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Abstract Accurately predicting the impacts of climate change on wildlife health requires a deeper understanding of seasonal rhythms in host–pathogen interactions. The amphibian pathogen,Batrachochytrium dendrobatidis(Bd), exhibits seasonality in incidence; however, the role that biological rhythms in host defences play in defining this pattern remains largely unknown.The aim of this study was to examine whether host immune and microbiome defences againstBdcorrespond with infection risk and seasonal fluctuations in temperature and humidity.Over the course of a year, five populations of Southern leopard frogs (Rana[Lithobates]sphenocephala) in Tennessee, United States, were surveyed for host immunity, microbiome and pathogen dynamics. Frogs were swabbed for pathogen load and skin bacterial diversity and stimulated to release stored antimicrobial peptides (AMPs). Secretions were analysed to estimate total hydrophobic peptide concentrations, presence of known AMPs and effectiveness ofBdgrowth inhibition in vitro. The diversity and proportion of bacterial reads with a 99% match to sequences of isolates known to inhibitBdgrowth in vitro were used as an estimate of predicted anti‐Bdfunction of the skin microbiome.Batrachochytrium dendrobatidisdynamics followed the expected seasonal fluctuations—peaks in cooler months—which coincided with when host mucosal defences were most potent againstBd. Specifically, the concentration and expression of stored AMPs cycled synchronously withBddynamics. Although microbiome changes followed more linear trends over time, the proportion of bacteria that can function to inhibitBdgrowth was greatest when risk ofBdinfection was highest.We interpret the increase in peptide storage in the fall and the shift to a more anti‐Bdmicrobiome over winter as a preparatory response for subsequent infection risk during the colder periods when AMP synthesis and bacterial growth is slow and pathogen pressure from this cool‐adapted fungus is high. Given that a decrease in stored AMP concentrations as temperatures warm in spring likely means greater secretion rates, the subsequent decrease in prevalence suggests seasonality ofBdin this host may be in part regulated by annual immune rhythms, and dominated by the effects of temperature.
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This content will become publicly available on December 24, 2025
Novel skin defense peptides and microbiota contribute to disease resilience of the Ngäbe-Buglé leopard frog
Some of the amphibian populations in Panama are demonstrating slow recovery decades after severe declines caused by the invasion of the fungal pathogenBatrachochytrium dendrobatidis(Bd). However, new species remain to be described and assessed for the mechanisms of disease resilience. We identified seven skin defense peptides from a presumably novel leopard frog species in the Tabasará range, at Buäbti (Llano Tugrí), Ngäbe-Buglé Comarca, and Santa Fe, Veraguas, Panama, herein called the Ngäbe-Buglé leopard frog. Two of the peptides were previously known: brevinin-1BLb fromRana (Lithobates) blairiand a previously hypothesized “ancestral” peptide, ranatuerin-2BPa. We hypothesized that the peptides are active againstBdand shape the microbiome such that the skin bacterial communities are more similar to those of other leopard frogs than of co-occurring host species. Natural mixtures of the collected skin peptides showed a minimum inhibitory concentration againstBdof 100 μg/ml, which was similar to that of other leopard frogs that have been tested. All sampled individuals hosted high intensity of infection withBd. We sampled nine other amphibian species in nearby habitats and found lower prevalence and intensities ofBdinfection. In addition to the pathogen load, the skin microbiomes were examined using 16S rRNA gene targeted amplicon sequencing. When compared to nine co-occurring amphibians, the Ngäbe-Buglé leopard frog had similar skin bacterial richness and anti-Bdfunction, but the skin microbiome structure differed significantly among species. The community composition of the bacterial skin communities was strongly associated with theBdinfection load. In contrast, the skin microbiome composition of the Ngäbe-Buglé leopard frog was similar to that of five North American leopard frog populations and the sympatric and congenericRana (Lithobates) warszewitschii, with 29 of the 46 core bacteria all demonstrating anti-Bdactivity in culture. Because of the highBdinfection load and prevalence in the Ngäbe-Buglé leopard frog, we suggest that treatment to reduce theBdload in this species might reduce the chytridiomycosis risk in the co-occurring amphibian community, but could potentially disrupt the evolution of skin defenses that provide a mechanism for disease resilience in this species.
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- PAR ID:
- 10594521
- Publisher / Repository:
- Frontiers
- Date Published:
- Journal Name:
- Frontiers in Amphibian and Reptile Science
- Volume:
- 2
- ISSN:
- 2813-6780
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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