Abstract
Diplosoma virens is a colonial ascidian hosting prokaryotic algae Prochloron sp. in the common cloacal cavity of the colonies and is sometimes parasitized by notodelphyid copepods. In ascidian–Prochloron symbiosis, it is generally known that the host larvae acquire the algal symbionts from their mother colonies to maintain the symbiosis. A histological study of the sexually mature colonies of D. virens showed that the algal symbionts attach to pre-hatching larvae on the rastrum (plant rake) projected from the postero-dorsal part of the larval trunk, and then the rastrum is packed in the posterior half of the larval trunk that will become a cloacal cavity after metamorphosis. This process is the same as that of D. simile. Monthly sampling of D. virens colonies showed that they have embryos in summer in Ryukyus, situated near the northern-most limit of the coral reefs in the West Pacific. While the frequencies of copepod parasitism were variable among the populations, the colonies from a highly parasitized population had a significantly smaller number of eggs/embryos per zooid than the colonies from the less parasitized populations. The parasites probably have an inhibitory impact on the sexual reproduction of the host colonies.
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Acknowledgements
We wish to thank the staff members of the Tropical Biosphere Research Center (University of the Ryukyus)—especially Professor K. Fujimori (Iriomote Station) for his hospitality and Mr. Y. Nakano (Sesoko Station) for providing the temperature data. The present study was partly supported by the Japan–Australia Research Cooperative Program, Grant-in-Aid for Scientific Research (#16570081) from the Japan Society for the Promotion of Science, and the 21st Century COE Project of the University of the Ryukyus.
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Communicated by T. Ikeda, Hakodate
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Hirose, E., Oka, A.T. & Akahori, M. Sexual reproduction of the photosymbiotic ascidian Diplosoma virens in the Ryukyu Archipelago, Japan: vertical transmission, seasonal change, and possible impact of parasitic copepods. Marine Biology 146, 677–682 (2005). https://doi.org/10.1007/s00227-004-1469-5
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DOI: https://doi.org/10.1007/s00227-004-1469-5