IN OR OUT? APPLICATION OF A MULTI-GENE ANALYSIS TESTING THE FIDELITY OF THE MORPHOLOGICALLY DIVERSE CLADE E ALLOGROMIID FORAMINFERA

Modern single chambered allogromiids are largely understudied representatives of early-evolving foraminifera despite their widespread presence in marine, freshwater and even terrestrial habitats. Unlike their polythalamous counterparts, taphonomic vulnerability, lack of a consistent fossil record and their simple gross morphology makes evolutionary affinities difficult to elucidate. Early phylogenetic studies using SSU rDNA sequences delineated 13 genetic clades, including clade E which includes taxa well represented marshes, mudflats, and estuaries of the Mid Atlantic Bight. Previous SSU based analyses suggest a loose genetic relationship, yet members lack gross morphological continuity. Preliminary examination of ‘clade E’ ultrastructure revealed some shared features of the test, particularly those of the inner organic lining (IOL). In this study, portions of the rapidly evolving sections of the SSU rDNA gene were aligned using secondary structure fold predictions as a guide. Unambiguously aligned SSU positions were concatenated with available actin and beta-tubulin sequences. The multi-gene Bayesian analysis under a GTR+I+G evolutionary model returns a monophyletic clade of ‘core’ taxa that can be considered true clade E members (Psammophaga spp., Xiphophaga spp. and Vellaria spp.). This core monophyletic group expands to include Niveus flexilis, Nellya rugosa and several undescribed taxa of previous reports (#5 cigar, Chocolate silver saccamminid, micrometula-like) when the SSU rDNA gene is used alone. In both the SSU and multi-gene trees, other prospective clade E taxa including ‘fusiform’, ‘duplin quartzball’, ‘fruitcake’ and ‘timber dock black and white saccamminid’ create polytomies with clade D taxa. Interestingly, SSU based trees lose deeper node resolution when non-clade E taxa are systematically removed from Bayesian analyses. Broad taxonomic sampling is required to improve tree resolution.