3,368 research outputs found
Effect of Ammonium Enrichment on Animal and Algal Biomass of the Coral Pocillopora damicornis
Algal and animal biomass parameters of colonies of the Pacific
coral Pocillopora damicornis (Linnaeus) were measured as a function of time of
exposure to elevated concentrations of seawater ammonium (20 and 50 uM
[(NH4)2S04]) ranging from 2 to 8 weeks. Areal concentrations of zooxanthellae,
chlorophyll, and protein increased with 20 uM ammonium addition. During
the 8-week period of exposure to 20 uM ammonium, the population density
of zooxanthellae increased from 3.5 to 7.5 x 105 cells cm-2, chlorophyll a
content of zooxanthellae increased from 5.7 to 8.6 pg, and animal protein
concentration doubled (from 0.74 to 1.38 mg cm-2). These data indicate that
both the coral animal and the zooxanthellae respond to the addition of exogenous
dissolved inorganic nitrogen provided as 20 uM ammonium. Growth of
the symbiotic association in response to the addition of 20 uM ammonium adds
further evidence to support the argument that growth of tropical symbioses is
limited by the availability of nitrogen. However, the coral response is likely to
depend on the concentration of ammonium provided, because the biomass
parameters of corals held at 50 uM ammonium did not change significantly
with time of exposure to the added nutrient
Seasonal Stability of a Flexible Algal-Cnidarian Symbiosis in a Highly Variable Temperate Environment
We evaluated the seasonal stability of two algal symbiont populations in the temperate intertidal sea anemone Anthopleura elegantissima on San Juan Island, Washington, where the relatively thermally tolerant dinoflagellate Symbiodinium muscatinei coexists with the less thermally tolerant chlorophyte Elliptochloris marina. Random collection of anemones along repeatedly sampled transects over four seasons and three shore heights revealed S. muscatinei to be the dominant symbiont, with E. marina mostly limited to anemones in the lower intertidal zone. At the lowest shore height sampled (+0.2 m), the proportion of E. marina was between 40% and 50% of the total symbiont population throughout the year. Symbiont distribution patterns persisted despite considerable seasonal variation in aerial exposure, temperature, irradiance, nutrients, and phytoplankton concentration, as well as a high potential for symbiont shuffling, with mixed-symbiont assemblages occurring in 51% of all anemones sampled. Symbiont density in anemones also changed little despite three- to fourfold-higher division frequencies of both symbionts during July and November. Although the intertidal zonation of these symbionts was stable over an annual period, we predict that their spatial distributions will be responsive to longer-term environmental change, and anticipate that this anemone symbiosis will be a useful and highly tractable barometer for future climate change, with this study serving as a baseline
The Role of β7 Integrins in CD8 T Cell Trafficking During an Antiviral Immune Response
The requirement of β7 integrins for lymphocyte migration was examined during an ongoing immune response in vivo. Transgenic mice (OT-I) expressing an ovalbumin-specific major histocompatibility complex class Iârestricted T cell receptor for antigen were rendered deficient in expression of all β7 integrins or only the ÎąEβ7 integrin. To quantitate the relative use of β7 integrins in migration in vivo, equal numbers of OT-I and OT-I-β7â/â or OT-I-ÎąEâ/â lymph node (LN) cells were adoptively transferred to normal mice. Although OT-I-β7â/â LN cells migrated to mesenteric LN and peripheral LN as well as wild-type cells, β7 integrins were required for naive CD8 T cell and B cell migration to Peyer's patch. After infection with a recombinant virus (vesicular stomatitis virus) encoding ovalbumin, β7 integrins became critical for migration of activated CD8 T cells to the mesenteric LN and Peyer's patch. Naive CD8 T cells did not enter the lamina propria or the intestinal epithelium, and the majority of migration of activated CD8 T cells to the small and large intestinal mucosa, including the epithelium, was β7 integrinâmediated. The ÎąEβ7 integrin appeared to play no role in migration during a primary CD8 T cell immune response in vivo. Furthermore, despite dramatic upregulation of ÎąEβ7 by CD8 T cells after entry into the epithelium, long-term retention of intestinal intraepithelial lymphocytes was also ÎąEβ7 independent
Identification of the Beagle 2 lander on Mars
The 2003 Beagle 2 Mars lander has been identified in Isidis Planitia at 90.43°âE, 11.53°âN, close to the predicted target of 90.50°âE, 11.53°âN. Beagle 2 was an exobiology lander designed to look for isotopic and compositional signs of life on Mars, as part of the European Space Agency Mars Express (MEX) mission. The 2004 recalculation of the original landing ellipse from a 3-sigma major axis from 174âkm to 57âkm, and the acquisition of Mars Reconnaissance Orbiter High Resolution Imaging Science Experiment (HiRISE) imagery at 30â
cm per pixel across the target region, led to the initial identification of the lander in 2014. Following this, more HiRISE images, giving a total of 15, including red and blue-green colours, were obtained over the area of interest and searched, which allowed sub-pixel imaging using super high-resolution techniques. The size (approx. 1.5âm), distinctive multilobed shape, high reflectivity relative to the local terrain, specular reflections, and location close to the centre of the planned landing ellipse led to the identification of the Beagle 2 lander. The shape of the imaged lander, although to some extent masked by the specular reflections in the various images, is consistent with deployment of the lander lid and then some or all solar panels. Failure to fully deploy the panels-which may have been caused by damage during landing-would have prohibited communication between the lander and MEX and commencement of science operations. This implies that the main part of the entry, descent and landing sequence, the ejection from MEX, atmospheric entry and parachute deployment, and landing worked as planned with perhaps only the final full panel deployment failing
The mass and density of the dwarf planet (225088) 2007 OR10
The satellite of (225088) 2007 OR10 was discovered on archival Hubble Space
Telescope images and along with new observations with the WFC3 camera in late
2017 we have been able to determine the orbit. The orbit's notable
eccentricity, e0.3, may be a consequence of an intrinsically eccentric
orbit and slow tidal evolution, but may also be caused by the Kozai mechanism.
Dynamical considerations also suggest that the moon is small, D 100
km. Based on the newly determined system mass of 1.75x10 kg, 2007 OR10
is the fifth most massive dwarf planet after Eris, Pluto, Haumea and Makemake.
The newly determined orbit has also been considered as an additional option in
our radiometric analysis, provided that the moon orbits in the equatorial plane
of the primary. Assuming a spherical shape for the primary this approach
provides a size of 123050 km, with a slight dependence on the satellite
orbit orientation and primary rotation rate chosen, and a bulk density of
1.750.07 g cm for the primary. A previous size estimate that
assumed an equator-on configuration (1535 km) would provide a
density of 0.92 g cm, unexpectedly low for a 1000
km-sized dwarf planet.Comment: Accepted for publication in Icaru
Synthesis, stereocontrol and structural studies of highly luminescent chiral tris-amidepyridyl-triazacyclononane lanthanide complexes
Symbiont presence and identity influence life history strategies of a temperate sea anemone
Along the North American Pacific coast, the common intertidal sea anemone Anthopleura elegantissima engages in facultative, flexible symbioses with Symbiodinium muscatinei (a dinoflagellate) and Elliptochloris marina (a chloro- phyte). Determining how symbiotic state affects host fitness is essential to understanding the ecological significance of engaging in such flexible relationships with diverse symbionts. Fitness consequences of hosting S. muscatinei, E. marina or negligible numbers of either symbiont (aposymbiosis) were investigated by measuring growth, cloning by fission and gonad development after 8.5 â 11 months of sustained exposure to high, moderate or low irradiance under seasonal environmental conditions. Both symbiotic state and irradiance affected host fitness, leading to divergent life-history strategies. Moderate and high irradiances led to a greater level of gonad development in individuals hosting E. marina, while high irradiance and high summer temperature promoted cloning in individuals hosting S. muscatinei and reduced fitness of aposymbiotic anemones. Associating with S. muscatinei may contribute to the success of A. elegantissima as a spatial competitor on the high shore: (i) by offsetting the costs of living under high temperature and irradiance conditions, and (ii) by promoting a high fission rate and clonal expansion. Our results suggest that basic life-history characteristics of a clonal cnidarian can be affected by the identity of the endosymbionts it hosts
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