Recent Reticulate Evolution in the Ecologically Dominant Lineage of Coccolithophores

Area of Science:

• Marine biology
• Phycology
• Evolutionary biology

Background:

• The Noëlaerhabdaceae family includes abundant marine phytoplankton, such as Emiliania huxleyi.
• Introgressive hybridization is a proposed mechanism for phylogenetic discrepancies in this lineage.
• Limited cultured species hinder comprehensive phylogenetic analysis.

Purpose of the Study:

• To characterize new Noëlaerhabdaceae culture strains from the southeast Pacific Ocean.
• To investigate phylogenetic relationships and potential hybridization within the Noëlaerhabdaceae family.
• To assess the taxonomic placement of Reticulofenestra parvula.

Main Methods:

• Isolation and morphological analysis (scanning electron microscopy) of five new culture strains.
• Phylogenetic analysis using five marker genes (nuclear 18S/28S rDNA, plastidial tufA, mitochondrial cox1/cox3).
• Comparison of sequences across different genomic compartments and with existing taxa.

Main Results:

• Four strains identified as Reticulofenestra parvula and one as Gephyrocapsa ericsonii.
• Ribosomal gene sequences of new strains were distinct from G. oceanica, G. muellerae, and E. huxleyi.
• Mitochondrial and plastidial gene sequences clustered with Emiliania huxleyi, indicating introgressive hybridization.

Conclusions:

• The findings strongly support past and potentially ongoing introgressive hybridization in Noëlaerhabdaceae.
• Evidence suggests the transfer of Reticulofenestra parvula to the genus Gephyrocapsa.
• Hybridization plays a significant role in phytoplankton speciation within large marine populations.