AUTHOR=Bendif El Mahdi , Probert Ian , Díaz-Rosas Francisco , Thomas Daniela , van den Engh Ger , Young Jeremy R. , von Dassow Peter 

TITLE=Recent Reticulate Evolution in the Ecologically Dominant Lineage of Coccolithophores

JOURNAL=Frontiers in Microbiology

VOLUME=7

YEAR=2016

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2016.00784

DOI=10.3389/fmicb.2016.00784

ISSN=1664-302X

ABSTRACT=<p>The coccolithophore family Noëlaerhabdaceae contains a number of taxa that are very abundant in modern oceans, including the cosmopolitan bloom-forming <italic>Emiliania huxleyi</italic>. Introgressive hybridization has been suggested to account for incongruences between nuclear, mitochondrial and plastidial phylogenies of morphospecies within this lineage, but the number of species cultured to date remains rather limited. Here, we present the characterization of 5 new Noëlaerhabdaceae culture strains isolated from samples collected in the south-east Pacific Ocean. These were analyzed morphologically using scanning electron microscopy and phylogenetically by sequencing 5 marker genes (nuclear <italic>18S</italic> and <italic>28S rDNA</italic>, plastidial <italic>tufA</italic>, and mitochondrial <italic>cox1</italic> and <italic>cox3</italic> genes). Morphologically, one of these strains corresponded to <italic>Gephyrocapsa ericsonii</italic> and the four others to <italic>Reticulofenestra parvula</italic>. Ribosomal gene sequences were near identical between these new strains, but divergent from <italic>G. oceanica, G. muellerae</italic>, and <italic>E. huxleyi</italic>. In contrast to the clear distinction in ribosomal phylogenies, sequences from other genomic compartments clustered with those of <italic>E. huxleyi</italic> strains with which they share an ecological range (i.e., warm temperate to tropical waters). These data provide strong support for the hypothesis of past (and potentially ongoing) introgressive hybridization within this ecologically important lineage and for the transfer of <italic>R. parvula</italic> to <italic>Gephyrocapsa</italic>. These results have important implications for understanding the role of hybridization in speciation in vast ocean meta-populations of phytoplankton.</p>