FORM FOLLOWS FUNCTION: ASSESSING THE ROLE OF DYNAMIC CNIDARIAN PHENOTYPES DURING STRESS

Abstract

The overarching goal of this dissertation is to explore how dynamic phenotypes influence the ability of cnidarian species to respond to environmental stress, with a particular focus on the upside-down jellyfish (Cassiopea xamachana) and the Florida false coral (Ricordea florida). By connecting morphology, physiology, and molecular biology, this work provides novel insights into the resilience of these species under conditions of climate-induced stress and highlights the potential adaptive mechanisms that support their success in rapidly changing marine environments. In Chapter 2, we establish that temperature acclimation significantly increases the thermal tolerance of C. xamachana medusae. Animals pre-conditioned to elevated temperatures display enhanced bell pulsation rates and improved survival under acute heat stress. Interestingly, while environmental history (i.e., collection site) does not influence thermal tolerance, pigmentation does. Specifically, individuals with blue-colored appendages demonstrate significantly higher survival rates under extreme temperatures compared to their brown counterparts. This observation suggests that pigmentation is correlated with underlying physiological or molecular mechanisms that confer resilience. Chapter 3 addresses the molecular underpinnings of blue pigmentation. Using a multi-omics approach that combined transcriptomics, genomics, and protein expression studies, we identified a novel gene family that appears to be responsible for the striking blue pigmentation in Cassiopea. Candidate genes exhibited tissue-specific expression patterns, with strong upregulation in pigmented tissues relative to non-pigmented tissues. Our attempts to heterologously express the pigment in E. coli were unsuccessful, very likely because its expression requires specific cofactors or chaperones. The findings support the hypothesis that Cassiopea pigment production is under tight transcriptional regulation and potentially linked to photoprotective, antioxidative, or stress-buffering roles. Chapter 4 extended our exploration of organismal responses to stress by examining the mucus microbiome of Ricordea florida. The mucus of this soft-bodied corallimorpharian harbored a highly diverse bacterial community dominated by Vibrio species. This microbiome was markedly distinct from surrounding seawater, suggesting selective enrichment by the host organism. Although traditionally viewed as pathogens, some Vibrio strains may play mutualistic roles in nutrient cycling or protection from other microbial invaders. Our results open the door for future exploration of host-microbe interactions in non-coral anthozoans, with important implications for understanding resilience and immune responses in cnidarians under stress.