title: Molecular evidence for distinct Antarctic lineages in the cosmopolitan terrestrial diatoms Pinnularia borealis and Hantzschia amphioxys.
abstract: Recent morphology-based studies indicate that freshwater diatom floras in the Antarctic comprise a significant share of endemics among a majority of apparently cosmopolitan species. Given the widespread (pseudo)cryptic species diversity in diatoms, we assessed the molecular divergence and temperature-dependent growth characteristics between Antarctic and non-Antarctic strains for two presumed species with a cosmopolitan distribution, namely Pinnularia borealis and Hantzschia amphioxys. Molecular phylogenies based on the plastid gene rbcL and the nuclear 28S rDNA (D1-D3 region) revealed that both taxa consist of multiple lineages, each including a distinct Antarctic lineage. A molecular clock estimates the origin of P. borealis at 35.8 (30-47) million years (Ma) ago, making this the oldest known diatom species complex. The Antarctic P. borealis lineage is estimated to have diverged 7.8 (2-15) Ma ago, after the geographical and thermal isolation of the Antarctic continent. Despite not being psychrophilic, the Antarctic lineages of P. borealis and H. amphioxys have a lower optimal growth temperature and upper lethal temperature than most lineages from more temperate regions, indicating niche differentiation. Together, this suggests that many presumed cosmopolitan Antarctic diatom species are in fact species complexes, possibly containing Antarctic endemics with low temperature preferences.
authors.affiliation: Laboratory of Protistology and Aquatic Ecology, Ghent University, Krijgslaan 281 - S8, 9000 Gent, Belgium.
authors.forename: Caroline
authors.initials: C
authors.lastname: Souffreau
authors.forename: Pieter
authors.initials: P
authors.lastname: Vanormelingen
authors.forename: Bart
authors.initials: B
authors.lastname: Van de Vijver
authors.forename: Tsvetelina
authors.initials: T
authors.lastname: Isheva
authors.forename: Elie
authors.initials: E
authors.lastname: Verleyen
authors.forename: Koen
authors.initials: K
authors.lastname: Sabbe
authors.forename: Wim
authors.initials: W
authors.lastname: Vyverman
mesh_terms: D000864:Antarctic Regions; D016000:Cluster Analysis; D004275:DNA, Ribosomal / Q000737:chemistry / Q000235:genetics; D017377:Diatoms / Q000145:classification* / Q000166:cytology / Q000235:genetics / Q000254:growth & development; D019143:Evolution, Molecular; D005618:Fresh Water / Q000382:microbiology*; D008853:Microscopy; D008969:Molecular Sequence Data; D010802:Phylogeny; D012335:RNA, Ribosomal / Q000235:genetics; D012273:Ribulose-Bisphosphate Carboxylase / Q000235:genetics; D017422:Sequence Analysis, DNA; D013696:Temperature
chemical_list: D004275:DNA, Ribosomal; D012335:RNA, Ribosomal; C065096:RNA, ribosomal, 26S; C101625:RbcL protein, plastid; D012273:Ribulose-Bisphosphate Carboxylase