Ribosomal DNA shows extremely low genetic divergence in a world-wide distributed, but disjunct and highly adapted marine protozoan ( Virgulinella fragilis, Foraminiferida)

• Published in: Marine micropaleontology Vol. 70; no. 1; pp. 8 - 19
• Main Authors: Tsuchiya, Masashi, Grimm, Guido W., Heinz, Petra, Stögerer, Karin, Ertan, Kemal Topaç, Collen, John, Brüchert, Volker, Hemleben, Christoph, Hemleben, Vera, Kitazato, Hiroshi
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 10-01-2009
• Subjects: Benthic foraminifera; Internal transcribed spacer; Marine; Molecular fixation rate; Molecular phylogeny; Small subunit rDNA; Virgulinella; Virgulinella fragilis; PSE, New Zealand; PSW, Namibia; PSE, New Zealand, North I., Wellington; AS, South Atlantic; INW, Japan; Virgulinella fragilis; Small subunit rDNA; Benthic foraminifera; Molecular phylogeny; Internal transcribed spacer; Molecular fixation rate
• ISSN: 0377-8398; 1872-6186
• DOI: 10.1016/j.marmicro.2008.10.001

Virgulinella fragilis can be mainly observed in different, separated, oxygen-depleted and sulfide-enriched environments around the world and seems to be well adapted to such extreme habitats. Dispersal mechanisms behind this geographical distribution pattern are not yet understood. To analyze the genetic differentiation of geographically isolated populations, we conducted molecular phylogenetic analyses of the small subunit (SSU) ribosomal DNA (rDNA) and internal transcribed spacers (ITS) of rDNA nucleotide sequences in populations of
V.
fragilis collected in the South Atlantic (upwelling area off Namibia) and in the Pacific (Wellington Harbor, New Zealand, and Namako-ike, Japan). Our molecular analyses revealed SSU rDNA and ITS sequences strikingly similar or identical among these three disjunct populations. Such a low molecular genetic differentiation, a fixation rate converging to zero, could either arise from rapid dispersal, ultraslow mutation rates due to a strictly asexual mode of reproduction, unlimited genetic exchange between populations or the existence of a resting stage for survival under unfavorable conditions. We discuss each explanation and conclude that
V.
fragilis might possibly represent a protozoan trapped in evolutionary stasis.