Abstract. Parasites are quite likely the most diverse guild of species on earth. Nevertheless, they remain under-documented despite their impact on the hea

The nature of standing genetic variation remains a central debate in population genetics, with differing perspectives on whether common variants are almost always neutral as suggested by neutral and n...

YouTube video by TEDx Talks

In simple microbial populations, the fitness effects of most selected mutations are generally taken to be constant, independent of genotype frequency. This assumption underpins predictions about evolutionary dynamics, epistatic interactions, and the maintenance of genetic diversity in populations. Here, we systematically test this assumption using beneficial mutations from early generations of the Escherichia coli Long-Term Evolution Experiment (LTEE). Using flow cytometry-based competition assays, we find that frequency-dependent fitness effects are the norm rather than the exception, occurring in approximately 80\% of strain pairs tested. Most competitions exhibit negative frequency-dependence, where fitness advantages decline as mutant frequency increases. Furthermore, we demonstrate that the strength of frequency-dependence is predictable from invasion fitness measurements, with invasion fitness explaining approximately half of the biological variation in frequency-dependent slopes. Additionally, we observe violations of fitness transitivity in several strain combinations, indicating that competitive relationships cannot always be predicted from fitness relative to a single reference strain alone. Through high-resolution measurements of within-growth cycle dynamics, we show that simple resource competition explains a substantial portion of the frequency-dependence: when faster-growing genotypes dominate populations, they deplete shared resources more rapidly, reducing the time available for fitness differences to accumulate. Our results demonstrate that even in a simple model system designed to minimize ecological complexity, subtle ecological interactions between closely related genotypes create frequency-dependent selection that can fundamentally alter evolutionary dynamics. ### Competing Interest Statement The authors have declared no competing interest.

Job title: Research position in Microbial Pharmacology and Population Biology (282139), Employer: UiT The Arctic University of Norway, Deadline: Wednesday, August 27, 2025

Cells require highly polymorphic receptors to perform accurate self/non-self recognition. In the amoeba Dicytostelium discoideum, polymorphic TgrB1 & TgrC1 proteins are used to bind sister cells and e...

Abstract. Most knowledge about bacterial evolution and ecological interactions comes from laboratory studies. One difference between the wild and most labo

In this work, we describe a targeted phage discovery method that allows immediate isolation of phages with specific traits. Currently, to find a phage with specific properties, huge libraries of phage...

Although bacteriophage genomes are under strong selective pressure for high coding density, they are still frequently invaded by mobile genetic elements (MGEs). Group II introns are MGEs that reduce h...

Nature Methods - Phylogenetic compression achieves performant and lossless compression of massive collections of microbial genomes, facilitating fast BLAST-like search and versatile alignment tasks.

Mission The Bay Area RaMP Program in Microbiome Sciences exists to increase potential for scientific advances by expanding the microbiome research workforce with well-trained, ethical scientists. Our...

Conflicts between levels of biological organization are central to evolution, from populations of multicellular organisms to selfish genetic elements in microbes. Plasmids are extrachromosomal, self-r...