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Where should we draw the lines between dinocyst “species”? Morphological continua in Black Sea dinocysts
Copyright policy )Abstract. The morphology of dinoflagellate cysts (dinocysts) is related not only to the genetics of the motile dinoflagellate from which it derives, but is also dependent on a range of environmental factors including salinity, temperature and nutrient status. Although this knowledge improves our understanding of the drivers behind dinocyst morphological variations, it makes the taxonomy governing their description somewhat complex. In basins such as the Black Sea, where environmental change can be extreme and occurs on relatively short (millennial) timescales, taxonomy becomes particularly challenging. Morphological continua can be observed between described forms, displaying a large range of intermediate phenotypes that do not necessarily correspond to any genetic difference. As these morphological nuances may preserve information about palaeoenvironments, it is important to find a systematic method of characterising morphotypes. Here, we show a dinocyst matrix within which dinocysts are described according to their similarity to (or difference from) described forms based on key descriptive parameters. In the example set out here, cyst shape and degree of process and/or ectophragm development are taken as two key parameters in Pyxidinopsis psilata and Spiniferites cruciformis, and can allow the description of intermediate forms even though the definitions do not overlap. We review some frequently occurring morphotypes and propose that using matrices to show the gradual variation between endmember forms is the most pragmatic approach until cyst–theca studies and genetic sequencing can be used to demonstrate relationships between genotypes and morphotypes. As prior studies propose salinity to be a primary driver of intraspecific variability, the endmembers presented may represent salinity extremes within an overall brackish environment. Although we cannot assign each morphotype to a value or a range of an environmental parameter (e.g. salinity) as the different morphotypes can occur in the same sample, using this matrix allows preservation of information about morphological variability without creating taxonomic categories that are likely to require alteration if genetic evidence becomes available.
Microsoft Academic Graph classification: Taxonomic rank Evolutionary biology Brackish water Endmember Environmental change Dinoflagellate biology.organism_classification biology Salinity Dinocyst Intraspecific competition
Library of Congress Subject Headings: lcsh:Geology lcsh:QE1-996.5
Paleontology
Paleontology
Microsoft Academic Graph classification: Taxonomic rank Evolutionary biology Brackish water Endmember Environmental change Dinoflagellate biology.organism_classification biology Salinity Dinocyst Intraspecific competition
Library of Congress Subject Headings: lcsh:Geology lcsh:QE1-996.5
- Department of Earth Sciences Faculty of Geosciences Utrecht University Netherlands
- University of Bristol (UoB) United Kingdom
- Utrecht University Netherlands
- University of Bristol United Kingdom
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Bijl, P. K., Brinkhuis, H., Egger, L. M., Eldrett, J. S., Frieling, J., Grothe, A., Houben, A. J. P., Pross, J., Kasia, K. S´ ., and Sluijs, A.: Comment on “Wetzeliella and Its Allies - the “Hole” Story: A Taxonomic Revision of the Paleogene Dinoflagellate Subfamily Wetzelielloideae” by Williams et al. (2015)”, Palynology, 41, 423-429, 2016.
Bista, D., Hoyle, T. M., Sangiorgi, F., and Flecker, R.: The connectivity history of the Black Sea over the last 1.2 million years, in preparation, 2019.
Boere, A. C., Rijpstra, W. I. C., De Lange, G. J., Sinninghe Damsté, J. S., and Coolen, M. J. L.: Preservation potential of ancient plankton DNA in Pleistocene marine sediments, Geobiology, 9, 377-393, https://doi.org/10.1111/j.1472-4669.2011.00290.x, 2011. [OpenAIRE]
Corradini, D. and Biffi, U.: Dinocyst study at the MessinianPliocene boundary in the Cava Serredi section, Tuscany, Italy, Bull. des centres Rech. Explor. Elf-Aquitaine, 12, 221-236, 1988.
de Vernal, A. and Marret, F.: Organic-Walled Dinoflagellate Cysts: Tracers of Sea-Surface Conditions, in: Developments in Marine Geology, Proxies in Late Cenozoic Paleoceanography, Vol. 1, edited by: Hillaire-Marcel, C. and de Vernal, A., 371-408, Elsevier, Oxford, 2007.
Ellegaard, M., Lewis, J., and Harding, I. C.: Cyst-theca relationship, life cycle and effects of temperature and salinity on the cyst morphology of Gonyaulax baltica sp. nov. (Dinophyceae) from the Baltic Sea area, J. Phycol., 38, 775-789, 2002.
Ellegaard, M., Dale, B., Mertens, K. N., Pospelova, V., and Ribeiro, S.: Dinoflagellate Cysts as Proxies for Holocene Environmental Change in Estuaries: Diversity, Abundance and Morphology Marianne, in: Applications of Paleoenvironmental Techniques in Estuarine Studies, Developments in Paleoenvironmental Research 20, Vol. 20, edited by: Weckström, K., Saunders, K., Gell, P., and Skilbeck, G., 295-312, Springer, Dordrecht, the Netherlands, 2017.
Evitt, W. R., Gocht, H., and Netzel, H.: Gonyaulax cysts from Lake Zrich sediments, Rev. Palaeobot. Palyno., 45, 35-46, 1985.
Fensome, R. A., Taylor, F. J. R., Norris, G., Sargeant, W. A. S., Wharton, D. I., and Williams, G. L.: A classification of living and fossil dinoflagellates. Micropaleontology, Special publication no. 7, Sheridan Press, Hanover, Pennsylvania, USA, 1993.
Ferguson, S., Warny, S., Escarguel, G., and Mudie, P. J.: MIS 5-1 dinoflagellate cyst analyses and morphometric evaluation of Galeacysta etrusca and Spiniferites cruciformis in southwestern Black Sea, Quaternary Int., 465, 117-129, https://doi.org/10.1016/j.quaint.2016.07.035, 2018.
- Department of Earth Sciences Faculty of Geosciences Utrecht University Netherlands
- University of Bristol (UoB) United Kingdom
- Utrecht University Netherlands
- University of Bristol United Kingdom
Abstract. The morphology of dinoflagellate cysts (dinocysts) is related not only to the genetics of the motile dinoflagellate from which it derives, but is also dependent on a range of environmental factors including salinity, temperature and nutrient status. Although this knowledge improves our understanding of the drivers behind dinocyst morphological variations, it makes the taxonomy governing their description somewhat complex. In basins such as the Black Sea, where environmental change can be extreme and occurs on relatively short (millennial) timescales, taxonomy becomes particularly challenging. Morphological continua can be observed between described forms, displaying a large range of intermediate phenotypes that do not necessarily correspond to any genetic difference. As these morphological nuances may preserve information about palaeoenvironments, it is important to find a systematic method of characterising morphotypes. Here, we show a dinocyst matrix within which dinocysts are described according to their similarity to (or difference from) described forms based on key descriptive parameters. In the example set out here, cyst shape and degree of process and/or ectophragm development are taken as two key parameters in Pyxidinopsis psilata and Spiniferites cruciformis, and can allow the description of intermediate forms even though the definitions do not overlap. We review some frequently occurring morphotypes and propose that using matrices to show the gradual variation between endmember forms is the most pragmatic approach until cyst–theca studies and genetic sequencing can be used to demonstrate relationships between genotypes and morphotypes. As prior studies propose salinity to be a primary driver of intraspecific variability, the endmembers presented may represent salinity extremes within an overall brackish environment. Although we cannot assign each morphotype to a value or a range of an environmental parameter (e.g. salinity) as the different morphotypes can occur in the same sample, using this matrix allows preservation of information about morphological variability without creating taxonomic categories that are likely to require alteration if genetic evidence becomes available.