Dissertation Research: Phylogeny and evolution of C4 photosynthesis in Pectis (Asteraceae)

这项研究考察了Pectis的进化，Pectis是一种约有85种植物的属，发现于北美和南美洲炎热干燥的地区。许多Pectis物种的不同寻常之处在于，它们通过“C4光合作用”(而不是大多数植物使用的“C3光合作用”)从空气中吸收碳。C4过程允许植物在炎热、干燥和/或营养匮乏的条件下生长得更好。C4光合作用可能使Pectis比它的C3近亲更快地扩展到新的环境和多样化。孔藻(约.30种)是被认为与Pectis关系最密切的属。大约。115种Pectis和Porophyllum，仅有32种进行了C3或C4光合作用研究。该项目的目标是a)利用碳同位素分析确定其余83个物种是C3还是C4；b)通过比较它们的DNA来确定这两个属之间的进化关系；c)比较C3和C4物种之间的多样性比率；以及d)检验关于Pectis的分类学、生物地理学和C4光合作用进化的假设。这项研究将首次全面了解Pectis的进化关系，并将增加我们对C4光合作用进化的理解。尽管许多研究赞扬了C4光合作用的适应性优点，但这项研究将是第一次在统计上检验光合作用和物种形成速率之间的相关性。

This study examines the evolution of Pectis, a genus of approximately 85 plant species found in hot, dry areas of North and South America. Many Pectis species are unusual in that they take up carbon from the air via "C4 photosynthesis" (versus "C3 photosynthesis," which most plants use). The C4 process allows plants to grow better in hot, dry and/or nutrient-starved conditions. C4 photosynthesis may have allowed Pectis to expand into new environments and diversify more rapidly than its C3 relatives. Porophyllum (approx. 30 species) is the genus thought to be most closely-related to Pectis. Of the approx. 115 species of Pectis and Porophyllum, only 32 have been surveyed for C3 or C4 photosynthesis. The goals of this project are to a) determine, using carbon isotope analysis, whether the remaining 83 species are C3 or C4; b) determine the evolutionary relationships between and among the two genera by comparing their DNA; c) compare rates of diversification between C3 and C4 species; and d) test hypotheses regarding taxonomy, biogeography, and the evolution of C4 photosynthesis in Pectis. This study will provide the first comprehensive understanding of the evolutionary relationships in Pectis and will add to our understanding of the evolution of C4 photosynthesis. Although many studies extol the adaptive virtues of C4 photosynthesis, this study will be the first to test statistically a correlation between photosynthesis and speciation rates.