Vance Thomas Vredenburg

Amphibians are declining worldwide, in large part due to chytridiomycosis: a disease of amphibian skin caused by the fungal pathogen, Batrachochytrium dendrobatidis (Bd). Resistance and tolerance to Bd infection can exhibit intra‐ and interspecific variation. This variation may depend, among other factors, on the host skin microbiome. In California's Sierra Nevada, endangered mountain yellow‐legged frogs (MYL frogs, Rana sierrae and Rana muscosa ) are highly susceptible to chytridiomycosis, while the co‐occurring Pacific chorus frog ( Pseudacris regilla ) is less susceptible and may function as a Bd reservoir host. To investigate whether distinct Bd dynamics for these sympatric hosts relate to differences in skin microbial communities, we (1) compared Bd infection of MYL frogs and P. regilla across 23 Sierra Nevada sites, and (2) characterized the bacterial component of host skin microbiomes (or bacteriomes). Bd infection prevalence was approximately 80% in both frog species, and average infection intensities on P. regilla and MYL frogs did not differ. In contrast, bacteriome compositions were markedly distinct. P. regilla had a more diverse skin bacteriome than MYL frogs, and only MYL frog bacteriome diversity correlated with Bd infection intensity. Additionally, the P. regilla bacteriome contained a higher richness of putative antifungal bacteria than MYL frogs. Differences in the bacteriomes of these sympatric hosts may be due to differences in physiology or life histories. Further work will be important in determining whether the greater diversity and apparent stability of the P. regilla microbiome is a cause or consequence of the host's innate Bd tolerance.

Aim: The emergence of the fungal pathogen Batrachochytrium dendrobatidis ( Bd ) in South America has been attributed to multiple introductions and subsequent spread in a bidirectional latitudinal wave along the primary Andean cordilleras. This is supported for Ecuador by anecdotal evidence of declines in Bd ‐susceptible genera such as Telmatobius and Atelopus around the mid‐1980s. We tested this hypothesis by combining published records of Bd with retrospective screenings of museum specimens (1950–2010) and surveys of contemporary populations to characterise the spatiotemporal and host‐specific emergence of Bd in Ecuador. Location: Ecuador. Methods: We assembled a database of Bd records in Ecuadorian anurans (> 7000 samples) and assessed its spatiotemporal emergence using generalised linear mixed models and spatial clustering approaches. Data were also used to identify Bd prevalence within four representative genera of Ecuadorian anurans ( Atelopus , Telmatobius , Gastrotheca and Pristimantis ). We also used Bayesian approaches to test the probability of the presence of Bd in Ecuador prior to the first positive record. Results: Our results overturn the prevailing narrative of Bd emergence in the Neotropics and provide a rare, long‐term view of an invasive pathogen's trajectory from introduction to persistence. We found that: (1) Bd likely represents a novel pathogen to Ecuador; (2) Bd was first detected in 1974 and had become widespread by 1980; (3) there is no evidence supporting a bidirectional wave of spread; and (4) the genera Atelopus , Telmatobius and Gastrotheca experienced epizootic disease dynamics, with declines peaking in the 1990s. Main Conclusions: We found that Bd is likely a novel pathogen that was introduced in the early 1970s and peaked in prevalence during the late 1980s and 1990s. The available evidence supports the conclusion that an outbreak of chytridiomycosis may have led to catastrophic declines in Ecuadorian amphibians. Disease dynamics have since subsided to enzootic coexistence in extant amphibian communities.

Initiatives to protect 30% of Earth by 2030 prompt evaluation of how to efficiently target shortcomings in the global protected area (PA) network. Focusing on amphibians, the most vulnerable vertebrate class, we illustrate the conservation value of microreserves, a term we employ here to refer to reserves of 2. We report that the network continues to under-represent threatened amphibians and that, despite this clear shortcoming in land-based conservation, the creation of PAs protecting amphibians slowed after 2010. By proving something previously assumed–that amphibians generally have smaller ranges than other terrestrial vertebrates–we demonstrate that microreserves could protect a substantial portion of many amphibian ranges, particularly threatened species. We find existing microreserves are capable of hosting an amphibian species richness similar to PAs 1000–10,00X larger, and we show that amphibians’ high beta diversity means that microreserves added to a growing PA network cover amphibian species 1.5—6x faster than larger size categories. We propose that stemming global biodiversity loss requires that we seriously consider the conservation potential of microreserves, using them to capture small-range endemics that may otherwise be omitted from the PA network entirely.

When you take the time to observe another organism, there is a sort of gravity that can take hold, a mixture of curiosity and connection that expands and strengthens the more you interact with that organism. Yet, in research, a connection with one's study organism can, at times, feel countercultural. Study organisms are sometimes viewed more as tools to conveniently study biological questions. Here, we explicitly highlight the importance of organism-centered research not only in scientific discovery, but also in conservation and in the communication and perception of science.

Species with extensive geographical ranges pose special challenges to assessing drivers of wildlife disease, necessitating collaborative and large-scale analyses. The imperilled foothill yellow-legged frog ( Rana boylii ) inhabits a wide geographical range and variable conditions in rivers of California and Oregon (USA), and is considered threatened by the pathogen Batrachochytrium dendrobatidis (Bd). To assess drivers of Bd infections over time and space, we compiled over 2000 datapoints from R. boylii museum specimens (collected 1897–2005) and field samples (2005–2021) spanning 9° of latitude. We observed a south-to-north spread of Bd detections beginning in the 1940s and increase in prevalence from the 1940s to 1970s, coinciding with extirpation from southern latitudes. We detected eight high-prevalence geographical clusters through time that span the species' geographical range. Field-sampled male R. boylii exhibited the highest prevalence, and juveniles sampled in autumn exhibited the highest loads. Bd infection risk was highest in lower elevation rain-dominated watersheds, and with cool temperatures and low stream-flow conditions at the end of the dry season. Through a holistic assessment of relationships between infection risk, geographical context and time, we identify the locations and time periods where Bd mitigation and monitoring will be critical for conservation of this imperilled species.

Introduction: Emerging infectious diseases are increasingly recognized as a global threat to wildlife. Pandemics in amphibians, caused by the fungal pathogen Batrachochytrium dendrobatidis (Bd), have resulted in biodiversity loss at a global scale. Genomic data suggest a complex evolutionary history of Bd lineages that vary in pathogenicity. Africa harbors a significant proportion of global amphibian biodiversity, and multiple Bd lineages are known to occur there; yet, despite the decline of many host species, there are currently no described Bd-epizootics. Here, we describe the historical and recent biogeographical spread of Bd and assess its risk to amphibians across the continent of Africa.Methods: We provide a 165-year view of host-pathogen interactions by (i) employing a Bd assay to test 4,623 specimens (collected 1908–2013); (ii) compiling 12,297 published Bd records (collected 1852–2017); (iii) comparing the frequency of Bd-infected amphibians through time by both country and region; (iv) genotyping Bd lineages; (v) histologically identifying evidence of chytridiomycosis, and (vi) using a habitat suitability model to assess future Bd risk.Results: We found a pattern of Bd emergence beginning largely at the turn of the century. From 1852–1999, we found low Bd prevalence (3.2% overall) and limited geographic spread, but after 2000 we documented a sharp increase in prevalence (18.7% overall), wider geographic spread, and multiple Bd lineages that may be responsible for emergence in different regions. We found that Bd risk to amphibians was highest in much of eastern, central, and western Africa.Discussion: Our study documents a largely overlooked yet significant increase in a fungal pathogen that could pose a threat to amphibians across an entire continent. We emphasize the need to bridge historical and contemporary datasets to better describe and predict host-pathogen dynamics over larger temporal scales.

Amphibians are a clade of over 8,400 species that provide unique research opportunities and challenges. With amphibians undergoing severe global declines, we posit that assessing our current understanding of amphibians is imperative. Focusing on the past five years (2016–2020), we examine trends in amphibian research, data, and systematics. New species of amphibians continue to be described at a pace of ∼150 per year. Phylogenomic studies are increasing, fueling a growing consensus in the amphibian tree of life. Over 3,000 species of amphibians are now represented by expert-curated accounts or data in AmphibiaWeb, AmphibiaChina, BIOWEB, or the Amphibian Disease Portal. Nevertheless, many species lack basic natural history data (e.g., diet records, morphological measurements, call recordings) and major gaps exist for entire amphibian clades. Genomic resources appear on the cusp of a rapid expansion, but large, repetitive amphibian genomes still pose significant challenges. Conservation continues to be a major focus for amphibian research, and threats cataloged on AmphibiaWeb for 1,261 species highlight the need to address land use change and disease using adaptive management strategies. To further promote amphibian research and conservation, we underscore the importance of database integration and suggest that other understudied or imperiled clades would benefit from similar assessments of existing data.

The recently-emerged amphibian chytrid fungus Batrachochytrium dendrobatidis (Bd) has had an unprecedented impact on global amphibian populations, and highlights the urgent need to develop effective mitigation strategies. We conducted in-situ antifungal treatment experiments in wild populations of the endangered mountain yellow-legged frog during or immediately after Bd-caused mass die-off events. The objective of treatments was to reduce Bd infection intensity (“load”) and in doing so alter frog-Bd dynamics and increase the probability of frog population persistence despite ongoing Bd infection. Experiments included treatment of early life stages (tadpoles and subadults) with the antifungal drug itraconazole, treatment of adults with itraconazole, and augmentation of the skin microbiome of subadults with Janthinobacterium lividum, a commensal bacterium with antifungal properties. All itraconazole treatments caused immediate reductions in Bd load, and produced longer-term effects that differed between life stages. In experiments focused on early life stages, Bd load was reduced in the 2 months immediately following treatment and was associated with increased survival of subadults. However, Bd load and frog survival returned to pre-treatment levels in less than 1 year, and treatment had no effect on population persistence. In adults, treatment reduced Bd load and increased frog survival over the entire 3-year post-treatment period, consistent with frogs having developed an effective adaptive immune response against Bd. Despite this protracted period of reduced impacts of Bd on adults, recruitment into the adult population was limited and the population eventually declined to near-extirpation. In the microbiome augmentation experiment, exposure of subadults to a solution of J. lividum increased concentrations of this potentially protective bacterium on frogs. However, concentrations declined to baseline levels within 1 month and did not have a protective effect against Bd infection. Collectively, these results indicate that our mitigation efforts were ineffective in causing long-term changes in frog-Bd dynamics and increasing population persistence, due largely to the inability of early life stages to mount an effective immune response against Bd. This results in repeated recruitment failure and a low probability of population persistence in the face of ongoing Bd infection.

The emerging fungal pathogen, Batrachochytrium dendrobatidis (Bd), which can cause a fatal disease called chytridiomycosis, is implicated in the collapse of hundreds of host amphibian species. We describe chytridiomycosis dynamics in two co-occurring terrestrial salamander species, the Santa Lucia Mountains slender salamander, Batrachoseps luciae, and the arboreal salamander, Aneides lugubris. We (1) conduct a retrospective Bd-infection survey of specimens collected over the last century, (2) estimate present-day Bd infections in wild populations, (3) use generalized linear models (GLM) to identify biotic and abiotic correlates of infection risk, (4) investigate susceptibility of hosts exposed to Bd in laboratory trials, and (5) examine the ability of host skin bacteria to inhibit Bd in culture. Our historical survey of 2,866 specimens revealed that for most of the early 20th century (~1920–1969), Bd was not detected in either species. By the 1990s the proportion of infected specimens was 29 and 17% (B. luciae and A. lugubris, respectively), and in the 2010s it was 10 and 17%. This was similar to the number of infected samples from contemporary populations (2014–2015) at 10 and 18%. We found that both hosts experience signs of chytridiomycosis and suffered high Bd-caused mortality (88 and 71% for B. luciae and A. lugubris, respectively). Our GLM revealed that Bd-infection probability was positively correlated with intraspecific group size and proximity to heterospecifics but not to abiotic factors such as precipitation, minimum temperature, maximum temperature, mean temperature, and elevation, or to the size of the hosts. Finally, we found that both host species contain symbiotic skin-bacteria that inhibit growth of Bd in laboratory trials. Our results provide new evidence consistent with other studies showing a relatively recent Bd invasion of amphibian host populations in western North America and suggest that the spread of the pathogen may be enabled both through conspecific and heterospecific host interactions. Our results suggest that wildlife disease studies should assess host-pathogen dynamics that consider the interactions and effects of multiple hosts, as well as the historical context of pathogen invasion, establishment, and epizootic to enzootic transitions to better understand and predict disease dynamics.

A basic tenet of animal behavior is that animal groupings (e.g. schools of fishes or flocks of birds) are widely influenced by predators. Many studies have focused on communication between individuals within the same species or different species within a defined social group; but predators typically select from a number of different co‐occurring species. To evaluate whether two distantly‐related species with similar predators share vocal information regarding predator threats, we conducted a field experiment in the Amazonian rainforest involving an avian prey‐species, a primate prey‐species and a shared predator. In our reciprocal field experiment, we elicited alarm calls from birds (bluish‐slate antshrikes Thamnomanes schistogynus ) and primates (saddle‐backed tamarins Leontocebus weddelli ) by exposing them to a trained raptor (bicolored hawk Accipiter bicolor ). We then played all types of recorded alarm calls back to birds and tamarins, and measured 1) the time to respond (for both birds and tamarins), and 2) the distance moved across the substrate (for tamarins). Our results show that both birds and tamarins were significantly more likely to flee when hearing vocal alarms compared to a control (a common bird call, the screaming piha Lipaugus vociferans ), regardless of the species who produced the alarm. In addition, tamarins moved significantly more upon hearing bird alarm calls when compared to the control. We suggest that signals regarding shared predators may be highly valued across prey from distinct social groups. These data support the hypothesis that overlapping potential predators can drive communication between distinct prey groups, resulting in taxonomically diverse eavesdropping networks within tropical rainforests.