ORCID Profile
0000-0001-8883-2968
Current Organisation
University of Alabama
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Publisher: The Royal Society
Date: 14-08-2019
Abstract: Wildlife disease dynamics are strongly influenced by the structure of host communities and their symbiotic microbiota. Conspicuous hibian declines associated with the waterborne fungal pathogen Batrachochytrium dendrobatidis (Bd) have been observed in aquatic-breeding frogs globally. However, less attention has been given to cryptic terrestrial-breeding hibians that have also been declining in tropical regions. By experimentally manipulating multiple tropical hibian assemblages harbouring natural microbial communities, we tested whether Bd spillover from naturally infected aquatic-breeding frogs could lead to Bd lification and mortality in our focal terrestrial-breeding host: the pumpkin toadlet Brachycephalus pitanga . We also tested whether the strength of spillover could vary depending on skin bacterial transmission within host assemblages. Terrestrial-breeding toadlets acquired lethal spillover infections from neighbouring aquatic hosts and experienced dramatic but generally non-protective shifts in skin bacterial composition primarily attributable to their Bd infections. By contrast, aquatic-breeding hibians maintained mild Bd infections and higher survival, with shifts in bacterial microbiomes that were unrelated to Bd infections. Our results indicate that Bd spillover from even mildly infected aquatic-breeding hosts may lead to dysbiosis and mortality in terrestrial-breeding species, underscoring the need to further investigate recent population declines of terrestrial-breeding hibians in the tropics.
Publisher: Elsevier BV
Date: 12-2017
DOI: 10.1016/J.DCI.2017.08.018
Abstract: Temperature variability, and in particular temperature decreases, can increase susceptibility of hibians to infections by the fungus Batrachochytrium dendrobatidis (Bd). However, the effects of temperature shifts on the immune systems of Bd-infected hibians are unresolved. We acclimated frogs to 16 °C and 26 °C (baseline), simultaneously transferred them to an intermediate temperature (21 °C) and inoculated them with Bd (treatment), and tracked their infection levels and white blood cell profiles over six weeks. Average weekly infection loads were consistently higher in 26°C-history frogs, a group that experienced a 5 °C temperature decrease, than in 16°C-history frogs, a group that experienced a 5 °C temperature increase, but this pattern only approached statistical significance. The 16°C-acclimated frogs had high neutrophil:lymphocyte (N:L) ratios (suggestive of a hematopoietic stress response) at baseline, which were conserved post-treatment. In contrast, the 26°C-acclimated frogs had low N:L ratios at baseline which reversed to high N:L ratios post-treatment (suggestive of immune system activation). Our results suggest that infections were less physiologically taxing for the 16°C-history frogs than the 26°C-history frogs because they had already adjusted immune parameters in response to challenging conditions (cold). Our findings provide a possible mechanistic explanation for observations that hibians are more susceptible to Bd infection following temperature decreases compared to increases and underscore the consensus that increased temperature variability associated with climate change may increase the impact of infectious diseases.
Publisher: Coastal Education and Research Foundation
Date: 07-2014
Publisher: Springer Science and Business Media LLC
Date: 28-09-2020
Publisher: The Royal Society
Date: 26-06-2019
Abstract: The host-associated microbiome is vital to host immunity and pathogen defense. In aquatic ecosystems, organisms may interact with environmental bacteria to influence the pool of potential symbionts, but the effects of these interactions on host microbiome assembly and pathogen resistance are unresolved. We used replicated bromeliad microecosystems to test for indirect effects of arthropod–bacteria interactions on host microbiome assembly and pathogen burden, using tadpoles and the fungal hibian pathogen Batrachochytrium dendrobatidis as a model host–pathogen system. Arthropods influenced host microbiome assembly by altering the pool of environmental bacteria, with arthropod–bacteria interactions specifically reducing host colonization by transient bacteria and promoting antimicrobial components of aquatic bacterial communities. Arthropods also reduced fungal zoospores in the environment, but fungal infection burdens in tadpoles corresponded most closely with arthropod-mediated patterns in microbiome assembly. This result indicates that the cascading effects of arthropods on the maintenance of a protective host microbiome may be more strongly linked to host health than negative effects of arthropods on pools of pathogenic zoospores. Our work reveals tight links between healthy ecosystem dynamics and the functioning of host microbiomes, suggesting that ecosystem disturbances such as loss of arthropods may have downstream effects on host-associated microbial pathogen defenses and host fitness.
Publisher: Springer Science and Business Media LLC
Date: 07-06-2022
DOI: 10.1186/S42523-022-00188-7
Abstract: Host microbiomes may differ under the same environmental conditions and these differences may influence susceptibility to infection. Amphibians are ideal for comparing microbiomes in the context of disease defense because hundreds of species face infection with the skin-invading microbe Batrachochytrium dendrobatidis (Bd), and species richness of host communities, including their skin bacteria (bacteriome), may be exceptionally high. We conducted a landscape-scale Bd survey of six co-occurring hibian species in Brazil’s Atlantic Forest. To test the bacteriome as a driver of differential Bd prevalence, we compared bacteriome composition and co-occurrence network structure among the six focal host species. Intensive s ling yielded ergent Bd prevalence in two ecologically similar terrestrial-breeding species, a group with historically low Bd resistance. Specifically, we detected the highest Bd prevalence in Ischnocnema henselii but no Bd detections in Haddadus binotatus . Haddadus binotatus carried the highest bacteriome alpha and common core ersity, and a modular network partitioned by negative co-occurrences, characteristics associated with community stability and competitive interactions that could inhibit Bd colonization. Our findings suggest that community structure of the bacteriome might drive Bd resistance in H. binotatus , which could guide microbiome manipulation as a conservation strategy to protect erse radiations of direct-developing species from Bd-induced population collapses.
Publisher: Elsevier BV
Date: 2023
Publisher: Springer Science and Business Media LLC
Date: 20-10-2021
DOI: 10.1007/S00248-021-01897-3
Abstract: Anthropogenic habitat disturbances can dramatically alter ecological community interactions, including host-pathogen dynamics. Recent work has highlighted the potential for habitat disturbances to alter host-associated microbial communities, but the associations between anthropogenic disturbance, host microbiomes, and pathogens are unresolved. Amphibian skin microbial communities are particularly responsive to factors like temperature, physiochemistry, pathogen infection, and environmental microbial reservoirs. Through a field survey on wild populations of Acris crepitans (Hylidae) and Lithobates catesbeianus (Ranidae), we assessed the effects of habitat disturbance and connectivity on environmental bacterial reservoirs, Batrachochytrium dendrobatidis (Bd) infection, and skin microbiome composition. We found higher measures of microbiome dispersion (a measure of community variability) in A. crepitans from more disturbed ponds, supporting the hypothesis that disturbance increases stochasticity in biological communities. We also found that habitat disturbance limited microbiome similarity between locations for both species, suggesting greater isolation of bacterial assemblages in more disturbed areas. Higher disturbance was associated with lower Bd prevalence for A. crepitans, which could signify suboptimal microclimates for Bd in disturbed habitats. Combined, our findings show that reduced microbiome stability stemming from habitat disturbance could compromise population health, even in the absence of pathogenic infection.
Publisher: Wiley
Date: 14-08-2017
Publisher: Springer Science and Business Media LLC
Date: 25-06-2018
DOI: 10.1038/S41598-018-27828-W
Abstract: Hybridization of parasites can generate new genotypes with high virulence. The fungal hibian parasite Batrachochytrium dendrobatidis ( Bd ) hybridizes in Brazil’s Atlantic Forest, a bio ersity hotspot where hibian declines have been linked to Bd , but the virulence of hybrid genotypes in native hosts has never been tested. We compared the virulence (measured as host mortality and infection burden) of hybrid Bd genotypes to the parental lineages, the putatively hypovirulent lineage Bd -Brazil and the hypervirulent Global Pandemic Lineage ( Bd -GPL), in a panel of native Brazilian hosts. In Brachycephalus ephippium , the hybrid exceeded the virulence (host mortality) of both parents, suggesting that novelty arising from hybridization of Bd is a conservation concern. In Ischnocnema parva , host mortality in the hybrid treatment was intermediate between the parent treatments, suggesting that this species is more vulnerable to the aggressive phenotypes associated with Bd -GPL. Dendropsophus minutus showed low overall mortality, but infection burdens were higher in frogs treated with hybrid and Bd -GPL genotypes than with Bd -Brazil genotypes. Our experiment suggests that Bd hybrids have the potential to increase disease risk in native hosts. Continued surveillance is needed to track potential spread of hybrid genotypes and detect future genomic shifts in this dynamic disease system.
Publisher: Wiley
Date: 15-11-2017
DOI: 10.1002/ECY.2019
Publisher: Wiley
Date: 20-12-2018
DOI: 10.1111/AEC.12695
Publisher: The Royal Society
Date: 12-06-2023
Abstract: With emerging diseases on the rise, there is an urgent need to identify and understand novel mechanisms of prophylactic protection in vertebrate hosts. Inducing resistance against emerging pathogens through prophylaxis is an ideal management strategy that may impact pathogens and their host-associated microbiome. The host microbiome is recognized as a critical component of immunity, but the effects of prophylactic inoculation on the microbiome are unknown. In this study, we investigate the effects of prophylaxis on host microbiome composition, focusing on the selection of anti-pathogenic microbes contributing to host acquired immunity in a model host–fungal disease system, hibian chytridiomycosis. We inoculated larval Pseudacris regilla against the fungal pathogen Batrachochytrium dendrobatidis ( Bd ) with a Bd metabolite-based prophylactic. Increased prophylactic concentration and exposure duration were associated with significant increases in proportions of putatively Bd -inhibitory host-associated bacterial taxa, indicating a protective prophylactic-induced shift towards microbiome members that are antagonistic to Bd. Our findings are in accordance with the adaptive microbiome hypothesis, where exposure to a pathogen alters the microbiome to better cope with subsequent pathogen encounters. Our study advances research on the temporal dynamics of microbiome memory and the role of prophylaxis-induced shifts in microbiomes contributing to prophylaxis effectiveness. This article is part of the theme issue ‘Amphibian immunity: stress, disease and ecoimmunology’.
Publisher: Elsevier BV
Date: 04-2017
Publisher: Inter-Research Science Center
Date: 12-09-2012
DOI: 10.3354/DAO02483
Abstract: The chytridiomycete fungus Batrachochytrium dendrobatidis (Bd) colonizes mouthparts of hibian larvae and superficial epidermis of post-metamorphic hibians, causing the disease chytridiomycosis. Fungal growth within host cells has been documented by light and transmission electron microscopy however, entry of the fungus into host cells has not. Our objective was to document how Bd enters host cells in the wood frog Lithobates sylvaticus, a species at high mortality risk for chytridiomycosis, and the bullfrog L. catesbeianus, a species at low mortality risk for chytridiomycosis. We inoculated frogs and documented infection with transmission electron microscopy. Zoospores encysted on the skin surface and produced morphologically similar germination tubes in both host species that penetrated host cell membranes and enabled transfer of zoospore contents into host cells. Documenting fungal and epidermal ultrastructure during host invasion furthers our understanding of Bd development and the pathogenesis of chytridiomycosis.
Publisher: Wiley
Date: 31-07-2012
Publisher: American Society of Ichthyologists and Herpetologists (ASIH)
Date: 12-2014
DOI: 10.1643/CE-13-061
Publisher: Wiley
Date: 14-10-2016
DOI: 10.1002/ECE3.2464
Publisher: Springer Science and Business Media LLC
Date: 24-08-2017
DOI: 10.1038/S41598-017-09950-3
Abstract: Unprecedented global climate change and increasing rates of infectious disease emergence are occurring simultaneously. Infection with emerging pathogens may alter the thermal thresholds of hosts. However, the effects of fungal infection on host thermal limits have not been examined. Moreover, the influence of infections on the heat tolerance of hosts has rarely been investigated within the context of realistic thermal acclimation regimes and potential anthropogenic climate change. We tested for effects of fungal infection on host thermal tolerance in a model system: frogs infected with the chytrid Batrachochytrium dendrobatidis . Infection reduced the critical thermal maxima (CT max ) of hosts by up to ~4 °C. Acclimation to realistic daily heat pulses enhanced thermal tolerance among infected in iduals, but the magnitude of the parasitism effect usually exceeded the magnitude of the acclimation effect. In ectotherms, behaviors that elevate body temperature may decrease parasite performance or increase immune function, thereby reducing infection risk or the intensity of existing infections. However, increased heat sensitivity from infections may discourage these protective behaviors, even at temperatures below critical maxima, tipping the balance in favor of the parasite. We conclude that infectious disease could lead to increased uncertainty in estimates of species’ vulnerability to climate change.
Publisher: Wiley
Date: 30-08-2016
Publisher: Springer Science and Business Media LLC
Date: 19-06-2023
DOI: 10.1038/S41467-023-38869-9
Abstract: PEAK pseudokinases regulate cell migration, invasion and proliferation by recruiting key signaling proteins to the cytoskeleton. Despite lacking catalytic activity, alteration in their expression level is associated with several aggressive cancers. Here, we elucidate the molecular details of key PEAK signaling interactions with the adapter proteins CrkII and Grb2 and the scaffold protein 14-3-3. Our findings rationalize why the dimerization of PEAK proteins has a crucial function in signal transduction and provide biophysical and structural data to unravel binding specificity within the PEAK interactome. We identify a conserved high affinity 14-3-3 motif on PEAK3 and demonstrate its role as a molecular switch to regulate CrkII binding and signaling via Grb2. Together, our studies provide a detailed structural snapshot of PEAK interaction networks and further elucidate how PEAK proteins, especially PEAK3, act as dynamic scaffolds that exploit adapter proteins to control signal transduction in cell growth/motility and cancer.
Publisher: Wiley
Date: 27-07-2016
DOI: 10.1002/ECE3.2256
Publisher: Springer Science and Business Media LLC
Date: 17-09-2019
DOI: 10.1038/S41598-019-49674-0
Abstract: Bullfrog farming and trade practices are well-established, globally distributed, and economically valuable, but pose risks for bio ersity conservation. Besides their negative impacts on native hibian populations as an invasive species, bullfrogs play a key role in spreading the frog-killing fungus Batrachochytrium dendrobatidis (Bd) in the natural environment. Bullfrogs are tolerant to Bd, meaning that they can carry high infection loads without developing chytridiomycosis. To test the potential of bullfrog farms as reservoirs for erse and virulent chytrid genotypes, we quantified Bd presence, prevalence and infection loads across approximately 1,500 farmed bullfrogs and in the water that is released from farms into the environment. We also described Bd genotypic ersity within frog farms by isolating Bd from dozens of infected tadpoles. We observed in iduals infected with Bd in all s led farms, with high prevalence (reaching 100%) and high infection loads (average 71,029 zoospore genomic equivalents). Average outflow water volume from farms was high (60,000 L/day), with Bd zoospore concentration reaching approximately 50 million zoospores/L. Because virulent pathogen strains are often selected when growing in tolerant hosts, we experimentally tested whether Bd genotypes isolated from bullfrogs are more virulent in native anuran hosts compared to genotypes isolated from native host species. We genotyped 36 Bd isolates from two genetic lineages and found that Bd genotypes cultured from bullfrogs showed similar virulence in native toads when compared to genotypes isolated from native hosts. Our results indicate that bullfrog farms can harbor high Bd genotypic ersity and virulence and may be contributing to the spread of virulent genotypes in the natural environment. We highlight the urgent need to implement Bd monitoring and mitigation strategies in bullfrog farms to aid in the conservation of native hibians.
No related grants have been discovered for Sasha Greenspan.