Dissertation Research: Biogeography of the Conyzinae and theEvolution of Agamospermy

在印第安纳大学Loren riesberg教授的指导下，研究生Richard Noyes正在研究向日葵亚族Conyzinae中约500种代表物种的系统发育关系，包括Erigeron （fleabanes）和Conyza （horseweeds）。据推测，Conyzinae起源于南美洲并向北传播，根据这些研究人员的初步DNA序列证据，Conyzinae的起源似乎是北美的一个向日葵群，它们已经向南传播到其他大陆，部分是作为不受精而播种的杂草（这种情况被称为无精子——蒲公英是一个更广为人知的例子）。进一步的野外样本采集、核基因（核糖体ITS区）和叶绿体基因（ndhF）的分子测序以及对传统形态特征的进一步研究将有助于该群体的系统发育重建。反过来，这种谱系框架有助于确定这些植物的地理迁移和进化轨迹，以及无精子条件的起源数量。美洲和非洲fleabane及其近亲的系统发育得到充分支持，将改善该群体的分类，并为鉴定提供可靠的标记。此外，研究还可以在有利于无精子起源的生态条件上取得进展，无精子是一种特殊的无性繁殖模式，已知存在于大型向日葵家族的几个谱系中。

9701347 Rieseberg Graduate student Richard Noyes, under the direction of Prof. Loren Rieseberg at Indiana University, is studying the phylogenetic relationships of representatives of the c. 500 species of the sunflower subtribe Conyzinae, including Erigeron (fleabanes) and Conyza (horseweeds). Presumed to have originated in South America and spread northward, the Conyzinae appear instead to be a Nopth American group of sunflowers in origin, based on preliminary DNA sequence evidence from these researchers, which have spread southward and to other continents, in part as weeds that set seed without fertilization (a condition named agamospermy--dandelions being the better known example). Additional field collecting of samples, followed by molecular sequencing of a nuclear gene (ribosomal ITS regions) and a chloroplast gene (ndhF) and further study of traditional morphological characters, are tasks that will lead to phylogenetic reconstructions for the group. In turn, that genealogical framework facilitates the determination of geographical migrations and tracks in the evolution of these plants, and of the number of origins of the agamospermous condition. A well supported phylogeny of the fleabanes and their relatives, for the Americas and Africa, will improve classification of the group and provide reliable markers for identification. Also, studies can then progress on the ecological conditions favoring the origin of agamospermy, a peculiar asexual mode of seed production known in several lineages of the large sunflower family.