters, while at Serra dos Órgãos they covered a broader elevational sweep from 980 to 2,200 meters over multiple years. This design intentionally combined a multi-year temporal breadth at one site with a focused spatial snapshot at another, providing a robust assessment of thermal biology across distinct montane thermal regimes.

The technical approach was elegantly non-invasive. Rather than handling frogs with cloacal thermometers, which can inflate body temperature readings through capture-induced stress, the researchers used a portable infrared digital thermometer to measure the dorsal skin surface from a fixed distance of 30 centimeters, ensuring the field of view focused exclusively on the animal’s body and avoiding interference from the background substrate. Air temperature was measured one centimeter above the substrate with a quick-reading thermometer, and substrate temperature was recorded immediately after capture at the same location. The team also measured snout-vent length with digital calipers, body mass with a precision scale, and elevation with GPS, while recording sex and the specific microhabitat type at each capture site, whether arboreal, bromeliad-dwelling, riparian, or terrestrial.

Only active individuals were measured. Frogs that were calling, moving, or foraging at the time of encounter provided body temperatures that reflected realized thermal status during activity, while inactive or sheltered animals were excluded. Sampling was primarily conducted between 30 minutes and 3 hours after dusk to standardize nocturnal encounters, with one notable exception: the small toad Melanophryniscus moreirae, the only diurnal species in the assemblage, was sampled during its peak daytime activity on high-altitude rocky outcrops around 2,450 meters.

The results paint a vivid picture of thermal life in these mountains. Body temperatures ranged from a chilly 12.2 degrees Celsius in the terrestrial leaf-litter frog Ischnocnema melanopygia to a comparatively balmy 22.1 degrees Celsius in the riparian Cycloramphus brasiliensis. The diurnal Melanophryniscus moreirae, sampled 50 times, exhibited significantly greater intraspecific thermal variation than the pooled nocturnal assemblage, a pattern consistent with exposure to the daily thermal heterogeneity of daytime activity. Among nocturnal species, the greatest intraspecific variation was observed in Aplastodiscus arildae, though the researchers caution that this observation is based on only three individuals and must be interpreted as preliminary.

The statistical analysis, using linear mixed-effects models with species identity as a random effect, delivered a clear verdict. Substrate temperature was the primary significant predictor of body temperature in nocturnal anurans, while air temperature lost significance when additional covariates were included. Microhabitat specialization also mattered: individuals captured in riparian habitats exhibited significantly higher body temperatures than those in other microhabitats, suggesting that streamside environments offer distinct thermal opportunities or constraints. In contrast, body size, body mass, and sex showed no significant effects, and the random effect variance attributed to species identity was negligible, indicating that thermoconformity is a generalized physiological pattern across the nocturnal assemblage rather than a trait of individual species.

Perhaps the most technically interesting result concerns thermal inertia. Physiological theory predicts that larger individuals, with their higher thermal inertia and lower surface area-to-volume ratios, should maintain more stable body temperatures under fluctuating conditions. To test this explicitly, the researchers regressed species-specific body temperature variability against mean body mass and found no significant relationship. Larger individuals did not exhibit greater thermal stability in this dataset. The strong collinearity between body mass and environmental temperatures suggests that environmental variables effectively capture the thermal variance that might otherwise be attributed to morphological traits, explaining why body mass lost significance in the full model. Environmental forcing, it turns out, exerts a stronger influence on frog body temperature than subtle morphological buffering capacity at the spatial scale considered here.

The conservation implications are sobering. In the relatively preserved montane forests of the study sites, dense canopy cover likely acts as a thermal buffer, dampening the amplitude of microclimatic fluctuations. But in areas where forest cover is reduced or fragmented, the loss of canopy-induced buffering would likely lead to significantly higher microclimatic thermal extremes, threatening amphibian persistence. Given that these species lack the physiological capacity to buffer their internal temperatures through active thermoregulation, they may become susceptible to thermal stress and dehydration in open, modified environments. The situation is compounded by elevation-dependent warming, the phenomenon of accelerated temperature increases at higher altitudes, and by projected nocturnal warming trends that may disproportionately affect thermally constrained nocturnal species.

The focal assemblage includes species of conservation concern, including the range-restricted endemic Ischnocnema parnaso, classified as Vulnerable by the IUCN Red List, and Melanophryniscus moreirae, which relies on the microclimatic stability of high-altitude rocky outcrops. The researchers propose a tiered conservation approach: prioritizing the protection of riparian buffers and areas with dense, multi-strata canopy cover, which serve as essential thermal refugia, and maintaining elevational connectivity where topographic conditions allow, facilitating local movements among microclimatically suitable habitats under future warming.

Ultimately, this study provides a foundational assessment of thermoconforming strategies in tropical montane amphibians, one that integrates physiological data with diel niche dynamics. The researchers acknowledge limitations, including uneven sampling effort across species, the inherent measurement noise of infrared thermometry for small ectotherms, and the absence of continuous fine-scale microhabitat covariates such as relative humidity, canopy cover density, or leaf litter depth. Future studies incorporating these factors, along with phylogenetically informed comparative models and explicit vulnerability metrics such as critical thermal limits and thermal safety margins, will be essential for predicting species persistence under ongoing climate change. For now, the message is clear: in these mountains, a frog’s thermal fate is coupled to the immediate thermal environment at the scale of substrate contact, and protecting that environment is protecting the frogs themselves.

Subject of Research: Ecology

Article Title: Environmental conditions and body temperature of anurans in mountain regions of the Atlantic Forest, Brazil

Article References: Amaral-Alves, I. M., Rocha, C. F. D., Nogueira-Costa, P., Almeida-Santos, P., Drummond, L. D. O., & Diele-Viegas, L. M. (2026). Environmental conditions and body temperature of anurans in mountain regions of the Atlantic Forest, Brazil. Frontiers in Amphibian and Reptile Science, 4, Article 1867020. https://doi.org/10.3389/famrs.2026.1867020

Image Credits: AI Generated

DOI: 10.3389/famrs.2026.1867020

Keywords: amphibians, thermal ecology, Atlantic Forest, climate change, ectotherms, Environmental, conditions, body, temperature, anurans, mountain, regions

The research took place in and around Namdapha Tiger Reserve, a 1,985-square-kilometer protected area in Arunachal Pradesh that lies within the Indo-Burma biodiversity hotspot, one of the eight hottest hotspots on Earth. The reserve contains what is considered the northernmost lowland tropical wet evergreen forest in the world, and its enormous elevation range, from 200 to 4,571 meters, transitions from wet evergreen forests to wet temperate forests with increasing altitude. That habitat heterogeneity supports highly diverse species assemblages, including several endemic species found nowhere else. Yet previous amphibian surveys in this region relied entirely on observer-based methods and never incorporated passive acoustic monitoring.

Passive acoustic monitoring, or PAM, involves deploying autonomous recording units that capture the sounds of vocalizing species without any human presence during the recording period. The technology has grown rapidly more affordable over the last decade, opening acoustic surveys to wildlife researchers worldwide. But the field remains heavily skewed: until 2018, only about 12 percent of PAM studies focused on frogs, with bats and birds dominating the literature. More striking still, a recent review found no PAM studies of anurans in Asia between 2013 and 2023, even though the continent accounts for 25.5 percent of all frog species. The new study set out to close that gap in a landscape where rugged topography, dense vegetation, seasonal flooding, and logistical constraints have long hampered comprehensive biodiversity assessments.

The team selected fourteen sampling locations in the tropical evergreen forest zone, each corresponding to one of four habitats: lakes and ponds, rivers and streams, roadside water puddles, and swamps within the forest. Data were collected at the beginning of the wet season in May and June 2023, deliberately timed to avoid the risk of floods and landslides in the following months. Song Meter Micro units from Wildlife Acoustics served as the recorders, each powered by three AA alkaline batteries with silica bags inside to prevent moisture accumulation. The devices were configured to a sampling rate of 44.1 kHz with a gain of 18 dB, saving individual recordings as 60-minute files. Each unit was strapped securely to a tree or plant roughly two meters above the ground and set to record from dusk to midnight, coinciding with the peak activity period of amphibians.

To make the comparison fair, the researchers standardized effort between methods. Each recorder captured six hours of audio per site, while a nocturnal visual encounter survey conducted the following evening between 19:00 and 21:00 used three surveyors with flashlights searching for two hours, totaling six person-hours. For analysis, the acoustic data were subsampled to ten randomly selected minutes per hour of recording, yielding 60 minutes of call material per site. Using Raven Pro software, two team members with expertise in frog calls listened to the recordings and scanned spectrograms, annotating identified calls and measuring dominant frequencies. Species richness was then estimated for each method using a non-parametric bootstrap approach, resampling the fourteen sites with replacement 1,000 times, and the two estimates were compared statistically.

The headline result: both methods detected 19 amphibian species, belonging to 17 genera, with PAM capturing six families and VES seven. Both methods detected 11 endemic species, and the bootstrap-derived 95 percent confidence intervals for regional richness, ranging between 14 and 19 species, overlapped completely. A statistical test confirmed no significant difference in regional species richness between the two methods. But the composition of what each method detected told a subtler story. The Jaccard similarity coefficient came out at 0.652, meaning about 65 percent of species were recorded by both methods while roughly 17 percent were unique to each one.

Grouping species by ecological traits revealed where each method shines. PAM proved especially effective at detecting arboreal and fossorial frogs, animals hidden in the canopy or underground, outside the observer’s field of view. VES detected more species inhabiting streams, possibly because torrential ambient noise around waterways reduces acoustic detection rates. The acoustic recorders picked up calls from species that visual surveys missed entirely, including Nasutixalus jerdonii and Zhangixalus smaragdinus, both arboreal. Most remarkably, the recordings contained call types that turned out to be science entirely new. A low-frequency call attributed to a putative Limnonectes species was formally described as a new species, Limnonectes motijheel, documented calling from mud nests beneath leaf litter. Another previously undocumented call type, inferred from its spectral and temporal features to be a cryptic species within the genus Raorchestes, was subsequently described as Raorchestes nasuta. The PAM method also detected five species, including Microhyla eos, Hylarana leptoglossa, Nidirana noadihing, and Gracixalus patkaiensis, that had never been documented in earlier surveys of the landscape, which reported 14 species in 1984 and 22 in 2009.

Conversely, four species were detected only by visual surveys: Amolops adicola, Duttaphrynus melanostictus, Odorrana livida, and an unidentified Limnonectes. Many Odorrana species produce complex ultrasonic calls, likely outside the detection frequency range of the recorders. Amolops adicola, a riverine species with peak calling activity documented in October, was probably simply not vocalizing during the May-June study window. The Asian common toad Duttaphrynus melanostictus, terrestrial and conspicuous, produces low-frequency, low-intensity calls that ambient noise may mask. These patterns echo a broader truth: visual surveys perform well for amphibians that are non-vocal, call infrequently or quietly, or live in acoustically noisy habitats.

When the two methods were combined, the mixed approach recorded 23 species, 21 percent more than either method alone, and the richness estimate was significantly higher than for PAM or VES individually. Species accumulation curves showed new species still being detected at a decelerating but positive rate for all three methods, with each additional site adding roughly 0.46 to 0.53 species. Nearly half the species detected by the mixed method appeared at a maximum of two sites, reflecting both habitat complexity and incomplete sampling. Extrapolation suggested the curve would approach an asymptote at about three times the current sampling effort, meaning roughly 40 sites spanning different elevations and habitats would be needed for a comprehensive inventory of the Namdapha landscape.

The study was not without constraints. Resource limitations restricted each recorder to a single night per site, though PAM’s full potential is typically realized through long-term deployments. Sampling was confined to the onset of the wet season, excluding full seasonal variation, and locations were based on previously surveyed accessible sites rather than the reserve’s complete altitudinal range. Even so, PAM detected a diverse assemblage including acoustically distinct taxa never recorded before, underscoring its sensitivity even under limited effort. The authors recommend deploying recorders for longer durations, sampling across multiple seasons, and complementing acoustics with visual surveys wherever possible. As amphibians remain the most threatened vertebrate class with an extinction rate showing no sign of decline, and with roughly 780 new species described between 2016 and 2020 alone, the message is clear: in the world’s most rugged rainforests, listening devices and human eyes are better together than either is alone.

Subject of Research: Comparative effectiveness of passive acoustic monitoring and visual encounter surveys for detecting anuran species in a tropical wet evergreen forest in the Indo-Burma biodiversity hotspot

Article Title: Frogs in sight and sound: passive acoustics and visual surveys reveal complementary species detection in tropical rainforest anurans

Article References: Rajiv, N. V., & Das, A. (2026). Frogs in sight and sound: passive acoustics and visual surveys reveal complementary species detection in tropical rainforest anurans. Herpetozoa, 39, 261-271. https://doi.org/10.3897/herpetozoa.39.e168386

Image Credits: AI Generated

DOI: 10.3897/herpetozoa.39.e168386

Keywords: passive acoustic monitoring, visual encounter surveys, anurans, tropical rainforest, Indo-Burma biodiversity hotspot, Namdapha Tiger Reserve, amphibian surveys, autonomous recording units, species richness, Northeast India, bioacoustics, conservation

The review, published in the journal Discover Ecology, followed the PRISMA framework for systematic reviews, searching four major databases in both English and Portuguese for studies on the diets of post-metamorphic frogs in Brazil. The team screened out work on tadpoles, gray literature such as conference abstracts and theses, and single predation records, ultimately retrieving 221 studies published between 1971 and June 2025. The very first Brazilian frog diet study appeared in 1971, when Ivan Sazima described marine invertebrates in the stomach contents of the frog Thoropa miliaris in the journal Ciência e Cultura. Remarkably, only nine additional dietary studies appeared during the entire twentieth century. The field only began to accelerate after 2000, and between 2019 and 2023 alone, researchers published 69 studies, nearly a third of everything ever written on the topic in Brazil.

That recent surge, the authors suggest, may have less to do with renewed scientific enthusiasm and more to do with austerity. Brazil’s research funding crisis in the late 2010s squeezed laboratory-based science hard, and dietary studies, which require little more than fieldwork, a dissection kit, and patience, became an accessible alternative for cash-strapped researchers. The pattern is visible in where the results are published. Of the 56 journals that have carried Brazilian frog diet studies, about a third have no impact factor at all, and the single most prolific outlet, Herpetology Notes, which published 26 studies, lacks one as well. Only 11 studies, about 5 percent, appeared in journals with an impact factor above two. Natural history research, the authors note, tends to be undervalued by high-profile journals, discouraging scientists from investing in it even as it underpins every hypothesis they test.

The taxonomic and geographic biases in the literature are stark. Hylidae, the treefrog family, dominates the record with 84 species studied, followed by Leptodactylidae with 55, Bufonidae with 23, and Microhylidae with 15. For two entire families, the Alsodidae and Centrolenidae, not a single Brazilian species has a documented diet. Geographically, the Atlantic Forest accounts for 110 studies, nearly half the total, followed by the Amazon with 47, the Cerrado with 32, the Caatinga with 23, the Pampa with 10, and the Pantanal with just 8. The imbalance extends to endemism. Brazil hosts 907 frog species found nowhere else, yet only 91 of them, about 10 percent, have had their diets described. Fifty of those are Atlantic Forest endemics and 32 are Amazonian, while just three Caatinga endemics and a single Pantanal endemic appear in the record.

The species that have been studied repeatedly share a predictable profile: they are common, widespread generalists. Leptodactylus fuscus and Physalaemus cuvieri lead the tally with 14 studies each, followed by Boana raniceps with 12 and Leptodactylus macrosternum with 11. Dendropsophus minutus and Leptodactylus fuscus occur in all six of Brazil’s major ecoregions, making them easy targets for fieldwork. Most of these well-studied frogs are opportunistic feeders, but the literature does contain striking exceptions. Physalaemus cicada is a termite specialist, Amazophrynella minuta appears to specialize in mites, and Phyllodytes edelmoi feeds mainly on ants. Boana raniceps favors beetles, while Scythrophrys sawayae and the pumpkin toadlet Brachycephalus brunneus show a marked preference for mites. Ontogenetic shifts have been documented too, with juveniles of Dendropsophus minutus and Leptodactylus podicipinus taking smaller prey than adults.

The most extraordinary dietary story in the Brazilian literature belongs to Xenohyla truncata, a Vulnerable treefrog endemic to the restinga habitats of coastal Rio de Janeiro. Unlike virtually every other frog on Earth, X. truncata actively eats fruit, nectar, and plant parts. Recent observations recorded it feeding on nectar from Iris x germanica and Cordia taguahyensis flowers, with pollen adhering to its body, raising the tantalizing possibility that this frog acts as a pollinator, a role almost unheard of among amphibians. Such discoveries illustrate why dietary research matters: without it, ecologists cannot map predator-prey interactions, estimate niche overlap among sympatric species, or understand the functional roles frogs play in their ecosystems. Yet only 34 of the 221 studies reviewed, about 15 percent, even measured prey availability in the environment, the baseline needed to distinguish true dietary preference from simple opportunity.

The conservation implications are sobering. Of Brazil’s 184 globally threatened frog species, only 12 have had their diets described, across just 15 studies. Those 12 include two Critically Endangered species, Adelophryne maranguapensis and Proceratophrys ararype, five Endangered species, and five Vulnerable ones. The picture is even bleaker for poorly known species: not one of the 62 species classified as Data Deficient by the IUCN has a documented diet, and nearly all of them are Brazilian endemics, with 40 confined to the Atlantic Forest. Among the seven threatened species with known diets, most turned out to be generalists, but Brachycephalus brunneus and Brachycephalus garbeanus feed primarily on mites, suggesting active foraging, while Adelophryne maranguapensis is an active forager and Crossodactylus timbuhy switches between active hunting and sit-and-wait tactics depending on whether prey is mobile or stationary.

Methodology is another frontier. A striking 81 percent of the reviewed studies relied on dissection, which requires killing the animals examined. Only 40 studies, about 18 percent, used stomach flushing, a non-lethal technique refined for anurans by Mirco Solé and colleagues in 2005 that induces frogs to regurgitate their stomach contents unharmed. Just one study applied flushing to a threatened species, the bromeliad-dwelling treefrog Phyllodytes tuberculosus. Nine studies mined museum specimens instead of collecting new animals, and only two used pure behavioral observation. The authors argue strongly for wider adoption of non-lethal methods, particularly for small, declining, or hard-to-access populations. More advanced tools remain rare: stable isotope analysis, which can trace whether a frog’s diet derives from terrestrial or aquatic food webs, has appeared in only a handful of studies, largely because its cost is prohibitive for researchers in middle-income countries facing chronic funding shortfalls. DNA-based techniques such as next-generation sequencing, which can identify prey from partially digested fragments with high taxonomic resolution, are almost entirely absent from Brazilian herpetology so far.

The review’s authors close with a call to action that doubles as a diagnosis of a discipline. Natural history, they argue, is the foundation on which all ecology rests, informing hypothesis development, data interpretation, and conservation decisions, yet it is increasingly neglected as researchers chase molecular and computational approaches that journals reward with prestige. They urge fieldwork using non-lethal methods across as many species as possible, greater use of scientific collections, and intensified effort in the Atlantic Forest, Amazon, and Cerrado, which despite ranking as the most-studied biomes still host hundreds of species with unknown diets, as well as in the Caatinga, Pampa, and Pantanal, where knowledge is nearly absent. Dietary data, they suggest, could even serve as an early-warning indicator of ecosystem change and anthropogenic impact. With amphibians now the most threatened vertebrate class on the planet, understanding what Brazil’s frogs eat is no longer a curiosity of natural history. It is a prerequisite for keeping them alive.

Subject of Research: Dietary ecology and knowledge gaps of Brazilian anuran amphibians

Article Title: Current state of the art in anuran dietary studies in Brazil

Article References: Moser, C. F., Ceron, K., Schuck, L. K., Santana, D. J., Solé, M., Iop, S., & Tozetti, A. M. (2025). Current state of the art in anuran dietary studies in Brazil. Discover Ecology, 1(1), Article 9. https://doi.org/10.1007/s44396-025-00008-7

Image Credits: AI Generated

DOI: 10.1007/s44396-025-00008-7

Keywords: anurans, frogs, diet, trophic ecology, Brazil, Atlantic Forest, Amazon, conservation, natural history, stomach flushing, biodiversity, threatened species