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1.
Summary Experiments conducted on rocky bottoms at 7–11 m depth in the San Juan Archipelago, Washington assessed effects of canopies
of understory kelps on growth of benthic suspension feeders, determined the mechanisms responsible for effects, and assessed
the influence of kelp canopies on survivorship of benthic fauna. Kelp canopics influenced growth rates of diverse suspension
feeders. At several sites the musselMytilus edulis, the barnacleBalanus glandula, and the serpulid polychaetePseudochitinopoma occidentalis grew faster on the bottom beneath kelp canopies than on nearby exposed substrata. The cheilostome bryozoanMembranipora membranacea showed a mixed response to kelp canopies, growing faster in exposed regions at one site, but faster beneath canopies at another.
There were no differences in growth of 2 other species (the cheilostome bryozoanCheilopora praelonga and the spongeMyxilla incrustans) between kelp and no-kelp treatments; however, some processes influenced by plant canopies affected their growth. Specific
mechanisms responsible for kelp effects on growth were assessed in a series of field experiments usingPseudochitinopoma, Membranipora, Cheilopora andMyxilla. Particulate deposition on the bottom, which is more intense beneath canopies, negatively affected growth of all 4 species.
Kelps also reduced rates of flow and prevented devented development of microalgal turfs beneath the canopy.Pseudochitinopoma grew faster in the weaker flows below canopies and bothCheilopora andMyxilla grew faster where there were no microalgal turfs. These other effects of kelp canopies were at least as important to growth
(in the cases ofCheilopora andMyxilla) or more important to growth (in the case ofPseudochitinopoma) than were the general, deleterious effects of higher sedimentation beneath canopies.
The lower growth rates caused by higher sedimentation beneath kelp canopies did not result in higher rates of animal mortality.
Surprisingly, kelp canopies typically did not influence mortality due to predation. For 7 of 12 taxa, mortality rates did
not differ between kelp-covered and exposed treatments. Significantly higher mortality occurred outside canopies for only
4 of 12 taxa, and for at least 2 of these 4 differences probably were not related to predation.Mytilus, a species rare at these depths, exhibited higher mortality beneath kelp canopies due to predation by crabs. Other macrophytes
in fresh and salt water, as well as some benthic animals that create complex, 3-dimensional habitats, should influence benthic
organisms and assemblages in ways analogous to the kelps acting through their effects on flow, particle transport, and shading. 相似文献
2.
Given the quiescent physical environment and the low rates of bioturbation in the deep sea, biologically produced structures, such as animals tubes, may play an important role in creating habitat heterogeneity. In San Diego Trough, the cirratulid polychaete Tharyx luticastellus builds and inhabits a robust mud concretion (a mudball). Mudballs are abundant and persist after the worm has died or abandoned them. Our analysis of twelve 6.6-cm-diameter cores from 32° 51.02 N, 117° 46.97 W, taken with the submersible SEA CLIFF, indicate that one of 29 species of harpacticoids common in San Diego Trough is associated with Tharyx mudballs. This species (of the genus Heteropsyllus) responded only to mudballs containing worms, suggesting that any effects of the inanimate structure were not the cause of the association. We could detect no difference in bacterial numbers in sediments between control and occupied-mudball samples. This result suggests that the response does not result from gross differences in food levels near a mudball, but the possibility that there are differences in some preferred food cannot be discounted. An univestigated possibility is that Heteropsyllus responds to occupied mudballs because the worm's presence deters some (presumably small) predator. 相似文献
3.
Donatella Zona Peter M. Lafleur Koen Hufkens Beniamino Gioli Barbara Bailey George Burba Eugénie S. Euskirchen Jennifer D. Watts Kyle A. Arndt Mary Farina John S. Kimball Martin Heimann Mathias Göckede Martijn Pallandt Torben R. Christensen Mikhail Mastepanov Efrén López-Blanco Albertus J. Dolman Roisin Commane Charles E. Miller Josh Hashemi Lars Kutzbach David Holl Julia Boike Christian Wille Torsten Sachs Aram Kalhori Elyn R. Humphreys Oliver Sonnentag Gesa Meyer Gabriel H. Gosselin Philip Marsh Walter C. Oechel 《Global Change Biology》2023,29(5):1267-1281
Long-term atmospheric CO2 concentration records have suggested a reduction in the positive effect of warming on high-latitude carbon uptake since the 1990s. A variety of mechanisms have been proposed to explain the reduced net carbon sink of northern ecosystems with increased air temperature, including water stress on vegetation and increased respiration over recent decades. However, the lack of consistent long-term carbon flux and in situ soil moisture data has severely limited our ability to identify the mechanisms responsible for the recent reduced carbon sink strength. In this study, we used a record of nearly 100 site-years of eddy covariance data from 11 continuous permafrost tundra sites distributed across the circumpolar Arctic to test the temperature (expressed as growing degree days, GDD) responses of gross primary production (GPP), net ecosystem exchange (NEE), and ecosystem respiration (ER) at different periods of the summer (early, peak, and late summer) including dominant tundra vegetation classes (graminoids and mosses, and shrubs). We further tested GPP, NEE, and ER relationships with soil moisture and vapor pressure deficit to identify potential moisture limitations on plant productivity and net carbon exchange. Our results show a decrease in GPP with rising GDD during the peak summer (July) for both vegetation classes, and a significant relationship between the peak summer GPP and soil moisture after statistically controlling for GDD in a partial correlation analysis. These results suggest that tundra ecosystems might not benefit from increased temperature as much as suggested by several terrestrial biosphere models, if decreased soil moisture limits the peak summer plant productivity, reducing the ability of these ecosystems to sequester carbon during the summer. 相似文献
4.
The selectins are a family of proteins that mediate leukocytetethering and rolling along the vascular endothelium. E-, P-,and L-selectin recognize various derivatives of the Lewisa andLewisx trisaccharides. The distribution of negative chargeson the Lewisa and Lewisx oligosaccharides appears to be an importantfactor in their binding by the selectins. Previous work exploringthis electrostatic dependence found that a series of syntheticanionic trisaccharides, 3'-sulfo, 3'-phospho, 6'-sulfo, and3',6'-disulfo Lewisa. (Glc), exhibited differing selectin inhibitoryefficacies. To explore the possibility that these differencesarise from conformational differences between the sugars, thesolution structures of these trisaccharides were determinedusing NMR and molecular dynamics simulations. Interproton distancesand interglycosidic torsion angles were determined at 37°Cusing NOESY buildup curves and 1D LRJ experiments, respectively.Data from both experiments agreed well with predictions madefrom 2000 picosecond unrestrained molecular dynamics simulations.We found that 3'-sulfation did not alter the core Lewisa conformation,a finding that reaffirms the results of previous study. In addition,we found that sulfation at the 6' position also leaves the trisaccharideconformation unperturbed. This is significant because the proximityof the 6'-sulfate group to the fucose ring might have alteredthe canonical Lewisa structure. The disulfate exhibited greaterflexibility than the other derivatives in dynamics simulations,but not so much as to affect NOE and heteronuclear couplingconstant measurements. Taken together, our findings supportthe use of Lewisa as a template onto which charged groups maybe added without significantly altering the trisaccharide'sstructure. oligosaccharides molecular dynamics simulations NMR sulfated Lewisa phosphorylated Lewisa 相似文献
5.
Twenty-four specimen of macroalgae were collected in nearshore waters of the island of Hawaii, identified, and maintained to examine how the epiphytic relationship between Gambierdiscus toxicus (isolate BIG12) varied among the macroalgal species. Gambierdiscus cells were introduced to Petri dishes containing 100 g samples of each macroalgal host, which were examined at two, 16, 24, and every 24–72 h thereafter, over a 29-day period. Gambierdiscus proliferated in the presence of some host species (e.g., Galaxaura marginata and Jania sp.), but grew little in the presence of other species (e.g., Portieria hornemannii). Gambierdiscus exhibited high survival rates (>99%) in the presence of Chaetomorpha sp., but died before the end of the experiment (after 21 days) with other host species (e.g., Dictyota and Microdictyon spp.). Gambierdiscus avoided contact with P. hornemannii, but averaged up to 30% attachment with other host species. The numbers of Gambierdiscus cells belonging to one of three classes (alive and attached; alive and unattached; and dead) were determined for each time point. The 24 algal hosts were grouped according to their commonalities relative to these three classes using a Bray-Curtis similarity index, similarity profile (SIMPROF) permutation tests, and Multi-Dimensional Scaling (MDS) analysis (PRIMER 6). The resultant six groupings were used to construct different Gambierdiscus growth profiles for the different algal hosts. Group A is characterized by a preponderance of unattached cells and high mortality rates. Groups B, C, E, and F also displayed high proportions of unattached cells, but mortality either occurred later (Groups B and C) or rates were lower (Groups E and F). Group D had the highest proportion of attached cells. Group E contained three out of the four chlorophyte species, while Group F contained the majority of the rhodophytes. Over 50% of the species in Group F are considered to be palatable, whereas Groups A, B, and C are composed of species that exhibit chemical defenses against herbivory. The results of this study coupled with previous findings indicate that Gambierdiscus is not an obligate epiphyte; it can be free-swimming and found in the plankton. The conditions that lead to changes between epiphytic and planktonic stages need to be better studied in order to determine how they affect Gambierdiscus growth and physiology, connectivity and dispersion mechanisms, and toxin movement up into the foodweb. 相似文献
6.
Jessica Cruz de Leon Nicole Scheumann Wandy Beatty Josh R. Beck Johnson Q. Tran Candace Yau Peter J. Bradley Keith Gull Bill Wickstead Naomi S. Morrissette 《Eukaryotic cell》2013,12(7):1009-1019
SAS-6 is required for centriole biogenesis in diverse eukaryotes. Here, we describe a novel family of SAS-6-like (SAS6L) proteins that share an N-terminal domain with SAS-6 but lack coiled-coil tails. SAS6L proteins are found in a subset of eukaryotes that contain SAS-6, including diverse protozoa and green algae. In the apicomplexan parasite Toxoplasma gondii, SAS-6 localizes to the centriole but SAS6L is found above the conoid, an enigmatic tubulin-containing structure found at the apex of a subset of alveolate organisms. Loss of SAS6L causes reduced fitness in Toxoplasma. The Trypanosoma brucei homolog of SAS6L localizes to the basal-plate region, the site in the axoneme where the central-pair microtubules are nucleated. When endogenous SAS6L is overexpressed in Toxoplasma tachyzoites or Trypanosoma trypomastigotes, it forms prominent filaments that extend through the cell cytoplasm, indicating that it retains a capacity to form higher-order structures despite lacking a coiled-coil domain. We conclude that although SAS6L proteins share a conserved domain with SAS-6, they are a functionally distinct family that predates the last common ancestor of eukaryotes. Moreover, the distinct localization of the SAS6L protein in Trypanosoma and Toxoplasma adds weight to the hypothesis that the conoid complex evolved from flagellar components. 相似文献
7.
8.
Jonathan D. Mosley Sara L. Van Driest Emma K. Larkin Peter E. Weeke John S. Witte Quinn S. Wells Jason H. Karnes Yan Guo Lisa Bastarache Lana M. Olson Catherine A. McCarty Jennifer A. Pacheco Gail P. Jarvik David S. Carrell Eric B. Larson David R. Crosslin Iftikhar J. Kullo Gerard Tromp Helena Kuivaniemi David J. Carey Marylyn D. Ritchie Josh C. Denny Dan M. Roden 《PloS one》2013,8(12)
A single mutation can alter cellular and global homeostatic mechanisms and give rise to multiple clinical diseases. We hypothesized that these disease mechanisms could be identified using low minor allele frequency (MAF<0.1) non-synonymous SNPs (nsSNPs) associated with “mechanistic phenotypes”, comprised of collections of related diagnoses. We studied two mechanistic phenotypes: (1) thrombosis, evaluated in a population of 1,655 African Americans; and (2) four groupings of cancer diagnoses, evaluated in 3,009 white European Americans. We tested associations between nsSNPs represented on GWAS platforms and mechanistic phenotypes ascertained from electronic medical records (EMRs), and sought enrichment in functional ontologies across the top-ranked associations. We used a two-step analytic approach whereby nsSNPs were first sorted by the strength of their association with a phenotype. We tested associations using two reverse genetic models and standard additive and recessive models. In the second step, we employed a hypothesis-free ontological enrichment analysis using the sorted nsSNPs to identify functional mechanisms underlying the diagnoses comprising the mechanistic phenotypes. The thrombosis phenotype was solely associated with ontologies related to blood coagulation (Fisher''s p = 0.0001, FDR p = 0.03), driven by the F5, P2RY12 and F2RL2 genes. For the cancer phenotypes, the reverse genetics models were enriched in DNA repair functions (p = 2×10−5, FDR p = 0.03) (POLG/FANCI, SLX4/FANCP, XRCC1, BRCA1, FANCA, CHD1L) while the additive model showed enrichment related to chromatid segregation (p = 4×10−6, FDR p = 0.005) (KIF25, PINX1). We were able to replicate nsSNP associations for POLG/FANCI, BRCA1, FANCA and CHD1L in independent data sets. Mechanism-oriented phenotyping using collections of EMR-derived diagnoses can elucidate fundamental disease mechanisms. 相似文献
9.
10.
Katherine S. Lindeburg Peter Almond Josh J. Roering Oliver A. Chadwick 《Plant and Soil》2013,367(1-2):57-75