High-Level Congruence of Myrionecta rubra Prey and Dinophysis Species Plastid Identities as Revealed by Genetic Analyses of Isolates from Japanese Coastal Waters

We analyzed cryptophyte nucleomorph 18S rRNA gene sequences retained in naturalMyrionecta rubra cells and plastid 16S rRNA gene andpsbA sequences retained in natural cells of severalDinophysis species collected from Japanese coastal waters. A total of 715 nucleomorph sequences obtained from 134M. rubra cells and 564 plastid 16S rRNA gene and 355psbA sequences from 71Dinophysis cells were determined. Almost all sequences inM. rubra andDinophysis spp. were identical to those ofTeleaulax amphioxeia , suggesting thatM. rubra in Japanese coastal waters preferentially ingestT .amphioxeia . The remaining sequences were closely related to those ofGeminigera cryophila andTeleaulax acuta . Interestingly, 37 plastid 16S rRNA gene sequences, which were different fromT. amphioxeia and amplified fromDinophysis acuminata andDinophysis norvegica cells, were identical to the sequence of aD. acuminata cell found in the Greenland Sea, suggesting that a widely distributed and unknown cryptophyte species is also preyed upon byM. rubra and subsequently sequestered byDinophysis . To confirm the reliability of molecular identification of the cryptophyteTeleaulax species detected fromM. rubra andDinophysis cells, the nucleomorph and plastid genes ofTeleaulax species isolated from seawaters were also analyzed. Of 19 isolates, 16 and 3 clonal strains were identified asT. amphioxeia andT. acuta , respectively, and no sequence variation was confirmed within species.T. amphioxeia is probably the primary source of prey forM. rubra in Japanese coastal waters. An unknown cryptophyte may serve as an additional source, depending on localities and seasons.