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[BCG05-02] Seasonal change in composition of algal genetic types, symbionts of a planktonic foraminifer
Keywords:planktonic foraminifera, algal symbiont, photosymbiosis, genetic type
Some planktonic foraminiferal species establish a nutritionally interdependent photosymbiosis with autotrophic microalgae. Photosymbiosis plays an important role for habitat selection of host. However, host-symbiont specificity in planktonic foraminifera has remained unclear because a same genetic type of algal symbiont was found over different planktonic foraminiferal species and geological distant areas (Shaked and de Vargas, 2006). Planktonic foraminifera digest algal symbionts as a source of nutrients for gametogenesis during their about one-month life cycle, suggesting that descendants could acquire microalgae from the environment after reproduction, though the species compositions of microalgae are different from each other in season and region. Given that host-symbiont association is not tight, genetic type composition of microalgal symbionts in planktonic foraminifera could vary with season and/or generation. Here, we examined genetic type composition of microalgal symbionts in a single planktonic foraminiferal species between summer and winter to show the seasonal changes of host-symbiotic relationship.
We focused on symbiotic dinoflagellate Pelagodinium beii in a planktonic foraminifer, Globigerinoides ruber Type Ia, collected from the Tosa Bay, Kochi Prefecture, Japan, in summer and winter. The genetic types of P. beii were identified based on the phylogenetic analysis of the 5.8S to large subunit (LSU) ribosomal DNA (rDNA) sequences. We identified five genetic types among each of 119 microalgal symbiont clones from 6 summer host individuals and 64 from 8 winter host individuals. Two P. beii genetic types were commonly found in both summer and winter, but three others were identified either in summer or winter. Moreover, two out of three genetic types were newly found in this study. Thus, P. beii shows high genetic diversity indicating the presence of new and unknown genetic types in the Northwest Pacific Ocean, where poor investigations have been conducted for microalgal symbionts in planktonic foraminifera. The composition difference of P. beii genetic types between summer and winter suggests that the host-symbiotic relationship could vary among seasons. Furthermore, most planktonic foraminiferal individuals contained a single genetic type of P. beii, suggesting that the host maintains a same microalgae after uptake from environment. As planktonic foraminifera supply nitrogen to microalgae symbionts through the host-symbiont interactions (LeKieffre et al., 2020), they could control the growth of algal symbionts during their life cycle, thereby ensuring a photosymbiosis system even in a vast expanse of ocean. Our findings showed that planktonic foraminifera have a somewhat flexibility in host-symbiont relationship, whereas they seem not to repeat free-living microalgae from environment. Such host-symbiont association may be benefit for planktonic foraminifera to obtain nutrient in oligotrophic pelagic oceans.
References
LeKieffre, C., Spero, H. J., Fehrenbacher, J. S., Russell, A. D., Ren, H., Geslin, E., & Meibom, A. (2020). Ammonium is the preferred source of nitrogen for planktonic foraminifer and their dinoflagellate symbionts. Proceedings of the Royal Society B: Biological Sciences, 287.
Shaked, Y., & De Vargas, C. (2006). Pelagic photosymbiosis: rDNA assessment of diversity and evolution of dinoflagellate symbionts and planktonic foraminiferal hosts. Marine Ecology Progress Series, 325, 59-71.
We focused on symbiotic dinoflagellate Pelagodinium beii in a planktonic foraminifer, Globigerinoides ruber Type Ia, collected from the Tosa Bay, Kochi Prefecture, Japan, in summer and winter. The genetic types of P. beii were identified based on the phylogenetic analysis of the 5.8S to large subunit (LSU) ribosomal DNA (rDNA) sequences. We identified five genetic types among each of 119 microalgal symbiont clones from 6 summer host individuals and 64 from 8 winter host individuals. Two P. beii genetic types were commonly found in both summer and winter, but three others were identified either in summer or winter. Moreover, two out of three genetic types were newly found in this study. Thus, P. beii shows high genetic diversity indicating the presence of new and unknown genetic types in the Northwest Pacific Ocean, where poor investigations have been conducted for microalgal symbionts in planktonic foraminifera. The composition difference of P. beii genetic types between summer and winter suggests that the host-symbiotic relationship could vary among seasons. Furthermore, most planktonic foraminiferal individuals contained a single genetic type of P. beii, suggesting that the host maintains a same microalgae after uptake from environment. As planktonic foraminifera supply nitrogen to microalgae symbionts through the host-symbiont interactions (LeKieffre et al., 2020), they could control the growth of algal symbionts during their life cycle, thereby ensuring a photosymbiosis system even in a vast expanse of ocean. Our findings showed that planktonic foraminifera have a somewhat flexibility in host-symbiont relationship, whereas they seem not to repeat free-living microalgae from environment. Such host-symbiont association may be benefit for planktonic foraminifera to obtain nutrient in oligotrophic pelagic oceans.
References
LeKieffre, C., Spero, H. J., Fehrenbacher, J. S., Russell, A. D., Ren, H., Geslin, E., & Meibom, A. (2020). Ammonium is the preferred source of nitrogen for planktonic foraminifer and their dinoflagellate symbionts. Proceedings of the Royal Society B: Biological Sciences, 287.
Shaked, Y., & De Vargas, C. (2006). Pelagic photosymbiosis: rDNA assessment of diversity and evolution of dinoflagellate symbionts and planktonic foraminiferal hosts. Marine Ecology Progress Series, 325, 59-71.