PNAS

Proceedings of the National Academy of Sciences (PNAS), a peer reviewed journal of the National Academy of Sciences (NAS) - an authoritative source of high-impact, original research that broadly spans...

pnas.org

Sex decreases the pleiotropic costs of local adaptation by purging hitchhiking load

Understanding the evolutionary mechanisms that maintain sex despite its direct costs is a long-standing challenge. Previous work has shown that sexual recombination can accelerate adaptation, in part ...

science.org

Genotype-fitness mapping of adaptive mutants reveals shifting low-dimensional structure across divergent environments

Predicting the effect of a genetic mutation on fitness is a major challenge in evolutionary biology. This study uses fitness effects of a large collection of adaptive yeast mutants in multiple lab env...

journals.plos.org

biorxiv.org

Provirus induction diversifies adaptive variation in Pseudomonas aeruginosa lysogen populations

Pseudomonas aeruginosa is a Gram-negative opportunistic pathogen that forms chronic infections in people with cystic fibrosis. Often P. aeruginosa strains are lysogens, infected with proviruses, that ...

biorxiv.org

BarTn7: Optimizing Bacterial Lineage Tracking at Sub-Species Resolution for Population Dynamics in Ecological and Evolutionary Studies

Communities of bacteria undergo population bottlenecks which are crucial to their population, ecological, and evolutionary dynamics. However, conventional amplicon sequencing cannot distinguish such d...

biorxiv.org

biorxiv.org

Frequency-dependent fitness effects are ubiquitous

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.

doi.org

A high-resolution two-step evolution experiment in yeast reveals a shift from pleiotropic to modular adaptation

Evolution is expected to involve mutations that are small and modular in effect, but recent findings suggest that mutations early in an adaptive process can have strong and pleiotropic effects. This s...

doi.org

Asynchronous abundance fluctuations can drive giant genotype frequency fluctuations

Nature Ecology & Evolution - Based on a combination of experiments and modelling, this study shows large stochastic fluctuations in genotype frequencies caused by intrinsic and extrinsic...

rdcu.be

Asynchronous abundance fluctuations can drive giant genotype frequency fluctuations

bioRxiv - the preprint server for biology, operated by Cold Spring Harbor Laboratory, a research and educational institution

biorxiv.org