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Abstract Human‐induced climate change, land use changes, and urbanization are predicted to dramatically impact landscape hydrology, which can have devastating impacts on aquatic organisms. For amphibians that rely on aquatic environments to breed and develop, it is essential to understand how the larval environment impacts development, condition, and performance later in life. Two important predicted impacts of climate change, urbanization, and land use changes are reduced hydroperiod and variable larval density. Here, we explored how larval density and hydroperiod affect development, morphology, physiology, and immune defenses at metamorphosis and 35 days post‐metamorphosis in the frogRana pipiens. We found that high‐density larval conditions had a large negative impact on development and morphology, which resulted in longer larval periods, reduced likelihood of metamorphosis, smaller size at metamorphosis, shorter femur to body length ratio, and reduced microbiome species evenness compared with animals that developed in low‐density conditions. However, animals from the high‐density treatment experienced compensatory growth post‐metamorphosis, demonstrating accelerated growth in body size and relative femur length compared with animals from the low‐density treatments, despite not “catching‐up” in size. We also observed an increase in relative gut length and relative liver size in animals that had developed in the high‐density treatment than those in the low‐density treatment, as well as higher bacterial killing ability, and greater jump distances relative to their leg length across different temperatures. Finally, metabolic rate was higher overall but especially at higher test temperatures for animals that developed under high‐density conditions, indicating that these animals may expend more energy in response to acute temperature changes. While the effects of climate change have direct negative effects on larval development and metamorphosis, animals can increase growth rate post‐metamorphosis; however, that compensatory growth might come at a cost and reduce their ability to cope with further environmental change such as increased temperatures. 

The use of museum specimens for research in microbial evolutionary ecology remains an under-utilized investigative dimension with important potential. Despite this potential, there remain barriers in methodology and analysis to the wide-spread adoption of museum specimens for such studies. Here, we hypothesized that there would be significant differences in taxonomic prediction and related diversity among sample type (museum or fresh) and sequencing strategy (medium-depth shotgun metagenomic or 16S rRNA gene). We found dramatically higher predicted diversity from shotgun metagenomics when compared to 16S rRNA gene sequencing in museum and fresh samples, with this differential being larger in museum specimens. Broadly confirming these hypotheses, the highest diversity found in fresh samples was with shotgun sequencing using the Rep200 reference inclusive of viruses and microeukaryotes, followed by the WoL reference database. In museum-specimens, community diversity metrics also differed significantly between sequencing strategies, with the alpha-diversity ACE differential being significantly greater than the same comparisons made for fresh specimens. Beta diversity results were more variable, with significance dependent on reference databases used. Taken together, these findings demonstrate important differences in diversity results and prompt important considerations for future experiments and downstream analyses aiming to incorporate microbiome datasets from museum specimens. 

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.