Biology subjects

Hernandez-Beltran, J. C. R.

Publications and source records attributed to Hernandez-Beltran, J. C. R..

3 recordsLinked to original sources

bioRxiv2026

Forging an evolutionary individual from separate replicators

Major evolutionary transitions occur when independently replicating particles unite into a higher-level individual. How selection comes to work on particle collectives and generates reliable heredity is unresolved. By packaging red and green plasmids in yeast cells we made plasmid communities units of selection: cell boundaries supplied discreteness, segregation generated variation, and cell division reproduced communities. Communities colouring cells yellow were preferentially propagated. Initially, yellow parents rarely produced yellow offspring, but continued selection aligned replicative fates of the two plasmids favouring recombinants that fused with the endogenous 2-micron element. Chimera stability was secured by mutations in FLP1, which encodes a recombinase that otherwise resolves fused replicons. Reliable collective heredity, here, a derived product of higher-level selection, marked completion of an evolutionary transition in individuality.

evolutionary biology↗

bioRxiv2025

Context-Dependent Adaptation in Structured Environments

Adaptive evolution often leads to niche specialization, but successful colonization of a new niche can depend as much on ecological context as on genetic change. This is especially true in spatially structured environments, where the physical construction of habitat and the order of arrival of mutants can shape evolutionary outcomes. In static broth cultures, the air-liquid interface (ALI) provides a high-oxygen niche typically colonized by mat-forming mutants. In Pseudomonas fluorescens, a range of single mutations that upregulate cellulose production give rise to "wrinkly spreader" (WS) types--canonical niche specialists that out-compete ancestral types at the ALI. Yet we discover that this is a half-truth: WS mutants frequently fail to establish when introduced alone at low density, but co-culture with ancestral types rescues colonization. Microscopy and model simulations show that ancestors physically scaffold the ALI, enabling stable attachment and facilitating the in situ emergence of an array of genetically diverse WS mutants. Ancestors later disperse, vacate the niche allowing WS mutant expansion. This transient asymmetric interaction reveals that even strongly adaptive mutations may require ecological facilitation to succeed. More broadly, our findings challenge simple narratives of adaptive replacement and underscore how transient ecological dependencies can shape the trajectory of evolutionary change.

evolutionary biology↗

bioRxiv2022

Plasmid stability in fluctuating environments:population genetics of multi-copy plasmids

Plasmids are extra-chromosomal genetic elements that encode a wide variety of phenotypes and can be maintained in bacterial populations through vertical and horizontal transmission, thus increasing bacterial adaptation to hostile environmental conditions like those imposed by antimicrobial sub-stances. To circumvent the segregational instability resulting from randomly distributing plasmids between daughter cells upon division, non-transmissible plasmids tend to be carried in multiple copies per cell, with the added benefit of exhibiting increased gene dosage and resistance levels. But carrying multiple copies also results in a high metabolic burden to the bacterial host, therefore reducing the overall fitness of the population. This trade-off poses an existential question for plasmids: What is the optimal plasmid copy number? In this manuscript, we address this question by postulating and analyzing a population genetics model to evaluate the interaction between selective pressure, the number of plasmid copies carried by each cell, and the metabolic burden associated with plasmid bearing in the absence of selection for plasmid-encoded traits. Parameter values of the model were estimated experimentally using Escherichia coli K12 carrying a multicopy plasmid encoding for a fluorescent protein and blaTEM-1, a gene conferring resistance to {beta}-lactam antibiotics. By numerically determining the optimal plasmid copy number for constant and fluctuating selection regimes, we show that plasmid copy number is a highly optimized evolutionary trait that depends on the rate of environmental fluctuation and balances the benefit between increased stability in the absence of selection with the burden associated with carrying multiple copies of the plasmid.

evolutionary biology↗