Person: Bittleston, Leonora
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Bittleston
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Leonora
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Bittleston, Leonora
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Publication Convergent Interactions Among Pitcher Plant Microcosms in North America and Southeast Asia(2016-08-03) Bittleston, Leonora; Pierce, Naomi E.; Pringle, Anne; Ellison, Aaron; Haig, DavidEcosystems are composed of diverse suites of organisms whose interactions are mediated by both the biotic and abiotic constraints of their environments. The complexity of ecosystems makes them both resilient and difficult to understand. Analyzing the patterns and constraints of biodiversity across different systems can provide insights about the processes governing the formation and maintenance of communities. One analytical tool is convergence, where similarities emerge from different origins. In this dissertation, I combine conceptual theory with empirical data to explore how natural selection repeatedly favors particular associations among different interacting species. In Chapter 1, I develop the concept of convergent interactions—the independent emergence of multispecies interactions with similar physiological or ecological functions. A convergent interaction framework facilitates prediction of the ecological roles of organisms (including microbes) in multispecies interactions and the selective pressures acting in poorly understood or newly discovered multispecies systems. The modified leaves of carnivorous pitcher plants are elegant natural systems for studying ecosystem dynamics, as they are discrete, naturally replicated microcosms that have evolved independently three times on different continents. Pitchers house entire communities of arthropods, protists, fungi and bacteria. In Chapter 2, I take advantage of the visibility and existing knowledge of pitcher plant insect inquilines to evaluate next-generation metabarcoding as a means of characterizing complete contained communities. Correspondence of phylogenetic trees and correlations of organism and sequence counts confirm the effectiveness of metabarcoding methods. Chapter 3 then extends the concept of convergent interactions to pitcher ecosystems. I characterize and compare the eukaryotic and bacterial communities from over 400 samples of pitcher microcosms from Nepenthes species in Southeast Asia and Sarracenia species in North America. Data from field collections as well as a relocation experiment are used to investigate whether convergence in form and function of a host extends to associated communities. Pitcher communities contain fewer species than those of surrounding habitats, and phylogenetically related subsets of bacteria and eukaryotes tend to colonize each system. When in a common environment, Nepenthes and Sarracenia communities converge in composition. The evolved pitcher form appears to strongly affect fundamental aspects of biodiversity within the pitcher ecosystem, including species richness, phylogenetic diversity, and community composition.Publication Convergence in Multispecies Interactions(Elsevier BV, 2016) Bittleston, Leonora; Pierce, Naomi; Ellison, Aaron; Pringle, Anne E.The concepts of convergent evolution and community convergence highlight how selective pressures can shape unrelated organisms or communities in similar ways. We propose a related concept, convergent interactions, to describe the independent evolution of multispecies interactions with similar physiological or ecological functions. A focus on convergent interactions clarifies how natural selection repeatedly favors particular kinds of associations among species. Characterizing convergent interactions in a comparative context is likely to facilitate prediction of the ecological roles of organisms (including microbes) in multispecies interactions, and selective pressures acting in poorly understood or newly discovered multispecies systems. We illustrate the concept of convergent interactions with examples: vertebrates and their gut bacteria; ectomycorrhizae; insect-fungal-bacterial interactions; pitcherplant food webs; and ants and ant-plants.Publication Origin and Examination of a Leafhopper Facultative Endosymbiont(Springer-Verlag, 2011) Degnan, Patrick H.; Bittleston, Leonora; Hansen, Allison K.; Sabree, Zakee L.; Moran, Nancy A.; Almeida, Rodrigo P. P.Eukaryotes engage in intimate interactions with microbes that range in age and type of association. Although many conspicuous examples of ancient insect associates are studied (e.g., Buchneraaphidicola), fewer examples of younger associations are known. Here, we further characterize a recently evolved bacterial endosymbiont of the leafhopper Euscelidius variegatus (Hemiptera, Cicadellidae), called BEV. We found that BEV, continuously maintained in E. variegatus hosts at UC Berkeley since 1984, is vertically transmitted with high fidelity. Unlike many vertically transmitted, ancient endosymbioses, the BEV. variegatus association is not obligate for either partner, and BEV can be cultivated axenically. Sufficient BEV colonies were grown and harvested to estimate its genome size and provide a partial survey of the genome sequence. The BEV chromosome is about 3.8 Mbp, and there is evidence for an extrachromosomal element roughly 53 kb in size (e.g., prophage or plasmid). We sequenced 438 kb of unique short-insert clones, representing about 12% of the BEV genome. Nearly half of the gene fragments were similar to mobile DNA, including 15 distinct types of insertion sequences (IS). Analyses revealed that BEV not only shares virulence genes with plant pathogens, but also is closely related to the plant pathogenic genera Dickeya, Pectobacterium, and Brenneria. However, the slightly reduced genome size, abundance of mobile DNA, fastidious growth in culture, and efficient vertical transmission suggest that symbiosis with E. variegatus has had a significant impact on genome evolution in BEV. Electronic supplementary material: The online version of this article (doi:10.1007/s00284-011-9893-5) contains supplementary material, which is available to authorized users.