Exceptionally preserved jellyfishes from the Middle Cambrian

Journal ArticleCnidarians represent an early diverging animal group and thus insight into their origin and diversification is key to understanding metazoan evolution. Further, cnidarian jellyfish comprise an important component of modern marine planktonic ecosystems. Here we report on exceptionally preserved cnidarian jellyfish fossils from the Middle Cambrian (,505 million years old) Marjum Formation of Utah. These are the first described Cambrian jellyfish fossils to display exquisite preservation of soft part anatomy including detailed features of structures interpreted as trailing tentacles and subumbrellar and exumbrellar surfaces. If the interpretation of these preserved characters is correct, their presence is diagnostic of modern jellyfish taxa. These new discoveries may provide insight into the scope of cnidarian diversity shortly after the Cambrian radiation, and would reinforce the notion that important taxonomic components of the modern planktonic realm were in place by the Cambrian period

Interspecific Differential Expression Analysis of RNA-Seq Data Yields Insight into Life Cycle Variation in Hydractiniid Hydrozoans

Hydrozoans are known for their complex life cycles, which can alternate between an asexually reproducing polyp stage and a sexually reproducing medusa stage. Most hydrozoan species, however, lack a free-living medusa stage and instead display a developmentally truncated form, called a medusoid or sporosac, which generally remains attached to the polyp. Although evolutionary transitions in medusa truncation and loss have been investigated phylogenetically, little is known about the genes involved in the development and loss of this life cycle stage. Here, we present a new workflow for evaluating differential expression (DE) between two species using short read Illumina RNA-seq data. Through interspecific DE analyses between two hydractiniid hydrozoans, Hydractinia symbiolongicarpus and Podocoryna carnea, we identified genes potentially involved in the developmental, functional, and morphological differences between the fully developed medusa of P. carnea and reduced sporosac of H. symbiolongicarpus. A total of 10,909 putative orthologs of H. symbiolongicarpus and P. carnea were identified from de novo assemblies of short read Illumina data. DE analysis revealed 938 of these are differentially expressed between P. carnea developing and adult medusa, when compared with H. symbiolongicarpus sporosacs, the majority of which have not been previously characterized in cnidarians. In addition, several genes with no corresponding ortholog in H. symbiolongicarpus were expressed in developing medusa of P. carnea. Results presented here show interspecific DE analyses of RNA-seq data to be a sensitive and reliable method for identifying genes and gene pathways potentially involved in morphological and life cycle differences between species

A Novel Mode of Colony Formation in a Hydrozoan through Fusion of Sexually Generated Individuals

SummaryColoniality, as displayed by most hydrozoans, is thought to confer a size advantage in substrate-limited benthic marine environments and affects nearly every aspect of a species' ecology and evolution [1,2]. Hydrozoan colonies normally develop through asexual budding of polyps that remain interconnected by continuous epithelia. The clade Aplanulata is unique in that it comprises mostly solitary species, including the model organism Hydra, with only a few colonial species [3,4]. We reconstruct a multigene phylogeny to trace the evolution of coloniality in Aplanulata, revealing that the ancestor of Aplanulata was solitary and that coloniality was regained in the genus Ectopleura. Examination of Ectopleura larynx development reveals a unique type of colony formation never before described in Hydrozoa, in that colonies form through sexual reproduction followed by epithelial fusion of offspring polyps to adults. We characterize the expression of manacle, a gene involved in foot development in Hydra [5], to determine polyp-colony boundaries. Our results suggest that stalks beneath the neck do not have polyp identity and instead are specialized structures that interconnect polyps. Epithelial fusion, brooding behavior, and the presence of a skeleton were all key factors behind the evolution of this novel pathway to coloniality in Ectopleura

Differential gene expression between functionally specialized polyps of the colonial hydrozoan Hydractinia symbiolongicarpus (Phylum Cnidaria)

Background: A colony of the hydrozoan Hydractinia symbiolongicarpus comprises genetically identical yet morphologically distinct and functionally specialized polyp types. The main labor divisions are between feeding, reproduction and defense. In H. symbiolongicarpus, the feeding polyp (called a gastrozooid) has elongated tentacles and a mouth, which are absent in the reproductive polyp (gonozooid) and defensive polyp (dactylozooid). Instead, the dactylozooid has an extended body column with an abundance of stinging cells (nematocysts) and the gonozooid bears gonophores on its body column. Morphological differences between polyp types can be attributed to simple changes in their axial patterning during development, and it has long been hypothesized that these specialized polyps arose through evolutionary alterations in oral-aboral patterning of the ancestral gastrozooid. Results: An assembly of 66,508 transcripts (>200 bp) were generated using short-read Illumina RNA-Seq libraries constructed from feeding, reproductive, and defensive polyps of H. symbiolongicarpus. Using several different annotation methods, approximately 54% of the transcripts were annotated. Differential expression analyses were conducted between these three polyp types to isolate genes that may be involved in functional, histological, and pattering differences between polyp types. Nearly 7 K transcripts were differentially expressed in a polyp-specific manner, including members of the homeodomain, myosin, toxin and BMP gene families. We report the spatial expression of a subset of these polyp-specific transcripts to validate our differential expression analyses. Conclusions: While potentially originating through simple changes in patterning, polymorphic polyps in Hydractinia are the result of differentially expressed functional, structural, and patterning genes. The differentially expressed genes identified in our study provide a starting point for future investigations of the developmental patterning and functional differences that are displayed in the different polyp types that confer a division of labor within a colony of H. symbiolongicarpus

Influences of functional variation on venom expression in hydractiniid hydrozoans

This presentation was given at the Gordon Research Conference: Venom Evolution, Function and Biomedical Applications – 5-10 August 2018, Mount Snow, VT, USACnidaria (jellyfish, hydra, sea anemones, etc) represent the earliest diverging venomous animal lineage. Cnidarians deploy venom for predation, defense, competition, and digestion. Recent evidence suggests venom composition can be influenced by age, diet, geography, and the presence of predators or prey. Although venom production and maintenance are central to the life history of cnidarians, little is known about their venom composition with respect to biological or ecological function. Hydractiniid hydrozoans are an ideal system for studying venom function and evolution due to their functionally specialized tissue types and complex life cycles. The hydractiniid Hydractinia symbiolongicarpus displays a division of labor among its polyps that comprise the colony: the gastrozooid (feeding and digestion), dactylozooid (defense and predation), and gonozooid (reproduction). Podocoryna carnea, a related hydractiniid hydrozoan, displays a complex life history that includes a benthic colonial stage and a pelagic medusa. Using publicly available RNA-seq data of the functionally specific polyp types of H. symbiolongicarpus and life cycle stages of P. carnea, we characterized the putative venom components and venom expression between these tissues. Based on this analysis, we can determine how the venom arsenal varies for specific tasks and between life cycle stages. Future work will include lineage-based transcriptomics on the stinging cells of H. symbiolongicarpus as well as functional characterization of specific venom components using CRISPR. Understanding how venom composition is influenced by various developmental and ecological factors will lead to a better understanding of venom diversity and function in cnidarians

Differentially expressed venoms in functionally specialized polyps of the colonial hydrozoan Hydractinia symbiolongicarpus

This presentation was given at the 7th European Evolution and Development Conference – 26-29th June, 2018, Galway, Ireland. The poster won third place in the EEDC Student Poster Presentation competition.Cnidaria (jellyfish, hydra, sea anemones, etc.) represent the earliest diverging venomous animal lineage. Venom is deployed in cnidarians for predation, defense, competition, and digestion. Recent evidence suggests venom composition can be influenced by age, diet, geography, and the presence of predators or prey. Although venom production and maintenance are central to the life history of cnidarians, little is known about their venom composition with respect to biological or ecological function. Hydractiniid hydrozoans are an ideal system for studying venom function and evolution due to their functionally specialized tissue types and complex life cycles. The hydractiniid Hydractinia symbiolongicarpus displays a division of labor among its polyps that comprise the colony: dactylozooids (defense and predation), gastrozooids (feeding and digestion), and gonozooids (reproduction). Using an existing transcriptome of the different functional polyp types of H. symbiolongicarpus, we characterized the putative venom components and venom expression between these tissues. By using functionally specific polyps of H. symbiolongicarpus, we can determine how the venom arsenal varies for specific tasks. Understanding how venom composition is influenced by various developmental and ecological factors will lead to a better understanding of venom diversity and function in cnidarians

Venom system variation and the division of labor in the colonial hydrozoan Hydractinia symbiolongicarpus

Cnidarians (jellyfish, hydroids, sea anemones, and corals) possess a unique method for venom production, maintenance, and deployment through a decentralized system composed of different types of venom-filled stinging structures called nematocysts. In many species, nematocyst types are distributed heterogeneously across functionally distinct tissues. This has led to a prediction that different nematocyst types contain specific venom components. The colonial hydrozoan, Hydractinia symbiolongicarpus, is an ideal system to study the functional distribution of nematocyst types and their venoms, given that they display a division of labor through functionally distinct polyps within the colony. Here, we characterized the composition and distribution of nematocysts (cnidome) in the different polyp types and show that the feeding polyp (gastrozooid) has a distinct cnidome compared to the reproductive (gonozooid) and predatory polyp (dactylozooid). We generated a nematocyst-specific reporter line to track nematocyst development (nematogenesis) in H. symbiolongicarpus, and were able to confirm that nematogenesis primarily occurs in the mid-region of the gastrozooid and throughout stolons (tubes of epithelia that connect the polyps in the colony). This reporter line enabled us to isolate a nematocyst-specific lineage of cells for de novo transcriptome assembly, annotate venom-like genes (VLGs) and determine differential expression (DE) across polyp types. We show that a majority of VLGs are upregulated in gastrozooids, consistent with it being the primary site of active nematogenesis. However, despite gastrozooids producing more nematocysts, we found a number of VLGs significantly upregulated in dactylozooids, suggesting that these VLGs may be important for prey-capture. Our transgenic Hydractinia reporter line provides an opportunity to explore the complex interplay between venom composition, nematocyst diversity, and ecological partitioning in a colonial hydrozoan that displays a division of labor

Nonclonal coloniality: Genetically chimeric colonies through fusion of sexually produced polyps in the hydrozoan Ectopleura larynx

Hydrozoans typically develop colonies through asexual budding of polyps. Although colonies of Ectopleura are similar to other hydrozoans in that they consist of multiple polyps physically connected through continuous epithelia and shared gastrovascular cavity, Ectopleura larynx does not asexually bud polyps indeterminately. Instead, after an initial phase of limited budding in a young colony, E. larynx achieves its large colony size through the aggregation and fusion of sexually (nonclonally) produced polyps. The apparent chimerism within a physiologically integrated colony presents a potential source of conflict between distinct genetic lineages, which may vary in their ability to access the germline. To determine the extent to which the potential for genetic conflict exists, we characterized the types of genetic relationships between polyps within colonies, using a RAD‐Seq approach. Our results indicate that E. larynx colonies are indeed comprised of polyps that are clones and sexually reproduced siblings and offspring, consistent with their life history. In addition, we found that colonies also contain polyps that are genetically unrelated, and that estimates of genome‐wide relatedness suggests a potential for conflict within a colony. Taken together, our data suggest that there are distinct categories of relationships in colonies of E. larynx, likely achieved through a range of processes including budding, regeneration, and fusion of progeny and unrelated polyps, with the possibility for a genetic conflict resolution mechanism. Together these processes contribute to the reevolution of the ecologically important trait of coloniality in E. larynx

Frizzled3 Expression and Colony Development in Hydractiniid Hydrozoans

Hydractiniid hydrozoan colonies are comprised of individual polyps connected by tube‐like stolons or a sheet‐like mat. Mat and stolons function to integrate the colony through continuous epithelia and shared gastrovascular cavity. Although mechanisms of hydrozoan polyp development have been well studied, little is known about the signaling processes governing the patterning of colonies. Here we investigate the Wnt receptor family Frizzled. Phylogenetic analysis reveals that hydrozoans possess four Frizzled orthologs. We find that one of these genes, Frizzled3 , shows a spatially restricted expression pattern in colony‐specific tissue in two hydractiniid hydrozoans, Hydractinia symbiolongicarpus and Podocoryna carnea , in a manner that corresponds to their distinct colony forms (stolonal mat in Hydractinia and free stolons in Podocoryna ). Interestingly, Frizzled3 was lost in the genome of Hydra , which is a solitary polyp and thus lacks colony‐specific tissue. Current evidence suggests that the Wnt signaling pathway plays a key role in the evolution of colony diversity and colony loss in Hydrozoa

Localization of Multiple Jellyfish Toxins Shows Specificity for Functionally Distinct Polyps and Nematocyst Types in a Colonial Hydrozoan

Hydractinia symbiolongicarpus is a colonial hydrozoan that displays a division of labor through morphologically distinct and functionally specialized polyp types. As with all cnidarians, their venoms are housed in nematocysts, which are scattered across an individual. Here, we investigate the spatial distribution of a specific protein family, jellyfish toxins, in which multiple paralogs are differentially expressed across the functionally specialized polyps. Jellyfish toxins (JFTs) are known pore-forming toxins in the venoms of medically relevant species such as box jellyfish (class Cubozoa), but their role in other medusozoan venoms is less clear. Utilizing a publicly available single-cell dataset, we confirmed that four distinct H. symbiolongicarpus JFT paralogs are expressed in nematocyst-associated clusters, supporting these as true venom components in H. symbiolongicarpus. In situ hybridization and immunohistochemistry were used to localize the expression of these JFTs across the colony. These expression patterns, in conjunction with known nematocyst type distributions, suggest that two of these JFTs, HsymJFT1c-I and HsymJFT1c-II, are localized to specific types of nematocysts. We further interpret JFT expression patterns in the context of known regions of nematogenesis and differential rates of nematocyst turnover. Overall, we show that JFT expression patterns in H. symbiolongicarpus are consistent with the subfunctionalization of JFT paralogs across a partitioned venom system within the colony, such that each JFT is expressed within a specific set of functionally distinct polyp types and, in some cases, specific nematocyst types