Researchers from the University of Neuchâtel and partner institutions collected 104 soil samples along five elevation gradients in two distant mountain ranges, the Spanish Sierra Nevada and the Swiss Alps, spanning two distinct biogeographic regions. Sampling took place in 2019 at 52 sites in forests and grasslands below the treeline, with every site visited twice — once in spring and once in summer. This design allowed the team to directly compare the magnitude of spatial turnover in protist communities against the magnitude of seasonal change, a question that has rarely been addressed for soil microeukaryotes across multiple gradients.

The methodological backbone of the study was environmental DNA metabarcoding. The team extracted DNA from roughly a gram of sieved soil, amplified the hypervariable V4 region of the 18S rRNA gene with universal eukaryotic primers, and sequenced the products on an Illumina MiSeq platform. After stringent quality filtering, chimera removal, error-model-based inference of amplicon sequence variants (ASVs), and a dedicated procedure to detect and correct tag-jumps — sequencing artifacts in which reads are assigned to the wrong sample — the final dataset contained more than 6.5 million cleaned reads representing nearly 20,000 eukaryotic ASVs. Of these, 11,706 ASVs were assigned to protists, with rarefaction curves indicating that sequencing depth had reached saturation for every sample regardless of region, habitat, or season.

The taxonomic picture was dominated by Cercozoa, a phylum of predominantly predatory and bacterivorous amoebae and flagellates, which contributed 4,445 ASVs and the largest share of reads. Ciliophora (1,725 ASVs), Apicomplexa (1,176 ASVs), the amoeboid group traditionally labeled Lobosa (1,131 ASVs), Conosa (968 ASVs), and Chlorophyta (488 ASVs) followed. The strong showing of Apicomplexa, a group famous for animal parasites such as the malaria agent Plasmodium, most likely reflects the pervasive parasitism of soil animals, a signal that has been increasingly recognized in environmental sequencing surveys. Green algae of the phylum Chlorophyta were more abundant in open grasslands than under forest canopies, consistent with their phototrophic lifestyle.

To quantify the relative roles of space and time, the authors decomposed total (gamma) diversity into three additive components: local alpha diversity, temporal beta diversity (the turnover of ASVs between spring and summer at the same plot), and spatial beta diversity (the turnover among plots within a habitat and region). The result was unambiguous. In the Swiss Alps, spatial turnover accounted for an average of 85.06 percent of total diversity, compared with just 3.84 percent for temporal turnover. In the Spanish Sierra Nevada the corresponding figures were 70.40 percent versus 14.17 percent. Local alpha diversity contributed the remainder and, except in Sierra Nevada grasslands, always exceeded the temporal component.

Ordination and statistical testing reinforced this hierarchy. Non-metric multidimensional scaling of Bray-Curtis dissimilarities revealed four distinct sample clusters separated along two axes: one splitting forests from grasslands and the other separating the Sierra Nevada from the Alps. Season, by contrast, left no visible imprint. A permutational analysis of variance confirmed that community composition differed significantly between regions and habitats and, to a lesser degree, across elevations, while the temporal variable and all its interactions were statistically non-significant. Variance partitioning showed that space, soil properties, and climate together explained 29 percent of community variation, whereas season alone explained none, contributing only about 3 percent in combination with the other factors.

The team then zoomed in on four of the most species-rich protist groups — Cercozoa, Ciliophora, Apicomplexa, and Lobosa — each exceeding 1,000 ASVs, to test whether the whole-community pattern held at finer taxonomic resolution. It did. None of the four groups showed significant seasonal shifts in alpha diversity indices, ordinations separated samples by habitat and region but not season, and diversity partitioning for every group showed spatial beta diversity dwarfing temporal turnover. The sole exception was Ciliophora, for which season explained a minor portion of community composition, yet even here the overarching pattern of spatial dominance remained intact.

The environmental drivers of community composition also proved temporally stable. Redundancy analyses with forward selection identified the same set of edaphic predictors in spring and summer within each region, even though the explanatory power of individual variables varied between seasons. In the Spanish Sierra Nevada, elevation and a composite variable combining soil organic matter, organic carbon, organic nitrogen, and residual humidity were the significant predictors, the latter likely reflecting the capacity of organic particles to retain water. In the Swiss Alps, soil pH, the carbon-to-nitrogen ratio, the nitrogen-to-phosphorus ratio, and bioavailable phosphorus emerged as key drivers — variables tied to organic matter turnover and nutrient cycling. That different sets of predictors operated in the two regions underscores how bedrock, climate, and vegetation jointly shape belowground communities, while their consistency across seasons within each region strengthens confidence in single-visit sampling.

Why does this matter beyond the world of protist ecology? Microorganisms divide far faster than plants and animals, so ecologists have long worried that microbial communities might fluctuate seasonally enough to confound comparisons among studies conducted at different times of year. If temporal turnover matched or exceeded spatial turnover, a survey of one mountain range sampled in May could not legitimately be compared with another sampled in July. The new findings lift that constraint for temperate mountain ecosystems: sampling once at any point between late spring and late summer should not bias beta diversity comparisons across elevation gradients, regions, or habitats. Given that logistical and financial realities frequently restrict large-scale and global sampling campaigns to a single visit per site, this is genuinely good news for the design of macroecological studies of soil life.

The authors also note important caveats. Their conclusions apply to temperate climates and to the spring–summer window; harsher seasons were excluded because snow cover, road access, and safety make winter and autumn sampling impractical at high elevations, even though snow insulates soils and allows microbial activity to continue beneath it. Hot, dry summer spells can sharply reduce protist abundance and activity, and drought sensitivity varies among protist groups, so climate change could rewrite the seasonal rules the study establishes. The findings may also not transfer to other climates or latitudes, and the eDNA-based approach has yet to be systematically validated against traditional microscopy for seasonal dynamics of soil protists. Moreover, the analyses did not cover phototrophic protists, which play important roles in grasslands. Still, as a baseline for a component of biodiversity long relegated to the margins of biogeography, the study’s message is clear and actionable: in Europe’s temperate mountains, the identity of a soil protist community is written primarily by its place on the landscape — its elevation, habitat, and soil chemistry — not by the calendar. Researchers planning large-scale soil biodiversity surveys can now schedule their fieldwork with one less worry, and conservation assessments of mountain biodiversity gain a firmer foundation for comparing sites across regions and seasons.

Subject of Research: Spatial versus seasonal beta diversity of soil protist communities along elevation gradients in the Swiss Alps and Spanish Sierra Nevada

Article Title: Higher spatial than seasonal beta diversity of soil protists along elevation gradients

Article References: Bruni, E. P., Lorite, J., Peñas, J., Mulot, M., Fournier, B., Vittoz, P., Mitchell, E. A. D., & Lentendu, G. (2024). Higher spatial than seasonal beta diversity of soil protists along elevation gradients. Frontiers of Biogeography, 17, Article e132637. https://doi.org/10.21425/fob.17.132637

Image Credits: AI Generated

DOI: 10.21425/fob.17.132637

Keywords: soil protists, beta diversity, elevation gradients, environmental DNA, metabarcoding, Swiss Alps, Sierra Nevada, seasonality, biogeography, Cercozoa, soil microbiology, mountain ecology

The findings carry weight far beyond a single warbler species. The Hermit Warbler has previously been identified as a surrogate species for the California Spotted Owl, and among more than 60 Sierra Nevada bird species analyzed in prior work, 13 are co-associated with the Spotted Owl, none more strongly than the Hermit Warbler. Because the warbler’s small body size means a small home range, researchers can monitor it with far greater sample sizes than the owl, giving them the statistical power to detect subtle population responses to environmental change that will likely apply to the larger, more charismatic species sharing the same old-forest habitat. In this sense, the warbler functions as a biological barometer for an entire community of old-forest specialists facing the combined pressures of warming and intensifying fire regimes.

To capture population dynamics at an ecosystem scale, the research team deployed autonomous recording units, known as ARUs, at 876 locations spanning six National Forests across the western slope of the Sierra Nevada. Each summer from 2021 through 2024, pairs of recorders were placed 500 to 900 meters apart, with 1.5 to 3 kilometers between pairs, and left running for approximately five weeks. The devices recorded continuously through a single omni-directional microphone at a sample rate of 32 kilohertz. For analysis, the team focused on audio captured between 5:00 and 9:00 in the morning and 6:00 to 8:00 in the evening, the windows when Hermit Warbler vocalizations are most likely to be heard. The study area ranged from 328 meters above sea level, where black oak mingles with ponderosa pine, up to 2,528 meters, where white fir dominates the canopy.

The acoustic data were processed with BirdNET, a convolutional neural network capable of identifying Hermit Warbler songs and the vocalizations of thousands of other species by sound. To ensure the AI’s predictions were trustworthy, the researchers manually validated 200 randomly selected BirdNET detections of Hermit Warbler vocalizations, half drawn from a broad score range and half from the upper range, then fit a logistic regression relating the prediction score to the probability that a given detection was correct. Only predictions with a probability of being a true positive of at least 0.99 were retained as observations. At this stringent threshold, precision was a perfect 1.0, meaning every retained detection was correct, while recall was 0.78, meaning the detector captured 78 percent of the target sounds actually present. This combination of extremely high precision and strong recall meant false positives and false negatives would have minimal influence on the final results.

Quantifying the environmental conditions at each recording site required equally sophisticated remote sensing. The team characterized fire severity and history using 30-meter resolution rasters of the Composite Burn Index, generated in Google Earth Engine from random forest models parameterized with latitude, climatic water deficit, and spectral indices from Landsat imagery spanning 1985 to 2023. Composite Burn Index values of 2.25 or higher were categorized as high-severity fire, corresponding to at least 75 percent canopy mortality. Fire data were summarized within a 120-meter buffer around each recorder as the proportion of unburned, low-to-moderate, and high-severity fire occurring 1 to 10 and 11 to 35 years before each sampling year. For the thermal environment, the researchers used 30-meter resolution mean relative summer temperature derived from the Landsat 8 Thermal Infrared Sensor, calculated from 2013 to 2018 as a median across a six-year time series. This in situ thermal measurement, rather than coarser gridded weather data interpolated from sparse stations, captured fine-scale conditions such as slope and aspect in the Sierra’s complex terrain.

A critical statistical challenge emerged because relative temperature and mean tree diameter were strongly negatively correlated, with a correlation coefficient of negative 0.77. Sites with larger trees are simply cooler. To disentangle these effects, the team fit a linear model of relative temperature as a function of tree diameter and used the residuals as a forest-structure-corrected measure of the thermal environment. Positive residuals indicated sites warmer than expected given their tree diameter, negative residuals indicated sites cooler than expected, and the resulting corrected measure was uncorrelated with tree diameter. This allowed the researchers to ask whether the warbler responded to temperature itself, independent of the forest structure that both creates cooler microclimates and defines the species’ preferred habitat.

The population dynamics were analyzed with a dynamic occupancy model, a hierarchical statistical framework that estimates site occupancy, colonization, and local extinction while accounting for imperfect detection. Each breeding season was divided into eight six-day secondary sampling periods, and the team applied careful filters to create encounter histories: observations before June 1 or after July 18 were excluded because they could reflect migration or post-breeding movement rather than stable breeding behavior, and any site with only a single vocalization in June was treated as unoccupied to guard against transient individuals or rare high-scoring false positives. Detection probability was modeled as a function of survey effort and ordinal date. Initial occupancy was modeled as a function of elevation, latitude, mean tree diameter, the temperature-corrected residuals, and the amount of high-severity fire in the prior ten years, while colonization and extinction were modeled against the same covariates. All covariates were scaled to allow direct effect size comparisons, and the team considered a covariate influential if the 85 percent confidence interval around its estimate did not overlap zero.

The results painted a coherent picture of a species contracting its range under pressure from both direct and indirect effects of climate change. Site occupancy fell from 0.658 in 2021 to 0.603 in 2024, an 8.3 percent decline. Initial occupancy was most strongly influenced by mean tree diameter, confirming the warbler’s old-forest association, but even after controlling for forest structure, birds were more likely to occupy sites cooler than expected for their tree diameter. Occupancy showed a striking non-linear latitudinal gradient: approximately 0.1 at the southern end of the study area, climbing to 0.78 slightly north of the midpoint near the South Fork of the American River, and reaching 0.84 at the northernmost extent. Colonization rates were higher in the north while extinction rates were higher in the south, producing a clear northward shift in the relative density of occupied sites. Elevation told a more complicated story: colonization increased with elevation, but extinction displayed a positive quadratic relationship, meaning the lower elevational boundary shifted upslope while the upper boundary did not show an unambiguous corresponding expansion.

The fire response was dramatic. At a completely unburned site, the annual probability of local extinction was 0.106 and the probability of colonization was 0.383. At a fully burned site, extinction probability soared to 0.883 while colonization collapsed to 0.0292. The warbler showed a strong extinction response to severe fire over a 1-to-10-year post-fire period and failed to colonize such areas over the same span, effectively treating locally extensive high-severity fire as a decadal loss of habitat. Notably, colonization was unaffected by high-severity fire occurring 11 to 35 years before the study period, suggesting some capacity for resilience if enough unburned habitat remains. The observed population decline could plausibly be attributed to the several large, severe fires that occurred during the study window, including the Dixie Fire, which burned almost 3,900 square kilometers of the northern Sierra Nevada with more than 20 percent at high severity, along with the Caldor and KNP Complex Fires. The apparent northward shift of the warbler population may have partially offset the Dixie Fire’s local effects, underscoring the importance of regional context when interpreting local studies.

The study’s implications for conservation are sobering but actionable. Limiting the occurrence of large, severe fires will be necessary to preserve this old-forest indicator, the authors conclude, but not sufficient: rising temperatures will lead to population declines even in the absence of habitat loss due to fire. Without proactive strategies that move away from strict fire suppression and incorporate principles of pre-colonial fire stewardship, continued intensification of contemporary fire regimes could drive further declines for the Hermit Warbler and the species that share its habitat. Meanwhile, the mixed evidence for upslope shifts suggests that simply moving to higher elevations may not be a viable climate adaptation strategy for the warbler, the Spotted Owl, or their co-associated species, particularly since high-elevation Sierra forests are not expected to provide short- to intermediate-term climate refugia due to complex interactions between canopy cover, microclimate, and prey. As climate change accelerates, understanding how species respond to shifting environmental conditions will be crucial for guiding adaptive management and ensuring the persistence of biodiversity in fire-prone landscapes, and this four-year bioacoustic monitoring framework offers a scalable template for tracking those responses across entire ecosystems.

Subject of Research: Combined effects of warming temperatures and high-severity wildfire on the range dynamics of an old-forest bird species in the Sierra Nevada

Article Title: Warm temperatures and severe fire drive a range contraction of an avian old-forest specialist in the Sierra Nevada, USA

Article References: Bielski, L., Keyser, S. R., Peery, M. Z., & Wood, C. M. (2026). Warm temperatures and severe fire drive a range contraction of an avian old-forest specialist in the Sierra Nevada, USA. Frontiers in Bird Science, 5, Article 1737313. https://doi.org/10.3389/fbirs.2026.1737313

Image Credits: AI Generated

DOI: 10.3389/fbirs.2026.1737313

Keywords: Hermit Warbler, Sierra Nevada, climate change, high-severity fire, passive acoustic monitoring, dynamic occupancy model, old-growth forest, range contraction, BirdNET, wildfire, bird conservation, Spotted Owl

The story begins with the genus Agriphila, a group of grass-feeding moths in the subfamily Crambinae that flutters across temperate Eurasia and North America. Europe hosts twenty-one species of the genus, twelve of which occur in the Iberian Peninsula. Among them, Agriphila deliella, originally described from Germany in 1813, enjoys a vast distribution stretching from Continental Europe through Asia Minor, North Africa, Transcaucasia, the West Siberian Plain and even Afghanistan. These moths fly from August to October in dry, open habitats covered with grasses, on which their larvae feed. In the Iberian Peninsula, A. deliella was first recorded in 1927 at Albarracín in Teruel, with later records from Serra da Estrela in Portugal and numerous Spanish localities including Zaragoza, Segovia, Burgos, Soria and Madrid.

Into this picture stepped the Polish lepidopterist Jan Błeszyński, who in 1959 described Agriphila hispanodeliella on the basis of five male specimens captured at Albarracín by Anthon Schmidt and deposited in the Hungarian National Museum in Budapest. Błeszyński noted several differences from A. deliella: the ground color of the forewing, the coloration of the wing veins and antennae, the size of the pointed prominence on the frons, and features of the male genitalia. Yet just six years later, in 1965, Błeszyński himself downgraded his species to a subspecies of A. deliella without providing any justification for the reversal. The taxonomic limbo deepened in 2008 when the specialist František Slamka suggested that the moth was merely a local variant of A. deliella, a judgment that effectively erased it from most faunistic treatments.

The resurrection of A. hispanodeliella rests on a series of specimens collected in the Sierra Nevada Natural Area in the province of Almería, in the extreme south-east of the Iberian Peninsula. Male moths were taken at several high-elevation sites between 2015 and 2025, including Puerto de la Ragua at 2,100 meters, Collado de Gabiarra at 2,120 meters, Fuente París at 1,940 meters and Cruz del Pescadero at 2,210 meters. These localities lie within the supra- and oromediterranean vegetation belts, open mountain landscapes rich in grasses, including the grey hair-grass Corynephorus canescens, which the researchers presume serves as the larval host plant. All voucher specimens are now deposited in the Research Collection of Animal Biology at the University of Murcia.

The morphological evidence assembled by the team is detailed and consistent. The redescribed males bear wingspans of 28 to 33 millimeters, notably larger than the approximately 27 millimeters typical of A. deliella. The forewings range from beige to creamy, marked with a distinct longitudinal white stripe running from the wing base to the outer margin, edged below by a short narrow brown line and above by a broad dark brown stripe, with two short parallel white lines above it and a broad brown band along the trailing edge. The male antennae are short and pectinate, weakly ringed in brown and greyish white, and the frons projects forward with a distinct pointed apex. Some individuals show much reduced markings and an almost uniformly pale beige forewing, revealing appreciable variation within the population.

The decisive anatomical differences emerge in the male genitalia, the traditional proving ground of moth taxonomy. In A. hispanodeliella the valva, a clasper-like structure, narrows to a relatively pointed apex, whereas in A. deliella it is clearly rounded. The costal arm is weakly developed and scarcely visible in the Spanish moth, while in A. deliella it is well developed and clearly separated from the valva. The uncus and gnathos are slender in A. hispanodeliella but broader in its congener, and the aedeagus is narrower with a distinct ventral thorn and no cornuti. Taken together, the wingspan, forewing pattern and genital architecture provide a reliable morphological diagnosis separating the two taxa.

Morphology alone, however, rarely settles debates of this kind, so the researchers turned to molecular evidence. Two legs were removed from each barcoded specimen and submitted to the Canadian Centre for DNA Barcoding in Guelph, Ontario, where the standard 658-base-pair barcode segment of the mitochondrial cytochrome c oxidase I gene, the COI-5P region, was sequenced using high-throughput protocols. The resulting sequences were deposited in GenBank and the Barcode of Life Data System, where all voucher data, images, sequences and trace files are publicly available. Genetic distances were computed with the Kimura 2-parameter model, and neighbor-joining and maximum-likelihood trees were reconstructed in MEGA6 from 56 nucleotide COI sequences, including reference material of A. deliella, A. tristella, A. selasella and A. aeneociliella, with the crambine Catoptria bolivari serving as an outgroup to root the tree.

The genetic results are striking. The COI sequences of A. hispanodeliella form their own barcode index number cluster, BOLD:AGX2565, and differ from A. deliella by a mean pairwise divergence of 3.5 percent. Against the other European congeners the distances are far larger still: an average of 8.33 percent across all comparisons, reaching a maximum of 9.2 percent relative to the three distinct BINs of A. tristella and a minimum of 6.8 percent relative to A. selasella. This magnitude of divergence falls squarely within the range reported for COI differences between recognized congeneric insect species, and it places A. hispanodeliella on a phylogenetically isolated branch that is well supported by both the molecular and the anatomical data. In other words, the moth that Błeszyński described in 1959 is exactly what he thought it was.

Despite this convergence of evidence, important questions remain open. The true extent of the species’ range is uncertain, because specimens from other parts of the Iberian Peninsula and from North Africa that were previously identified as A. deliella may in fact belong to the resurrected species, or may not; re-examination is needed. It is also unknown whether A. hispanodeliella and A. deliella occur together in northern Spain, and whether their ranges overlap or meet along a contact zone. The female of A. hispanodeliella has never been described, leaving female genitalia, which earlier authors identified as the key missing evidence, still unstudied. The researchers emphasize that new molecular datasets covering these areas will be crucial to resolving the biogeography of the pair, and that biological investigation of the living moths would further cement the case.

The rehabilitation of Agriphila hispanodeliella carries implications beyond nomenclatural housekeeping. As an endemic restricted to a handful of localities in the center and south-east of the Iberian Peninsula, and confined to high mountain grasslands that are vulnerable to climate change and habitat degradation, the species now requires assessment in its own right rather than being subsumed within a widespread Eurasian generalist. The study also illustrates the power of DNA barcoding to correct historical taxonomic decisions made with limited material and no genetic tools, a century-scale correction that transforms a forgotten synonym into a recognized component of Europe’s biodiversity. For a moth no larger than a thumb-width of grass blade, it is a remarkable second act in the mountains of Andalusia.

Subject of Research: Taxonomic resurrection and DNA barcoding of the Iberian grass moth Agriphila hispanodeliella

Article Title: Redescription and DNA barcoding of Agriphila hispanodeliella Błeszyński, 1959, bona sp., stat. rev. from the Iberian Peninsula ( Lepidoptera , Pyraloidea , Crambinae )

Article References: Girdley, J., Garre, M., Rubio, R. M., & Ortiz, A. S. (2026). Redescription and DNA barcoding of Agriphila hispanodeliella Błeszyński, 1959, bona sp., stat. rev. from the Iberian Peninsula (Lepidoptera, Pyraloidea, Crambinae). Nota Lepidopterologica, 49, 109-116. https://doi.org/10.3897/nl.49.191476

Image Credits: AI Generated

DOI: 10.3897/nl.49.191476

Keywords: Agriphila hispanodeliella, Lepidoptera, Crambidae, DNA barcoding, COI gene, Sierra Nevada, Iberian Peninsula, taxonomy, species delimitation, endemic species, BOLD, mountain biodiversity

Bd is arguably the most destructive pathogen ever documented in wild vertebrates. The chytrid fungus has decimated amphibian populations on every continent where amphibians live, driving scores of species toward extinction and reshaping entire ecosystems in its wake. Because Bd is an aquatic organism that infects its hosts through the skin, researchers and wildlife managers have generally focused their attention on the water bodies where amphibians congregate to breed, treating those brief aquatic gatherings as the principal arenas of transmission. For the Yosemite toad, a species that spends the vast majority of its life on land, this reasoning suggested a comforting conclusion: the toads should be at comparatively low risk, vulnerable only during the short window of the mating season when they enter the water.

The new study, published in Functional Ecology by UCLA ecologist Dave Daversa and colleagues, demolishes that assumption. When the researchers surveyed toads emerging from their winter hibernation burrows, they found previously healthy animals carrying heavy fungal loads. The infections, in other words, were not being acquired in the breeding pools at all. They were building up underground, during the coldest and most hostile months of the Sierra Nevada year, in the abandoned rodent burrows that the toads use as winter refuges. The results of the surveillance study, Daversa said, were completely unexpected, sharply contrasting with the prevailing view that the high-risk season for Bd infection occurs when amphibians are breeding in water.

The Yosemite toad, Anaxyrus canorus, is a small and distinctive resident of the high country, living almost exclusively within Yosemite National Park and neighboring Sequoia and Kings Canyon national parks. The toads measure only about one to three inches long, and they walk rather than hop, an unusual gait that suits their slow, deliberate lifestyle in meadow habitats. Females are larger than males and wear bumpy skin mottled in attractive shades of green, while males are less colorful. The species breeds in small pools formed by snowmelt, but for much of the year the toads keep to land, sheltering from predators and extreme temperatures in burrows abandoned by rodents. When the brutal High Sierra winter arrives, they hibernate in these underground chambers, sometimes buried beneath many feet of snow.

That lifestyle has not shielded the species from decline. Climate change is rendering the toads’ mountain habitats drier and hotter, and fewer tadpoles are surviving to adulthood. Infection with Bd, which is fatal to the toads, is widespread across their range. The combined pressures led the federal government to list the Yosemite toad as threatened under the Endangered Species Act in 2014, and California classifies it as a highest-priority species of special concern. In an effort to bolster wild populations, toads have been reared at the San Francisco Zoo and returned to Yosemite, but until now it was not understood how the fungus might be undermining those reintroduction efforts.

To find out, a team of researchers from UCLA and Yosemite National Park conducted an intensive surveillance program from 2021 through 2023, designed to determine how Bd prevalence and severity varied across seasons and life stages. The researchers compared toads before and after cohorts entered winter dormancy, capturing metamorphs — juvenile toads that had recently completed metamorphosis — from high-altitude locations near Tioga Pass. They took skin swabs from the animals immediately after they emerged from hibernation in May, again during the summer, and once more before hibernation in September. The following spring, during early snowmelt, they returned and sampled the same individual toads as they emerged from hibernation. A parallel survey sampled toads at every phase of the life cycle, producing a total of 1,800 samples collected over three years at six sites.

Each swab was screened for Bd using established molecular techniques, including polymerase chain reaction tests of the same kind that became familiar worldwide during the COVID-19 pandemic. Daversa noted that the pandemic made it easier to explain to hikers he encountered along the trails what he was doing as he swabbed toads. The laboratory results, however, were anything but routine. The data unambiguously identified the winter months of underground dormancy as the key season of rapid Bd proliferation, and the effect was particularly pronounced in metamorphs, the youngest and most vulnerable life stage. Toads that had tested clean or carried only trace infections in the autumn emerged from their burrows in spring bearing strong infections acquired on land.

The finding stunned the research community because it contradicted nearly everything scientists believed they knew about the pathogen’s biology. Bd was thought to grow best under more moderate conditions, and the toads were assumed to be at low risk precisely because they spend so little time in water. The idea that the fungus could not merely survive but actively multiply at the super-low temperatures of a Sierra winter — either above ground or inside the burrows — came as a genuine surprise. UCLA conservation biologist and study co-author Brad Shaffer said it certainly appears that the Bd fungus has the ability to move between individuals, adding that its capacity to increase in number on land at such low temperatures is a real surprise.

Several important questions remain unresolved. The researchers cannot yet say for certain that toads are contracting new infections inside the burrows themselves. An alternative explanation is that the animals enter hibernation carrying very light, undetectable infections, and that for reasons still unknown each individual then develops a heavy fungal load over the winter. Studying the burrows directly during hibernation is extraordinarily difficult because the chambers lie buried beneath deep snow for months at a time. UCLA wildlife disease ecologist and co-author Jamie Lloyd-Smith framed the puzzle in terms of how pathogens persist in host populations with extremely seasonal life histories, observing that this fungus is not supposed to grow happily at such low temperatures. One hypothesis the team speculates about involves the host’s own defenses: the immune state of a hibernating toad may drop even lower than the fungus’s ability to grow, allowing infections to run unchecked while the animal lies dormant and cold-stunned.

Whatever the precise mechanism proves to be, the discovery has already changed conservation practice on the ground. Reintroducing captive-reared toads at the metamorphic stage, or younger, would be cheaper and easier for the program based at the San Francisco Zoo. But because the youngest toads are precisely the ones most at risk of devastating overwinter Bd infections, managers now release animals only after several years of growth, when they have reached a size and maturity at which the winter fungal surge poses less of a threat. Follow-up studies are planned to pin down exactly how the fungus persists and spreads in the burrows, and whether the hibernating toads’ suppressed immune systems hold the key. For a species clinging to survival in one of America’s most beloved national parks, the finding offers something rare: a genuine strategic insight into an enemy that, until now, had been hiding in the toads’ own homes.

Subject of Research: Winter proliferation of the amphibian chytrid fungus Batrachochytrium dendrobatidis in the hibernation burrows of Yosemite toads

Article Title: Yosemite toad killer may be hiding in their own homes

Article References: Yosemite toad killer may be hiding in their own homes. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: Yosemite toad, Batrachochytrium dendrobatidis, chytrid fungus, amphibian disease, hibernation, burrows, conservation biology, Endangered Species Act, captive rearing, reintroduction, Sierra Nevada, UCLA

Freshwater ecosystems rank among the most biodiverse and most threatened environments on Earth, and headwater streams sit at the top of the conservation agenda because of their outsized influence on the biodiversity, functioning, and connectivity of entire river networks. In Mediterranean mountains, where irrigated agriculture and climate change have extensively reshaped flow regimes, these small streams face mounting pressure. Sierra Nevada, a designated Biosphere Reserve and a recognized Mediterranean biodiversity super hotspot, offers a striking case study. There, careo ditches have been documented since the eighth to tenth centuries, diverting snowmelt from headwater reaches and distributing it across upper slopes to artificially recharge aquifers in weathered fractured rock, extending water availability for lowland farms and towns through the dry season.

A research team led by scientists from the University of Almeria, the Andalusian Centre for Global Change, and the Geological and Mining Institute of Spain examined five first- and second-order headwater streams on the southern face of the park, in the Alpujarra region, at altitudes between 1800 and 2000 meters. In each stream, a small, rudimentary weir built of loose rocks and gravel diverts water into a careo ditch. The researchers compared upstream reference reaches with downstream flow-impacted reaches, sampling benthic macroinvertebrates in spring during snowmelt and in autumn after the prolonged dry period, while continuously monitoring discharge and water temperature from November 2022 onward.

The magnitude of diversion was severe. Proportional flow reduction downstream of the weirs most frequently ranged from 76 to 98 percent of upstream discharge, with mean reductions exceeding 0.85 for much of the year in the Cáñar, Mecina, and Bérchules streams. In absolute terms, downstream flows often fell below 10 liters per second. Yet despite these extreme withdrawals, the impacted reaches never dried. They remained perennial throughout the year, maintaining the longitudinal hydrological connectivity that ecologists consider critical for stream life. The team attributes this persistence to two concurrent processes: seepage returning from the leaky weirs and unlined or poorly sealed ditches, and groundwater effluents from the region’s weathered hard-rock aquifers.

The groundwater signal was unmistakable in the temperature records. Downstream reaches showed significantly higher winter temperatures despite their lower discharge, along with lower summer maxima and reduced spring daily fluctuations, a thermal fingerprint of groundwater-fed baseflow. Water chemistry, by contrast, remained remarkably stable across reach types, with only slightly lower oxygen and higher salinity downstream, differences that were not statistically significant. Total dissolved nitrogen was actually higher upstream, suggesting stronger surface runoff influence at reference sites. This chemical stability matters, because it means that any ecological differences between reaches could be traced primarily to physical habitat alteration, such as reduced flow diversity and increased sedimentation, rather than to water quality degradation.

The biological consequences were nuanced. Macroinvertebrate density was substantially reduced downstream, particularly in spring, when it was roughly 50 percent lower than at upstream sites, a pattern consistent across all functional feeding groups and supported by medium effect sizes. The prolonged duration of the reduction, which persisted for at least a full year, contracted the wetted channel width by 63 to 85 percent, slashing total benthic abundance per reach length to about one-tenth of reference values. The authors warn that this decline in benthic production, together with reduced insect drift and emergence, likely creates severe food shortages for trout and riparian insectivorous predators that depend on aquatic insects crossing the land-water interface.

Surprisingly, local alpha diversity and interlocal beta diversity, measured as taxa richness, Shannon diversity, and community turnover, did not differ significantly between upstream and downstream reaches, and community composition showed no detectable separation in ordination analyses. The researchers propose that the maintenance of hydrological connectivity prevented the impacted reaches from degrading into isolated pools, a fate that typically traps invertebrates, intensifies predation, and triggers prey population collapse. Groundwater subsidies may also have mitigated local diversity losses, since moderate upwelling is known to enhance macroinvertebrate abundance and richness in alpine streams by moderating the harsh abiotic stress imposed by meltwater.

However, the buffering was incomplete, and the damage emerged at larger scales. Regional gamma diversity, estimated from rarefaction curves, was significantly lower in the sets of downstream reaches in both seasons, indicating that even small, non-significant losses of local richness can accumulate into substantial regional declines. Sensitive components of the community also eroded: the taxonomic richness of collector-gatherers dropped significantly in spring, and several biotic indices based on the pollution- and disturbance-sensitive insect orders Ephemeroptera, Plecoptera, and Trichoptera, the EPT taxa, declined significantly at impacted sites. Notably, the IBMWP index, the regulatory standard for Iberian river biomonitoring, classified both reach types as being of good quality and failed to distinguish them, suggesting that current monitoring frameworks may be blind to the early functional erosion caused by flow diversion unless they incorporate EPT-driven metrics.

The study’s most consequential implication concerns the global push toward irrigation efficiency. Modern water policy has favored concrete-lined canals and sealed infrastructure that minimize seepage, yet the Sierra Nevada findings suggest that these very inefficiencies, the leaky weirs and porous ditches of the traditional system, are essential to sustaining downstream flow and biodiversity, particularly in reaches that lack groundwater inflow. The authors invoke the well-documented irrigation efficiency paradox, in which saving water at the infrastructure scale can paradoxically intensify overall water consumption and ecological harm, and they argue that reversing the efficiency-first trend is urgent to halt river degradation in biodiversity-rich mountain regions.

Ultimately, the researchers argue that preserving as many stream reaches as possible under natural or ecologically compatible flow regimes is mandatory in biodiversity hotspots, because moderate local losses compound into regional extirpation. As climate change intensifies aridity across the Mediterranean and agricultural water demands climb, the centuries-old careo systems, increasingly framed as nature-based solutions for aquifer recharge, offer a rare example of human water infrastructure coexisting with, and even underwriting, freshwater conservation. The lesson from Sierra Nevada is that sometimes the most valuable feature of an irrigation system is not how efficiently it moves water, but how much it lets slip away.

Subject of Research: Ecological effects of traditional irrigation water diversion on benthic macroinvertebrate biodiversity in Sierra Nevada headwater streams

Article Title: Leakage from Traditional Irrigation Systems and Groundwater Upwelling Buffer the Impact of Heavy Streamflow Diversion on Benthic Biodiversity

Article References: Casas, J. J., Fenoy, E., Rubio-Ríos, J., Villegas, J., Salinas-Bonillo, M. J., Zakaluk, T., Martos-Rosillo, S., & Cabello, J. (2026). Leakage from Traditional Irrigation Systems and Groundwater Upwelling Buffer the Impact of Heavy Streamflow Diversion on Benthic Biodiversity. Water Resources Management, 40(11), Article 517. https://doi.org/10.1007/s11269-026-04861-3

Image Credits: AI Generated

DOI: 10.1007/s11269-026-04861-3

Keywords: benthic macroinvertebrates, headwater streams, irrigation ditches, groundwater upwelling, hydrological connectivity, water abstraction, Sierra Nevada, EPT taxa, biotic indices, environmental flows, Mediterranean mountains, biodiversity conservation