The model marine diatom <it>Thalassiosira pseudonana </it>likely descended from a freshwater ancestor in the genus <it>Cyclotella</it>

• Main Authors: Julius Matthew L, Beszteri Bánk, Alverson Andrew J, Theriot Edward C
• Format: Article
• Language: English
• Published: BMC 2011-05-01
• Series: BMC Evolutionary Biology
• Subjects: <it>Cyclotella nana</it>; diatom; freshwater; marine; model species; <it>Thalassiosira pseudonana</it>
• Online Access: http://www.biomedcentral.com/1471-2148/11/125

<p>Abstract</p> <p>Background</p> <p>Publication of the first diatom genome, that of <it>Thalassiosira pseudonana</it>, established it as a model species for experimental and genomic studies of diatoms. Virtually every ensuing study has treated <it>T. pseudonana </it>as a marine diatom, with genomic and experimental data valued for their insights into the ecology and evolution of diatoms in the world's oceans.</p> <p>Results</p> <p>The natural distribution of <it>T. pseudonana </it>spans both marine and fresh waters, and phylogenetic analyses of morphological and molecular datasets show that, 1) <it>T. pseudonana </it>marks an early divergence in a major freshwater radiation by diatoms, and 2) as a species, <it>T. pseudonana </it>is likely ancestrally freshwater. Marine strains therefore represent recent recolonizations of higher salinity habitats. In addition, the combination of a relatively nondescript form and a convoluted taxonomic history has introduced some confusion about the identity of <it>T. pseudonana </it>and, by extension, its phylogeny and ecology. We resolve these issues and use phylogenetic criteria to show that <it>T. pseudonana </it>is more appropriately classified by its original name, <it>Cyclotella nana</it>. <it>Cyclotella </it>contains a mix of marine and freshwater species and so more accurately conveys the complexities of the phylogenetic and natural histories of <it>T. pseudonana.</it></p> <p>Conclusions</p> <p>The multitude of physical barriers that likely must be overcome for diatoms to successfully colonize freshwaters suggests that the physiological traits of <it>T. pseudonana</it>, and the genes underlying those traits, might differ from those of strictly marine diatoms. The freshwater ancestry of <it>T. pseudonana </it>might therefore confound generalizations about the physiological and metabolic properties of marine diatoms. The freshwater component of <it>T. pseudonana</it>'s history merits careful consideration in the interpretation of experimental data collected for this important model species.</p>