Effects of Density on Spatial Aggregation and Habitat Associations of the Glass Frog Espadarana (Centrolene) prosoblepon

Influence of environmental factors and body condition on the post-oviposition behavior in the emerald glass frog Espadarana prosoblepon (Centrolenidae)

In species with parental care behaviors, parents may adjust the intensity and duration of their care if fluctuation in factors such as environmental variables or body condition affects offspring survival. In the face of environmental changes, many egg-laying species remain with their clutch for extended periods if this behavioral adjustment provides tangible benefits to the offspring. However, the length of time parents stay with the offspring may also differ depending on the individual's body condition. In the glass frog family (Centrolenidae), several species exhibit long-term egg attendance in which they remain with their clutch for several days after oviposition takes place. For some of them, changes in environmental variables lead to increased parental care efforts. For the species in which parents remain with their offspring for a short period (less than 24 hours), it is less clear if this constitutes parenting behavior, and whether parents adjust their efforts as a function of environmental change or the parent's body condition remains unexplored. We studied a population of the Emerald Glass Frog, Espadarana prosoblepon, a species that exhibits a short period of quiescence after oviposition (less than three hours). Our study aimed to determine whether females alter the length of their post-oviposition quiescence period in response to changes in environmental variables (i.e., temperature, humidity, rainfall, and mean wind speed) or female body condition. Pairs in amplexus were captured in the field and transported to semi-natural enclosures to record the duration of post-oviposition quiescence using infrared cameras. Females' post-oviposition quiescence lasted an average of 67.4 ± 26.6 min (range = 22.7-158.3 min). We did not find a significant relationship between the duration of the post-oviposition quiescence and any of the environmental variables tested. Similarly, post-oviposition quiescence duration was not influenced by female body condition. Because the variation observed in the duration of post-oviposition quiescence was not related to changes in extrinsic (environmental) or intrinsic (body condition) factors, we found no evidence that females of E. prosoblepon modify their post-oviposition behavior in response to any of the variables examined in this study. Future research investigating the adaptive significance of the post-oviposition quiescence observed in this species is needed to understand how this behavior is related to parental care efforts.

Tropical snake diversity collapses after widespread amphibian loss

Biodiversity is declining at unprecedented rates worldwide. Yet cascading effects of biodiversity loss on other taxa are largely unknown because baseline data are often unavailable. We document the collapse of a Neotropical snake community after the invasive fungal pathogen Batrachochytrium dendrobatidis caused a chytridiomycosis epizootic leading to the catastrophic loss of amphibians, a food source for snakes. After mass mortality of amphibians, the snake community contained fewer species and was more homogeneous across the study site, with several species in poorer body condition, despite no other systematic changes in the environment. The demise of the snake community after amphibian loss demonstrates the repercussive and often unnoticed consequences of the biodiversity crisis and calls attention to the invisible declines of rare and data-deficient species.

Eco-evolutionary rescue promotes host-pathogen coexistence

Emerging infectious pathogens are responsible for some of the most severe host mass mortality events in wild populations. Yet, effective pathogen control strategies are notoriously difficult to identify, in part because quantifying and forecasting pathogen spread and disease dynamics is challenging. Following an outbreak, hosts must cope with the presence of the pathogen, leading to host-pathogen coexistence or extirpation. Despite decades of research, little is known about host-pathogen coexistence post-outbreak when low host abundances and cryptic species make these interactions difficult to study. Using a novel disease-structured N-mixture model, we evaluate empirical support for three host-pathogen coexistence hypotheses (source-sink, eco-evolutionary rescue, and spatial variation in pathogen transmission) in a Neotropical amphibian community decimated by Batrachochytrium dendrobatidis (Bd) in 2004. During 2010-2014, we surveyed amphibians in Parque Nacional G. D. Omar Torríjos Herrera, Coclé Province, El Copé, Panama. We found that the primary driver of host-pathogen coexistence was eco-evolutionary rescue, as evidenced by similar amphibian survival and recruitment rates between infected and uninfected hosts. Average apparent monthly survival rates of uninfected and infected hosts were both close to 96%, and the expected number of uninfected and infected hosts recruited (via immigration/reproduction) was less than one host per disease state per 20-m site. The secondary driver of host-pathogen coexistence was spatial variation in pathogen transmission as we found that transmission was highest in areas of low abundance but there was no support for the source-sink hypothesis. Our results indicate that changes in the host community (i.e., through genetic or species composition) can reduce the impacts of emerging infectious disease post-outbreak. Our disease-structured N-mixture model represents a valuable advancement for conservation managers trying to understand underlying host-pathogen interactions and provides new opportunities to study disease dynamics in remnant host populations decimated by virulent pathogens.

External Reinfection of a Fungal Pathogen Does not Contribute to Pathogen Growth

Chytridiomycosis is an emerging infectious disease of amphibians caused by the fungal pathogen Batrachochytrium dendrobatidis (Bd), which has led to devastating declines in amphibian populations worldwide. Current theory predicts that Bd infections are maintained through both reproduction on the host's skin and reinfection from sources outside of the host. To investigate the importance of external reinfection on pathogen burden, we infected captive-bred individuals of the highly susceptible Panamanian Golden Frog, Atelopus glyphus, and wild-caught glass frogs, Espadarana prosoblepon, with Bd. We housed the animals in one of three treatments: individually, in heterospecific pairs, and in conspecific pairs. For 8 weeks, we measured the Bd load and shedding rate of all frogs. We found that Atelopus had high rates of increase in both Bd load and shedding rate, but pathogen growth rates did not differ among treatments. The infection intensity of Espadarana co-housed with Atelopus was indistinguishable from those housed singly and those in conspecific pairs, despite being exposed to a large external source of Bd zoospores. Our results indicate that Bd load in both species is driven by pathogen replication within an individual, with reinfection from outside the host contributing little to the amplification of host fungal load.

Disassembly of a tadpole community by a multi-host fungal pathogen with limited evidence of recovery

Emerging infectious diseases can cause host community disassembly, but the mechanisms driving the order of species declines and extirpations following a disease outbreak are unclear. We documented the community disassembly of a Neotropical tadpole community during a chytridiomycosis outbreak, triggered by the generalist fungal pathogen, Batrachochytrium dendrobatidis (Bd). Within the first 11 months of Bd arrival, tadpole density and occupancy rapidly declined. Species rarity, in terms of tadpole occupancy and adult relative abundance, did not predict the odds of tadpole occupancy declines. But species losses were taxonomically selective, with glassfrogs (Family: Centrolenidae) disappearing the fastest and tree frogs (Family: Hylidae) and dart-poison frogs (Family: Dendrobatidae) remaining the longest. We detected biotic homogenization of tadpole communities, with post-decline communities resembling one another more strongly than pre-decline communities. The entire tadpole community was extirpated within 22 months following Bd arrival, and we found limited signs of recovery within 10 years post-outbreak. Because of imperfect species detection inherent to sampling species-rich tropical communities and the difficulty of devising a single study design protocol to sample physically complex tropical habitats, we used simulations to provide recommendations for future surveys to adequately sample diverse Neotropical communities. Our unique data set on tadpole community composition before and after Bd arrival is a valuable baseline for assessing amphibian recovery. Our results are of direct relevance to conservation managers and community ecologists interested in understanding the timing, magnitude, and consequences of disease outbreaks as emerging infectious diseases spread globally.