| Summary: | The Cercozoa is an extremely diverse and poorly understood group of
amoeboflagellated microeukaryotes that are united mainly by molecular phylogenetic data; a
concrete synapomorphy at the morphological level has yet to be identified for the group. In
order to better understand the biodiversity and evolutionary history of this lineage, I explored
several marine benthic habitats in British Columbia, Canada and characterized novel
cercozoans with high-resolution light microscopy and electron microscopy. Comparative
ultrastructural studies using scanning and transmission electron microscopy on some of the
newly discovered taxa demonstrated several novel features, including putative primary
endosymbionts in one lineage (i.e., Auranticordis) and homologous patterns of muciferous
bodies beneath the cell surface in another lineage. I coupled these morphological data with
molecular phylogenetic analyses of small subunit (SSU) and large subunit (LSU) rDNA
sequences and comparative analyses of polyubiquitin genes. This approach provided
evidence that a concatenation of SSU and LSU rDNA sequences improves the phylogenetic
resolution within the Cercozoa and that an insertion of one or two amino acids at the
junctions between monomers in the polyubiquitin gene is a universal molecular signature for
cercozoans (and foraminiferans). This study also enabled me to discover and describe eleven
new species and five new genera, which underscores how poorly we currently understand the
diversity of these marine microeukaryotic predators. The acquired SSU rDNA sequences
from these novel lineages enabled me to provide the cellular identities of several
environmental DNA sequence clades previously containing only uncharacterized taxa; these
data also demonstrated the effectiveness of using a 600-bp fragment of the SSU rRNA gene
for delimiting cercozoan species with limited morphological variation.
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