Ecological and genetical mechanisms of hybrid speciation in the genus Trillium

Trillium属是温带林地的代表性植物之一，目前在北美和东亚（包括日本）之间呈不间断分布。该属共有46种，已知有10种分布在东亚。在这些东亚种中，有8种分布在日本的北海道。此外，根据染色体研究，我们还知道这8个物种由3个物种和5个杂交和/或杂交衍生物种组成，它们形成多倍体系列，2x, 3x, 4x, 6x。相比之下，所有的北美物种都是二倍体。为了阐明东亚万元林自然杂交和物种形成的生态机制，本文以三倍体T. hagae （T.*hagae）为研究对象，该物种是二倍体T. kamtschschaticum和四倍体T.tschonoskii之间的自然杂交物种。这种杂交物种通常发生在亲本种共生生长的地方。本研究对三种疣子属植物的育种体系、开花个体的空间分布格局和开花物候特征进行了实地考察，并对其细胞质DNA进行了RFLP分析。结果表明，hagae主要是由T.kamtschaticum（母系）和T.tschonoskii（父系）杂交而来。

The genus Trillium is one of the representative temperate woodland elements which currently show disjunct distribution between North America and eastern Asia including Japan. The genus consists of 46 species and 10 species are known to occur in eastern Asia. Of those eastern Asiatic, species, eight species occur in Hokkaido, Japan. Furthemore, based on the chromosome studies, it has been also known that the eight species consist of three species and five hybrid and/or hybrid derivative species from putative hybridization among the three basic species, and they form polyploid series, 2x, 3x, 4x, 6x. By contrast, all of the North America species are known to be diploid.In order to clarify the ecological mechanisms of natural hybridization and speciation in the eastern Asiatic Trillium, I focused on T.*hagae (triploid species), which is a natural hybrid species between T.kamtschaticum (diploid species) and T.tschonoskii (tetraploid species). This hybrid species commonly occurs where both parental species grow sympatrically. In this study, breeding system, spatial distribution patterns of flowering individuals and flowering phenology of the three Trillium species were examined in the field, and RFLP analysis of cytoplasmic DNA was also employed. As a result, it was suggested that T.hagae is predominantly derived from the hybridization between T.kamtschaticum (maternal) and T.tschonoskii (paternal).