Virulence as a Model for Interplanetary and Interstellar Colonisation - Parasitism or Mutualism

In the light of current scientific assessments of human-induced climate change, we investigate an experimental model to inform how resource-use strategies may influence interplanetary and interstellar colonisation by intelligent civilisations. In doing so, we seek to provide an additional aspect for refining the famed Fermi Paradox. The model described is necessarily simplistic, and the intent is to simply obtain some general insights to inform and inspire additional models. We model the relationship between an intelligent civilisation and its host planet as symbiotic, where the the relationship between the symbiont and the host species (the civilisation and the planets ecology, respectively) determines the fitness and ultimate survival of both organisms. We perform a series of Monte Carlo Realisation simulations, where civilisations pursue a variety of different relationships/strategies with their host planet, from mutualism to parasitism, and can consequently 'infect' other planets/hosts. We find that parasitic civilisations are generally less effective at survival than mutualist civilisations, provided that interstellar colonisation is inefficient (the maximum velocity of colonisation/infection is low). However, as the colonisation velocity is increased, the strategy of parasitism becomes more successful, until they dominate the 'population'. This is in accordance with predictions based on island biogeography and r/K selection theory. While heavily assumption dependent, we contend that this provides a fertile approach for further application of insights from theoretical ecology for extraterrestrial colonisation - while also potentially offering insights for understanding the human-Earth relationship and the potential for extraterrestrial human colonisation.Comment: 18 pages, 7 figures, published in the International Journal of Astrobiolog

Ecological niche of plant pathogens

Disease ecology is a new approach to the understanding of the spread and dynamics of pathogens in natural and man-made environments. Defining and describing the ecological niche of the pathogens is one of the major tasks for ecological theory, as well as for practitioners preoccupied with the control and forecasting of established and emerging diseases. Niche theory has been periodically revised, not including in an explicit way the pathogens. However, many progresses have been achieved in niche modeling of disease spread, but few attempts were made to construct a theoretical frame for the ecological niche of pathogens. The paper is a review of the knowledge accumulated during last decades in the niche theory of pathogens and proposes an ecological approach in research. It quest for new control methods in what concerns forest plant pathogens, with a special emphasis on fungi like organisms of the genus Phytophthora. Species of Phytophthora are the most successful plant pathogens of the moment, affecting forest and agricultural systems worldwide, many of them being invasive alien organisms in many ecosystems. The hyperspace of their ecological niche is defined by hosts, environment and human interference, as main axes. To select most important variables within the hyperspace, is important for the understanding of the complex role of pathogens in the ecosystems as well as for control programs. Biotic relationships within ecosystem of host-pathogen couple are depicted by ecological network and specific metrics attached to this. The star shaped network is characterized by few high degree nodes, by short path lengths and relatively low connectivity, premises for a rapid disturbance spread

Synthetic Symbiosis under Environmental Disturbances

By virtue of complex ecologies, the behavior of mutualisms is challenging to study and nearly impossible to predict. However, laboratory engineered mutualistic systems facilitate a better understanding of their bare essentials. On the basis of an abstract theoretical model and a modifiable experimental yeast system, we explore the environmental limits of self-organized cooperation based on the production and use of specific metabolites. We develop and test the assumptions and stability of the theoretical model by leveraging the simplicity of an artificial yeast system as a simple model of mutualism. We examine how one-off, recurring, and permanent changes to an ecological niche affect a cooperative interaction and change the population composition of an engineered mutualistic system. Moreover, we explore how the cellular burden of cooperating influences the stability of mutualism and how environmental changes shape this stability. Our results highlight the fragility of mutualisms and suggest interventions, including those that rely on the use of synthetic biology.IMPORTANCE The power of synthetic biology is immense. Will it, however, be able to withstand the environmental pressures once released in the wild. As new technologies aim to do precisely the same, we use a much simpler model to test mathematically the effect of a changing environment on a synthetic biological system. We assume that the system is successful if it maintains proportions close to what we observe in the laboratory. Extreme deviations from the expected equilibrium are possible as the environment changes. Our study provides the conditions and the designer specifications which may need to be incorporated in the synthetic systems if we want such "ecoblocs" to survive in the wild

Tree Species Diversity Increases with Conspecific Negative Density Dependence Across an Elevation Gradient

Elevational and latitudinal gradients in species diversity may be mediated by biotic interactions that cause density-dependent effects of conspecifics on survival or growth to differ from effects of heterospecifics (i.e. conspecific density dependence), but limited evidence exists to support this. We tested the hypothesis that conspecific density dependence varies with elevation using over 40 years of data on tree survival and growth from 23 old-growth temperate forest stands across a 1,000-m elevation gradient. We found that conspecific-density-dependent effects on survival of small-to-intermediate-sized focal trees were negative in lower elevation, higher diversity forest stands typically characterised by warmer temperatures and greater relative humidity. Conspecific-density-dependent effects on survival were less negative in higher elevation stands and ridges than in lower elevation stands and valley bottoms for small-to-intermediate-sized trees, but were neutral for larger trees across elevations. Conspecific-density-dependent effects on growth were negative across all tree size classes and elevations. These findings reveal fundamental differences in biotic interactions that may contribute to relationships between species diversity, elevation and climate

Fungal grass endophytes and arthropod communities: lessons from plant defence theory and multitrophic interactions

Alkaloids produced by systemic fungal endophytes of grasses are thought to act as defensive agents against herbivores. Endophytic alkaloids may reduce arthropod herbivore abundances and diversity in agronomic grasses. Yet, accumulating evidence, particularly from native grasses, shows that herbivore preference, abundances and species richness are sometimes greater on endophyte-infected plants, even those with high alkaloids, contrary to the notion of defensive mutualism. We argue that these conflicting results are entirely consistent with well-developed concepts of plant defence theory and tri-trophic interactions. Plant secondary chemicals and endophytic alkaloids often fail to protect plants because: (1) specialist herbivores evolve to detoxify and use defensive chemicals for growth and survival; and (2) natural enemies of herbivores may be more negatively affected by alkaloids than are herbivores. Endophytes and their alkaloids may have profound, but often highly variable, effects on communities, which are also consistent with existing theories of plant defence and community genetics

Filling Key Gaps in Population and Community Ecology

We propose research to fill key gaps in the areas of population and community ecology, based on a National Science Foundation workshop identifying funding priorities for the next 5–10 years. Our vision for the near future of ecology focuses on three core areas: predicting the strength and context-dependence of species interactions across multiple scales; identifying the importance of feedbacks from individual interactions to ecosystem dynamics; and linking pattern with process to understand species coexistence. We outline a combination of theory development and explicit, realistic tests of hypotheses needed to advance population and community ecology

Coevolutionary Dynamics and the Conservation of Mutualisms

The vast majority of studies in conservation biology focus on a single species at a time. However, many of the anthropogenic threats that species face occur via disrupted or enhanced interactions with other organisms. According to one recent analysis, interactions with introduced species, such as predators, parasites, and pathogens, are the eighth leading cause of species endangerment worldwide; they are the primary cause of endangerment in Hawaii and Puerto Rico (Czech and Krausman 1997). Altering interactions not only has ecological effects, but also it can generate selective pressures and evolutionary responses, which may either favor or disfavor the evolutionary persistence of species and interactions. An increased focus on interspecific interactions will thus enlighten our efforts to conserve species and, more pointedly, our ability to understand when species will and will not respond evolutionarily to conservation threats. Such a focus is also critical for efforts to conserve communities as units, because interactions are the crucial and poorly understood link between threatened species and threatened species assemblages. Different types of interspecific interactions are subject to, and generate, some-what different ecological and evolutionary threats. Predator and pathogen introductions can lead to reduction, local exclusion, or extinction of native species (Savidge 1987; Schofield 1989; Kinzie 1992; Steadman 1995; Louda et al. 1997). Rapid evolution in the enemies and/or the victims may also result (Dwyer et al. 1990; Singer and Thomas 1996; Carroll et al. 1998)

Varieties of living things: Life at the intersection of lineage and metabolism

publication-status: Publishedtypes: Articl

THE ROLE OF MICROBIAL ENDOSYMBIONTS IN SORGHUM HALEPENSE INVASIONS: EVIDENCE OF A NEW INVASION STRATEGY, MICROBIALLY ENHANCED COMPETITIVE ABILITY (MECA)

Invasive plants can profoundly alter ecosystem processes, and tremendous economic costs are often associated with these disturbances. Attributes like higher growth rates, increased biomass, and enhanced chemical defenses have been documented in many invasive plants. When expanding into new ranges, these traits frequently allow invasive plants to outcompete native plant communities. Current theories suggest these invasive attributes are plant-regulated; however, my work shows that bacterial endosymbionts can regulate these traits in the invasive grass Sorghum halepense. Using culture and molecular approaches, I found the invasive grass harbors several bacterial organisms inside the roots and rhizomes. These bacterial endosymbionts were isolated from within plant tissues and identified using 16S-rRNA gene sequencing. Numerous physiological functions of these plant-associated bacterial isolates were confirmed using in vitro studies, including the capacity for N2-fixation, iron siderophore production (iron chelation), phosphate solubilization, and production of the plant-growth hormone indole-3-acetic acid (IAA). In long-term field studies conducted within the Fort Worth Nature Center & Refuge spanning 46-months, alterations to several soil biogeochemical cycles across an S. halepense invasion gradient were documented. Heavily invaded soils had increased plant-available forms of essential macronutrients (nitrogen, phosphorus, potassium, and magnesium) and trace metals (copper, iron, manganese, and zinc) compared to moderately and non-invaded soils. Using a novel antibiotic approach, I restricted growth of the bacterial endosymbionts within the plant and found they significantly increased plant biomass, and altered resource allocation enhancing rhizomatous growth. Plants with endosymbionts significantly inhibited the growth of a native prairie grass, Schizachyrium scoaparium, which is frequently displaced by the invader in tallgrass prairie ecosystems. Restricting bacterial growth completely removed these competitive effects. Plants with bacterial endosymbionts also had increased production of the herbivore-defense compound, dhurrin, contained in leaves. When leaves from plants with bacterial endosymbionts were fed to a generalist insect herbivore (Tricoplusia ni), the insect could not grow and experienced significant mortality. Restricting bacterial growth resulted in a 6-fold decrease in dhurrin, in conjunction with significant increases in insect growth and survival. These results suggest microbial endosymbionts significantly contribute to S. halepense invasions by enhancing the plant traits of biomass, growth rate, competitive effects, and herbivore-defense. This works shows that these invasive plant traits are microbially-mediated. This novel invasion strategy is referred to as Microbially Enhanced Competitive Ability (MECA), in which microbial associations significantly contribute to a range of plant traits that directly correspond to invasion success