title: There are high levels of functional and genetic diversity in Oxyrrhis marina.
abstract: Oxyrrhis marina, a widely distributed marine protist, is used to model heterotrophic flagellate responses in microbial food webs. Although clonal variability occurs in protists, assessments of intraspecific diversity are rare; such assessments are critical, particularly where species are used as models in ecological studies. To address the extent of intraspecific variation within O. marina, we assessed diversity among 11 strains using 5.8S rDNA and ITS sequences. The 5.8S rDNA and ITS regions revealed high divergence between strains: 63.1% between the most diverse. To compare O. marina diversity relative to other alveolates, 18S rDNA sequences for five strains were analysed with sequences from representatives of the major alveolate groups. 18S rDNA also revealed high divergence in O. marina. Additionally, consistent with phylogenies based on protein coding genes, maximum likelihood analysis indicated that O. marina was monophyletic and ancestral to the dinoflagellates. To assess ecophysiological differences, growth rates of seven O. marina strains were measured at 10 salinities (10-55 per thousand). Two salinity responses occurred: one group achieved highest growth rates at high salinities; the other grew best at low salinities. There was no clear correlation between molecular, ecophysiological, or geographical differences. However, salinity tolerance was associated with habitat type: intertidal strains grew best at high salinities; open-water strains grew best at low salinities. These data indicate the need to examine many strains of a species in both phylogenetic and ecological studies, especially where key-species are used to model ecological processes.
authors.affiliation: School of Biological Sciences, University of Liverpool, BioSciences Building, Crown Street Liverpool, L69 7ZB, United Kingdom. clowe@liv.ac.uk
authors.forename: Chris D
authors.initials: CD
authors.lastname: Lowe
authors.forename: Adam
authors.initials: A
authors.lastname: Day
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Kemp
authors.forename: David J S
authors.initials: DJ
authors.lastname: Montagnes
mesh_terms: D000818:Animals; D016054:DNA, Protozoan / Q000737:chemistry; D004275:DNA, Ribosomal / Q000737:chemistry; D021903:DNA, Ribosomal Spacer / Q000737:chemistry; D004141:Dinoflagellida / Q000145:classification / Q000235:genetics* / Q000502:physiology*; D014644:Genetic Variation; D010802:Phylogeny; D012337:RNA, Ribosomal, 18S; D012340:RNA, Ribosomal, 5.8S; D012623:Seawater / Q000469:parasitology; D017422:Sequence Analysis, DNA; D012965:Sodium Chloride
chemical_list: D016054:DNA, Protozoan; D004275:DNA, Ribosomal; D021903:DNA, Ribosomal Spacer; D012337:RNA, Ribosomal, 18S; D012340:RNA, Ribosomal, 5.8S; D012965:Sodium Chloride