Larval and early juvenile development of Lithodes santolla (Molina, 1782) (Decapoda: Anomura: Lithodidae) reared at different temperatures in the laboratory

The southern king crab, Lithodes santolla Molina, is distributed in cold-temperate and subantarctic waters ranging from the southeastern Pacific island of Chiloé (Chile) and the deep Atlantic waters off Uruguay, south to the Beagle Channel (Tierra del Fuego, Argentina/Chile). Recent investigations have shown that its complete larval development from hatching to metamorphosis, comprising three zoeal stages and a megalopa, is fully lecithotrophic, i.e. independent of food. In the present study, larvae were individually reared in the laboratory at seven constant temperatures ranging from 1 to 18 °C, and rates of survival and development through successive larval and early juvenile stages were monitored throughout a period of 1 year. The highest temperature (18 °C) caused complete mortality within 1 week; only a single individual moulted under this condition, 2 days after hatching, to the second zoeal stage, while all other larvae died later in the zoea I stage. At the coldest condition (1 °C), 71% of the larvae reached the zoea III stage, but none of these moulted successfully to a megalopa. A temperature of 3 °C allowed for some survival to the megalopa stage (17-33% in larvae obtained from two different females), but only a single individual passed successfully, 129 days after hatching, through metamorphosis to the first juvenile crab instar. At all other experimental conditions (6, 9, 12 and 15 °C), survival through metamorphosis varied among temperatures and two hatches from 29% to 90% without showing a consistent trend. The time of nonfeeding development from hatching to metamorphosis lasted, on average, from 19 days at 15 °C to 65 days at 6 °C. The relationship between the time of development through individual larval or juvenile stages (D) and temperature (T) was described as a power function (D=aT^b, or log[D]=log[a]blog[T]). The same model was also used to describe the temperature dependence of cumulative periods of development from hatching to later larval or juvenile stages. One year after hatching, the 7th (6 °C) to 9th (15 °C) crab instar was reached. Under natural temperature conditions in the region of origin of our material (Beagle Channel, Argentina), L. santolla should reach metamorphosis in October-December, i.e. ca. 2 months after hatching (taking place in winter and early spring). Within 1 year from hatching, the crabs should grow approximately to juvenile instars VII-VIII. Our results indicate that the early life-history stages of L. santolla tolerate moderate cold stress as well as planktonic food-limitation in winter, implying that this species is well adapted to subantarctic environments with low temperatures and a short seasonal plankton production.     

Effects of nitrogen addition on nitrogen metabolism and carbon reserves in the temperate seagrass Posidonia oceanica

The effect of repeated N additions on a dense, shallow meadow of Posidonia oceanica (L.) Delile in the NW Mediterranean was studied over a year. N was added biweekly both to the sediment and to the water column as ammonium and nitrate. The most obvious result of these additions was an overall increase in N content (% DW) in all tissues of fertilized plants; this increase was maximum in rhizomes, with values of 5% N reached, which confirmed the storage capacities of these organs.Fertilization affected the different N fractions in distinct ways. The free amino acid (FAA) concentration increased the most, particularly in rhizomes and roots, suggesting the function of these compounds for N storage and, probably, translocation. The non-soluble N fraction also increased greatly. The total soluble protein (TSP) and the inorganic N forms concentrations were less sensitive to fertilization, and only increased moderately in a few cases. N assimilation, assessed through in vivo glutamine synthetase (GS) activity, was maximum in leaves after the peak of growth, which coincided with the lowest N values in both control and fertilized plants. Thus assimilation was probably greatest at the period of highest N deficiency. Growth rates did not respond to N enrichment. Another clear effect of N addition was to decrease carbon reserves. In effect, the concentration of total non-structural carbohydrate (TNC) greatly decreased in rhizomes of fertilized plants, coinciding with the increase in FAA. We conclude that increased nitrogen availability can affect plant survival through the decrease in their carbon reserves, crucial for P. oceanica overwintering. This interaction between N and C metabolism helps to explain changes in benthic vegetation after steadily increasing coastal water eutrophication.     

伊比利亚河共生的当年生鳟和埃布罗河鳟的夏季摄食关系

1996-1998年8月在Larraun河(埃布罗河流域,西班牙北部)共捕获306尾埃布罗河(鱼岁)和185尾0龄的鳟,分析比较了胃含物组成,并测定了种间的食物重叠.食物的个数百分比组成表明两种都主要摄食水生无脊椎动物.摄食策略图显示两种都是摄食不同食物 种类的广食性种类.另外,比较胃含物和底栖大型无脊椎动物群落表明,0龄的鳟和埃布罗河(鱼岁)不摄食光螺科、钩虾科、细蜉科、 四节蜉科和卷襀科的物种,而喜食摇蚊科、五节蜉科和毛翅目物种.尽管简化的Morisitas指数表明Larraun河中这两种鱼之间的食物重叠是显著的,但由于栖息地不同和摄食的可塑性可以降低种间的竞争,使得该水域的这两种鱼能以相对较大的数量共存.然而,在食物资源和可用栖息地有限的河域,埃布罗河(鱼岁)的引入,其适应性和可塑性有可能威胁单独存在的鳟     

伊比利亚河共生的当年生鳟和埃布罗河鲒的夏季摄食关系

1996—1998年8月在Larraun河（埃布罗河流域,西班牙北部）共捕获306尾埃布罗河鱥和185尾0龄的鳟,分析比较了胃含物组成,并测定了种间的食物重叠。食物的个数百分比组成表明两种都主要摄食水生无脊椎动物。摄食策略图显示两种都是摄食不同食物种类的广食性种类。另外,比较胃含物和底栖大型无脊椎动物群落表明,0龄的鳟和埃布罗河鱥不摄食光螺科、钩虾科、细蜉科、四节蜉科和卷稹科的物种,而喜食摇蚊科、五节蜉科和毛翅目物种。尽管简化的Monsita’s指数表明Larraun河中这两种鱼之间的食物重叠是显著的,但由于栖息地不同和摄食的可塑性可以降低种间的竞争,使得该水域的这两种鱼能以相对较大的数量共存。然而,在食物资源和可用栖息地有限的河域,埃布罗河鱥的引入,其适应性和可塑性有可能威胁单独存在的鳟     

The flavodoxin from Helicobacter pylori: structural determinants of thermostability and FMN cofactor binding

Flavodoxin has been recently recognized as an essential protein for a number of pathogenic bacteria including Helicobacter pylori, where it has been proposed to constitute a target for antibacterial drug development. One way we are exploring to screen for novel inhibitory compounds is to perform thermal upshift assays, for which a detailed knowledge of protein thermostability and cofactor binding properties is of great help. However, very little is known on the stability and ligand binding properties of H. pylori flavodoxin, and its peculiar FMN binding site together with the variety of behaviors observed within the flavodoxin family preclude extrapolations. We have thus performed a detailed experimental and computational analysis of the thermostability and cofactor binding energetics of H. pylori flavodoxin, and we have found that the thermal unfolding equilibrium is more complex that any other previously described for flavodoxins as it involves the accumulation of two distinct equilibrium intermediates. Fortunately the entire stability and binding data can be satisfactorily fitted to a model, summarized in a simple phase diagram, where the cofactor only binds to the native state. On the other hand, we show how variability of thermal unfolding behavior within the flavodoxin family can be predicted using structure-energetics relationships implemented in the COREX algorithm. The different distribution and ranges of local stabilities of the Anabaena and H. pylori apoflavodoxins explain the essential experimental differences observed: much lower Tm1, greater resistance to global unfolding, and more pronounced cold denaturation in H. pylori. Finally, a new strategy is proposed to identify using COREX structural characteristics of equilibrium intermediate states populated during protein unfolding.     

Trace-fossils and minor discontinuities in a marl limestone rhythmite, Lower-Middle Kimmeridgian, southern Spain

In a fine-grained Lower to Middle Kimmeridgian marly limestone rhythmite succession, with scarce benthos, fluctuations in ecological and depositional conditions that affected the substrate are detected by analysing trace-fossil assemblages. The dominant grey mudstones with Chondrites and Planolites superimposed on lumpy matrix sediments indicate both late colonisation of dysaerobic mixed layers and the completeness of the stratigraphic record. Major disruptions in rhythmic deposition and substrate colonisation are recorded at the base of thick intercalations of marls in sedimentary packages that were related to tectonic instability. Minor disruptions affected only the deposition of the overlying limestone beds. The trace-fossils reveal changes in the ecological and depositional conditions affecting the substrate during deposition of monotonous marly limestone rhythmites at levels of resolution higher than biostratigraphic, ecostratigraphic and taphonomic resolution. This research demonstrates the application of trace-fossil analysis to approach stratigraphic completeness (maturation) in homogeneous marly limestone rhythmites     

Components of phenotypic variation in avian ornamental and non-ornamental feathers

Phenotypic variation, measured as the coefficient of variation (CV), is usually larger in secondary sexual characters than in ordinary morphological traits. We tested if intraspecific differences in the CV between ornamental and non-ornamental feather traits in 67 evolutionary events of feather ornamentation in birds were due to differences in (1) the allometric pattern (slope of the regression line when regressing trait size on an indicator of body size), or (2) the dispersion of observations around the regression line. We found that only dispersion of observations around the regression line contributed significantly to total variation. A large dispersion of observations around the regression line for ornamental feathers is consistent with these characters showing condition-dependence, supporting indicator models of sexual selection more strongly than a pure Fisher process. Ornamental feathers in males demonstrated negative allometry when regressed on tarsus length, which is a measure of skeletal body size. This finding is consistent with ornamental feather traits being subject to directional selection due to female mate preferences, where large body size is less important than in male–male competition. This pattern of phenotypic variation for avian secondary sexual characters contrasts with patterns of variation for insect genitalia, supposedly subject to sexual selection, since the latter traits only differ from ordinary morphology traits in allometry coefficient. The prevailing regime of selection (directional or stabilizing) and the effects of environmental factors are proposed to account for these differences among traits.     

Detection of a Salmonella enterica Serovar California Strain Spreading in Spanish Feed Mills and Genetic Characterization with DNA Microarrays

We performed an epidemiological study on Salmonella isolated from raw plant-based feed in Spanish mills. Overall, 32 different Salmonella serovars were detected. Despite its rare occurrence in humans and animals, Salmonella enterica serovar California was found to be the predominant serovar in Spanish feed mills. Different typing techniques showed that isolates of this serovar were genetically closely related, and comparative genomic hybridization using microarray technology revealed 23 S. enterica serovar Typhimurium LT2 gene clusters that are absent from serovar California.     

Colonization behaviour of Pseudomonas fluorescens and Sinorhizobium meliloti in the alfalfa (Medicago sativa) rhizosphere

The colonization ability of Pseudomonas fluorescens F113rif in alfalfa rhizosphere and its interactions with the alfalfa microsymbiont Sinorhizobium meliloti EFB1 has been analyzed. Both strains efficiently colonize the alfalfa rhizosphere in gnotobiotic systems and soil microcosms. Colonization dynamics of F113rif on alfalfa were similar to other plant systems previously studied but it is displaced by S. meliloti EFB1, lowering its population by one order of magnitude in co-inoculation experiments. GFP tagged strains used to study the colonization patterns by both strains indicated that P. fluorescens F113rif did not colonize root hairs while S. meliloti EFB1 extensively colonized this niche. Inoculation of F113rif had a deleterious effect on plants grown in gnotobiotic systems, possibly because of the production of HCN and the high populations reached in these systems. This effect was reversed by co-inoculation. Pseudomonas fluorescens F113 derivatives with biocontrol and bioremediation abilities have been developed in recent years. The results obtained support the possibility of using this bacterium in conjunction with alfalfa for biocontrol or rhizoremediation technologies.