Biology subjects

Moeller, H. V.

Publications and source records attributed to Moeller, H. V..

7 recordsLinked to original sources

bioRxiv2026

Spliceosome loss in the red tide ciliate Mesodinium rubrum presents a symbiotic cul-de-sac

Mesodinium rubrum, a marine microbial eukaryote associated with some of the largest red tides on Earth, has the remarkable ability to commandeer the plastids, mitochondria and nuclei from the alga Teleaulax amphioxeia for photosynthesis. Here we report analyses of assemblies of M. rubrums two nuclear genomes. Unexpectedly, M. rubrum appears to have completely lost its spliceosomal introns, most spliceosomal molecules, and the key genes for an intron splicing-associated process, Nonsense-mediated mRNA Decay (NMD). In contrast, non-spliceosomal tRNA introns have been retained, as have thousands of intron analogs spliced out of DNA during ciliate somatic genome development (internal eliminated sequences - IESs). Intron-containing genes, especially from intron-rich species like T. amphioxeia, would likely be defunct if horizontally transferred to a host without a spliceosome like M. rubrum, and thus we propose that introns can be a roadblock to progressive endosymbiotic genomic integration.

genomics↗

bioRxiv2026

Epigenetic Intelligence: How Organisms Track Their Environment Through Molecular Memory

The regulation of gene expression by epigenetic markers is a growing area of focus for researchers who seek to explain rapid phenotypic acclimatization to environmental change. Yet even as empirical datasets accumulate exponentially, the mechanistic underpinnings of epigenetic changes and their role in connecting environmental variation with the regulation of gene function remain unclear. Here, we use a stochastic model of epigenetic change to generate three testable predictions: (1) that organisms require environmental feedback to track their environments through epigenetic responses, (2) that this tracking requires coordination between the addition and removal of epigenetic markers, and (3) that epigenetically driven tracking is only effective under specific subsets of environmental variability. Despite the intuitiveness of these postulates, few to no experimental studies directly test them. We review correlational evidence consistent with the models predictions, describe hypothetical mechanisms by which epigenetic strategies could evolve, and clearly identify knowledge gaps and urgent experimental needs in the field. Overall, the field of environmental epigenetics is poised for major advances, which can be enhanced through the continued synthesis of mathematical frameworks and empirical data.

genetics↗

bioRxiv2025

Emergent metabolic parasitism driven by organelle sequestration

Stable acquisitions of metabolism, such as the endosymbiotic incorporation of eukaryotic chloroplasts, are thought to proceed through mechanisms that increase the genetic repertoire of the host and allow for vertical integration of new metabolism. Here we test these predictions using the chloroplast-stealing marine ciliate genus Mesodinium by comparing transcriptomes from species that represent a spectrum from full heterotrophy to nearly full phototrophy. In contrast to theory, we find a striking divestment in metabolic autonomy with increased reliance on acquired photosynthesis. Indeed, the highly photosynthetic, red tide-forming Mesodinium rubrum appears to have lost the capacity to synthesize amino acids, metabolize fatty acids, and produce peroxisomes. Our results portray a metabolic parasite, masquerading as a free-living ciliate, yet incapable of satisfying most of its basic anabolic needs.

evolutionary biology↗

bioRxiv2025

New niches for larger phytoplankton in a warmer, more resource-limited ocean

Warming and nutrient limitation are major stressors that affect primary production in the ocean, with cascading impacts on the food web. Yet, we lack a mechanistic understanding of how phytoplankton manage multiple stressors and the implications of these responses for phytoplankton biogeography. By combining theory, proteome allocation modeling, and climate projections, we identified two potential competing strategies for multi-stressor growth: (1) nutrient efficient smaller cells, or (2) heat-tolerant larger cells. We found that Prochlorococcus are more vulnerable in warmer, "heat-stressed", tropical regions due to greater heat sensitivity and lower lipid storage capacity to buffer oxidative stress, indicating a potential ecological niche for larger phytoplankton with lower sensitivity to oxidative stress, such as Synechococcus and picoeukaryotes. Our findings advocate for the inclusion of phytoplankton heat-stress responses in global models to more accurately predict their ecological niches as the climate warms.

ecology↗

bioRxiv2024

Maturing giant kelp develop depth-specific microbiomes

Giant kelp (Macrocystis pyrifera) is a photosynthetic macroalga that produces dissolved organic carbon (DOC), essential for marine bacteria and food webs. The bacterial communities residing on giant kelp blades consume and compete for complex carbohydrates, contributing to the microbiome community structure. In this study, we investigate how the microbiome changes in response to the age and depth of giant kelp blades and assess how these changes relate to differences in the hosts photophysiology. We find that the microbial community increases in richness and evenness as kelp blades age. While the microbiomes of juvenile blades are stochastic, communities on mature blades coalesce into less variable, depth-specific community types. Differentially abundant genera in mature microbiomes include members of Bacteroidia and Gammaproteobacteria, known for carbohydrate degradation, and Planctomycetes, which often produce protective secondary metabolites. These shifts in microbiome communities are associated with increased maximum quantum yield of photosystem II of mature blades; therefore, they may be linked to enhanced DOC exudation. By shedding light on these dynamics, our study contributes to a better understanding of the complex interplay between macroalgae, their respective microbiomes, and the surrounding marine environment.

microbiology↗

bioRxiv2022

MODELING THE METABOLIC EVOLUTION OF MIXOTROPHIC PHYTOPLANKTON IN RESPONSE TO RISING OCEAN SURFACE TEMPERATURES

BackgroundClimate change is expected to lead to warming in ocean surface temperatures which will have unequal effects on the rates of photosynthesis and heterotrophy. As a result of this changing metabolic landscape, directional phenotypic evolution will occur, with implications that cascade up to the ecosystem level. While mixotrophic phytoplankton, organisms that combine photosynthesis and heterotrophy to meet their energetic and nutritional needs, are expected to become more heterotrophic with warmer temperatures due to heterotrophy increasing at a faster rate than photosynthesis, it is unclear how evolution will influence how these organisms respond to warmer temperatures. In this study, we used adaptive dynamics to model the consequences of temperature-mediated increases in metabolic rates for the evolution of mixotrophic phytoplankton, focusing specifically on phagotrophic mixotrophs. ResultsWe find that mixotrophs tend to evolve to become more reliant on phagotrophy as temperatures rise, leading to reduced prey abundance through higher grazing rates. However, if prey abundance becomes too low, evolution favors greater reliance on photosynthesis. These responses depend upon the trade-off that mixotrophs experience between investing in photosynthesis and phagotrophy. Mixotrophs with a convex trade-off maintain mixotrophy over the greatest range of temperatures; evolution in these "generalist" mixotrophs was found to exacerbate carbon cycle impacts, with evolving mixotrophs exhibiting increased sensitivity to rising temperature. ConclusionsOur results show that mixotrophs may respond more strongly to climate change than predicted by phenotypic plasticity alone due to evolutionary shifts in metabolic investment. However, the type of metabolic trade-off experienced by mixotrophs as well as ecological feedback on prey abundance may ultimately limit the extent of evolutionary change along the heterotrophy-phototrophy spectrum.

evolutionary biology↗

bioRxiv2022

Evidence for evolutionary adaptation of mixotrophic nanoflagellates to warmer temperatures

Mixotrophs, organisms that combine photosynthesis and heterotrophy to gain energy, play an important role in global biogeochemical cycles. Metabolic theory predicts that mixotrophs will become more heterotrophic with rising temperatures, potentially creating a positive feedback loop that accelerates carbon dioxide accumulation in the atmosphere. Studies testing this theory have focused on phenotypically plastic (short-term) thermal responses of mixotrophs. However, as small organisms with short generation times and large population sizes, mixotrophs may rapidly evolve in response to climate change. Here we present data from a 3-year experiment quantifying the evolutionary response of two mixotrophic nanoflagellates to temperature. We found evidence for adaptive evolution through increasing growth rates in the obligately mixotrophic strain, but not in the facultative mixotroph. All lineages showed trends of increased carbon use efficiency, flattening of thermal reaction norms, and a return to homeostatic gene expression. Generally, mixotrophs evolved reduced photosynthesis and higher grazing with increased temperatures, suggesting that evolution may act to exacerbate mixotrophs effects on global carbon cycling.

ecology↗