Biology subjects

Patton, G.

Publications and source records attributed to Patton, G..

3 recordsLinked to original sources

bioRxiv2025

Historical Contingency Limits Adaptive Diversification in a Spatially Structured Environment

Understanding how genotype-by-environment (GxE) interactions influence evolutionary trajectories and contribute to historical contingency is key to predicting evolution. In spatially structured, heterogeneous environments, populations often diversify into ecotypes, resulting in niche specialization. However, the ability to specialize depends not only on ecological opportunity but also on whether genetic variation permits access to novel niches, as genetic disruptions may inhibit adaptation unless alternative trajectories or compensatory mutations are subsequently accessible. Previously, we demonstrated that Escherichia coli populations rapidly diversify into two co-existing ecotypes in a nutrient-rich, spatially structured environment. The adaptation of both ecotypes results in benefits only perceived in the spatially structured culture tube environment. Here, diversification is initiated by first-step mutations associated with the overexpression of genes encoding the type 1 fimbria, the major attachment pilus involved in biofilm development, enabling range expansion and allowing E. coli to occupy the surface-air interface of the culture tube. To investigate how first-step mutations shape evolutionary trajectories, we experimentally evolved wild-type and fimbrial-deficient ({Delta}fimA) E. coli for 91 days in both structured (tube) and unstructured (flask) environments. While a fimA deletion initially confers a fitness benefit by avoiding the cost of insufficient biofilm formation, it ultimately prevents range expansion in structured environments and is not compensated by expression of cryptic fimbriae by the end of experimental evolution. As a result, {Delta}fimA populations show constrained adaptation in tubes compared to wild-type. Alternatively, both genotypes perform similarly in flasks, where biofilm formation is not advantageous and whole population sequencing reveals that flask-evolved populations similar early mutational trajectories. Our results highlight the ruggedness of the adaptive landscape in structured environments and show how an initially beneficial mutation can trap a lineage on a local fitness peak, underscoring the importance of GxE interactions and early mutational events in shaping the predictability and contingency of evolutionary outcomes.

evolutionary biology↗

bioRxiv2024

Bacterial cross-feeding can promote gene retention by lowering gene expression costs

Cross-feeding is prevalent in microbial communities. Through time, cross-feeding is thought to enrich for loss-of-function mutations, thereby creating or reinforcing dependencies between community members. However, few studies have compared how cross-feeding affects the evolutionary trajectory of partners compared to monoculture conditions. Here we compared mutations that were differentially enriched in bacterial monocultures versus cocultures pairing phototrophic Rhodopseudomonas palustris with fermentative Escherichia coli in an obligate cross-feeding relationship based on the exchange of nitrogen and carbon for 650-800 generations. Opposite trends for the number of differentially enriched mutations were observed for each species; R. palustris accumulated more unique mutations in monoculture whereas E. coli accumulated more unique mutations in coculture. Contrary to expectations, the emergence of additional dependencies was more apparent for both species in monoculture, even though additional layers of cross-feeding involving iron and adenine were present in coculture. We reasoned that iron and adenine cross-feeding occurred at levels sufficient to repress gene expression in the recipient, thereby promoting gene retention by lowering gene cost. Thus, the influence of cross-feeding on evolutionary trajectories can vary with organisms and conditions, and there are situations where cross-feeding can limit, rather than promote, emergent dependencies. IMPORTANCEBacteria commonly engage in cross-feeding where nutrients are transferred between neighbors. Cross-feeding is thought to alleviate energy expenditures for genes whose role can be met by cross-fed nutrients, leading to eventual gene loss. However, few examples have been documented, especially in comparison to monocultures where bacteria are grown without a cross-feeding partner. Here we grew cocultures pairing phototrophic Rhodopseudomonas palustris with fermentative Escherichia coli alongside corresponding monocultures for 650-800 generations. While coculture conditions required obligate exchange of nitrogen and carbon, additional cross-feeding of adenine and iron likely occurred. Contrary to expectations, iron and uncharacterized dependencies emerged in monocultures but not in cocultures. Low expression for iron scavenging and adenine synthesis genes in cocultures suggested that cross-feeding repressed gene expression, thereby lowering gene cost. Thus, whereas there are likely cases where cross-feeding makes costly genes dispensable, there are also cases where cross-feeding lowers gene cost, thereby promoting gene retention.

microbiology↗

bioRxiv2020

A longitudinal analysis of puberty-related cortical development

The brain undergoes extensive structural changes during adolescence, concurrent to puberty-related physical and hormonal changes. While animal research suggests these biological processes are related to one another, our knowledge of brain development in humans is largely based on age-related processes. Thus, the current study characterized puberty-related changes in human brain structure, by combining data from two longitudinal neuroimaging cohorts. Beyond normative changes in cortical thickness, we examined whether individual differences in the rate of pubertal maturation (or "pubertal tempo") was associated with variations in cortical trajectories. Participants (N = 192; scans = 366) completed up to three waves of MRI assessments between 8.5 and 14.5 years of age, as well as questionnaire assessments of pubertal stage at each wave. Generalized additive mixture models were used to characterize trajectories of cortical development. Results revealed widespread linear puberty-related changes across much of the cortex. Many of these changes, particularly within the frontal and parietal cortices, were independent of age-related development. Males exhibiting faster pubertal tempo demonstrated greater thinning in the precuneus and frontal cortices than same-aged and -sex peers. Findings suggest that the unique influence of puberty on cortical development may be more extensive than previously identified, and also emphasize important individual differences in the coupling of these developmental processes.

neuroscience↗