R-3 Repository :: Browsing by Author "Rudgers, Jennifer A."

Browsing by Author "Rudgers, Jennifer A."

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Anoplolepis gracilipes invasion of the Samoan Archipelago: Can mutualisms with native species amplify ecological consequences?
(2011) Savage, Amy Marie; Rudgers, Jennifer A.; Whitney, Kenneth D.
Integrating mutualism into the study of ecological communities is likely to be critical to understanding community dynamics and to predict the consequences of anthropogenic changes to ecosystems. Invasive species are among the greatest of these threats to global biodiversity. Throughout the Pacific, the invasive ant Anoplolepis gracilipes associates mutualistically with Morinda citrifolia , a native plant with extrafloral nectaries (EFN). I tested the hypothesis that these interactions can mediate invader impacts Anoplolepis gracilipes abundances were positively correlated with the dominance of EFN-bearing plants per site and negatively correlated with the species richness of native ants. Additionally, A. gracilipes displayed a higher magnitude of responses to nectar than other dominant ants. Mutualisms also had significant impacts on the structure of arthropod communities. These effects were strongest when A. gracilipes dominated local ant assemblages. These results suggest that novel mutualisms between invasive and native species can facilitate the impacts of invasions on communities.
Biochar and Microbial Signaling: Production Conditions Determine Effects on Microbial Communication
(American Chemical Society, 2013) Masiello, Caroline A.; Chen, Ye; Gao, Xiaodong; Liu, Shirley; Cheng, Hsiao-Ying; Bennett, Matthew R.; Rudgers, Jennifer A.; Wagner, Daniel S.; Zygourakis, Kyriacos; Silberg, Jonathan J.; Bioengineering; Biosciences; Chemical and Biomolecular Engineering; Earth, Environmental and Planetary Sciences
Charcoal has a long soil residence time, which has resulted in its production and use as a carbon sequestration technique (biochar). A range of biological effects can be triggered by soil biochar that can positively and negatively influence carbon storage, such as changing the decomposition rate of organic matter and altering plant biomass production. Sorption of cellular signals has been hypothesized to underlie some of these effects, but it remains unknown whether the binding of biochemical signals occurs, and if so, on time scales relevant to microbial growth and communication. We examined biochar sorption of N-3-oxo-dodecanoyl-L-homoserine lactone, an acyl-homoserine lactone (AHL) intercellular signaling molecule used by many gram-negative soil microbes to regulate gene expression. We show that wood biochars disrupt communication within a growing multicellular system that is made up of sender cells that synthesize AHL and receiver cells that express green fluorescent protein in response to an AHL signal. However, biochar inhibition of AHL-mediated cell–cell communication varied, with the biochar prepared at 700 °C (surface area of 301 m2/g) inhibiting cellular communication 10-fold more than an equivalent mass of biochar prepared at 300 °C (surface area of 3 m2/g). These findings provide the first direct evidence that biochars elicit a range of effects on gene expression dependent on intercellular signaling, implicating the method of biochar preparation as a parameter that could be tuned to regulate microbial-dependent soil processes, like nitrogen fixation and pest attack of root crops.
The Consequences of Plant Species Diversity and Genetic Diversity for Populations, Communities, and Ecosystems
(2011) Crawford, Kerri Margaret; Rudgers, Jennifer A.
Plant species diversity plays an important role in structuring communities and mediating ecosystem processes. Experiments have shown increasing plant species richness increases primary productivity, arthropod species richness, nutrient cycling, and community stability. Because effects of diversity are driven by variation among individuals, it is expected that genetic diversity within a species may mimic the effects of species diversity. Indeed, recent experimental evidence has confirmed this prediction. However, few studies have simultaneously investigated the effects of plant species diversity and genetic diversity in the same system. Therefore, the relative importance of species diversity and genetic diversity for community structure and ecosystem processes remains unresolved, and, importantly, potential interactions between levels of diversity have rarely been investigated. Interactive effects between genetic diversity and species diversity are particularly important to investigate, as natural systems are composed of several genotypes of many different species. Here, I investigated how plant species diversity and genetic diversity influenced populations, communities, and ecosystems. First, I tested whether genetic diversity within populations of a weedy annual plant, Arabidopsis thaliana, influenced population success. Increasing genetic diversity increased several measures of population viability, including seedling emergence, biomass production, flowering duration, and seed set. This result suggests that highly genetically diverse populations, such as populations created from multiple introductions, may be more able to colonize novel environments than less genetically diverse populations. Next, I simultaneously manipulated plant species diversity and genetic diversity within a dominant plant species in a common garden. This experiment addressed how both levels of diversity influenced a key ecosystem process, primary productivity. Plant species diversity and genetic diversity interactively influenced biomass production, with productivity increasing the most with genetic diversity when high levels of species diversity were present. Finally, I explored how plant diversity in the common garden influenced arthropod community composition, and found that genetic diversity influenced arthropods more strongly than plant species diversity. Altogether, my work underscores the importance of understanding how plant species diversity and genetic diversity interactively influence ecological communities in order to gain a more holistic view of how communities are structured and what factors control ecosystem functioning.
Elucidating the Roles of PEX19 and Prenylation in Arabidopsis Peroxisomes
(2012-09-05) Stoddard, Jerrad; Bartel, Bonnie; Shamoo, Yousif; Farach-Carson, Cindy; Braam, Janet; Rudgers, Jennifer A.
Peroxisomes are organelles originating from the endoplasmic reticulum. Peroxisome biogenesis requires multiple peroxins, including PEX19, a prenylated protein that helps deliver peroxisomal membrane proteins in yeast and mammals. Arabidopsis thaliana PEX19 is encoded by two isogenes, PEX19A and PEX19B. I demonstrate that pex19A and pex19B insertional mutants lack obvious abberant physiological phenotypes. I provide evidence that pex19A pex19B double mutants are inviable, that PEX19B is more abundant than PEX19A in young seedlings, that Arabidopsis PEX19 is farnesylated in vivo, and that YFP-PEX19 predominantly associates with what appears to be a subcellular membrane regardless of its prenylation state. I show that farnesyltransferase mutants apparently contain only non-prenylated PEX19 and lack phenotypes that would indicate inefficient peroxisome activity. My analysis of PEX19 suggests that PEX19 prenylation is dispensable for peroxisome biogenesis, and has generated tools for future studies of the earliest steps in peroxisome biogenesis in plants.
Fungal Symbionts as Manipulators of Plant Reproductive Biology
(The University of Chicago, 2013-04) Gorischek, Alexander M.; Afkhami, Michelle E.; Seifert, Elizabeth K.; Rudgers, Jennifer A.
Symbioses have shaped the evolution of life, most notably through the fixation of heritable symbionts into organelles. The inheritance of symbionts promotes mutualism and fixation by coupling partner fitness. However, conflicts arise if symbionts are transmitted through only one sex and can shift host resources toward the sex through which they propagate. Such reproductive manipulators have been documented in animals with separate sexes but not in other phyla or sexual systems. Here we investigated whether the investment in male relative to female reproduction differed between hermaphroditic host plants with versus without a maternally inherited fungal symbiont. Plants with the fungus produced more seeds and less pollen than plants lacking the fungus, resulting in an ∼40% shift in functional gender and a switch from male-biased to female-biased sex allocation. Given the ubiquity of endophytes in plants, reproductive manipulators of hermaphrodites may be widespread in nature.
Infrastructure to factorially manipulate the mean and variance of precipitation in the field
(Wiley, 2023) Rudgers, Jennifer A.; Luketich, Anthony; Bacigalupa, Melissa; Baur, Lauren E.; Collins, Scott L.; Hall, Kristofer M.; Hou, Enqing; Litvak, Marcy E.; Luo, Yiqi; Miller, Tom E. X.; Newsome, Seth D.; Pockman, William T.; Richardson, Andrew D.; Rinehart, Alex; Villatoro-Castañeda, Melissa; Wainwright, Brooke E.; Watson, Samantha J.; Yogi, Purbendra; Zhou, Yu
Extensive ecological research has investigated extreme climate events or long-term changes in average climate variables, but changes in year-to-year (interannual) variability may also cause important biological responses, even if the mean climate is stable. The environmental stochasticity that is a hallmark of climate variability can trigger unexpected biological responses that include tipping points and state transitions, and large differences in weather between consecutive years can also propagate antecedent effects, in which current biological responses depend on responsiveness to past perturbations. However, most studies to date cannot predict ecological responses to rising variance because the study of interannual variance requires empirical platforms that generate long time series. Furthermore, the ecological consequences of increases in climate variance could depend on the mean climate in complex ways; therefore, effective ecological predictions will require determining responses to both nonstationary components of climate distributions: the mean and the variance. We introduce a new design to resolve the relative importance of, and interactions between, a drier mean climate and greater climate variance, which are dual components of ongoing climate change in the southwestern United States. The Mean × Variance Experiment (MVE) adds two novel elements to prior field infrastructure methods: (1) factorial manipulation of variance together with the climate mean and (2) the creation of realistic, stochastic precipitation regimes. Here, we demonstrate the efficacy of the experimental design, including sensor networks and PhenoCams to automate monitoring. We replicated MVE across ecosystem types at the northern edge of the Chihuahuan Desert biome as a central component of the Sevilleta Long-Term Ecological Research Program. Soil sensors detected significant treatment effects on both the mean and interannual variability in soil moisture, and PhenoCam imagery captured change in vegetation cover. Our design advances field methods to newly compare the sensitivities of populations, communities, and ecosystem processes to climate mean × variance interactions.
Mammalian herbivores restrict the altitudinal range limits of alpine plants
(Wiley, 2021) Lynn, Joshua S.; Miller, Tom E.X.; Rudgers, Jennifer A.
Although rarely experimentally tested, biotic interactions have long been hypothesised to limit low-elevation range boundaries of species. We tested the effects of herbivory on three alpine-restricted plant species by transplanting plants below (novel), at the edge (limit), or in the centre (core) of their current elevational range and factorially fencing-out above- and belowground mammals. Herbivore damage was greater in range limit and novel habitats than in range cores. Exclosures increased plant biomass and reproduction more in novel habitats than in range cores, suggesting demographic costs of novel interactions with herbivores. We then used demographic models to project population growth rates, which increased 5–20% more under herbivore exclosure at range limit and novel sites than in core habitats. Our results identify mammalian herbivores as key drivers of the low-elevation range limits of alpine plants and indicate that upward encroachment of herbivores could trigger local extinctions by depressing plant population growth.
Mechanisms underlying the costs and benefits in grass-fungal endophyte symbioses
(2010) Davitt, Andrew James; Rudgers, Jennifer A.
Nearly all plants have developed symbiotic associations with microbes above- and belowground. These symbionts often alter the ecology of their hosts by enhancing nutrient uptake, increasing stress tolerance, or providing protection from host enemies. Understanding the dynamics of symbiosis requires testing how ecological factors alter not only the fitness consequences of the symbiosis, but also the rate of symbiont transmission. Here we asked how changes in the biotic and abiotic context alter both the costs and benefits of interactions between grass hosts and symbiotic fungal endophytes and rates of symbiont transmission. First, we assessed how shade and the presence of endophyte symbiosis affected host plant growth across six grass species. Our results demonstrate a novel benefit of endophyte symbiosis via the amelioration of shade stress. Second, we examine how interactions between a fungal endophyte and its grass host change along a gradient of water availability and in the presence versus absence of soil microbes. We show that benefits of the symbiosis were strongest when water was limiting. Together, our results highlight the context dependent nature of grass endophyte symbioses.
Microbial symbionts buffer hosts from the demographic costs of environmental stochasticity
(Wiley, 2024) Fowler, Joshua C.; Ziegler, Shaun; Whitney, Kenneth D.; Rudgers, Jennifer A.; Miller, Tom E. X.
Species' persistence in increasingly variable climates will depend on resilience against the fitness costs of environmental stochasticity. Most organisms host microbiota that shield against stressors. Here, we test the hypothesis that, by limiting exposure to temporally variable stressors, microbial symbionts reduce hosts' demographic variance. We parameterized stochastic population models using data from a 14-year symbiont-removal experiment including seven grass species that host Epichloë fungal endophytes. Results provide novel evidence that symbiotic benefits arise not only through improved mean fitness, but also through dampened inter-annual variance. Hosts with “fast” life-history traits benefited most from symbiont-mediated demographic buffering. Under current climate conditions, contributions of demographic buffering were modest compared to benefits to mean fitness. However, simulations of increased stochasticity amplified benefits of demographic buffering and made it the more important pathway of host–symbiont mutualism. Microbial-mediated variance buffering is likely an important, yet cryptic, mechanism of resilience in an increasingly variable world.
Niche Differentiation in the Dynamics of Host-Symbiont Interactions: Symbiont Prevalence as a Coexistence Problem
(The University of Chicago Press, 2014-04) Miller, Tom E.X.; Rudgers, Jennifer A.
Heritable symbioses can have important ecological effects and have triggered important evolutionary innovations. Current predictions for long-term symbiont prevalence are based on their fitness benefits and vertical transmission rates but ignore nonlinear competitive feedbacks among symbiotic and symbiont-free hosts. We hypothesized that such feedbacks function as stabilizing mechanisms, promoting coexistence of host types and maintaining intermediate symbiont frequency at the population scale. Using a model grass/endophyte symbiosis, we manipulated competition within and between endophyte-symbiotic (E+) and endophyte-free (E-) hosts and fit competition models to experimental data. We show for the first time that symbiont-structured competition can generate stable coexistence of E+ and E- hosts, even under perfect vertical transmission. Niche differentiation was the key to coexistence, causing hosts of each type to limit themselves more strongly than each other. These results establish roles for nonlinear competitive dynamics and niche differentiation in the ecology and evolution of heritable symbionts.
Nitrogen, biochar, and mycorrhizae: Alteration of the symbiosis and oxidation of the char surface
(Elsevier, 2014) LeCroy, Chase; Masiello, Caroline A.; Rudgers, Jennifer A.; Hockaday, William C.; Silberg, Jonathan J.
In some cases amending soil with biochar improves fertility, although the exact mechanisms through which biochar alters soil processes are not well understood. In other cases, however, biochar amendment can have no effect on plant growth, or can have negative effects. When crop benefits occur, simultaneous amendment with biochar and mineral nutrients causes results that are not additive, suggesting that biochar may be capable of improving the efficiency of nutrient uptake by plants, but the mechanisms of this synergy remain unknown. One possible mechanism that has not been fully explored is alterations to the plant-mycorrhizal fungus mutualism, a relationship that occurs in most land plants. In a 4 week greenhouse experiment, we investigated possible effects of the presence of biochar, mycorrhizal fungi, and nitrogen fertilizer on sorghum seedling growth. Results indicated that the combined treatment of biochar, mycorrhizal fungi, and high nitrogen decreased aboveground plant biomass by 42% relative to the mycorrhizae and high nitrogen treatment, while simultaneously promoting mycorrhizal root colonization. This is evidence for an induced parasitism of the mycorrhizal fungus in the presence of nitrogen and biochar within the 4 week timescale of our experiments. Using x-ray photoelectron spectroscopy, we found evidence of increased surface oxidation on biochar particles over the 4 weeks of our trial, consistent with sorption of labile, plant derived dissolved organic matter or char oxidation, either via biotic or abiotic processes. Biochar in soils with mycorrhizae but without sufficient nitrogen showed more surface oxidation than other treatment combinations, and showed a significantly greater fraction of surface carbon present in carbonyl (ﾖCdouble bond; length as m-dashO) functionalities. Our results suggest that soil nitrogen acts as a switch controlling the ability of char to influence the mycorrhizal symbiosis and, in turn, the degree to which the fungi oxidize the char surface.
Symbiosis lost: Imperfect vertical transmission of fungal endophytes in native grasses
(2007) Afkhami, Michelle Elizabeth; Rudgers, Jennifer A.
Vertically transmitted symbionts associate with some of the most ecologically dominant species on Earth, and their fixation has led to major evolutionary transitions (e.g., mitochondria, chloroplasts). While transmission has been well documented for parasites, for most mutualist symbionts it remains unknown whether vertical transmission is imperfect (symbiont not transmitted to all offspring) in nature and during which host life history stage the symbiont is lost. Through quantitative natural history surveys of fungal endophytes in native grasses, we show that transmission was imperfect for all seven species examined. The type and degree of loss depended on the population and host species, suggesting that transmission varies across geographic mosaics. Our results open new directions for understanding cooperation and conflict in the system. For example, imperfect transmission provides a previously unexplored avenue for host sanctions against costly symbionts. Similarly, endophytes gain opportunities for partner choice that would not exist if transmission were perfect.
The Evolutionary Ecology of Stereoisomeric Sesquiterpene Lactones in Xanthium strumarium
(2012-11-30) Ahern, Jeffrey; Whitney, Kenneth D.; Rudgers, Jennifer A.; Parry, Ronald J.; Siemann, Evan
The ecological factors that maintain defensive chemical variation within and between plant species have intrigued ecologists for decades. While theory posits that polymorphisms may be maintained different forms of balancing selection, relatively few expe
The Role of Host Demographic Storage in the Ecological Dynamics of Heritable Symbionts
(The University of Chicago Press, 2016) Bibian, Andrew J.; Rudgers, Jennifer A.; Miller, Tom E.X.
Heritable symbioses are widespread and ecologically important. Many host organisms have complex life cycles that include diverse opportunities for symbionts to affect their host and be lost during development. Yet, existing theory takes a simplified view of host demography. Here, we generalize symbiosis theory to understand how demographic “storage” in the form of dormant or prereproductive life stages can modify symbiosis dynamics. Using grass-endophyte symbioses as context, we developed models to contrast the role of the seed bank (a storage stage) against the reproductive stage in symbiont persistence and prevalence. We find that the seed bank is as important as or more important than the reproductive stage in driving symbiont dynamics, as long as passage through the seed bank is obligate. Flexible entry to the seed bank substantially weakens its influence on symbiont persistence but can modify prevalence in counterintuitive ways. Our models identify a role for legacy effects, where hosts that lose symbionts retain their demographic influence. The retention of benefits via legacy effects can reduce symbiont prevalence and even cause prevalence to decline with increasing benefits to hosts because symbiont-free hosts carry those benefits. Our results resolve connections between individual-level host-symbiont interactions and population-level patterns, providing guidance for empirical studies.
VARIATION IN SPECIES INTERACTIONS AND THEIR EVOLUTIONARY CONSEQUENCES
(2013-05-13) Chamberlain, Scott A.; Whitney, Kenneth D.; Rudgers, Jennifer A.; Cox, Dennis D.; Rudolf, Volker H. W.
Species interactions restrict or promote population growth, structure communities, and contribute to evolution of diverse taxa. I seek to understand how multiple species interactions are maintained, how human altered species interactions influence evolution, and explore factors that contribute to variation in species interactions. In Chapter 1, I examine how plants interact with multiple guilds of mutualists, many of which are costly interactions. The evolution of traits used to attract different mutualist guilds may be constrained due to ecological or genetic mechanisms. I asked if two sets of plant traits that mediate interactions with two guilds of mutualists, pollinators and ant bodyguards, were positively or negatively correlated across 36 species of Gossypium (cotton). Traits to attract pollinators were positively correlated with traits to attract ant bodyguards. Rather than interaction with one mutualist guild limiting interactions with another mutualist guild, traits have evolved to increase attraction of multiple mutualist guilds simultaneously. In Chapters 2 and 3, motivated by the fact that agriculture covers nearly 50% of the global vegetated land surface, I explore the consequences of changes in plant mutualist and antagonist guilds in agriculture for selection on plant traits. I first explore how agriculture alters abundance and community structure of mutualist pollinators and antagonist seed predators of wild Helianthus annuus texanus. Mutualists were more abundant near crops, whereas antagonists were more abundant far from crops near natural habitat. In addition, mutualist pollinator communities were more diverse near sunflower crops. Plant mutualists and antagonists respond differently to agriculture. Next, I explore how these changes in abundance and community structure of mutualists and antagonists influenced natural selection on H. a. texanus floral traits. Natural selection on heritable floral traits differed near versus far from crop sunflowers, and overall selection was more heterogeneous near crop sunflowers. Furthermore, mutualist pollinators and antagonist seed predators mediated these differences in selection. Finally, in Chapter 4, I ask if variation in interaction outcomes differs across types of species interactions. Furthermore, I examined the relative importance of factors that create context-dependency in species interactions. Using meta-analysis of 353 papers, we found that mutualisms were more likely to change sign of the interaction outcome when compared across contexts than competition, and predation was the least likely to change sign. Overall, species identity caused the greatest variation in interaction outcomes: whom you interact with is more important for context-dependency than where or when the interaction occurs. Additionally, the most important factors driving context-dependency differed significantly among species interaction types. Altogether, my work makes progress in understanding how species maintain interactions with multiple guilds of mutualists, how agriculture alters species interactions and subsequent natural selection, and the variation in species interaction outcomes and their causes.

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