Biology subjects

Keenan, O.

Publications and source records attributed to Keenan, O..

2 recordsLinked to original sources

bioRxiv2025

The legacy of past climate warming: strong local adaptation in rear-edge populations

Improving forecasts of species responses to climate change has become a central challenge in ecology and evolution as species distributions are increasingly disrupted by ongoing climate warming. Insight into this challenge may be gained through a better understanding of evolutionary responses to past climate change. The rear edges of species distributions are typically relict populations persisting in former glacial refugia at warmer range limits. As such, they form natural laboratories to study the evolutionary outcomes of past climate warming. Three such outcomes have been proposed for rear-edge populations: maintenance of high diversity due to long-term persistence, strong genetic drift following habitat decline, and strong local adaptation allowing persistence despite environmental change. Empirical studies rarely explicitly test these alternate outcomes limiting our understanding of evolutionary responses to warming climates. We tested all three evolutionary outcomes at the rear edge of the North American herb Campanula americana, by assessing genetic variation in a genome-wide population genetic study, drift load as measure of fitness decline due to drift in a controlled crossing study, and local adaptation in a transplant study. Rear-edge populations exhibited reduced genetic diversity within populations and high differentiation among populations, typically interpreted as evidence of genetic drift, yet show limited drift load. Instead, these populations expressed strong local adaptation, thriving in rear-edge habitats that were unsuitably warm for populations in the expanded range. This indicates that warm-edge populations may persist under warming climates by gradually adapting, even in the face of genetic erosion. Our findings highlight the importance of explicitly testing for all evolutionary outcomes, and particularly going beyond measures of genetic variation, when inferring evolutionary history. More broadly, these findings identify rear-edge populations not as relics of decline, but as underappreciated models for studying successful adaptation under long-term climate change.

evolutionary biology↗

bioRxiv2025

Enterococcus faecalis modulates phase variation in Clostridioides difficile

To adapt and persist in the gastrointestinal tract, many enteric pathogens, including Clostridioides difficile, employ strategies such as phase variation to generate phenotypically heterogeneous populations. Notably, the role of the gut microbiota and polymicrobial interactions in shaping population heterogeneity of invading pathogens has not been explored. Here, we show that Enterococcus faecalis, an opportunistic pathogen that thrives in the inflamed gut during C. difficile infection, can impact the phase variable CmrRST signal transduction system in C. difficile. The CmrRST system controls multiple phenotypes including colony morphology, cell elongation, and cell chaining in C. difficile. Here we describe how interactions between E. faecalis and C. difficile on solid media lead to a marked shift in C. difficile phenotypes associated with phase variation of CmrRST. Specifically, E. faecalis drives a switch of the C. difficile population to the cmr-ON state leading to chaining and a rough colony morphology. This phenomenon preferentially occurs with E. faecalis among the enterococci, as other enterococcal species do not show a similar effect, suggesting that the composition of the polymicrobial environment in the gut is likely critical to shaping C. difficile population heterogeneity. Our findings shed light on the complex role that microbial ecology and polymicrobial interactions can have in the phenotypic heterogeneity of invading pathogens. IMPORTANCE STATEMENTClostridioides difficile is an enteric pathogen with critical implications for public health. The microbial ecosystem in which C. difficile resides shapes the behavior and fitness of C. difficile; however, the mechanisms underlying these interactions are not well defined. Here, we demonstrate that Enterococcus faecalis, an opportunistic pathogen known to co-colonize the gut with C. difficile, influences phase variation and downstream growth phenotypes in C. difficile. This phenomenon represents a new paradigm by which co-residing bacteria can modulate phase variation dynamics in C. difficile or other enteric pathogens. Understanding factors that influence C. difficile behavior may elucidate new therapeutic strategies, especially in complex polymicrobial infections.

microbiology↗