The calcium current in inner segments of rods from the salamander (Ambystoma tigrinum) retina.

Solitary rod inner segments were isolated from salamander retinae. Their Ca current was studied with the 'whole-cell, gigaseal' technique (Hamill, Marty, Neher, Sakmann & Sigworth, 1981). The soluble constituents of the cytoplasm exchanged with the solution in the pipette. The external solution could be changed during continuous perfusion. Membrane voltage was controlled with a voltage clamp. After permeant ions other than Ca were replaced with impermeant ions (i.e. tetraethylammonium as a cation, and aspartate or methanesulphonate as an anion), an inward current remained. It activated at approximately -40 mV, reached a maximum at approximately 0 mV, and decreased as the membrane was further depolarized. The size of the current increased when Ba was substituted for external Ca. The current was blocked when Ca was replaced with Co. The voltage at which the current was half-maximum shifted from approximately -22 to -31 mV during the initial 3 min of an experiment. The maximum amplitude of the current continuously declined during the entire course of an experiment. The time course for activation of the Ca current following a step of depolarization could be described by the sum of two exponentials. The time constant of the slower exponential was voltage dependent. Deactivation following repolarization could also be described by the sum of two exponentials. Both time constants for deactivation were independent of voltage (between -30 and 0 mV) and faster than the slower time constant for activation. When the internal Ca concentration was buffered by 10 mM-EGTA, the Ca current did not inactivate during several seconds of maintained depolarization. When the concentration of EGTA was reduced to 0.1 mM, the Ca current declined and the membrane conductance decreased during several seconds of maintained depolarization. This inactivation was incomplete and only occurred after a substantial quantity of Ca entered. Following repolarization the Ca conductance recovered from inactivation. In contrast, the continuous decline observed during the course of an experiment (item 3) was not reversible. The difference suggests that inactivation and the decline are distinct processes

Microbial Response to the MC-252 Oil and Corexit 9500 in the Gulf of Mexico

The Deepwater Horizon spill released over 4.1 million barrels of crude oil into the Gulf of Mexico. In an effort to mitigate large oil slicks, the dispersant Corexit 9500 was sprayed onto surface slicks and injected directly at the wellhead at water depth of 1,500 m. Several research groups were involved in investigating the fate of the MC-252 oil using newly advanced molecular tools to elucidate microbial interactions with oil, gases, and dispersant. Microbial community analysis by different research groups revealed that hydrocarbon degrading bacteria belonging to Oceanospirillales, Colwellia, Cycloclasticus, Rhodobacterales, Pseudoalteromonas, and methylotrophs were found enriched in the contaminated water column. Presented here is a comprehensive overview of the ecogenomics of microbial degradation of MC-252 oil and gases in the water column and shorelines. We also present some insight into the fate of the dispersant Corexit 9500 that was added to aid in oil dispersion process. Our results show the dispersant was not toxic to the indigenous microbes at concentrations added, and different bacterial species isolated in the aftermath of the spill were able to degrade the various components of Corexit 9500 that included hydrocarbons, glycols, and dioctyl sulfosuccinate

Sexual reproduction and biometry of the nonzooxanthellate papillose cup coral Paracyathus pulchellus

Basic information on the reproductive biology of many scleractinian corals species is limited or entirely lacking, particularly from temperate zones, though it is essential for a better understanding of their ecology. This study describes the morphological aspects and the annual cycle of gametogenesis and biometric parameters of the papillose cup coral Paracyathus pulchellus collected at Palinuro (Italy, Southern Tyrrhenian Sea), filling a knowledge gap about the reproductive biology of a widespread Mediterranean and Northern Atlantic coral. Samples of P. pulchellus were collected by SCUBA diving between 5- and 10-meters depth during 18 monthly collections from June 2010 to December 2011. Sexually active polyps displayed either oocytes or spermaries, indicating that P. pulchellus was gonochoric. The sex ratio of sexually active polyps was 1:1. Gametogenesis began with undifferentiated germ cells arose in the gastrodermis that migrated towards the mesoglea of the mesentery where they completed the development. During spermatogenesis, spermary diameter increased from 25 to 83 µm. Oocyte diameter ranged from 9 to 146 µm and during oogenesis the nucleus/cytoplasm ratio decreased due to the accumulation of yolk. The nucleus migrated to the periphery of the oocyte adhering closely to the cell membrane. No embryo was observed in the coelenteric cavity of the polyps, suggesting an external development of planktotrophic larvae due to the small-sized mature oocytes and a possible broadcast spawning reproductive mode. Gonadal index of both females and males increased significantly from August until November and fertilization took place from November to January. Only sexually inactive individuals were observed from February to April, suggesting a quiescence period in both males and females. Seasonal variations in water temperature and photoperiod may have a key role in regulating gametogenesis. The analysis of the main biometric parameters (polyp width, height, dry skeletal mass, volume, surface/volume ratio and bulk skeletal density) showed a negative correlation between size and skeletal density, and no sexual dimorphism

Reproduction of the azooxanthellate coral Caryophyllia inornata is not affected by temperature along an 850 km gradient on the Western Italian coast

The Intergovernmental Panel on Climate Change (IPCC) predicted that ocean surface temperature will rise of 0.6–2.0◦C by 2100. Ocean warming is expected to produce strong impacts on marine ecosystems such as coral reefs, affecting their physiological events including reproductive processes. To date, relatively few studies have examined the effects of climate change on the reproductive success of temperate corals and even less in the azooxanthellate ones. This study examined the reproductive output of the azooxanthellate Mediterranean coral Caryophyllia inornata along a wide latitudinal gradient of seawater temperature and solar radiation. A total of 260 samples, collected from five populations along the Western Italian coast, have been analyzed through histological techniques. The intriguing aspects characterizing all populations of C. inornata along the latitudinal gradient are a strong male-biased sex ratio and the presence of embryos in all stages of development throughout the year in females, males, and sexually inactive individuals. This peculiarity could suggest a mixed strategy of sexual and asexual reproduction in this species as has been observed for some anemones of the genus Actinia. Fecundity and spermary abundance (i.e., the number of reproductive elements per body volume unit), gonadal index (i.e., the percentage of body volume occupied by the germ cells) and fertility (i.e., the number of embryos per body volume unit) in females, males and sexually inactive individuals were unrelated to solar radiation and temperature along the latitudinal gradient. These results suggest that the reproduction in C. inornata is not affected by increasing solar radiation and temperature. The lack of zooxanthellae could make this species less dependent on these environmental parameters, as previously hypothesized for another azooxanthellate species, Leptopsammia pruvoti, investigated along the same gradient

Ocean warming and acidification detrimentally affect coral tissue regeneration at a Mediterranean CO2 vent

Among the main phenomena that are causing significant changes in ocean waters are warming and acidification, largely due to anthropogenic activities. Growing evidence suggests that climate change is having more substantial and rapid effects on marine communities than on terrestrial ones, triggering several physiological responses in these organisms, including in corals. Here we investigated, for first time in the field, the combined effect of increasing seawater acidification and warming on tissue regeneration rate of three Mediterranean scleractinian coral species characterized by different trophic strategies and growth modes. Balanophyllia europaea (solitary, zooxanthellate), Leptopsammia pruvoti (solitary, non-zooxanthellate) and Astroides calycularis (colonial, non-zooxanthellate) specimens were transplanted, during a cold, intermediate, and warm period, along a natural pH gradient generated by an underwater volcanic crater at Panarea Island (Mediterranean Sea, Italy), characterized by continuous and localized CO2 emissions at ambient temperature. Our results show a decrease in regenerative capacity, especially in the zooxanthellate species, with increasing seawater temperature and acidification, with demonstrated species-specific differences. This finding suggests that increasing seawater temperature and acidification could have a compounding effect on coral regeneration following injury, potentially hindering the capacity of corals to recover following physical disturbance under predicted climate change

A system in balance? ? Implications of deep vertical mixing for the nitrogen budget in the northern Red Sea, including the Gulf of Aqaba (Eilat)

International audienceWe investigated the implications of deep winter mixing for the nitrogen budget in two adjacent systems, the northern Red Sea proper, and the Gulf of Aqaba. Both are subtropical oligotrophic water bodies. The main difference is that in the gulf deep winter mixing takes place regularly, whereas the northern Red Sea proper is permanently stratified. In the Gulf of Aqaba, we observed significantly lower nitrate deficits, i.e. deviations from the Redfield ratio, than in the northern Red Sea proper. Assuming that other external inputs and losses in N or P are very similar in both systems, the higher nitrate deficit can be explained by either lower nitrogen fixation in the (stratified) northern Red Sea, which seems unlikely. An alternative explanation would be higher rates of benthic denitrification than in the gulf. By comparing the two systems we have indirect evidence that benthic denitrification was much lower in the Gulf of Aqaba due to higher oxygen concentrations. This we attributed to the occurrence of deep winter mixing, and as a consequence, the nitrate deficit was close to zero (i.e. N:P ratio close to "Redfield"). If both nitrogen fixation and benthic denitrification take place, as in the northern Red Sea proper, the result was a positive nitrate deficit (i.e. a deficit in nitrate) in the ambient water. The nitrate deficit in the northern Red Sea was observed in spite of high iron deposition from the surrounding desert. Our results strongly support the concept of nitrogen as the proximate, and phosphate as the ultimate limiting nutrient for primary production in the sea. This must not be neglected in efforts for protecting the adjacent reefs against eutrophication

The secondary infall model of galactic halo formation and the spectrum of cold dark matter particles on Earth

The spectrum of cold dark matter particles on Earth is expected to have peaks in velocity space associated with particles which are falling onto the Galaxy for the first time and with particles which have fallen in and out of the Galaxy only a small number of times in the past. We obtain estimates for the velocity magnitudes and the local densities of the particles in these peaks. To this end we use the secondary infall model of galactic halo formation which we have generalized to take account of the angular momentum of the dark matter particles. The new model is still spherically symmetric and it admits self-similar solutions. In the absence of angular momentum, the model produces flat rotation curves for a large range of values of a parameter $\epsilon$ which is related to the spectrum of primordial density perturbations. We find that the presence of angular momentum produces an effective core radius, i.e. it makes the contribution of the halo to the rotation curve go to zero at zero radius. The model provides a detailed description of the large scale properties of galactic halos including their density profiles, their extent and total mass. We obtain predictions for the kinetic energies of the particles in the velocity peaks and estimates for their local densities as functions of the amount of angular momentum, the age of the universe and $\epsilon$.Comment: LaTeX, 39 pages including 18 figure

The fundamental cycle of concept construction underlying various theoretical frameworks

In this paper, the development of mathematical concepts over time is considered. Particular reference is given to the shifting of attention from step-by-step procedures that are performed in time, to symbolism that can be manipulated as mental entities on paper and in the mind. The development is analysed using different theoretical perspectives, including the SOLO model and various theories of concept construction to reveal a fundamental cycle underlying the building of concepts that features widely in different ways of thinking that occurs throughout mathematical learning

Low and variable pH decreases recruitment efficiency in populations of a temperate coral naturally present at a CO2 vent

Atmospheric carbon dioxide enrichment alters seawater carbonate chemistry, thus threatening calcifying organisms such as corals. Coral populations at carbon dioxide vents are natural acidification experiments that mimic organism responses to seawater pH values projected for 2100. Even if demographic traits are paramount information to assess ecological relationships and habitat suitability, population dynamics studies on corals thriving under acidified conditions are lacking. Here, we investigate the demography and reproduction of popu- lations of the solitary, symbiotic, temperate coral Balanophyllia europaea naturally living along a pH gradient at a Mediterranean CO2 vent. Gametogenesis and larval production were unaffected while recruitment efficiency collapsed at low and variable pH, contributing to coral abundance decline and suggesting that life stages between larval release and early polyp growth are hindered by acidification. Exploring these processes is crucial to assess coral fate in the forthcoming acidified oceans, to preserve coral ecosystems and the socioeconomic ser- vices they provide