LINKing chrysophyte resting stages to their species by correlating DNA sequences

Chrysophytes (classes Chrysophyceae and Synurophyceae) produce siliceous resting stages (stomatocysts) that are known to be powerful indicators of past environmental conditions (e.g., climate). These stomatocysts are not yet, for the most part, linked to their species. Stomatocysts are therefore identified as numbered morphotypes, i.e., an artificial taxonomy based on their morphology. This causes taxonomic uncertainties and errors in the indicator- based reconstructions. Furthermore, the autecological information from the species cannot be used in paleoecological studies. This project aims to link stomatocysts to the species that produce them by correlating DNA sequences from both. Stomatocysts will be obtained from cultures and field samples. DNA from single stomatocysts will be amplified by polymerase chain reaction (PCR), cleaned and re-amplified (if necessary), sequenced, and aligned with existing sequences for chrysophyte species using phylogenetic analysis. The sequences of interest are the nuclear-encoded SSU rRNA and the chloroplast-encoded rbcL genes. After PCR amplification, the stomatocyst used for each amplification will be identified by scanning electron microscopy. DNA sequences from identified stomatocysts will be stored in a database. Stomatocysts with an orphan sequence (sequence for the species not yet identified) can thus be assigned to their species as soon as the sequence becomes available, without further laboratory work. This study will help to evaluate the artificial stomatocyst taxonomy, and the ecology and paleoecology from the stomatocysts will be compared with autecological data from each species. It will help to improve paleoenvironmental reconstructions based on stomatocysts. The project will provide a sound method for linking vegetative and resting stages that can also be applied to other organisms.