Biology subjects

Ohmer, M.

Publications and source records attributed to Ohmer, M..

4 recordsLinked to original sources

bioRxiv2026

Thermal variability interacts with infection load and the evolution of host-parasite defense

Rising temperatures and unpredictable weather patterns are directly linked to emerging infectious diseases that threaten global biodiversity. Thermal variability affects host-parasite interactions, and understanding how animal hosts respond to temperature variability and parasite infection is paramount for conservation and for predicting zoonotic spillover. Hosts employ two strategies to defend against parasites: resistance (inhibiting or limiting infection) and tolerance (limiting the negative effects of infection). This observation raises a fundamental question: How does thermal variability affect the expression and evolution of resistance versus tolerance? Subsequently, how does the evolution of resistance versus tolerance influence parasite load dynamics? Here, we first review why temperature may differentially affect resistance and tolerance mechanisms, thereby altering host selection and eco-evolutionary disease outcomes. Second, to highlight the importance of these interactions, we present a model that illustrates key potential effects of temperature variability on host defense mechanisms. Our model demonstrates that temperature variability alone could drive lower infection prevalence and loads, but it also selects for host tolerance, ultimately leading to higher net prevalence and loads. We also find widely divergent outcomes depending on how temperature impacts defense strategies. These results highlight key areas for future empirical and theoretical work on the interactions among temperature variability, infection load, and host defense evolution.

ecology↗

bioRxiv2025

Exploring local and regional drivers of microbial biodiversity across freshwater ponds

AimPonds are isolated, highly variable environments that exhibit low spatial autocorrelation of environmental variables and have island-like features, which may give rise to unique biogeographic patterns compared to terrestrial and lotic environments. Here, we evaluate whether commonly observed biogeographical patterns apply to microbial biodiversity in pond fungal and bacterial communities. Specifically, we tested (1) whether these communities follow latitudinal diversity gradients and distance decay relationships, and (2) if variation in community composition or richness was related to specific environmental or land-use factors. LocationEastern, USA Time periodSummer, 2022 TaxaBacteria and Fungi MethodsWe collected water and muck from 39 ponds across 8 states in the Eastern USA. We extracted DNA from these samples and sequenced sections of the 16S rRNA and ITS1 genes to survey the bacterial and fungal communities, before evaluating biogeographical patterns. ResultsWe found evidence of latitudinal diversity gradients in muck fungal communities, but not bacterial communities. We observed weak distance decay relationships in all sample types. Community richness was related to some environmental filters, where conductivity was positively related to water bacterial richness, but negatively related to muck fungal richness. Environmental drivers explained low to moderate variation in microbial composition, with temperature universally linked to microbial biodiversity. ConclusionsPond microbiomes exhibit unique biogeographic patterns depending on the microhabitat and microbial taxa in question, with land use and abiotic conditions, especially temperature, explaining some variation in microbial biodiversity across sites. Our findings suggest that the low spatial autocorrelation in environmental conditions and the lack of connectivity across ponds provides a useful framework for investigating localized drivers of microbial diversity.

ecology↗

bioRxiv2021

Host Species is Linked to Pathogen Genotype for the Amphibian Chytrid Fungus (Batrachochytrium dendrobatidis)

Host-pathogen specificity can arise from certain selective environments mediated by both the host and pathogen. Therefore, understanding the degree to which host species identity is correlated with pathogen genotype can help reveal historical host-pathogen dynamics. One animal disease of particular concern is chytridiomycosis, typically caused by the global panzootic lineage of the amphibian chytrid fungus (Batrachochytrium dendrobatidis, Bd), termed the Bd-GPL. This pathogen lineage has caused devastating declines in amphibian communities around the world. However, the origin of Bd-GPL and the fine-scale transmission dynamics of this lineage have remained a mystery. This is especially the case in North America where Bd-GPL is widespread, but disease outbreaks occur sporadically. Herein, we use Bd genetic data collected throughout the United States from amphibian skin swab and cultured isolate samples to investigate Bd genetic patterns. We highlight two case studies in Pennsylvania and Nevada where Bd-GPL genotypes are strongly correlated with host species identity. Specifically, in some localities bullfrogs (Rana catesbeiana) are infected with Bd-GPL lineages that are distinct from those infecting other sympatric amphibian species. Overall, we reveal a previously unknown association of Bd genotype with host species and identify the eastern United States as a Bd diversity hotspot and potential ancestral population for Bd-GPL.

molecular biology↗

bioRxiv2019

Metabolic labeling of RNAs uncovers hidden features and dynamics of the Arabidopsis thaliana transcriptome

Transcriptome analysis by RNA sequencing (RNA-seq) has become an indispensable core research tool in modern plant biology. Virtually all RNA-seq studies provide a snapshot of the steady-state transcriptome, which contains valuable information about RNA populations at a given time, but lacks information about the dynamics of RNA synthesis and degradation. Only a few specialized sequencing techniques, such as global run-on sequencing (GRO-seq), have been applied in plants and provide information about RNA synthesis rates. Here, we demonstrate that RNA labeling with a modified, non-toxic uridine analog, 5-ethynyl uridine (5-EU), in Arabidopsis thaliana seedlings provides insight into the dynamic nature of a plant transcriptome. Pulse-labeling with 5-EU allowed the detection and analysis of nascent and unstable RNAs, of RNA processing intermediates generated by splicing, and of chloroplast RNAs. We also conducted pulse-chase experiments with 5-EU, which allowed us to determine RNA stabilities without the need for chemical inhibition of transcription using compounds such as actinomycin and cordycepin. Genome-wide analysis of RNA stabilities by 5-EU pulse-chase experiments revealed that this inhibitor-free RNA stability measurement results in RNA half-lives much shorter than those reported after chemical inhibition of transcription. In summary, our results show that the Arabidopsis nascent transcriptome contains unstable RNAs and RNA processing intermediates, and suggest that half-lives of plant RNAs are largely overestimated. Our results lay the ground for an easy and affordable nascent transcriptome analysis and inhibitor-free analysis of RNA stabilities in plants.

plant biology↗