Protoperidinium minutum (Dinophyceae) from Portugal: cyst–theca relationship and phylogenetic position on the basis of single-cell SSU and LSU rDNA sequencing

Abstract

Ribeiro S., Lundholm N., Amorim A. and Ellegaard M. 2010. Protoperidinium minutum (Dinophyceae) from Portugal: cyst–theca relationship and phylogenetic position on the basis of single-cell SSU and LSU rDNA sequencing. Phycologia 49: 48–63. DOI: 10.2216/09-11.1

Round brown spiny cysts are common elements of Recent and Quaternary dinoflagellate cyst records and are often used to infer past climate conditions. Echinidinium and Islandinium, two cyst-based genera composed of round brown spiny cysts, are believed to have affinities within the Protoperidiniaceae. However, their biological counterparts are still virtually unknown. In this study, we examined the cyst–theca relationship of an Echinidinium-like cyst isolated from recent sediments of the Portuguese coast. The cysts (25–34 µm) had an intercalary theropylic archeopyle and numerous processes (4–9 µm) with tapered stems and minutely expanded tips. Germinated cells were identified as Protoperidinium minutum on the basis of theca morphology and tabulation. This taxon has a complicated taxonomic history and most likely represents a complex of species with very similar thecae but different cyst morphologies. To provide a first step in elucidating the phylogeny of P. minutum and its evolutionary relationship among the Protoperidiniaceae, we undertook the first molecular study of this taxon on the basis of small-subunit (SSU) and large-subunit (LSU) ribosomal (r)DNA genetic sequences obtained through single-cell polymerase chain reaction. On the basis of SSU rDNA analysis, P. minutum formed a clade together with the Diplopsaloideae, not grouping together with the other Protoperidinium species. LSU rDNA-based phylogenies indicate P. minutum as early divergent within the Protoperidiniaceae. The evolutionary significance of round brown spiny cysts produced by P. minutum-like species and diplopsalids is discussed.

Key Words::

• Cyst–theca relationship
• Diplopsaloideae
• Dinoflagellate cysts
• Echinidinium
• Islandinium
• LSU
• Protoperidiniaceae
• Protoperidinium minutum
• Single-cell PCR
• SSU

ACKNOWLEDGMENTS

SR is grateful to Mårten Flø Jørgensen for advice regarding the molecular work. Paula Campos and Tom Gilbert from Eske Willerslev's Ancient DNA and Evolution Research Group are thanked for facilitating access to the Clean Lab. Gert Hansen helped with recommendations for the SEM and Jens Høeg kindly operated the Z-drive-equipped microscope. Øjvind Moestrup, António Calado and Yuri Oklodkov are acknowledged for useful comments and for sharing their literature collections. Henning Knudsen and Mikako Sasa kindly translated literature from the Japanese. This work has been partially financed through the project “Changes in community structure and microevolution in marine protists” by the Danish Research Council, and project HABCOL (PDCT/MAR/60086/2004) by the Portuguese Foundation for Science and Technology. SR holds a PhD scholarship from the Portuguese Foundation for Science and Technology (SFRH/BD/30847/2006). Two anonymous reviewers are acknowledged for their comments, which helped to improve the manuscript.