Biology subjects

Ricks, K.

Publications and source records attributed to Ricks, K..

5 recordsLinked to original sources

bioRxiv2026

Mutualisms as engines for rapid adaptation: Rhizobium evolution facilitates plant drought resistance

Mutualisms play critical roles in organismal stress tolerance; yet environmental stressors may simultaneously alter the evolution of the mutualism itself. Stress may have particularly strong impacts on the evolution of microbial mutualists due to their capacity for rapid genetic change. Here we used a legume-rhizobia mutualism, in which plants exchange carbon for symbiotically fixed nitrogen, to evaluate how mutualisms evolve in response to stressors. We experimentally evolved populations of Rhizobium leguminasarum in a full factorial design, manipulating drought and nitrogen. We quantified genomic changes in Rhizobium populations as well as their quality as partners with their plant host, Trifolium repens. Drought selected for context- dependent stress benefits to the host; drought-adapted Rhizobium strains provided increased benefits to the host under drought, but fewer benefits to the host in well-watered environments. Conversely, nitrogen fertilization selected for decreased Rhizobium partner quality. Comparative genomics indicated that selection on standing structural variants along the symbiotic plasmid may underpin these drought benefits, specifically along genes associated with desiccation tolerance. These results suggest that stress can expand the benefits rhizobia provide to their legume hosts beyond nitrogen fixation, with rapid symbiont evolution an engine in promoting adaptive plant phenotypes. SIGNIFICANCE STATEMENTWhile mutualisms are fundamental to ecosystem functioning, they are often assumed to break down under environmental stress. We showed the opposite can happen. Here, we factorially manipulated drought stress and nitrogen fertilization and experimentally evolved a model legume-rhizobia mutualism, where rhizobial-bacteria trade nitrogen for plant carbon. When droughted, the symbiotic bacteria rapidly evolved new traits that made them better partners under drought, improving plant growth within just a few generations. Evolution occurred mainly on a specialized bacterial plasmid, a mobile piece of DNA distinct from the main genome. By contrast, added nitrogen fertilizer led to decreases in bacterial benefits. These findings suggest that mutualisms are not simply fragile in the face of global change, but can expand mutualistic benefits to buffer partners against stress. CLASSIFICATIONBiological Sciences, Evolution

evolutionary biology↗

bioRxiv2026

Stress adaptation of free-living microbes generates novel benefits to plant hosts

Most microbes that live in or on hosts are not obligate symbionts. Instead, they often cycle between host-associated and free-living phases and experience selection in both environments. The benefits that microbes confer to hosts are often assumed to be a product of host-microbe (co)evolution, but microbial benefits to hosts may also evolve independent of the host-microbe interaction, while the microbe is free-living. We investigated this hypothesis by experimentally evolving a beneficial Allorhizobium bacterium we had previously isolated from duckweed (Lemna japonica). We evolved this Allorhizobium strain in the absence of any host at high and low salinity and at high and low nitrogen, and then tested how the evolved strains performed as symbionts when host-associated. Microbial salinity adaptation drove the emergence of novel benefits to host plants in high-salinity environments. However, these locally adaptive benefits emerged only when microbes evolved under low-nitrogen conditions; microbial adaptation to high nitrogen reduced plant growth. Bacterial phenotyping indicated that the same microbial traits that underlie salinity adaptation mediate host benefits. Whole-genome sequencing of the evolved strains revealed significant genomic shifts between selective treatments, including plasmid variation and point mutations associated with osmotic regulation. The emergence of the microbial benefits to hosts, as a byproduct of microbial adaptation, highlights that these benefits do not require targeted host-microbe co-evolution. Rather, predicting the evolutionary trajectory of these symbioses may require understanding both the abiotic and biotic selective agents acting on key microbial traits mediating the host-microbe interaction.

microbiology↗

bioRxiv2025

A continuum of ecology and evolution contributes to mutualism breakdown between legumes and rhizobia

Ecology and evolution jointly shape community responses to environmental perturbations, yet these processes are often examined separately, even in microorganisms where both occur over short time-scales. For example, during mutualism breakdown, shifts in diverse microbial communities might coincide with evolutionary changes in mutualistic traits within key symbionts. Here we study the legume-rhizobium mutualism after 33 years of nitrogen fertilization. Pairing a manipulative inoculation study with full-length 16S rRNA amplicon sequencing provides incomparable resolution across biological scales: whole bacterial community, genus Rhizobium, Rhizobium ASVs, and symbiosis plasmids. Clover host plant growth is first limited by symbiont availability; clovers preferred partner declines in N-addition soils, while a diverse, largely uncharacterized Rhizobium community increases. This ecological change is compounded by a concurrent evolutionary decline in the quality of the preferred symbiont through changing frequencies of symbiotic plasmids. These shifts make mutualists both rarer and inferior, reducing the benefits hosts receive from mutualism.

microbiology↗

bioRxiv2025

Rediscovery and ecology of the Capulin Mountain Alberta arctic butterfly: informing data collection for rare endemics

Insect conservation in the southwestern United States is hindered by limited information on distribution, phenology, and habitat, especially for small-range endemics. The Capulin Mountain Alberta Arctic butterfly (Oeneis alberta capulinensis F.M. Brown, 1970), a New Mexico Species of Greatest Conservation Need, is restricted to the Raton Mesa Complex and threatened by isolation, low dispersal, and extirpation from its type locality. We surveyed historic and potential sites to document current distribution, refine flight phenology, investigate larval host plant use, and assess habitat condition. Our results confirm extant populations, identify the larval host plant (Festuca idahoensis Elmer), and describe habitat as montane grasslands with limited woody encroachment. A habitat suitability model predicted additional potentially occupied areas, highlighting under-explored habitat for future monitoring. This study provides the first comprehensive ecological assessment of O. a. capulinensis and establishes a framework for documenting poorly known endemic insects to guide future research and survey design.

ecology↗

bioRxiv2022

Humoral immunogenicity of a Coronavirus Disease 2019 (COVID-19) DNA Vaccine in Rhesus Macaques (Macaca mulatta) Delivered using Needle-free Jet Injection

A SARS-CoV-2 DNA vaccine targeting the spike protein and delivered by jet injection, nCOV-S(JET), previously shown to protect wild-type and immunosuppressed Syrian hamsters (Mesocricetus auratus), was evaluated via two needle-free delivery methods in rhesus macaques (Macaca mulatta). The methods included intramuscular delivery of 2 mg per vaccination with the PharmaJet Stratis device and intradermal delivery of 0.4 mg per vaccination with the PharmaJet Tropis device. We hypothesized that the nCOV-S(JET) vaccine would mount detectable neutralizing antibody responses when delivered by needle-free jet injection by either the intradermal or intramuscular route. When delivered intramuscularly, the vaccines elicited neutralizing and variant (Beta, Gamma, and Delta) cross-neutralizing antibodies against SARS-CoV-2 in all six animals after three vaccinations. When delivered at a lower dose by the intradermal route, strong neutralizing antibody responses were only detected in two of six animals. This study confirms that a vaccine previously shown to protect in a hamster model can elicit neutralizing and cross-neutralizing antibodies against SARS-CoV-2 in nonhuman primates. We posit that nCOV-S(JET) has the potential for use as booster vaccine in heterologous vaccination strategies against COVID-19.

immunology↗