Browsing by Subject "Phenotypic plasticity"

Now showing 1 - 3 of 3
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    Light access and leaf trait variation within and among tree species across diverse mixtures within a common garden
    (2019-11-05) Williams, Laura J; Cavender-Bares, Jeannine; Reich, Peter B; Paquette, Alain; Messier, Christian; will3972@umn.edu; Williams, Laura J
    This dataset includes trait measurements for 2615 leaves of common temperate-boreal tree species alongside estimates of their light access. Trait values affect how plants function, with consequences that propagate through scales of ecological organization to affect ecosystem function. However, the pathway connecting trait expression to ecosystem function is complicated by feedbacks: trait expression may vary within species in response to community diversity, and trait expression also determines a community’s functional diversity. In this study, we quantify the extent to which light access – which past studies suggest affects trait expression and differs as a result of interactions among plants – differs consistently with community diversity and explains intraspecific trait variation in trees. In a common garden, trees of five angiosperm and seven gymnosperm species were planted to form 37 communities ranging widely in species and functional diversity whereby confounding environmental variation was minimized. We sampled leaves of each species to characterize intraspecific variation within crowns, among trees within communities, and among communities in three traits – leaf size, specific leaf area and nitrogen concentration – and estimated each leaf’s access to light.
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    Paling in Comparison: The Role of Sex and Temperature in Melanin-Based Immune Function
    (2017-10) Ehrlich, Rebecca
    Sex differences in disease susceptibility have been observed across a wide range of species, yet we lack a strong understanding of how environmental context influences these patterns. In this thesis, I take a life-history approach to investigating the plasticity of immunological sex differences in insects. Insects rely on the pigment melanin for both immune function and the structure and coloration of the cuticle (i.e. integument). Although many studies have shown evidence of correlations between immunity and cuticle pigmentation, most do not take into account the many potential modes of selection acting on cuticle melanism. Given that the biochemical precursors of melanin are a common currency in thermoregulation, sexual ornamentation, and immune function in insects, we hypothesized that sex differences in melanin-based resource allocation contribute to sex differences in immunity, and that the thermal environment will moderate this influence. My thesis work focused on the interactive effects of sexual selection and thermal selection on cuticle melanism and immunity in the Pacific field cricket (Teleogryllus oceanicus). After rearing crickets under multiple temperatures, we found, as predicted, that females invested more in immunity, males invested more in cuticle melanism, and both immune function and cuticle melanism were reduced in individuals that developed under warmer temperatures. Our results suggest that sex-specific investment in melanin corresponds with sex differences in immunity and that thermoregulation may act as an immune constraint under high temperatures, thus regulating the extent to which males and females diverge in disease susceptibility. By quantifying melanin-based traits underlying strategies for both reproduction and survival in insects, this study sheds light onto the selective forces shaping sex differences in immunity and insect life-history in general.
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    Resource hoarding facilitates cheating in the legume-rhizobia symbiosis and bet-hedging in the soil.
    (2010-06) Ratcliff, William C.
    The carbon that rhizobia in root nodules receive from their host powers both reproduction and the synthesis of the storage polyester poly3-hydroxybutyrate (PHB), as well as N2 fixation, which mainly benefits the host. Rhizobia escaping nodules can use stored PHB to survive starvation and reproduce up to 3-fold, but PHB synthesis is energetically expensive and trades-off with N2 fixation. As a result, PHB synthesis is a central mechanism in the evolution of conflict between rhizobia and legumes, and should be included in estimates of rhizobial fitness. Some rhizobia have evolved sophisticated mechanisms to increase PHB accumulation, such as the production of rhizobitoxine, a chemical inhibitor of legume ethylene synthesis. Rhizobitoxine reduces host growth, decreasing rhizobia per nodule for all strains on a plant, but substantially increases PHB accumulation for rhizobitoxine-producing rhizobia. In addition to enhancing reproduction, PHB has a role in bet-hedging: when starved, free-living high-PHB rhizobia divide asymmetrically, forming dormant, high-PHB „persisters‟ that survive long-term starvation and antibiotic treatment, and low-PHB „growers‟ that are sensitive to these stresses. Sinorhizobium meliloti integrates bet hedging and phenotypic plasticity, forming fewer high-PHB persister cells when low competitor density predicts shorter-term starvation. Declining populations may select for delayed reproduction when there is a trade-off between reproduction and longevity, as there is with starving S. meliloti.