Speciation in the genus Stevia of Mexico and Brazil

在现代植物系统学中，一个有趣的挑战是通过重建几乎所有物种之间的系统发育关系，为具有明显适应性差异的特定植物类群建立一个综合案例研究。甜菊属（Asteraceae; Eupatorieae）因其在生活史性状和生殖系统上具有极高的差异性，为此类研究提供了很好的机会。我们已经研究了墨西哥种之间的系统发育关系，但以下问题仍未得到解答。这个项目的目的是通过在墨西哥和巴西进行一系列的实地考察来收集回答这些问题的材料。(1)极多态物种甜菊糖究竟是一个单一的生物物种，还是一些隐种的复合体？(2)巴西有无精子多倍体吗？(3)墨西哥和巴西的物种是如何相互关联的？为了回答问题(1)，我们在墨西哥的杜兰戈、哈利斯科、米却肯、格雷罗和瓦哈卡州进行了实地调查。结果表明，在5个不同的地区发现了2种以上的隐性二倍体物种共存。AFLP分析表明，两对隐种的分化是由于适应岩石生境的不同环境条件而产生的，而两对不同生态生境的隐种则是在系统发育的基础上产生分化的。这些结果表明，甜菊糖自其起源以来，在不同的环境条件下不断分化。为了回答问题(2)，我们在巴西的圣保罗州、圣卡塔琳娜州和巴西南大州进行了实地调查。为了回答上述问题(3)，我们利用ITS序列构建了甜叶菊墨西哥种和巴西种的系统发育树。结果表明巴西种为墨西哥甜菊属的一个分支。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