Pam Hallock – University of South Florida

The Hadean and Archaean oceans were far different from those of the modern Earth and those early conditions fostered the emergence of a diverse array of both autotrophic and heterotrophic metabolic pathways in prokaryotic Archaea and Eubacteria. Autotrophic processes require an energy source, a source of dissolved inorganic carbon, a proton source, and essential nutrients. Early microbial forms evolved in aquatic environments lacking free oxygen, but rich in hydrogen sulfide and methane as energy sources for chemoautotrophs and sunlight for photoautotrophs, which utilized Fe2+, H2S, or H2O as proton donors. The latter, oxygenic photosynthesis, released oxygen (O2) as a “waste productâ€, profoundly altering the oceans, the atmosphere, and the evolution of life on Earth. As oxygenic photosynthesis altered sunlit aquatic environments, the subsequent development of oxygen-dependent ATP-generating pathways resulted in more than an order of magnitude energy yield from each organic carbon molecule utilized.

The evolutionary breakthrough, resulting in the symbioses that produced Eukaryota, emerged when anaerobic Protoarchaeota engulfed, but did not digest, α-proteobacteria that had developed oxygen-independent ATP-

generating pathways. Those α-proteobacteria ultimately evolved to become oxygen-dependent mitochondria. As this symbiosis was heterotrophic, a third essential step was establishment of symbioses between early eukaryotes and photosynthetic bacteria, resulting in the eukaryotic algae. Essential to these symbioses was the resistance of the engulfed symbionts to digestion by the host.

Subsequent steps, which occurred many times in Proterozoic and Phanerozoic history, were the development of kleptoplasty and actual algal symbioses. Such “mixotrophic†pathways, that is, the ability to both feed and photosynthesize, can provide the holobiont (host plus photosynthetic symbionts) access to literally orders of magnitude more energy (as fixed carbon) than would be available to a purely heterotrophic organism in the same environment. However, the maintenance and reproduction of two metabolic systems has a variety of costs. Kleptoplastic and facultative mixotrophs can harvest photosynthetic plastids or algae that can provide energetic benefits when food is scarce. Mixotrophic systems that calcify can thrive in environments where dissolved nutrients are very limiting, and calcification can provide both protection and phosphate sequestration. But what are the energetic benefits of mixotrophy to soft-bodied organisms like Cassiopea that thrive in environments where particulate organic carbon is relatively abundant?”

Christina Hamlet – Bucknell University

Though relatively sessile, Cassiopea drive large amounts of fluid around their bells using pulsatile contractions. Nutrient capture, temperature regulation, and waste removal all take place neat the complicated oral arms structure. Depending on the configuration of the oral arms, the flow around the jellyfish may encounter a ‘solid structure’ (plate) or a ‘leaky structure’ (rake). By reconfiguring their arms, Cassiopea can affect whether water is directed through the arms or around it, changing the flow dynamics and the organism’s interaction with its environment. In this talk, I will discuss the computational modeling of these dynamics, some results, and future directions.

David Michael Baker– The University of Hong Kong

Title: Isotopic insights on nutritional symbioses across populations and phylogenies

Understanding the role of diet in shaping the ecology and evolution of species is a steadfast pursuit. Yet, resolving the relative importance of dietary sources in an organisms’ energy and growth budgets is particularly difficult within nutritional symbioses – such as those ubiquitous amongst shallow marine invertebrates (corals, bivalves, jellyfish, sponges) and their microbial symbionts. Increasingly, stable isotope approaches are employed to resolve diet – often as an alternative to exhaustive and potentially misleading examinations of ingestion (e.g. particle removal, substrate depletion, etc.). Here, I will share results from a novel application of Stable Isotope Bayesian Ellipses in R (SIBER) to symbiotic partnerships – from reef building corals, to giant clams. Heterotrophy – as evidenced by little overlap in host and symbiont isotopic niche areas correlates well with large polyp size (corals) and slower growth rates (clams) – whereas autotrophy is linked to an elevated conservation status. Other factors, such as seasonal variation in trophic plasticity, fatty acid and amino acid compound-specific isotope analysis, and how all of this can inform effective management and restoration action will be discussed.

Malte Ostendarp – University of Bremen

The upside-down jellyfish Cassiopea increasingly occurs in many (sub-) tropical coastal habitats such as mangrove forests, seagrass meadows, and coral reefs. Its mixotrophic lifestyle and ecophysiological plasticity as well as a high regenerative capacity may be reasons for its success. While the regeneration of umbrella tissue and body structures (i.e. rhopalia and oral arms) was already demonstrated, it remains unclear whether a fully functioning medusa can regenerate from only umbrella tissue. In this study, we thus investigated the regeneration of umbrella fragments over time. We conducted a laboratory experiment for which we used 18 Cassiopea medusae of three different size classes that were cut into two pieces each, one fragment with oral arms and one without. Over a total observation period of 5 weeks, we regularly monitored survival, pulsation behavior, growth and the regeneration pattern of fragments. Findings revealed that 100% of the fragments with oral arms and 88% of the fragments without oral arms survived. Pulsation behavior occurred in all fragments and lasted until the end of the experiment in 94% of all fragments. The umbrella area of fragments without oral arms showed a significantly higher decrease in the first two weeks compared to fragments with oral arms. A complete regeneration of umbrella tissue was observed in all fragments, with and without oral arms alike, and 50% of all fragments even regenerated rhopalia or oral arms as body structures after 33 days. These results suggest an outstanding regenerative capacity of Cassiopea jellyfish after fragmentation. This may contribute to (i) explain the currently observed success of upside-down jellyfish and (ii) extend our knowledge about its regeneration process, which might even act as an asexual reproduction mode in Cassiopea.

Marta Mammone – Pennsylvania State University

The regenerative capacity of Scyphozoans (Phylum Cnidaria) has been relatively understudied. The model organism Cassiopea xamachana hosts photosynthetic dinoflagellate symbionts in the host’s motile amoebocyte cells. A handful of studies have reported regeneration in the polyps of C. xamachana, but the mechanisms underlying regeneration have not been fully explored. Despite undergoing drastic developmental changes when symbiotic, the effect of symbiont presence and species on host regeneration has never been explored. C. xamachana polyps were decapitated when aposymbiotic, and symbiotic with both a homologous and a heterologous symbiont species. Regeneration and asexual budding were observed, and EdU labeling was performed to observe patterns of cell proliferation in regenerating polyps. The presence of symbionts increased likelihood to regenerate, yet symbiont species did not affect success of regeneration. No blastema or dividing cells were observed, implying cell proliferation is not the primary mechanism behind regeneration in polyps of C. xamachana.

Victoria Sharp– Pennsylvania State University.

Cassiopea xamachana is quickly spreading in popularity as a model organism across the world and many researchers start their lab cultures from scratch. Cassiopea care is unique to other jellyfish and even to coral, and keeping a reproductively-active and healthy population is critical for successful lab work. Here I will give a brief summary on the bare necessities on keeping all life stages of C. xamachana alive.

Kaitlin Kitch- Pennsylvania State University.

Cassiopea xamachana serve as a model organism to study symbiotic interactions between Cnidarians and their mutualistic partners. This study tests the optimal conditions, considering both light and nutrient availability, for Cassiopea xamachana polyp survival and reproduction in a laboratory setting. Six genetically identical polyps were subjected to each treatment. To test the effects of light, six polyps were kept in the dark 24 hours per day and six polyps were kept in the light incubator, where they experienced 12 hours of light and 12 hours of dark per day. To test the effects of nutrients, separate polyps were fed artemia supplemented with Spirulina, Algemac, S presso, and all the nutrients (Spirulina, Algemac, S presso, and Pavlova) in addition to a control plate being fed untreated artemia. Each plate of six polyps was fed one type of artemia three times per week for 31 days. To measure growth, buds were counted three times per week for 31 days for both experiments. For the light experiment, polyps exposed to light produced over eight times as many buds as polyps kept in the dark. In regards to nutrition, polyps supplemented with Algemac produced the most buds, followed by those supplemented with S. presso, polyps supplemented with all nutrients, then polyps supplemented with Spirulina. All treatments produced significantly more buds than the control polyps. Additionally, the polyps undergoing nutritional treatments were exposed to their symbiont after the first phase. For the second phase, the polyps were observed for three weeks, and the date each strobilated was recorded. Contrary to the first experiment, polyps treated with all nutrients strobilated the quickest followed by the control polyps.

Jacob Snyder- Pennsylvania State University.

Most reef-building corals form intracellular mutualisms with dinoflagellate endosymbiont algae in the family Symbiodiniaceae, which fulfill a majority of their energetic budget and partly define their response to environmental change. Warming ocean temperatures disrupt coral-symbiont mutualisms during coral bleaching events, triggering mass mortality in reefs and depriving humans of an economically and ecologically significant resource. This investigation monitors the population growth and photochemical efficiency of five cultured species of Symbiodiniaceae, spanning three genera, under ambient and elevated temperatures to derive thermotolerance ratios. Here, I confirm the thermal tolerance of Symbiodinium microadriaticum and the thermal sensitivity of Symbiodinium tridacnidorum, as established in prior literature; yet, I characterize Durusdinium trenchii as thermally susceptible, challenging its status as an extremophile. Significantly, our results suggest that Breviolum aenigmatum and Breviolum pseudominutum -largely understudied species- exhibit thermal sensitivity and moderate thermal tolerance, respectively. This study provides insight into the within- and between-genera differences in symbionts- susceptibility to heat stress to characterize their potential capacity to confer tolerance to a symbiotic host in the face of environmental change.

Caroline Link – New College of Florida

 The coral genus Acropora is a primary reef-building taxon widely found in Florida and throughout the Greater Caribbean

region. Two species in particular, A. cervicornis and A. palmata have been listed as critically endangered and are a main focus of numerous major restoration efforts. Recent studies have found that Symbiodiniaceae species differ in their physiological thermotolerances and determined symbiont identity is likely a key determinant of a coral hostâ€TMs susceptibility to thermal stress. Despite the importance of symbiont identity and thermotolerance in supporting the rapid acclimation of corals to increased temperatures, the specific degrees of thermotolerance both between species and among strains of the same species remain largely unknown. Our understanding of Acroporaâ€TMs primary symbiont species Symbiodinium fitti (type A3) is particularly limited because of the difficulty in establishing and maintaining in vitro cultures. Our project aims to develop a new methodology for culturing S. fitti by establishing in hospite cultures within Cassiopea xamachana polyps instead.

Bailey Steinworth – University of Florida

Though the life cycle of Cassiopea xamachana has been well described, the embryonic stages preceding the planula have not yet been characterized in detail. These early embryonic stages of cnidarians vary in important ways that can help us understand the evolution of body forms across Cnidaria and Metazoa as a whole. Within Medusozoa, the stages leading up to the planula are particularly important for understanding evolution, because the polyp and medusa body forms in many lineages have diverged so much it can be difficult to establish morphological homology. C. xamachana embryos are naturally brooded by the mother until they reach a swimming stage, but can be collected as fertilized zygotes released onto the oral disc region at a consistent time each day, based on the light cycle. Though the exact site and time of fertilization remains unclear, collected zygotes undergo their first cleavage approximately two hours after collection when kept at room temperature (about 25°C), and develop into swimming planula competent to settle and become polyps within six days. Gastrulation occurs between 24 to 48 hours after the first cleavage and appears to proceed by invagination. Between 72 to 96 hours, the blastopore closes and the endoderm and ectoderm become separate layers of cells. At around five to six days old, the planula becomes competent to settle in the presence of a bacterial or chemical cue, though in the presence of antibiotics the planula will remain in the swimming form for extended periods of time. The first morphological changes of settlement occur when the leading.

Cody Miner – University of Florida

Like many other cnidarians, Cassiopea harbors photosynthetic dinoflagellate endosymbionts in the Family Symbiodiniaceae. The relationship in Cassiopea is unique in that some of their symbiotic gastrodermal cells, containing this algae, undergo an epithelial-to-mesenchymal transition and enter the mesoglea matrix. Dissociation of the gastrodermis and epidermis allows for isolation of this mesoglea with its embedded cells, allowing for the separation of two symbiotic cell types within a single species. We have also developed an electroporation protocol that allows for the knockdown of gene targets in asexual buds. This is in pursuit of a larger study to explore the mechanism of this transition through RNA sequencing and subsequent functional validation.

Natalia B. Lopez-Figueroa – University of South Florida

Bioindicators are used to detect environmental changes and provide quantifiable metrics of the health of ecosystems. Recent work with scyphozoans of the genus Cassiopea has revealed their potential as bioindicators in tropical coastal ecosystems, responding to disturbance of sediments and to pollutants. The ecosystems of Jobos Bay NERR (JBNERR) are under constant threat of degradation by anthropogenic activity, sea-level rise and associated hydrological changes. Because migration of these ecosystems is limited by coastal development, implementing effective management-action plans are essential. The focus of this project is to assess the potential of Cassiopea as bioindicators of nutrient pollution and other anthropogenic disturbances in coastal ecosystems. Research goals include to: (1) assess distributions of Cassiopea in the shallow subtidal zone adjacent to JBENRR; (2) compare two methods of assessments using photogrammetry ; and (3) determine percentage coverage of Cassiopea in areas of high, mild and low human development areas. Nine sites have been established in areas of Jobos Bay, three each as high, mild, and low human impact. Each site includes five transects within a 10 x 25 m plot. Videographic surveys are performed two ways: (1) a total recording of each transects and (2) recording 0.25 m2 quadrats every 2 m along the 10 m transect for percentage coverage. Random quadrat tosses are also performed within the plot to compare methods to determine which method provides a better estimate of the population structure. Preliminary data show that Cassiopea populations respond to extreme climatic events such as the passing of Hurricane Fiona when populations migrated from near creek outlets to 3.2 km offshore. This project will further characterize these readily observed organisms as low-cost bioindicators to provide rapid environmental assessment to inform mitigation and restoration practices. The results of this project will. provide a baseline to create long-term jellyfish biomonitoring program in Puerto Rico and perhaps the Caribbean.

Colin Anthony – Tohoku University.

As the internet expands and the globe becomes more connected, science is more accessible than ever. Here, we use rhizostome jellyfish observations from iNaturalist (including Cassiopea) to provide a framework for modeling marine distributions from publicly available data. This type of analysis is highly valuable for predicting currently undescribed populations or future biological invasions. During this demonstration, we revealed heavy ‘Western’ participation bias. Therefore, we recommend initiating collaborations with regional experts, public figures, and hobbyists to begin mitigating participation bias present in iNaturalist data.

Edmee Royen – University of Liege

The symbiotic partnership between cnidarians and dinoflagellates from the family Symbiodiniaceae constitutes the basis of remarkably diverse ecosystems. This tight association between the cnidarian host and the intracellular photosymbionts displays a complex energetic metabolism, involving respiration from both partners and photosynthesis from the dinoflagellate symbionts. Despite the major importance of these two critical processes, their interplay and regulations remain poorly studied. Abiotic factors can unsettle the symbiotic balance, leading to the collapse of the partnership and threatening the survival of entire ecosystems. Among them, the rise in sea water temperature is getting more and more concerning as global warming takes place.

To address this topic, our first approach consisted in subjecting Cassiopea, an established model organism for photosynthetic jellyfish, to a mild hyperthermic stress for 28 days. Despite an increase of 6°C of the water temperature, the stressed jellyfish kept on growing over the experiment, similarly to their control counterparts. In both groups, the symbiont density remained remarkably constant, as opposed to the bleaching that has already been observed in other photosynthetic cnidarians. Along this experiment, several photosynthetic parameters were measured, among which the

relative electron transport rates through both photosystems. No differences could be observed between the two jellyfish populations, and the relationship between the activity of PSII and PSI, measured concurrently, remained linear, indicating

the absence of adjustment related to a circular electron flow in the dinoflagellate. The relative electron transport rate through PSII was also measured simultaneously with the production of dioxygen. Our results also show a linear relationship between these photosynthetic parameters, suggesting the absence of alternative electron flow involving oxygen, such as the Mehler reaction, in stressed jellyfish. The measurement of the level of pigments in Symbiodinium cells hints at an adaptation of the photosynthetic apparatus to heat stress, with the slight increase of the amount of total pigments per cell and the transient rise in the deepoxidation of xanthophylls. A re-organization of the light-harvesting complexes of the dinoflagellate is also suggested by the variation of the relative importance of peaks corresponding to the main antennae on fluorescence spectra measured at 77K. Despite the minor impact of heat stress on the photosynthesis of symbiotic Cassiopea, an increased respiration along with an increase in bell pulsation rate were observed in the heat-stressed population. To dig more into the cellular scale, we are repeating this long-lasting heat stress experiment, collecting samples to carry out bottom-up proteomics analysis. The production of reactive oxygen species is also investigated, along with the fatty acid composition of both symbiotic partners.

All in all, our work aims at taking advantage of the biophysical and spectroscopic techniques in the context of the mutualistic partnership between cnidarians and dinoflagellates, as well as its disruption. Our results show the tolerance of Cassiopea andromeda jellyfish and their dinoflagellate symbionts to a long-lasting hyperthermic stress.

Kaden Muffet – Texas A&M University at Galveston

Photosymbiosis is central to success in many cnidarians. This symbiosis is often influenced by bacterial microbiome of the host organism. While many anthozoans have sequenced natural microbiomes, this data is absent for Cassiopea. Sampling internal and external microbial communities from 34 medusae from across eight Keys in August 2021, we were able to identify that the largest components of the low-diversity Cassiopea-associated community are Endozoicomonas, Vibrio and Mycoplasma.

Madison Emery – University of Texas at Arlington

Many cnidarians form a mutualistic intracellular symbiosis with algae in the family Symbiodiniaceae. In order to establish and maintain intracellular symbiont populations, cnidarian immunity must be suppressed. This likely results in a tradeoff between the nutrition gained from the symbionts and the hostsâ€TM ability to successfully respond to pathogens. We found that in the facultatively symbiotic upside-down jellyfish Cassiopea, symbiotic polyps are more susceptible to the pathogenic bacteria Serratia marcescens relative to their aposymbiotic counterparts. To better understand the mechanisms of this difference in susceptibility, we quantified gene expression of symbiotic and aposymbiotic polyps at 24 hours following exposure to the bacterial pathogen. We found that the master immune regulator NFkB was downregulated in symbiotic control polyps, supporting the hypothesis that symbiotic polyps are immunosuppressed. In response to S. marcescens, both symbiotic states had significant gene ontology enrichments for immune terms in their differentially expressed genes. However, the symbiotic polyps also had enrichments indicative of an unfolded protein response. This suggests that the symbiotic polyps are mounting an immune response that is damaging their proteins and may be more inflammatory.

Vivian Li – Pennsylvania State University

Cnidarians, including Cassiopea, depend on microalgal endosymbionts (Symbiodiniaceae) for resources that support growth, development, reproduction and metabolism. The specificity of host-symbiont relationships in cnidarians seem to suggest that this specificity is driven by very specific nutrient needs (or waste removal needs?) from both sides that have developed over evolutionary time. Examining how microbiomes benefit free-living symbiont cells in culture may tell us more about symbiont physiology and how it behaves in symbiosis with different hosts.

My research examines relationships between Symbiodiniaceae and their bacterial microbiomes, seeking to answer the question of how Symbiodiniaceae microbiomes influence their physiologies from an eco-evolutionary perspective. I am characterizing the microbiomes of 20 Symbiodiniaceae lab cultures spanning a wide range of physiological traits and phylogenetic placement. I will determine the community structure and composition of the microbiomes of each of these cultures using amplicon sequencing of the 16S rRNA gene. I will then investigate the putative metabolic capabilities of key/core microbiome members that may be contributing to distinct host phenotypic characteristics.
By identifying the benefits that Symbiodiniaceae cells are getting from bacteria in free-living cultures, we could perhaps learn more about the nutrient needs (and/or waste removal needs) of Symbiodiniaceae in hospite. Studying Symbiodiniaceae microbiomes thus generates valuable inside in to the health and functioning of cnidarian holobionts, providing new perspectives for conservation in the face of climate change.

Justin Dalrymple – Florida International University

Coral bleaching is the expulsion of intracellular photosymbionts by their coral hosts in response to stress. While bleaching is projected to be a growing problem for the world’s reefs, molecular mechanisms underpinning bleaching remain unclear. We performed a mechanism-agnostic screen to identify underlying candidate pathways in the model symbiotic anthozoan Exaiptasia diaphana. Anemones were exposed to 1,280 human pharmaceuticals for 96 hours before bleaching was assessed by fluorescence. Since pharmaceuticals interact with known targets, this approach represents a novel method for understanding the mechanistic basis of dysbiosis. Preliminary analysis reveals over 70 compounds that cause bleaching in anemones, including medications prescribed for psychiatric disorders, osteoporosis and blood pressure.

Michael Hewitt – Pennsylvania State University

Marine heatwaves associated with climate change and subsequent mass coral-bleachings have prompted decades of increased interest in the vital symbiosis between reef-building corals and mutualistic dinoflagellates in the family Symbiodiniaceae (zooxanthellae). The upside down jellyfish Cassiopea xamachana is a useful model system for studying symbiosis establishment, and competition between their potential symbionts. Previous studies have looked at competition between symbiont species in this system, however, none have looked at competition under heat stress. In some corals, thermotolerant symbionts may be more successful under high heat than their less tolerant counterparts. We ran competition experiments between three symbiont species known to establish symbiosis with C. xamachana; the jellyfish’s homologous symbiont Symbiodinium microadriaticum, and the heterologous symbionts Breviolum minutum, as well as the thermally tolerant Durusdinium trenchii. Each experiment paired species against one another, at different starting concentrations (25:75, 50:50, 75:25). The experiments were run under both control (27 C) and heat-stressed (32 C) conditions. Under control temperatures S. mic. and D. trenchii both competitively displaced B. min., but when competing against one another there was less of a clear winner in either direction. Under heat-stress, the polyps that were given heterologous symbionts did poorly; only two ephyrae established symbiosis and all polyps appeared bleached, however the polyps that were given the homologous symbiont continued strobilating throughout the experiment. Under heat stress, S. mic. dominated both of the other species. These results suggest that partner specificity in C. xamachana is somewhat strong and although the system can harbor heterologous symbionts, these foreign symbionts do not help the animal survive during heat stress even if the symbionts themselves are thermotolerant.

Megan Maloney – Auburn University
Upside-down jellyfish (Cassiopea sp.) are highly tolerant to stresses associated with ever-changing marine environments, particularly extreme temperature changes. This may be due to their ability to modulate rates of bell pulsation, which may promote feeding, oxygen exchange, and symbiont uptake. Additionally, Cassiopea exhibit conspicuous color variation, in both hue and number of colored appendages. To test the capacity of temperature acclimation to influence thermal tolerance on Cassiopea color morphs, adult Cassiopea were acclimated for 30 days to two temperature treatments (26°C or 33°C), and subsequently exposed to acute heat stress. Individuals acclimated at 33°C survived to significantly higher lethal temperatures compared to those acclimated at 26°C. Additionally, Cassiopea with blue appendages survived to significantly higher temperatures and exhibited less change in bell pulsation rates compared to non-blue individuals. These results indicate that Cassiopea can acclimatize to elevated temperatures and suggest that phenotypic plasticity and coloration may play a critical role in survival during heat stress.

Addie Harrison – University of Arizona.

Nematocysts are stinging organelles found in organisms such as jellyfish, anemones, and hydrozoans. The immersed boundary method is used to couple the elastic equations and the fluid equations to numerically simulate nematocyst firing and ejecting dynamics. The model simulates the barb moving with a prescribed motion towards a flexible circle target in two dimensions. In our firing model, we altered parameters for prey size, viscosity of the fluid, and lengths for applying force. Our preliminary results show that the nematocysts ability to accurately hit and puncture a surface it is projected to hit can vary based on the acceleration used to fire as well as the target’s size and makeup.

Christine Wu – National Experimental High School at Hsinchu Science Park, Taiwan.

Based on the publication “Cassiosomes are stinging-cell structures in the mucus of the upside-down jellyfish Cassiopea xamachana” (Cheryl L. Ames et al. 2020), we reported the presence of Cassiosomes in the mucus of the jellyfish Cassiopea andromeda from Taiwan.
Cassiopea andromeda, a type of upside-down jellyfish, often attaches itself to the bottom of water bodies with its bell facing downwards. We observed that Cassiopea andromeda releases mucus in response to water disturbance and the presence of prey. Within the mucus, we confirmed the presence of cassiosomes, which are cell-like structures composed of nematocysts and symbiotic zooxanthellae algae released from the sac-like structures on the jellyfish’s vesicular appendages. Upon contacting Artemia salina, cassiosomes can cause death within 30 (±10) seconds, indicating that they enable Cassiopea andromeda to effectively capture and feed on its prey.

Tan Kei Chloe – Tohoku University

Using DNA molecular barcoding, our primary goals are to uncover the co-evolution of specific Symbiodiniaceae and Rhizostomeae taxa. Targeting mitochondrial 16S rRNA and COI and nuclear ITS gene fragment in oral arms and umbrella tissues of rhizostome jellyfish from aquariums in Japan, combined with available sequence data in GenBank we reconstructed a phylogenetic tree. Next, we followed the same protocol to identify the Symbiodiniaceae hosted by each jellyfish taxon using Symbiodiniaceae genus-level specific ITS2 gene region primers. Both rhizostome and endosymbiont gene targets were amplified with varied difficulty depending on tissue type. Reconstructed phylogenetic trees included our samples from four families and five genera of rhizostome jellyfish and their respective associated Symbiodinieacea at the generic level. During this study we developed a new protocol to target both the symbiont and jellyfish host simultaneously, thereby speeding up validation of the presence or absence of Symbiodiniaceae in rhizostome taxa. Moving forward, using molecular data from this study and additional samples and morphological data from microscopic observation and the literature, we aim to reconstruct the co-evolution of Symbiodiniaceae diversity in Rhizostomeae.

Emily Van Buren – University of Texas at Arlington

Many members of the phylum Cnidaria have independently evolved to host unicellular dinoflagellate Symbiodiniacae. Studies regarding symbiosis often focus on the cellular biology of the cnidarian host during this symbiosis establishment, leaving much to be understood regarding the symbiont’s expression and role in cnidarian-algal symbiosis. Transcriptomic studies can improve our knowledge in understanding how algal symbionts maintain or change expression to remain established in different cnidarian hosts. As Porites asteroides and Cassiopeia convergently evolved to preferentially host the same genus Symbiodiniacae, the expression of Symbiodiniacae in these two cnidarian hosts can be used to determine if there is a core gene expression pattern required for cnidarian- algal symbiosis or if different gene expression patterns are required for establishment in different cnidarian hosts. In this study, we used differential gene expression, machine learning, and predictive modeling to identify genes and candidate biomarkers associated with cnidarian host in Symbiodiniacae.

Raúl González-Pech – Pennsylvania State University

Cladocopium infistulum (family Symbiodiniaceae; ITS2 type C2) is an ecologically specialized dinoflagellate symbiont of giant clams in the west Pacific. Unlike most symbiotic Symbiodiniaceae, which reside intracellularly (within the host’s cells), C. infistulum inhabits the extracellular spaces of the bivalve’s digestive diverticula. This species exhibits high thermotolerance in contrast to other clam symbionts within the family (e.g. Symbiodinium tridacnidorum), which are physiologically susceptible to elevated temperatures. Furthermore, C. infistulum is phylogenetically basal to the large Cladocopium C15 species complex, a recent radiation that features high host specificity toward important reef-building corals found across the Indo-Pacific, as well as high thermotolerance generally. Previous analyses of microsatellite loci suggested that C. infistulum, like other Cladocopium, has undergone whole-genome duplication prior to diversification within the genus. Therefore, C. infistulum represents a key species to investigate extracellular symbiosis, thermotolerance, and the role of genome duplication in the ecological and evolutionary success of Cladocopium. Here, we present a genome assembly of C. infistulum (culture rt-203) produced by combining long- and short-read sequencing and compare it to the three other available Cladocopium genomes. We found evidence of segmental duplication, rather than whole genome duplication, and uncovered no obvious links between genome duplication and adaptation to extracellular symbiosis or thermotolerance. Nevertheless, these data highlight variation in genome evolution across the Symbiodiniaceae, and provide insight into the processes that shape molecular divergence and speciation among congeneric dinoflagellates.

Joseph Brennan – The University of Hong Kong

Photosynthates produced by Symbiodiniaceae can benefit the metabolism and growth of their cnidarian hosts through nutrient translocation. However, environmental perturbation such as increased temperatures can lead to increased retention of these nutrients in symbionts, and can therefore lead to an increased respiratory demand in the host. Our study will test novel methods assessing the impact of symbiont primary productivity on host Î ́2H. We will utilize Cassiopea xamachana as a model cnidarian host in association with various species of Symbiodiniaceae.