1. Culture methods for the maintenance of symbiotic adult and juvenile Convoluta roscoffensis have been developed. The growth of adults but not juveniles is dependent on nitrogen enrichment of the medium. 2. Electron microscopic studies suggest that the algal symbionts in adult Convoluta are intracellular. 3. Structural studies of the gametes and early development of Convoluta are described. 4. Relevant aspects of the biology of the natural Convoluta symbiont, Platymonas convolutae, and a range of related algae have been studied. The growth of all Platymonas and Tetraselmis species tested except P.convolutae is stimulated by 0.1 M glucose. Glucose supports the growth of T.tetrathele, T.suecica and P.subcordiformis in darkness. P.convolutae and T.tetrathele have two uptake systems for uric acid, which conform to Michaelis-Menten kinetics; a high affinity system, operating in the concentration range 0.2-4.5 pM, and a low affinity system, operating at higher concentrations of uric acid. Uric acid uptake by P.convolutae is abolished by uncouplers of phosphorylation. Exogenous uric acid is accumulated in cells of Platymonas and Tetraselmis species up to internal concentrations of 0.3 M. P. convolutae metabolises (2-14C) uric acid to (14 C) carbon dioxide in the dark. 5. Aposymbiotic juvenile and symbiotic adult Convoluta, under standard culture conditions, contain solid uric acid. The uric acid content of juveniles declines on infection with P.convolutae and related species. Uric acid is utilised in the adult symbiosis, particularly under conditions of nitrogen demand. 6. Motile cells of P.convolutae and related species and Chlamydomonas coccoides aggregate around Convoluta eggs. These algae 'settle' on the eggs, by an interaction initiated by contact between the algal flagella and egg capsule surface. Living and killed algae are trapped by the capsules. No evidence that P.convolutae cells exhibit chemotaxis towards Convoluta eggs has been obtained. 7. Juvenile Convoluta ingest species of Platymonas and Tetraselmis, Prasinocladus marinus and Chlamydomonas coccoides but no other algae tested. Ingestion of P.convolutae is not affected by pretreatment of the cells with lectins or proteolytic enzymes, but is reduced if the algae are killed. 8. Cells of C.coccoidea, but not P.convolutae and related species, are disrupted in juvenile Convoluta. 9. Juvenile Convoluta form a viable symbiosis with P.convolutae, Pr.marinus, T.tetrathele and T.verrucosa under laboratory conditions. The structural changes of P.convolutae and T.verrucosa during the development of the symbiosis are described. 10. It is proposed that Convoluta discriminate against species unrelated to P.convolutae on initial contact and in the digestive region of the host. Evidence for a recognition mechanism discriminating between P.convolutae and related species is discussed. The nature of the recognition mechanism(s) has not been established.

Graciously We Receive is an ethnographic documentary film about Hearts for Homes, a volunteer Christian outreach organization that does no-cost home repairs for low income elderly homeowners. Graciously We Receive examines the symbiotic relationships between volunteers and the homeowners, addressing the need to be needed by meeting the needs of others. Using qualitative research methods derived from the social sciences, Graciously We Receive represents an advancement in media-based research methods. with the introduction of quick cine-ethnography, which combines quick ethnography methods and grounded theory for data acquisition and analysis, Graciously We Receive applies anthropological research methods to documentary film production.

Contemporary biology belongs among the most diversified sciences; yet one of its most fundamental and controversial questions is surprisingly: "What is life?". The aim of this study is to point out that biology is special among other natural sciences because its need of the notion of meaning. Meaning takes the central position in the biological rea-soning. Compared to other sciences, biology has to reflect the dimension of information and its interpretation: language-like properties, communication and interpretation belong to the basic characteristics of life. In spite of the fact, most contemporary theories of evo-lution deny active participation of living beings on the very process - living being come out of its description as puppets or zombies controlled by external forces. As a remedy from such a situation, biology should start with a new model for living entities. A bene-ficial methapor seems to be that of natural languages, i.e. an analogy between a net of historical interactions and conventional ways of interpretation of meaning in (i) living entities and (ii) in system of natural languages. I consider as the most appropriate biolo-gical systems for modeling of such a network of symbiotic interactions, i. e. the pheno-menon of symbiosis and especially symbiogenesis. Keywords: life,...

Symbiotic nitrogen fixation occurs in plants harboring nitrogen-fixing bacteria within the plant tissue. The most widely studied association is between the legumes and rhizobia. In this relationship the plant (legumes) provides the bacteria (rhizobia) with reduced carbon derived from photosynthesis in exchange for reduced atmospheric nitrogen. This allows the plant to survive in soil, which is low in available of nitrogen. Rhizobia infect and enter plant root and reside in organs known as nodules. In the nodules the bacteria fix atmospheric nitrogen. The association between the legume, Medicago truncatula and the bacteria Sinorhizobium meliloti, has been studied in detail. Medicago mutants that have defects in nodulation help us understand the process of nitrogen fixation better. One such mutant is the Mtnip-1. Mtnip-1 plants respond to S. meliloti by producing abnormal nodules in which numerous aberrant infection threads are produced, with very rare rhizobial release into host plant cells. The mutant plant Mtnip-1 has an abnormal defense-like response in root nodules as well as defects in lateral root development. Three alleles of the Mtnip/latd mutants, Mtnip-1, Mtlatd and Mtnip-3 show different degrees of severity in their phenotype. Phylogenetic analysis showed that MtNIP/LATD encodes a protein belonging to the NRT1(PTR) family of nitrate, peptide, dicarboxylate and phytohprmone transporters. Experiments with Mtnip/latd mutants demonstrats a defective nitrate response associated with low (250 μM) external nitrate concentration rather than high (5 mM) nitrate concentration. This suggests that the mutants have defective nitrate transport. To test if MtNIP/LATD was a nitrate transporter, Xenopus laevis oocytes and Arabidopsis thaliana mutant plants Atchl1-5, defective in a major nitrate transporter AtNRT1.1(CHL1), were used as surrogate expression systems. Heterologous expression of MtNIP/LATD in X. laevis oocytes and Atchl1-5 mutant plants conferred on them the ability to take up nitrate from external media with high affinity, thus demonstrating that MtNIP/LATD was a high affinity nitrate transporter. Km for MtNIP/LATD was determined to be approximately160 μM in the X. laevis system and 113 μM in the Arabidopsis Atchl1-5 mutant lines thus supporting the previous observation of MtNIP/LATD being a high affinity nitrate transporter. X. laevis expressing the mutant Mtnip-1 and Mtlatd, were unable to transport nitrate. However X. laevis oocytes, expressing the less severe mutant allele Mtnip-3 were able to transport nitrate suggesting another role of the Mtnip/latd besides high affinity nitrate transport. Experimental evidence suggested that MtNIP/LATD might transport another substrate beside nitrate. MtNIP/LATD levels are regulated by phytohormones. Experiments performed with ABA (abscisic acid), IAA (indole acetic acid) and histidine as substrates in X. laevis system show that the MtNIP/LATD mRNA injected oocytes efflux IAA but do not transport histidine or ABA. When wild type A17 and mutant Mtnip-1 and Mtnip-3 plants, grown in the presence of different sources of nitrogen were screened in herbicide chlorate, a structural analog of nitrate, the A17 and Mtnip-3 mutant showed levels of susceptibility that was different from mutant Mtnip-1 lines. Evidence suggested that the amount of chlorate transported into the plants were regulated by the C:N status of the A17 and Mtnip-3 plants. This regulation was missing in the Mtnip-1 lines thus suggesting a sensor function of MtNIP/LATD gene.

No description available.

Coral reefs are declining globally, calling for better ways to quantify coral health and predict resilience to future stress. The relationship between bleaching and fitness is key, as is reserve capacity to deal with physical trauma. This dissertation is an integrative study of the coral-algal symbiosis, holobiont performance under varied environmental conditions, and interactions between holobiont and environment on coral colony health and ability to recover from routine partial damage. I utilize the facultatively symbiotic, temperate coral Astrangia poculata as a natural model to explore the dynamics of colony health, performance, and the influence of environmental and nutritional stress under stable aposymbiotic and symbiotic states. Unlike most tropical hermatypic corals that rely heavily upon photosynthetic symbionts for energy, A. poculata can (1) flexibly use both heterotrophic and autotrophic nutritional pathways and (2) exist in naturally occurring, stable, and measurable aposymbiotic and symbiotic states. I begin by describing the impacts of environmentally relevant (winter, summer, and above range) temperatures on small-scale wound healing and recovery. Next, I explore the effects of nutritional and symbiotic states by comparing wound recovery, total colony health, host behavior, and symbiont performance in fed and starved colonies. Finally, I generate a novel reference transcriptome for A. poculata, and use computational approaches to characterize variation in gene expression between the symbiotic and aposymbiotic states. This analysis reveals that regardless of temperature, and with or without the potential for heterotrophic nutritional sources, a relationship with Symbiodinium enhances wound recovery and resilience to stress. Compromised healing ability and tissue cover at low temperatures suggest that in temperate stony corals, recovery and survival are more impacted by winter conditions than by exposure to high summer temperatures. Differential expression analysis revealed predictable enhancements to photosynthesis-related gene expression in symbiotic colonies. Together these results illuminate the complex interactions among symbiotic state, stress, recovery, and performance. We propose that studies like ours that examine the effects of combined stressors, as opposed to a monotonic focus on coral bleaching per se, are essential to clinical diagnosis and stewardship for coral reefs subjected to intense, cumulative human impacts.

Organismal invasions have repeatedly been cited as both a driving force behind global change and beneficiaries of that change. Although many drivers of these invasions have been well studied, few studies have addressed invasions through the perspective of native symbiont communities. In the Mountain Lake region of Virginia, crayfish host diverse assemblages of obligate cleaning symbionts known as branchiobdellida. This cleaning symbiosis has been found to result in significant fitness benefits for native crayfish. Historical survey work showed that invasive crayfish, known to be intolerant of symbionts, were introduced into the region by the 1960s. I carried out an extensive regional survey to determine how this invasion has progressed and what impacts it is having on the native crayfish-branchiobdellida symbiosis. Survey results show that invasive crayfish have successfully spread throughout the region, resulting in the displacement of native crayfish. Additionally, findings suggest that invasion results in significantly reductions in abundance and richness in native symbiont communities. To determine mechanisms contributing to observed impacts on native symbionts, I carried out a study that simulated displacement of native crayfish by invasive crayfish in a controlled setting. This study found that as native crayfish are increasingly displaced by invasive crayfish, both symbiont dispersal and survival are negatively affected. This potential loss of symbiosis caused by invasion may reduce symbionts on native crayfish below abundances necessary for fitness benefits, exacerbating the negative impacts of invasions and presenting a major conservation issue in invaded systems. / M. S. / Introductions of non-native organisms are widely recognized for the negative impacts they have on native biodiversity. Although ongoing study has been directed at understanding many of the factors contributing to invasions, few studies address invasion through the perspective of native symbionts. In the Mountain Lake region of Virginia, crayfish host multiple species of small worms, known as crayfish worms, that provide cleaning services to their crayfish host. These services have been found to provide health benefits to native crayfish. Historical surveys found that invasive crayfish, known to be intolerant of crayfish worms, were introduced into the region by the 1960s. To determine how far invasive crayfish have spread and what impacts they are having on native organisms, I carried out a survey of the region. This survey found that invasive crayfish are now widespread in the region. Additionally, findings suggest that the introduction of invasive crayfish results in reductions in both the number of worms and worm species present. These reductions may be significant enough to prevent health benefits given to native crayfish from occurring. In addition to this survey, I carried out a study under controlled settings to determine what causes negative impacts on native crayfish worms. This study found that as invasive crayfish displace native crayfish, crayfish worms are increasingly killed due to the intolerance of invasive crayfish to the worms. These findings suggest symbiosis should be included in studies of invaded systems if we are to fully understand the introduction and spread of invasive species.

published_or_final_version / Biological Sciences / Doctoral / Doctor of Philosophy

No description available.

Plants and animals have evolved unique morpho-physiological adaptions to cope with the harsh and steep environmental gradients that characterise the mangrove ecosystem. However, the capacity of these two main components of the system to thrive, and the extraordinary productivity of mangrove forests in extreme conditions, has been overlooked in terms of the role of the microbiome. By combining approaches that included molecular microbial ecology, biogeochemical analyses, microscopy, raman spectroscopy and microsensor measurements, this thesis aimed to investigate the potential role of bacterial symbiosis in the adaptation of mangrove crabs to their environment and subsequently how these different animals modify their environment. Finally, with a field-based approach monitoring microbial communities, sediment metabolism and plant performance, the thesis aimed to investigate the plant/animal/bacterial dynamics in relation to seasonal environmental changes to contribute to understand the mangrove plant productivity paradox of high productivity under conditions of limited nutrents. Crab species were associated with distinct gill-bacteria communities, that produced carotenoids, according with their level of terrestrial adaptation. These carotenoids may be involved in protecting the gills from oxidative stress during air exposure. The main groups of ecosystem engineering crabs in mangroves had significant but diverse effects on the sediment environment and microbiome predominantly related to their ecology (i.e. filter feeder vs herbivore). Burrows increase aerobic microbial activity in the immediate burrow wall with a cascade effect on sediment microbial communities and nutrient distribution observed consistently across mangroves in different locations and with diverse environmental conditions. Microorganisms play an important role in adapting crabs on their evolutionary path to land and could contribute to the success of their colonization. At high population densities, of more than 50 individuals per square meter in some mangroves, these crabs deeply impact the functioning of the mangrove ecosystem, affecting microbial networks and nutrient recycling in the sediment, which may ameliorate conditions for plant growth. The microbiome is an understudied component of mangroves that lies at the basis of the functioning of these systems, influencing the success of the animal inhabitants (ecosystem engineers) that deeply modify the sediment microbiome, therefore influencing ecosystem functioning and resilience and, potentially, the success of the plants themselves (ecosystem architects).