ABSTRACT
Meiosis and syngamy generate an alternation between two ploidy stages, but the timing of these two processes varies widely across taxa, thereby generating life cycle diversity. One hypothesis suggests that life cycles with long-lived haploid stages are correlated with selfing, asexual reproduction, or both. Though mostly studied in angiosperms, selfing and asexual reproduction are often associated with marginal habitats. Yet, in haploid-diploid macroalgae, these two reproductive modes have subtle but unique consequences whereby predictions from angiosperms may not apply. Along the western Antarctic Peninsula, there is a thriving macroalgal community, providing an opportunity to explore reproductive system variation in haploid-diploid macroalgae at high latitudes where endemism is common. Plocamium sp. is a widespread and abundant red macroalga observed within this ecosystem. We sampled 12 sites during the 2017 and 2018 field seasons and used 10 microsatellite loci to describe the reproductive system. Overall genotypic richness and evenness were high, suggesting sexual reproduction. Eight sites were dominated by tetrasporophytes, but there was strong heterozygote deficiency, suggesting intergametophytic selfing. We observed slight differences in the prevailing reproductive mode among sites, possibly due to local conditions (e.g., disturbance) that may contribute to site-specific variation. It remains to be determined whether high levels of selfing are characteristic of macroalgae more generally at high latitudes, due to the haploid-diploid life cycle, or both. Further investigations of algal life cycles will likely reveal the processes underlying the maintenance of sexual reproduction more broadly across eukaryotes, but more studies of natural populations are required.
Subject(s)
Plocamium , Rhodophyta , Seaweed , Animals , Ecosystem , Heterozygote , Antarctic Regions , Rhodophyta/genetics , Seaweed/genetics , Reproduction , Life Cycle StagesABSTRACT
Respiratory syncytial virus (RSV) is a highly contagious human pathogen that poses a significant threat to children under the age of two, and there is a current need for new small molecule treatments. The Antarctic sponge Suberites sp. is a known source of sesterterpenes, and following an NMR-guided fractionation procedure, it was found to produce several previously unreported metabolites. Neosuberitenone (1), with a new carbon scaffold herein termed the 'neosuberitane' backbone, six suberitenone derivatives (2-7), an ansellane-type terpenoid (8), and a highly degraded sesterterpene (9), as well as previously reported suberitenones A (10) and B (11), were characterized. The structures of all of the isolated metabolites including absolute configurations are proposed on the basis of NMR, HRESIMS, optical rotation, and XRD data. The biological activities of the metabolites were evaluated in a range of infectious disease assays. Suberitenones A, B, and F (3) were found to be active against RSV, though, along with other Suberites sp. metabolites, they were inactive in bacterial and fungal screens. None of the metabolites were cytotoxic for J774 macrophages or A549 adenocarcinoma cells. The selectivity of suberitenones A, B, and F for RSV among other infectious agents is noteworthy.
Subject(s)
Porifera , Suberites , Animals , Child , Humans , Respiratory Syncytial Viruses , Antarctic Regions , Terpenes/chemistry , Sesterterpenes/chemistryABSTRACT
AbstractAccurate species delimitation is crucial to understanding biodiversity. In the northern Gulf of Mexico, recent genetic evidence has suggested that the tricolor Luidia lawrencei is not a species distinct from the gray Luidia clathrata. We collected Luidia specimens from Apalachee Bay, Florida, and morphologically identified 11 as L. clathrata and 16 as L. lawrencei. We sequenced 1074 bp of the cytochrome c oxidase subunit I (COI) and found ~14% divergence between L. clathrata and L. lawrencei, suggesting two distinct species (within-species divergence was <1%). Two specimens were phenotypically L. lawrencei (i.e., tricolor morph) but mitochondrially were L. clathrata. Our findings lend support to maintaining L. clathrata and L. lawrencei as distinct species. However, the species boundary between these two taxa may be porous, and ongoing hybridization may occur when the two species are found in sympatry. Future work with nuclear markers is warranted to determine the frequency of hybridization and the extent of introgression. Clarifying the genetic relationship between these species will provide a baseline for assessing ongoing changes in connectivity of these two highly abundant sea stars in the rapidly warming northern Gulf of Mexico.
Subject(s)
Electron Transport Complex IV , Starfish , Animals , Base Sequence , Electron Transport Complex IV/genetics , Gulf of MexicoABSTRACT
Six new halogenated butenolides, tongalides A-C (1-3) and their acetylated congeners (4-6), were isolated from an extract of the Antarctic rhodophyte Delisea sp. that displayed significant antibiotic activity. The structures of the compounds were determined by analysis of data acquired by spectroscopic and spectrometric techniques including NMR, HRESIMS, optical rotation, and X-ray diffraction studies. The newly isolated compounds were assayed for antibacterial activity, but exhibited no growth inhibition of ESKAPE pathogens. The extract bioactivity was attributed to the previously reported Z-acetoxyfimbrolide A also isolated from the extract, providing further evidence that the exocyclic double bond is essential to the antibacterial activity of the structurally related fimbrolide class of metabolite.
Subject(s)
4-Butyrolactone , Anti-Bacterial Agents , 4-Butyrolactone/analogs & derivatives , Antarctic Regions , Anti-Bacterial Agents/chemistry , Molecular Structure , Plant ExtractsABSTRACT
The consequences of defensive secondary metabolite concentrations and interspecific metabolite diversity on grazers have been extensively investigated. Grazers which prefer certain food sources are often found in high abundance on their host and as a result, understanding the interaction between the two is important to understand community structure. The effects of intraspecific diversity, however, on the grazer are not well understood. Within a single, localized geographic area, the Antarctic red seaweed Plocamium sp. produces 15 quantitatively and qualitatively distinct mixtures of halogenated monoterpenes ("chemogroups"). Plocamium sp. is strongly chemically defended which makes it unpalatable to most grazers, except for the amphipod Paradexamine fissicauda. We investigated differences in the feeding and growth rates of both Plocamium sp. and P. fissicauda, in addition to grazer reproductive output, in relation to different chemogroups. Some chemogroups significantly reduced the grazer's feeding rate compared to other chemogroups and a non-chemically defended control. The growth rate of Plocamium sp. did not differ between chemogroups and the growth rates of P. fissicauda also did not show clear patterns between the feeding treatments. Reproductive output, however, was significantly reduced for amphipods on a diet of algae possessing one of the chemogroups when compared to a non-chemically defended control. Hence, intraspecific chemodiversity benefits the producer since certain chemogroups are consumed at a slower rate and the grazer's reproductive output is reduced. Nevertheless, the benefits outweigh the costs to the grazer as it can still feed on its host and closely associates with the alga for protection from predation.
Subject(s)
Plocamium , Animals , Antarctic Regions , Monoterpenes/chemistry , Plocamium/chemistry , Predatory BehaviorABSTRACT
The common Antarctic red alga Plocamium sp. is rich in halogenated monoterpenes with known anticancer and antimicrobial properties and extracts of Plocamium sp. have strong ecological activity in deterring feeding by sympatric herbivores. Plocamium sp. collected near Anvers Island, Antarctica showed a high degree of secondary metabolite diversity between separate individuals. GC/MS results revealed 15 different combinations of metabolites (chemogroups) across individuals, which were apparent at 50% or greater Bray-Curtis similarity and also clearly distinguishable by eye when comparing chromatographic profiles of the secondary metabolomes. Sequencing of the mitochondrial cox1 gene revealed six distinct haplotypes, of which the most common two had been previously reported (now referred to as Haplotypes 1 and 2). With the exception of one individual, three of the chemogroups were only produced by individuals in Haplotype 1. All the other 12 chemogroups were produced by individuals in Haplotype 2, with five of these chemogroups also present in one of the four new, less common haplotypes that only differed from Haplotype 2 by one base pair. The functional relevance of this metabolomic and genetic diversity is unknown, but they could have important ecological and evolutionary ramifications, thus potentially providing a foundation for differential selection.
Subject(s)
Monoterpenes/chemistry , Plocamium/genetics , Animals , Antarctic Regions , Aquatic Organisms , Gas Chromatography-Mass Spectrometry , Metabolomics , Molecular StructureABSTRACT
The Antarctic sponge Dendrilla antarctica is rich in defensive terpenoids with promising antimicrobial potential. Investigation of this demosponge has resulted in the generation of a small chemical library containing diterpenoid secondary metabolites with bioactivity in an infectious disease screening campaign focused on Leishmania donovani, Plasmodium falciparum, and methicillin-resistant Staphylococcus aureus (MRSA) biofilm. In total, eleven natural products were isolated, including three new compounds designated dendrillins B-D (10-12). Chemical modification of abundant natural products led to three semisynthetic derivatives (13-15), which were also screened. Several compounds showed potency against the leishmaniasis parasite, with the natural products tetrahydroaplysulphurin-1 (4) and dendrillin B (10), as well as the semisynthetic triol 15, displaying single-digit micromolar activity and low mammalian cytotoxicity. Triol 15 displayed the best profile against the liver-stage malaria parasites, while membranolide (5) and dendrillin C (11) were strong hits against MRSA biofilm cultures.
Subject(s)
Anti-Infective Agents/pharmacokinetics , Diterpenes/pharmacology , Leishmania/drug effects , Porifera/chemistry , Animals , Antarctic Regions , Anti-Infective Agents/chemistry , Biofilms , Biological Products/isolation & purification , Diterpenes/chemistry , Hepatocytes , Humans , Molecular Structure , Plasmodium falciparum/drug effectsABSTRACT
Dense macroalgal forests on the Western Antarctic Peninsula serve important ecological roles both in terms of considerable biomass for primary production as well as in being ecosystem engineers. Their function within the Antarctic ecosystem has been described as a crucial member of a community-wide mutualism which benefits macroalgal species and dense assemblages of associated amphipod grazers. However, there is a cheater within the system that can feed on one of the most highly chemically defended macroalgal hosts. The amphipod Paradexamine fissicauda has been found to readily consume the finely branched red macroalga Plocamium cartilagineum. This amphipod grazer not only feeds on its host, but also appears to sequester its host's chemical defenses for its own utilization. This review summarizes what we know about both of these exceptions to the community-wide mutualism.
Subject(s)
Seaweed , Animals , Antarctic Regions , Ecosystem , Forests , SymbiosisABSTRACT
From the CH2Cl2 extract of the Antarctic sponge Dendrilla antarctica we found spongian diterpenes, including previously reported aplysulphurin (1), tetrahydroaplysulphurin-1 (2), membranolide (3), and darwinolide (4), utilizing a CH2Cl2/MeOH extraction scheme. However, the extracts also yielded diterpenes bearing one or more methyl acetal functionalities (5-9), two of which are previously unreported, while others are revised here. Further investigation of diterpene reactivity led to additional new metabolites (10-12), which identified them as well as the methyl acetals as artifacts from methanolysis of aplysulphurin. The bioactivity of the methanolysis products, membranoids A-H (5-12), as well as natural products 1-4, were assessed for activity against Leishmania donovani-infected J774A.1 macrophages, revealing insights into their structure/activity relationships. Four diterpenes, tetrahydroaplysulphurin-1 (2) as well as membranoids B (6), D (8), and G (11), displayed low micromolar activity against L. donovani with no discernible cytotoxicity against uninfected J774A.1 cells. Leishmaniasis is a neglected tropical disease that affects one million people every year and can be fatal if left untreated.
Subject(s)
Biological Products/pharmacology , Diterpenes/pharmacology , Leishmania donovani/drug effects , Parasites/drug effects , Animals , Antarctic Regions , Diterpenes/chemistry , Humans , Molecular StructureABSTRACT
The subtidal red alga Plocamium cartilagineum was collected from the Western Antarctic Peninsula during the 2011 and 2017 austral summers. Bulk collections from specific sites corresponded to chemogroups identified by Young et al. in 2013. One of the chemogroups yielded several known acyclic halogenated monoterpenes (2-5) as well as undescribed compounds of the same class, anverenes B-D (6-8). Examination of another chemogroup yielded an undescribed cyclic halogenated monoterpene anverene E (9) as its major secondary metabolite. Elucidation of structures was achieved through one-dimensional (1D) and 2D nuclear magnetic resonance (NMR) spectroscopy and negative chemical ionization mass spectrometry. Compounds 1-9 show moderate cytotoxicity against cervical cancer (HeLa) cells.
Subject(s)
Monoterpenes/chemistry , Monoterpenes/pharmacology , Plocamium/chemistry , Antarctic Regions , Cell Line, Tumor , Cell Survival/drug effects , HeLa Cells , Humans , Hydrocarbons, Halogenated/chemistry , Hydrocarbons, Halogenated/isolation & purification , Hydrocarbons, Halogenated/pharmacology , Inhibitory Concentration 50 , Molecular Conformation , Monoterpenes/isolation & purification , Nuclear Magnetic Resonance, BiomolecularABSTRACT
The microbiome of sea urchins plays a role in maintaining digestive health and innate immunity. Here, we investigated the effects of long-term (90 day) exposure to elevated seawater temperatures on the microbiome of the common, subtropical sea urchin Lytechinus variegatus The community composition and diversity of microbes varied according to the type of sample collected from the sea urchin (seawater, feed, intestines, coelomic fluid, digested pellet and faeces), with the lowest microbial diversity (predominately the order Campylobacterales) located in the intestinal tissue. Sea urchins exposed to near-future seawater temperatures maintained the community structure and diversity of microbes associated with their tissues. However, marginal, non-significant shifts in microbial community structure with elevated temperature resulted in significant changes in predicted metagenomic functions such as membrane transport and amino acid and carbohydrate metabolism. The predicted changes in key metabolic categories suggest that near-future climate-induced increases in seawater temperature could shift microbial community function and impact sea urchin digestive and immune physiology.
Subject(s)
Climate Change , Hot Temperature/adverse effects , Lytechinus/microbiology , Microbiota , Seawater/analysis , Animals , Oceans and Seas , Random AllocationABSTRACT
Marine CO2 seeps allow the study of the long-term effects of elevated pCO2 (ocean acidification) on marine invertebrate biomineralization. We investigated the effects of ocean acidification on shell composition and structure in four ecologically important species of Mediterranean gastropods (two limpets, a top-shell snail, and a whelk). Individuals were sampled from three sites near a volcanic CO2 seep off Vulcano Island, Italy. The three sites represented ambient (8.15pH), moderate (8.03pH) and low (7.73pH) seawater mean pH. Shell mineralogy, microstructure, and mechanical strength were examined in all four species. We found that the calcite/aragonite ratio could vary and increased significantly with reduced pH in shells of one of the two limpet species. Moreover, each of the four gastropods displayed reductions in either inner shell toughness or elasticity at the Low pH site. These results suggest that near-future ocean acidification could alter shell biomineralization and structure in these common gastropods.
Subject(s)
Animal Shells/drug effects , Calcium Carbonate/analysis , Carbon Dioxide/adverse effects , Gastropoda/chemistry , Seawater/chemistry , Animal Shells/chemistry , Animal Shells/ultrastructure , Animals , Biomechanical Phenomena , Calcification, Physiologic/drug effects , Italy , Mediterranean Sea , Microscopy, Electron, Scanning , Oceans and Seas , Species Specificity , X-Ray DiffractionABSTRACT
Long-standing theory predicts that the intensity of consumer-prey interactions declines with increasing latitude, yet for plant-herbivore interactions, latitudinal changes in herbivory rates and plant palatability have received variable support. The topic is of growing interest given that lower-latitude species are moving poleward at an accelerating rate due to climate change, and predicting local interactions will depend partly on whether latitudinal gradients occur in these critical biotic interactions. Here, we assayed the palatability of 50 seaweeds collected from polar (Antarctica), temperate (northeastern Pacific; California), and tropical (central Pacific; Fiji) locations to two herbivores native to the tropical and subtropical Atlantic, the generalist crab Mithraculus sculptus and sea urchin Echinometra lucunter. Red seaweeds (Rhodophyta) of polar and temperate origin were more readily consumed by urchins than were tropical reds. The decline in palatability with decreasing latitude is explained by shifts in tissue organic content along with the quantity and quality of secondary metabolites, degree of calcification or both. We detected no latitudinal shift in palatability of red seaweeds to crabs, nor any latitudinal shifts in palatability of brown seaweeds (Phaeophyta) to either crabs or urchins. Our results suggest that evolutionary pressure from tropical herbivores favored red seaweeds with lower palatability, either through the production of greater levels of chemical defenses, calcification, or both. Moreover, our results tentatively suggest that the "tropicalization" of temperate habitats is facilitated by the migration of tropical herbivores into temperate areas dominated by weakly defended and more nutritious foods, and that the removal of these competing seaweeds may facilitate the invasion of better-defended tropical seaweeds.
Subject(s)
Herbivory , Plants , Animals , Antarctic Regions , California , Climate , Climate Change , Ecosystem , Phaeophyceae , Sea Urchins , SeaweedABSTRACT
A new rearranged spongian diterpene, darwinolide, has been isolated from the Antarctic Dendroceratid sponge Dendrilla membranosa. Characterized on the basis of spectroscopic and crystallographic analysis, the central seven-membered ring is hypothesized to originate from a ring-expansion of a spongian precursor. Darwinolide displays 4-fold selectivity against the biofilm phase of methicillin-resistant Staphylococcus aureus compared to the planktonic phase and may provide a scaffold for the development of therapeutics for this difficult to treat infection.
Subject(s)
Anti-Bacterial Agents/chemistry , Biofilms/drug effects , Diterpenes/chemistry , Methicillin-Resistant Staphylococcus aureus/drug effects , Animals , Antarctic Regions , Anti-Bacterial Agents/isolation & purification , Anti-Bacterial Agents/pharmacology , Cell Line , Diterpenes/isolation & purification , Diterpenes/pharmacology , Inhibitory Concentration 50 , Methicillin-Resistant Staphylococcus aureus/growth & development , Mice , Microbial Sensitivity Tests , Molecular Structure , Porifera/chemistryABSTRACT
Cold-water conditions have excluded durophagous (skeleton-breaking) predators from the Antarctic seafloor for millions of years. Rapidly warming seas off the western Antarctic Peninsula could now facilitate their return to the continental shelf, with profound consequences for the endemic fauna. Among the likely first arrivals are king crabs (Lithodidae), which were discovered recently on the adjacent continental slope. During the austral summer of 2010 â 2011, we used underwater imagery to survey a slope-dwelling population of the lithodid Paralomis birsteini off Marguerite Bay, western Antarctic Peninsula for environmental or trophic impediments to shoreward expansion. The population density averaged â¼ 4.5 individuals × 1,000 m(-2) within a depth range of 1,100 â 1,500 m (overall observed depth range 841-2,266 m). Images of juveniles, discarded molts, and precopulatory behavior, as well as gravid females in a trapping study, suggested a reproductively viable population on the slope. At the time of the survey, there was no thermal barrier to prevent the lithodids from expanding upward and emerging on the outer shelf (400- to 550-m depth); however, near-surface temperatures remained too cold for them to survive in inner-shelf and coastal environments (<200 m). Ambient salinity, composition of the substrate, and the depth distribution of potential predators likewise indicated no barriers to expansion of lithodids onto the outer shelf. Primary food resources for lithodids--echinoderms and mollusks--were abundant on the upper slope (550-800 m) and outer shelf. As sea temperatures continue to rise, lithodids will likely play an increasingly important role in the trophic structure of subtidal communities closer to shore.
Subject(s)
Crustacea/physiology , Animals , Antarctic Regions , Climate Change , Female , Male , Population Dynamics , Sexual Behavior, AnimalABSTRACT
The threat that ocean acidification (OA) poses to marine ecosystems is now recognized and U.S. funding agencies have designated specific funding for the study of OA. We present a research framework for studying OA that describes it as a biogeochemical event that impacts individual species and ecosystems in potentially unexpected ways. We draw upon specific lessons learned about ecosystem responses from research on acid rain, carbon dioxide enrichment in terrestrial plant communities, and nitrogen deposition. We further characterize the links between carbon chemistry changes and effects on individuals and ecosystems, and enumerate key hypotheses for testing. Finally, we quantify how U.S. research funding has been distributed among these linkages, concluding that there is an urgent need for research programs designed to anticipate how the effects of OA will reverberate throughout assemblages of species.
Subject(s)
Acids/chemistry , Oceans and Seas , Research , Carbon Cycle , Ecosystem , United StatesABSTRACT
Hard bottom communities along the western Antarctic Peninsula region are dominated by thick macroalgal forests, which support high densities of mesograzers, particularly amphipods, and also numerous gastropods. The macroalgae are chemically defended from consumption by the mesograzers and other herbivores and they provide the mesograzers a chemically defended refuge from predation by omnivorous fish. The macroalgae benefit in return because the mesograzers remove epiphytic algae from them. Since these two assemblages are major components of the community, this can be viewed as a community-wide mutualism. Most subcomponents of these interactions have also been documented in lower latitude communities and the similarities and differences between the communities in Antarctica and in other regions are discussed.
ABSTRACT
Reactive oxygen species (ROS) are commonly produced by algal, vascular plant, and animal cells involved in the innate immune response as cellular signals promoting defense and healing and/or as a direct defense against invading pathogens. The production of reactive species in macroalgae upon injury, however, is largely uncharacterized. In this study, we surveyed 13 species of macroalgae from the Western Antarctic Peninsula and show that the release of strong oxidants is common after macroalgal wounding. Most species released strong oxidants within 1 min of wounding and/or showed cellular accumulation of strong oxidants over an hour post-wounding. Exogenous catalase was used to show that hydrogen peroxide was a component of immediate oxidant release in one of five species, but was not responsible for the entire oxidative wound response as is common in vascular plants. The other component(s) of the oxidant cocktail released upon wounding are unknown. We were unable to detect protein nitration in extracts of four oxidant-producing species flash frozen 30 s after wounding, but a role for reactive nitrogen species such as peroxynitrite cannot be completely ruled out. Two species showed evidence for the production of a catalase-activated oxidant, a mechanism previously known only from the laboratory and from the synthetic drug isoniazid used to kill the human pathogen Mycobacterium tuberculosis. The rhodophyte Palmaria decipiens, which released strong oxidants after wounding, also produced strong oxidants upon grazing by a sympatric amphipod, suggesting that oxidants are involved in the response to grazing.