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

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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.