TWO MICROBIOME STUDIES PROVIDE INSIGHTS INTO EVOLUTIONARY HISTORIES OF HOST FORAMINIFERAL TAXA

Microbiome research is providing breakthroughs to understanding the importance of microbial associations in eukaryotic organisms. Insights into evolutionary histories of several benthic foraminiferal species were revealed in two studies that examined different aspects of their microbiomes. A genomic study based upon rbcL and 18S DNA sequences of the endosymbionts of four extant species of Amphistegina revealed results consistent with both morphologic features and what is known of their evolutionary histories. Morphologic features shared by the Am. gibbosa−Am. lessonii–Am. lobifera group are recognized in an Upper Eocene−Oligocene species, Am. waiareka. Similarly, Am. radiata shares distinct morphologic features with Am. eyrensi, also from the Eocene. Our study revealed family-level differences in diatom symbionts, suggesting that the two Amphistegina lineages independently acquired their symbionts. The second study investigated microbes associated with four western Atlantic species of benthic foraminifera that host three kinds of algal endosymbionts. The porcelaneous Soritidae were represented by Archaias angulatus and Cyclorbiculina compressa, both hosting chlorophyte symbionts, and Sorites orbiculus, hosting dinoflagellate symbionts. The fourth species, Am. gibbosa, is a hyaline taxon with diatom symbionts. Bacterial DNA extraction, followed by amplification and amplicon sequencing of the V4 variable region of the 16S rRNA gene, revealed that all examined Ar. angulatus and C. compressa specimens shared 31 microbial Operational Taxonomic Units (OTUs). When compared with sequences from S. orbiculus, the three species shared 26 OTUs, indicating that phylogenetic relatedness of host taxa had more influence on core microbiomes than algal-symbiont taxa. When the core microbiome of the soritids was compared with that of Am. gibbosa, only one OTU was unquestionably shared. Moreover, the core microbiome for Am. gibbosa was dominated by Proteobacteria, similar to earlier findings for the microbiome of Am. lobifera, an Indo-Pacific taxon. These two studies reveal the potential of molecular genomics tools to investigate evolutionary histories of foraminifers not only through their own genetic lineages but also through the lineages of core microbial associations and algal symbionts.