DISSERTATION RESEARCH: Evolution of hyperaccumulation in wild Helianthus: a phylogenetically explicit assessment of evolutionary history and adaptive hypotheses

超过500种开花植物是金属超积累者，这意味着它们有能力将高浓度的通常有毒的金属吸收到它们的茎组织中。这种自然能力可以用于有用的技术应用，包括植物修复（利用植物清理污染地区的环境）以及生物强化（用铁等关键营养物质丰富作物）。本研究的主要目的是了解金属超积累能力的发展如何依赖于金属耐受性，以及金属超积累能力如何对野生植物有益。过度积累对植物的好处包括减少草食和疾病，提高耐旱性和减少竞争。这项研究将使用太阳花属（向日葵）来测试这些提议的好处，太阳花属是一组在北美栖息地发现的多种物种。许多人都知道向日葵是农业和园艺上重要的作物品种，向日葵本身就是至少五种不同重金属的超积累者。本研究不仅可以提高我们对植物生态学的认识，还将为向日葵的改良育种和技术应用提供直接的认识。本文以35种野生向日葵品种为研究对象，通过温室操作研究，建立了由10个不同处理水平组成的土壤镍梯度，分析了耐受性和超积累的进化相互作用。超积累的假定成本和收益将在温室实验中进行检验，该实验将量化与健身相关的成本，同时评估五种主要的适应性假设。一个系统发育明确的方法来研究金属超富集的演化可以显著地提高对金属超富集的生态和进化背景的理解。更广泛地说，这项研究将促进新出现的进化毒理学领域的进一步发展，并将实施新的系统发育比较方法来评估环境响应特性，允许改进一系列工具来解决现有和新出现的环境问题。

Over 500 species of flowering plants are metal hyperaccumulators, meaning they possess the ability to take up extremely high concentrations of normally toxic metals into their shoot tissues. This natural ability may be harnessed for useful technological applications, including phytoremediation (the use of plants for environmental cleanup of polluted areas) as well as biofortification (the enrichment of crops with key nutrients like iron). The broad objective of the proposed research is to understand how the development of metal hyperaccumulation ability depends on metal tolerance, and how hyperaccumulation ability may benefit wild plants. Proposed benefits of hyperaccumulation to plants have included reduced herbivory and disease, improved drought tolerance, and reduced competition. This research will test these proposed benefits using the genus Helianthus (the sunflowers), a group of diverse species found in habitats across North America. Sunflowers are known to many for the agriculturally and horticulturally important crop species Helianthus annuus, which is itself a known hyperaccumulator of at least five different heavy metals. In addition to improving our understanding of plant ecology, this research will provide direct insights into hyperaccumulator physiology for the improved breeding and use of sunflower in technological applications.The evolutionary interactions of metal tolerance and metal hyperaccumulation will be assessed using 35 wild Helianthus species, through a manipulative greenhouse study generating a soil nickel gradient consisting of ten separate treatment levels, in which the evolution of tolerance and hyperaccumulation are parsed apart as separate and distinct traits. The putative costs and benefits of hyperaccumulation will be examined in greenhouse experiments which will quantify fitness-related costs while simultaneously evaluating five leading adaptive hypotheses. A phylogenetically explicit approach to the study of metal hyperaccumulation evolution can dramatically improve the understanding of the ecological and evolutionary context of metal hyperaccumulation. More broadly, this research will promote further development of the newly emerging field of evolutionary toxicology and will implement novel phylogenetic comparative methods for assessing environmentally responsive traits, allowing for an improved range of tools to address existing and emerging environmental concerns.