We investigate the cyst-theca relationship of Impagidinium caspienense. Through an incubation experiment, we succeeded in examining the motile stage. Additional molecular analysis of single-cyst PCR (LSU and SSU rDNA) reveal that the cyst is related to the species Gonyaulax baltica Ellegaard et al. (). The ability of this species to belong to two types of cyst-based genera (spiniferate and impagidinioid) suggests that environmental (particularly salinity) and not genetic factors explain the formation of both morphotypes by G. baltica, which provides evidence for heterospory in this species. The affiliation to G. baltica demonstrates that I. caspienense is not endemic to the Caspian Sea. The phylogenetic position of several other gonyaulacoid species is also documented: Impagidinium pallidum, Ataxiodinium choane, Pyxidinopsis psilata, Spiniferites belerius, and Spiniferites ramosus. The LSU and SSU rDNA based phylogenies suggest that the genera Impagidinium and Spiniferites are not monophyletic, and that P. psilata and A. choane are close to Gonyaulax verior and Gonyaulax polygramma, respectively. In addition, this study accentuates the importance of cyst morphology in the classification of the Gonyaulacales.
Bibliographical noteFunding Information:
K.N.M. thanks Anna Godhe for providing surface sediment from Kattegat, Marianne Ellegaard for assistance with SEM during his stay in Copenhagen, and David Wall for discussions regarding Ataxiodinium. The Natural Science and Engineering Research Council of Canada (NSERC) is acknowledged for partial funding of this project to V.P. (Discovery Grant). The VENUS (Victoria Experimental Network Under the Sea), ONC (Ocean Networks Canada), R/V Thompson, and ROPOS (Remotely Operated Platform, Canadian Scientific Submersible Facility) teams are thanked for their assistance with sample collection in the Strait of Georgia. A.J.P. acknowledges funding by a Marie Curie Integration Grant (FP7-PEOPLE-2011-CIG 304178) and NSERC (Discovery Grant). Two anonymous reviewers and the associate editor are acknowledged for constructive comments that improved the manuscript.
- Ataxiodinium choane
- Baltic Sea
- Impagidinium pallidum
- Pyxidinopsis psilata
- Spiniferites belerius
- Spiniferites ramosus