There are two main, nonexclusive hypotheses that might explain how these taxa have remained distinct: “opportunity” and “host selection.” The opportunity hypothesis is based on the distinct and almost completely nonoverlapping range of plant hosts of the subspecies , which could severely limit contact between them and hence limit opportunity for IHR. This hypothesis is strengthened if it could be established that genetic exchange typically occurs in the plant host. On the other hand, the opportunity hypothesis would be weakened if genetic exchange typically occurs in the insect vector, since different subspecies can colonize the same insect . The host selection hypothesis proposes that different plant hosts impose strong host-specific selection such that, even if IHR occurs relatively frequently, most of the bacteria resulting from such exchange are maladapted and do not survive. Even moderate levels of recombination would be expected to generate high levels of genetic variability; however, very little genetic variability was observed within the mulberry type despite evidence of large-scale IHR and a broad geographical occurrence within the United States. This near monomorphism of the mulberry-type isolates suggests that plant host specialization places severe constraints on the genome; i.e., bucket flower the shift to the new host seems to have eliminated all but a narrowly defined set of genotypes.
If the host shift had been due to some other genetic change, such as the acquisition of new extrachromosomal genes,then these genes would be expected to be seen in a number of different genetic backgrounds, which they are not. Thus, in summary, X. fastidiosa subsp. morus provides an important example for understanding the role of homologous recombination in bacterial adaptive evolution. We have been able to associate a clear ecological shift with a high level of recombination. But we are left with a puzzle. The data are consistent with X. fastidiosa subsp. morus and the recombinant-group X. fastidiosa subsp. multiplex originating from a single large-scale IHR, with no unambiguous evidence of any similar events involving the strains of X. fastidiosa subsp. fastidiosa currently found in the United States. Was this initial event a conjugation, followed by DNA fragmentation within the bacterial cell which resulted in large-scale recombination, or was it associated with a period during which conditions promoted a high rate of transformation, conditions that no longer prevail or occur only rarely? At present, it is far from clear if one or both of these possibilities could account for the pattern of evolution illustrated in Fig. 2.Traumatic brain injury accounts for approximately 90% of brain injuries, and is associated with cognitive dysfunction and long-term disability. As a result of domestic incidents, military combat, traffic accidents, and sports, TBI can compromise broad aspects of neuronal function. Patients often experience problems in the domains of learning, memory, and affective functions that can profoundly influence quality of life. Existing therapeutic strategies for TBI have not been successful in counteracting the heterogeneous TBI pathology nor improving the quality of life of patients. Hence, identifying interventions with broad applicability seems necessary for effective management of TBI.
Dietary polyphenols have significant positive effects on brain health via protecting neurons against injury and enhancing neuronal function. Evidence supports the neuromodulatory effects of flavonoid-rich blueberry, particularly in promotion of brain plasticity, and counteracting behavioral deficits.[8] In the United States, demand for blueberries has increased, with 2017 fresh per capita consumption of 1.79 pounds per person. Several reports indicate that blueberry dietary supplementation improves memory, learning, and general cognitive function, and protects against neuronal injury associated with stroke. Moreover, it has been shown that blueberries possess potent antioxidant capacity through their ability to reduce free radical formation or upregulating endogenous antioxidant defenses. These studies suggest that blueberry supplementation can have the potential to be used to overcome the broad pathology of TBI. Given the lack of information about the effects of blueberry intake immediately after TBI, we have performed studies to assess the effects of blueberry extracts during the acute phase of TBI. Evidence suggests that TBI is characterized by dysfunction in synaptic plasticity, elevated levels of free radicals, plasma membrane dysfunction, which can contribute to the behavioral dysfunction. Oxidative stress is part of the pathology of TBI and compromises neuronal function. In particular, excessive free radical formation leads to accumulation of lipid oxidation byproducts such as 4-hydroxynonenal with subsequent impairments in plasma membrane fluidity, receptor signaling across the membrane to deteriorate synaptic plasticity and reduce neuronal excitability.
Deficiencies in brain derived neurotrophic factor reduce the brain plasticity necessary to cope with the effects of TBI.[23] BDNF activates cAMP-responsive element-binding protein , a multifaceted transcriptional regulator involved in synaptic plasticity essential for learning and memory. BDNF is known to bind to TrkB receptors, leading to activation of Ca2+/calmodulin-dependent protein kinase II , required for synaptic processes involved in behavior. Several observations indicate that the flavonoids exert action through modulation of signaling pathways to promote synaptic and neuronal function. Accordingly, in the current study, we investigated whether blueberry supplementation would counteract TBI pathology by involving BDNF-related pathways involved in synaptic plasticity and oxidative stress to influence cognitive behaviors.Like much of science in the last century , this dissertation rejects the dualism of human and nature. Humans are inextricably a part of nature. And, as humans are a part of nature, so too is agriculture. Earth provides the constraints and opportunities for human life, and in return humans have shaped and modified Earth . The relatively stable climate of the Holocene era enabled humans to begin engaging in agriculture, whereas in the previous era, the Pleistoscene, which had comparatively fast and extreme changes in climate with recurring growth and retreats of glaciers, humans could only engage in hunting and gathering . For 2.5 million years, Homo physiological and sociocultural characteristics evolved for survival on Earth when their population and impact were relatively small . However, “small” no longer characterizes the only remaining hominid species, Homo sapiens, in terms of either its population or its impact. Humans have induced significant changes to Earth’s biogeochemistry by way of agriculture systems, and more recently, by way of our large consumption of fossil fuels and other natural resources .Steffen et al. list agriculture as one of the human enterprises that thrust Earth into what some scientists propose should be called the Anthropocene epoch because of the ways humans have induced significant changes to Earth’s biogeochemistry . In concert with other enterprises such as industry and international commerce, agriculture is “transforming Earth’s land surface, altering its biogeochemical and hydrologic cycles, adding and deleting species, destroying and modifying ecosystems, and ultimately changing climate and biological diversity” . Agriculture has alarming effects on ecosystem health and diversity , and climate change . Researchers and activists have criticized agriculture for falling short on addressing global issues of malnutrition , and for perpetuating social inequality for farmers . These issues have propelled a decades long effort by researchers, activists, institutions, and governments into a more sustainable agriculture. However, cut flower bucket creating and engaging in sustainable agriculture is challenging because it necessarily grapples with complexity from the natural ecosystems it must function within as well as the social ecologies that govern the morals, standards, and markets that shape the agrifood system. The most notable effort towards sustainable agriculture among institutions, researchers, and activists is to reframe agriculture as an agroecosystem . An agroecosystem, sometimes called an agricultural ecosystem, is defined as a site or integrated region of agriculture production understood as an ecosystem and is characterized as “ a hierarchy ascending from the level of the individual plant or animal all the way to national systems linked by international trade” . This dissertation research supports the formation of local agroecosystems by grassroots sustainable agriculture activists. Specifically, I explore how grassroots sustainable agriculture communities of practice can aggregate distributed knowledge necessary for sustainable polyculture design. Sustainable polycultures are assemblages of complementary and mutually beneficial plant species, typically composed primarily of perennials, and are one kind of food- and other provision-producing construct in an agroecosystem. A community of practice is defined by Eckert as “a collection of people who engaPermaculture also manipulates human-created outputs into services for their ecosystem. ge on an ongoing basis in some common endeavor.” Members of a community of practice know each other and use similar language, routines, and tools in context of forming and contributing to the community . This dissertation engages with permaculture and agroecology – the philosophical and scientific underpinnings of the two participating grassroots sustainable agriculture communities. Permaculture is an ecological design philosophy and social movement that encourages people to provide for their own food, energy, shelter, and other material and non-material needs in a sustainable way .
Permaculture utilizes services of the encompassing natural environment for people to generate their material and nonmaterial needs. Agroecology is an agricultural practice and scientific field that applies ecology to agriculture . In building sustainable agroecosystems, agroecologists manipulate the flow of agricultural inputs and outputs in a way that is supported by and supports the encompassing ecosystem . In both permaculture and agroecology, the designed systems operate as a part of the ecosystem, both utilizing the resources and services provided by their ecosystems in an ethical, measured way, and also conscientiously accounting for the outputs.The philosophical and scientific underpinnings of the participating communities frequently clashed with the values embedded in the information technologies they adopted, including ones used to look for and manage plant information. Although ITs are well-suited to address the information complexities the participating communities encounter, many current IT initiatives, while well-meaning, fail to enact real-world change because they neglect deep engagement with their communities. The many facets of HCI research, such as action research, participatory research, activist research, and valuesensitive design, are well-suited to deeply engage with communities in the design of IT. This dissertation aims to provide an example of how to involve communities in the development of IT artifacts for sustainable agriculture and strengthen efforts around the globe that support sustainability via technological interventions.The grassroots sustainable agriculture communities that participated in this research featured sustainable polycultures as the foundational element of their agroecosystem designs. In terms of ecosystem organization, a sustainable polyculture is equivalent to a community of living organisms within an agroecosystem, meaning an assemblage of a various species living together in a particular place and interacting with each other. Sustainable polycultures have species in many vertical layers, optimizing the uses of space and services from other plants like shade or soil stabilization . Other elements include those that support sustainable polycultures, such as a grey water system . Greywater systems were used to water fruit trees, which are often require more water than other species, in sustainable polycultures.Sustainable polycultures mimic natural ecosystems. Natural ecosystems are complex adaptive systems with high species and genetic diversities and complex trophic interactions. Sustainable polycultures require a similar degree of complexity to maintain the properties of natural ecosystems, like trophic interactions, that are beneficial for growing crops . Newcomers to the concept of sustainable polycultures often find their complexity and appeal difficult to understand without a visceral experience. The next section presents two examples of sustainable polycultures in different settings and ecosystems that have been used in a community or literature as a concept introduction.This section presents two examples of sustainable polycultures. The first is a representation of sustainable polycultures as observed and written by Brad Lancaster in the Sonoran Desert. His depiction of a mesquite-based sustainable polyculture for agricultural production, which he refers to as a guild in the text, is based on his and a mentor’s observations of plant-ecosystem relationships in the wild. The second is an example scenario that attempts to demonstrate both the complexity and appeal of a sustainable polyculture in Central Florida. Alex Stringfellow, an early participant of this research, and I envisioned and authored this scenario todemonstrate a sustainable polyculture’s complexity and nature in a backyard setting – a setting that was common in the grassroots communities.Creating an implementable sustainable polyculture design requires designers to identify one or more key species to serve as the underpinning of the sustainable polyculture. The key species has to be suitable for the environment and typically has some significant human value . The designer then performsa functional analysis to identify the key species’ intrinsic characteristics, needs, and products or services. A species’ needs are its inputs, including sunlight, water, and nutrients. A species’ products or services are its outputs, such as fruit, shade, mulch, protection from wind, and pest-deterring oils.