Elucidation of the symbiotic mechanism and its evolutional significance on the red algal symbiont in foraminifer.

本研究以有孔虫与红藻的共生为研究对象，对它们的系统发育进行了比较，以阐明这种共生的起源和维持机制。以前，共生红藻被鉴定为紫球藻。从分子系统发育分析的结果来看，从有孔虫中分离到的红藻共生体均为单系，与典型的紫球藻不同，与共生体完全相同。另一方面，含有红藻共生体的有孔虫也是单系。这些结果表明，古前有孔虫与红藻共生的单一来源。然而，同一地区不同有孔虫物种的红藻共生体之间的遗传距离比不同地区同一有孔虫物种的红藻共生体的遗传距离更近。因此，寄主有孔虫可能通过多次切换共生体扩大了分布范围和栖息地。

In this study, I focused on a symbiosis between a foraminifers and red algae, and conducted a phylogenetic comparisons among them to clarify the origin and maintenance mechanism of this symbiosis. Formerly, the symbiotic red algae were identified as Porphyridium purpureum. From the results of the molecular phylogenetic analysis, however, all red algal symbionts isolated from the foraminifers were monophyletic and different form typical P. purpureum, which was identical to symbiont. On the other hands, foraminifers having red algal symbionts were also monophyletic. Those results suggested that the single origin of the symbiosis with red algal symbiont in ancient Peneroplidaean foraminifer. However, genetic distances between red algal symbionts collected form different foraminiferan species in the same area were closer than those of the symbionts from same foraminiferan species in the different area. Therefore, the host foraminifers may have extended their distribution ranges and habitats with switching their symbionts in several times.