112 research outputs found
Ultrastructure of metamorphosis in Hydractinia echinata
The fine structure of metamorphosis in the athecate hydroid, Hydractinia echinata, is described. Metamorphosis was induced in two ways: by exposing planulae to appropriate microflora and by temporary exposure to an ionic imbalance. Larvae induced to metamorphose by ionic imbalance differed considerably in behavior, but little in fine structure, from those induced by microflora. Metamorphosis was initiated by the discharge of nematocysts and loss of neurosensory cells, followed by secretion of mucus from gland cells and dense-staining granules from supportive cells. Associated with these events is a severe folding of the larva and permanent adherence of the larva to the substratum by its anterior end. Following movement of remaining gland cells across the mesoglea into the endoderm-and movement of interstitial cells into the ectoderm, the metamorphosing planula extends tentacle rudiments and stolonal buds, eventually elongating into a primary polyp
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Effects of an Artificial Lunar Cycle on Reproduction in the sea anemone Aiptasia sp.pdf
The tropical sea anemone, Aiptasia sp., is a model organism within the phylum cnidaria, a group that includes globally threatened corals which are the bio-engineers of coral reefs.
Aiptasia reproduce both sexually, in a process known as spawning, and asexually, mainly through a process known as pedal laceration. During spawning, either visible egg bundles or microscopic sperm are released into the water column. During pedal laceration, small pieces of pedal disc separate from the body column and form new anemones. Many cnidarians, particularly corals, show lunar periodicity in their spawning behavior, by spawning often after a full moon.
In this experiment five individual Aiptasia genotypic strain were subjected to an artificial sunlight (white light) and moonlight (LED light) cycle for one year and anemones were examined regularly to determine the timing and amount of sexual and asexual reproduction. Over the course of one year, pedal laceration counts, oral disc diameter measurements, and the number and length of spawning events were measured. Results concluded that Aiptasia did not reproduce on a monthly basis and showed weak synchrony of spawning events.Keywords: Reproduction, Aiptasi
Transcriptome analysis of a cnidarian – dinoflagellate mutualism reveals complex modulation of host gene expression
BACKGROUND: Cnidarian – dinoflagellate intracellular symbioses are one of the most important mutualisms in the marine environment. They form the trophic and structural foundation of coral reef ecosystems, and have played a key role in the evolutionary radiation and biodiversity of cnidarian species. Despite the prevalence of these symbioses, we still know very little about the molecular modulators that initiate, regulate, and maintain the interaction between these two different biological entities. In this study, we conducted a comparative host anemone transcriptome analysis using a cDNA microarray platform to identify genes involved in cnidarian – algal symbiosis. RESULTS: We detected statistically significant differences in host gene expression profiles between sea anemones (Anthopleura elegantissima) in a symbiotic and non-symbiotic state. The group of genes, whose expression is altered, is diverse, suggesting that the molecular regulation of the symbiosis is governed by changes in multiple cellular processes. In the context of cnidarian – dinoflagellate symbioses, we discuss pivotal host gene expression changes involved in lipid metabolism, cell adhesion, cell proliferation, apoptosis, and oxidative stress. CONCLUSION: Our data do not support the existence of symbiosis-specific genes involved in controlling and regulating the symbiosis. Instead, it appears that the symbiosis is maintained by altering expression of existing genes involved in vital cellular processes. Specifically, the finding of key genes involved in cell cycle progression and apoptosis have led us to hypothesize that a suppression of apoptosis, together with a deregulation of the host cell cycle, create a platform that might be necessary for symbiont and/or symbiont-containing host cell survival. This first comprehensive molecular examination of the cnidarian – dinoflagellate associations provides critical insights into the maintenance and regulation of the symbiosis
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EvoDevo meets ecology: the Ninth Okazaki Biology Conference on Marine Biology
The “9th Okazaki Biology Conference: Marine Biology II” held at the National Institute for Basic Biology (NIBB) in
Okazaki, Japan and at the Okinawa Institute of Science and Technology (OIST) in Okinawa, Japan (14–19 October
2012) bridged the fields of EvoDevo, symbiosis and coral reef ecology.Keywords: Dinoflagellate,
Evolution,
Symbiodinium,
Bacterial Symbionts,
Ctenophora,
Cnidaria,
Symbiosi
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Effects of an artificial Lunar cycle on reproduction in the sea anemone Aiptasia sp.
The tropical sea anemone, Aiptasia sp., is a model organism within the phylum cnidaria, a group that includes globally threatened corals which are the bio-engineers of coral reefs.
Aiptasia reproduce both sexually, in a process known as spawning, and asexually, mainly through a process known as pedal laceration. During spawning, either visible egg bundles or microscopic sperm are released into the water column. During pedal laceration, small pieces of pedal disc separate from the body column and form new anemones. Many cnidarians, particularly corals, show lunar periodicity in their spawning behavior, by spawning often after a full moon.
In this experiment five individual Aiptasia genotypic strain were subjected to an artificial sunlight (white light) and moonlight (LED light) cycle for one year and anemones were examined regularly to determine the timing and amount of sexual and asexual reproduction. Over the course of one year, pedal laceration counts, oral disc diameter measurements, and the number and length of spawning events were measured. Results concluded that Aiptasia did not reproduce on a monthly basis and showed weak synchrony of spawning events
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Cell Biology of Cnidarian-Dinoflagellate Symbiosis
The symbiosis between cnidarians (e.g., corals or sea anemones) and intracellular dinoflagellate algae of the genus Symbiodinium is of immense ecological importance. In particular, this symbiosis promotes the growth and survival of reef corals in nutrient-poor tropical waters; indeed, coral reefs could not exist without this symbiosis. However, our fundamental understanding of the cnidarian-dinoflagellate symbiosis and of its links to coral calcification remains poor. Here we review what we currently know about the cell biology of cnidarian-dinoflagellate symbiosis. In doing so, we aim to refocus attention on fundamental cellular aspects that have been somewhat neglected since the early to mid-1980s, when a more ecological approach began to dominate. We review the four major processes that we believe underlie the various phases of establishment and persistence in the cnidarian/coral-dinoflagellate symbiosis: (i) recognition and phagocytosis, (ii) regulation of host-symbiont biomass, (iii) metabolic exchange and nutrient trafficking, and (iv) calcification. Where appropriate, we draw upon examples from a range of cnidarian-alga symbioses, including the symbiosis between green Hydra and its intracellular chlorophyte symbiont, which has considerable potential to inform our understanding of the cnidarian-dinoflagellate symbiosis. Ultimately, we provide a comprehensive overview of the history of the field, its current status, and where it should be going in the future.Keywords:
inorganic carbon uptake,
Anemone aiptasia pallida,
Coral stylophora pistillata,
Pocillopora damicornis linnaeus,
Host release factor,
Free amino acids,
Reef building corals,
Alga invertebrate symbiosis,
Symbiodinium microadriaticum freudenthal,
Green hydra symbiosi
Genetic Variation in Heat Tolerance of the Coral Platygyra Daedalea Indicates Potential for Adaptation to Ocean Warming
Ocean warming represents the greatest threat to the persistence of reef ecosystems. Most coral populations are projected to experience temperatures above their current bleaching thresholds annually by 2050. Adaptation to higher temperatures is necessary if corals are to persist in a warming future. While many aspects of heat stress have been well studied, few data are available for predicting the capacity for adaptive cross-generational responses in corals. Consistent sets of heat tolerant genomic markers that reliably predict thermal tolerance have yet to be identified. To address this knowledge gap, we quantified the heritability and genetic variation associated with heat tolerance in Platygyra daedalea from the Great Barrier Reef. We tracked the survival of ten quantitative genetic crosses of larvae produced form six parental colonies in a heat tolerance selection experiment. We also identified allelic shifts in heat-selected (35°C) survivors compared with paired, non-selected controls (27°C). The narrow-sense heritability of survival under heat stress was 0.66 and a total of 1,069 single nucleotide polymorphisms (SNPs) were associated with different survival probabilities. While 148 SNPs were shared between several experimental crosses, no common SNPs were identified for all crosses, which suggests that specific combinations of many markers are responsible for heat tolerance. However, we found two regions that overlap with previously identified loci associated with heat tolerance in Persian Gulf populations of P. daedalea, which reinforces the importance of these markers for heat tolerance. These results illustrate the importance of high heritability and the complexity of the genomic architecture underpinning host heat tolerance. These findings suggest that this P. daedalea population has the genetic prerequisites for adaptation to increasing temperatures. This study also provides knowledge for the development of high throughput genomic tools which may screen for variation within and across populations to enhance adaptation through assisted gene flow and assisted migration
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The Role of Complement in Cnidarian-Dinoflagellate Symbiosis and Immune Challenge in the Sea Anemone Aiptasia pallida
The complement system is an innate immune pathway that in vertebrates, is responsible for initial recognition and ultimately phagocytosis and destruction of microbes. Several complement molecules including C3, Factor B, and mannose binding lectin associated serine proteases (MASP) have been characterized in invertebrates and while most studies have focused on their conserved role in defense against pathogens, little is known about their role in managing beneficial microbes. The purpose of this study was to (1) characterize complement pathway genes in the symbiotic sea anemone Aiptasia pallida, (2) investigate the evolution of complement genes in invertebrates, and (3) examine the potential dual role of complement genes Factor B and MASP in the onset and maintenance of cnidarian-dinoflagellate symbiosis and immune challenge using qPCR based studies. The results demonstrate that A. pallida has multiple Factor B genes (Ap_Bf-1, Ap_Bf-2a, and Ap_Bf-2b) and one MASP gene (Ap_MASP). Phylogenetic analysis indicates that the evolutionary history of complement genes is complex, and there have been many gene duplications or gene loss events, even within members of the same phylum. Gene expression analyses revealed a potential role for complement in both onset and maintenance of cnidarian-dinoflagellate symbiosis and immune challenge. Specifically, Ap_Bf-1 and Ap_MASP are significantly upregulated in the light at the onset of symbiosis and in response to challenge with the pathogen Serratia marcescens suggesting that they play a role in the initial recognition of both beneficial and harmful microbes. Ap_Bf-2b in contrast, was generally downregulated during the onset and maintenance of symbiosis and in response to challenge with S. marcescens. Therefore, the exact role of Ap_Bf-2b in response to microbes remains unclear, but the results suggest that the presence of microbes leads to repressed expression. Together, these results indicate functional divergence between Ap_Bf-1 and Ap_Bf-2b, and that Ap_Bf-1 and Ap_MASP may be functioning together in an ancestral hybrid of the lectin and alternative complement pathways. Overall, this study provides information on the role of the complement system in a basal metazoan and its role in host-microbe interactions.Keywords: Symbiodinium, symbiosis, Serratia marcescens, Aiptasia, cnidarians, complement, innate immunit
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Generation and analysis of transcriptomic resources for a model system on the rise: the sea anemone Aiptasia pallida and its dinoflagellate endosymbiont
<p>Abstract</p> <p>Background</p> <p>The most diverse marine ecosystems, coral reefs, depend upon a functional symbiosis between cnidarian hosts and unicellular dinoflagellate algae. The molecular mechanisms underlying the establishment, maintenance, and breakdown of the symbiotic partnership are, however, not well understood. Efforts to dissect these questions have been slow, as corals are notoriously difficult to work with. In order to expedite this field of research, we generated and analyzed a collection of expressed sequence tags (ESTs) from the sea anemone <it>Aiptasia pallida </it>and its dinoflagellate symbiont (<it>Symbiodinium </it>sp.), a system that is gaining popularity as a model to study cellular, molecular, and genomic questions related to cnidarian-dinoflagellate symbioses.</p> <p>Results</p> <p>A set of 4,925 unique sequences (UniSeqs) comprising 1,427 clusters of 2 or more ESTs (contigs) and 3,498 unclustered ESTs (singletons) was generated by analyzing 10,285 high-quality ESTs from a mixed host/symbiont cDNA library. Using a BLAST-based approach to predict which unique sequences derived from the host versus symbiont genomes, we found that the contribution of the symbiont genome to the transcriptome was surprisingly small (1.6–6.4%). This may reflect low levels of gene expression in the symbionts, low coverage of alveolate genes in the sequence databases, a small number of symbiont cells relative to the total cellular content of the anemones, or failure to adequately lyse symbiont cells. Furthermore, we were able to identify groups of genes that are known or likely to play a role in cnidarian-dinoflagellate symbioses, including oxidative stress pathways that emerged as a prominent biological feature of this transcriptome. All ESTs and UniSeqs along with annotation results and other tools have been made accessible through the implementation of a publicly accessible database named AiptasiaBase.</p> <p>Conclusion</p> <p>We have established the first large-scale transcriptomic resource for <it>Aiptasia pallida </it>and its dinoflagellate symbiont. These data provide researchers with tools to study questions related to cnidarian-dinoflagellate symbioses on a molecular, cellular, and genomic level. This groundwork represents a crucial step towards the establishment of a tractable model system that can be utilized to better understand cnidarian-dinoflagellate symbioses. With the advent of next-generation sequencing methods, the transcriptomic inventory of <it>A. pallida </it>and its symbiont, and thus the extent of AiptasiaBase, should expand dramatically in the near future.</p
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