Integrated morphological and molecular genetic taxonomy in North Sea jellyfish
In collaboration with Dr. Silke Laakmann, research scientist in the DZMB working group
Molecular Taxonomy of Marine Organisms we combined morphological determinations of living and preserved jellyfish specimens with molecular genetic analyses.
Jellyfish (Scypho- and Hydromedusae) are widespread and diverse representatives of the gelatinous zooplankton and thus attract attention in many ecological and taxonomic studies. However, the correct identification of different developmental stages (see figure) and the adequate fixation of their gelatinous bodies are challenging tasks in jellyfish taxonomy. Most diagnostic features are still recognizable in sample material fixed in formaldehyde-seawater 4%. In contrast, fixation in ethanol, the most common preservative for later DNA analysis, causes distortion of morphological features often impeding a clear and valid identification of medusae.
This integrative taxonomic approach was realized successfully for more than 30 scypho- and hydromedusaen species occurring in the German Bight, North Sea (Laakmann & Holst 2013, Holst & Laakmann 2013). Molecular taxonomy provides an additional tool for species identification, particularly useful for the identification of stages with few diagnostic morphological features, for example young ephyrae. In addition genetic analysis are helpful for the discrimination of closely related species with a similar or identical morphology.
Our studies provide the link between morphological and molecular genetic discrimination and identification methods demonstrating the power of this integrated approach in cnidarian taxonomy. Based on our collection that includes morphological and DNA vouchers, mitochondrial and nuclear sequences, we are now able to identify ethanol-preserved species independently from the preserved tissue type and from the developmental stage of the specimen.