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

本研究以有孔虫和红藻之间的共生关系为研究对象，通过系统发育比较，阐明了这种共生关系的起源和维持机制。以前，共生红藻被鉴定为紫球藻。分子系统发育分析结果表明，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（P.purpureum）不同，而紫球藻与共生体完全相同。另一方面，与红藻共生的有孔虫也是单系的。这些结果表明，在古Peneroplidae有孔虫中与红藻共生体的共生是单一起源的。但同一地区不同有孔虫种共生藻之间的遗传距离较近，而同一地区不同有孔虫种共生藻之间的遗传距离较远。因此，寄主有孔虫可能通过多次转换共生体扩大了其分布范围和生境。

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.