Speciation in the genus Stevia of Mexico and Brazil

现代植物系统学中一个有趣的挑战是建立一个针对特定植物组的综合案例研究，通过重建该组中几乎所有物种之间的系统发育关系来显示显著的适应性差异。甜叶菊属(Asteraceae；Eupatorieae)为此类研究提供了一个很好的机会，因为它在生活史特征和生殖系统上具有极高的差异性。我们已经研究了墨西哥物种之间的系统发育关系，但以下问题仍未得到回答。这个项目的目的是通过在墨西哥和巴西进行一系列田间试验来收集材料来回答这些问题。(1)极端多态的甜叶菊是单个生物物种还是一些神秘物种的复合体？(2)巴西是否存在无精子植物多倍体？(3)墨西哥和巴西物种之间是如何联系的？为了回答问题(1)，我们在…进行了实地调查。更多的墨西哥杜兰戈、哈利斯科、米却肯州、格雷罗州和瓦哈卡州。结果，在五个不同的地区观察到两个以上的隐二倍体物种共存。AFLP分析表明，两对隐名种由于适应不同岩石生境的环境条件而产生了新的分化，而处于不同生态环境中的两对隐种则在系统发育的基础上发生了分化。这些发现表明，自甜菊起源以来，它继续在不同的环境条件下分化。为了回答问题(2)，我们在巴西的圣保罗、圣卡塔琳娜和南里奥格兰德州进行了实地调查。对收集的材料进行细胞学检查，发现巴西甜菊属植物全部为有性二倍体。为了回答问题(3)，我们利用ITS序列构建了墨西哥和巴西甜菊属植物的系统发育树。结果表明，巴西种为墨西哥甜叶菊的一个分支。较少

An interesting challenge in modem plant systematics is to establish a synthetic case study for a particular group of plants that shows conspicuous adaptive divergence by reconstructing a phylogenetic relationship among almost all species of the group. The genus Stevia (Asteraceae; Eupatorieae) provides a good opportunity for such study because it contains extremely high divergence in life histry traits and reproductive systems.We already studied phylogenetic relationship among Mexican species, but the following questions remain unanswered. The purpose of this project was to collect materials for answering these questions by carrying out a series of field expecitions in Mexico and Brazil.(1)Whether an extremely polymorphic species Stevia origanoides is a single biological species or a complex of some cryptic species?(2)Is there any agamospermous polyploidy in Brazil?(3)How Mexican and Brazilian species are related to each other?To answer the question (1), we carried out field surveys in … More Durango, Jalisco, Michoacan, Guerrero and Oaxaca states of Mexico. As a results, co-occurrence of more than two cryptic diploid species was observed in five different areas. AFLP analysis showed that of two pairs of cryptic species were recently diverged as a result of adaptation to different environmental conditions of rocky habitats while two cryptic species in distinct ecological habitats were diverged at the base of phylogeny. These findings suggest that Stevia origanoides sensu lato continued to diverge to different environmental conditions since its origin.To answer the question (2), we carried out field surveys in Sao Paulo, Santa Catarina, and Rio Grande do Sul states of Brazil. Cytological examinations of the materials collected revealed that all species of Stevia in Brazil were sexual diploidsTo answer the question (3), we constructed a phylogenetic tree of Mexican and Brazilian species of Stevia by using ITS sequences. The results showed that Brazilian species is a branch of Mexican Stevia. Less