Phylogenetic analyses of Symbiodinium isolated from Waminoa and their anthozoan hosts in the Ryukyu Archipelago, southern Japan

Abstract

It is known that the genus Waminoa (order Acoela, Family Convolutidae) associates with anthozoans (Scleractinia, Octocorallia, Zoantharia) and feeds on the mucus of their host. Despite the close relationship between Waminoa and its host species, it is known from phylogenetic analyses of sequences of the internal transcribed spacer 2 of ribosomal DNA (ITS-2) that photosymbiotic Symbiodinium isolated from Waminoa are different from the Symbiodinium of their anthozoan hosts. Additionally, Waminoa inherit their Symbiodinium and Amphidinium via vertical transmission. In the current study, we looked for and collected Waminoa from different anthozoan hosts from the Ryukyu Archipelago in southern Japan, and then examined the Symbiodinium of Waminoa as well as hosts’ Symbiodinium, and utilized sequences of the hyper-variable non-coding region of the plastid minicircle (psbAncr) in order to re-examine the diversity of Symbiodinium within Waminoa. In the resulting psbAncr phylogenetic tree, all Symbiodinium within Waminoa comprised a unique group within Clade C, all with the same genotype in the psbAncr phylogenetic tree. Our results reconfirm that most Waminoa host their own lineage of Symbiodinium, and demonstrate that Waminoa are also found on azooxanthellate anthozoan hosts, as we found Waminoa on Siphonogorgia sp., expanding their potential known habitat. Additionally, two Symbiodinium from Waminoa from both shallow (4 m) and mesophotic (32 m) depths were not included in main group of Symbiodinium from Waminoa in the ITS-2 phylogenetic tree, although we could not acquire psbAncr sequences for these specimens. Therefore it is possible that undetected Symbiodinium diversity may yet exist within Waminoa, and future work at shallow to mesophotic depths examining both zooxanthellate and azooxanthellate hosts may find more Waminoa and Symbiodinium diversity.