A MARINE PATHOGENIC PROTIST ACROSS SCALES: HOST-MICROBIOME INTERACTION, PROVENANCE, MORPHOLOGY AND TAXONOMICAL CHARACTERIZATION OF THE SCUTICOCILIATE PARASITE OF DIADEMATIDAE

Emerging marine diseases pose growing threats to biodiversity and ecosystem stability, yet the ecological behavior, taxonomic identity, and host interactions of many pathogens remain poorly resolved. This dissertation presents an investigation into how the scuticociliate parasite responsible for mass mortality in Diadematidae sea urchins across the Caribbean and Indo-Pacific impacts its host, the pathogens provenance, and its taxonomic placement based on morphological and genetic variables. Combining molecular techniques, bacterial and archaeal microbiome profiling, 18S rRNA phylogenetics, and scuticociliate ultrastructural characterization, this collection of work aims to elucidate to intricacies of Diadema antillarum scuticociliatosis (DaSc) and the Philaster-clade (DaScPc) ciliate etiological agent. A bacterial and archaeal microbiome survey of affected urchins demonstrated conserved minor shifts in bacterial composition compared to unaffected urchins, with enrichment of taxa such as Fangia hongkongensis and Psychrobium spp. These enriched bacteria were designated as disease biomarkers due to their detection in two DaSc-affected urchin species from disparate geographical locations. Survey of museum specimens extended the temporal lens of the investigation, detecting DaScPc-related 18S rRNA sequences in grossly normal urchins from prior decades, which suggests the presence of closely related ciliates, but doesn’t confirm them being exclusively DaScPc. Bacterial signatures of the disease in 2022 do not appear in the museum specimen microbial libraries. Ultrastructural and morphometric analyses of DaScPc, revealed novel and differentiating features of its morphology, including a buccal nodular protrusion, polarized extrusome-like vesicles, and mid-body ciliary bundling. This is the first study to characterize internal ultrastructure of ciliates within this genus, elucidating organelle presence and location within the cell. The lack of visible micronucleus structures raises questions regarding if its presences depends on the ciliate’s life stage or if the imaging technique missed it in the sections visualized. The morphological and ultrastructural characterization, coupled with multi-locus phylogenetic analysis confirmed its genetic separation from other Philaster spp., supporting its designation as a new species, which has been named Philaster diademavorans sp. nov.. Collectively, this dissertation advances understanding of marine protistan disease ecology, highlights the value of integrative diagnostics and archival material, and provides a taxonomic foundation for future studies on ciliate pathogen-host dynamics in coral reef ecosystems.

Name thesis:degree_name

Ph. D., Microbiology

Level thesis:degree_level

Doctor of Philosophy

Discipline thesis:degree_discipline

Microbiology

Grantor

Cornell University

Year dc:date.issued

2025

Author dc:creator

• Vilanova Cuevas, Brayan

Committee members dc:contributor.committeemember

• Feaga, Heather
• Hendry, Tory
• Angert, Esther

• Disease ecology
• Echinoderms
• Microbial Ecology
• Protist
• Scuticociliatosis

Language dc:language.iso

en

DOI

https://doi.org/10.7298/c8cy-0n19

Dc Identifier Other

ProQuest Submission ID: 15338
ProQuest Publication ID: 32283768

OAI identifier oai:identifier

oai:ecommons.cornell.edu:1813/121036