Oxygen-18 enrichment of planktonic foraminifera due to gametogenic calcification below the euphotic zone

Empty shells of spinose planktonic foraminifera on the seabed are significantly enriched in oxygen-18 as compared with the shells of their living counterparts in surface waters. This enrichment is due to gametogenic calcification, which extracts calcium carbonate from deeper and colder waters as the shell sinks below the euphotic zone. JEAN-CLAUDE DUPLESSY.     

Spatial and temporal distribution of geminiviruses in leafhoppers of the genus cicadulina monitored by conventional and quantitative polymerase chain reaction

ABSTRACT Spatial and temporal distribution of Maize streak virus (MSV, family Geminiviridae, genus Mastrevirus) was monitored in the vector species Cicadulina mbila and the nonvector species C. china? using conventional and real-time quantitative polymerase chain reaction. Sustained feeding on MSV-infected plants showed that virus accumulation reaches a maximum in C. china?, but not in C. mbila. After a 3-day acquisition access feeding period (AAP), MSV was detected in the gut, the hemolymph, and the head of C. mbila, but only in the gut of C. china?. Similarly, Digitaria streak virus (genus Mastrevirus), which is not transmitted by either of the two species, was only detected in the gut. MSV was detected in the hemolymph of C. mbila 3 h after the beginning of the AAP. Although viral DNA progressively decreases in the vector and nonvector species after a 3-day AAP, MSV DNA remained stable in the salivary glands of C. mbila.     

Effect of Oil Overlay on Inhibition Potential of Roscovitine in Sheep Cumulus‐Oocyte Complexes

Inhibitors of cyclin‐dependent kinases, as roscovitine, have been used to prevent the spontaneous resumption of meiosis in vitro and to improve the oocyte developmental competence. In this study, the interference of oil overlay on the reversible arrest capacity of roscovitine in sheep oocytes as well as its effects on cumulus expansion was evaluated. For this, cumulus‐oocyte complexes (COCs) were cultured for 20 h in TCM 199 with 10% foetal bovine serum (Control) containing 75 μm roscovitine (Rosco). Subsequently, they were in vitro matured (IVM) for further 18 h in inhibitor‐free medium with LH and FSH. The culture was performed in Petri dishes under mineral oil (+) or in 96 well plates without oil overlay (?) at 38.5°C and 5% CO₂. At 20 and 38 h, the cumulus expansion and nuclear maturation were evaluated under stereomicroscope and by Hoechst 33342 staining, respectively. No group presented cumulus expansion at 20 h. After additional culture with gonadotrophins, a significant rate of COCs from both Control groups (+/?) exhibited total expansion while in both Rosco groups (+/?) the partial expansion prevailed. Among the oocytes treated with roscovitine, 65.2% were kept at GV in the absence of oil overlay while 40.6% of them reached MII under oil cover (p < 0.05). This meiotic arrest was reversible, and proper meiosis progression also occurred in the Control groups (+/?). So, the culture system without oil overlay improved the meiotic inhibition promoted by roscovitine without affecting the cumulus expansion rate or the subsequent meiosis progression.     

Comparison of experimental designs for estimating quantitative genetic parameters in fish

Four popular experimental designs for estimating variance components of additive genetic effects and (secondarily) dominance and maternal effects in fish (full‐sib families, half‐sib families, nested design and factorial design) were compared. The error variances of the estimators were formulated as functions of the true (hypothetical) values of genetic and environmental variances, depending on the experimental design considered, and whether the families were reared separately or mixed. Half‐sib families and rectangular (many sires×few dams) factorial design were most useful for the estimation of heritability. The nested design appeared much less adequate. The minimum experimental capacity for obtaining accurate estimates was 100 lots in separate rearing or 1000 fish in mixed rearing. A larger experimental capacity is required when dominance and maternal effects as well as heritability are to be estimated because these different estimations, requiring contradictory conditions, cannot be simultaneously optimized.     

Impact of selective logging on genetic composition and demographic structure of four tropical tree species

Over-exploitation and fragmentation are serious problems for tropical forests. Most sustainable forest management practices avoid clear-cuts and apply selective logging systems focused on a few commercial species. We applied a simulation model to estimate the impact of such selective logging scenarios on the genetic diversity and demography of four tropical tree species from French Guiana. The simulations used data on genetic and demographic composition, growth, phenology and pollen and seed dispersal obtained for Dicorynia guianensis, Sextonia rubra, Symphonia globulifera and Vouacapoua americana at the experimental site in Paracou. Whereas Symphonia globulifera serves as a model for a species with low logging pressure, the other three species represent the most exploited tree species in French Guiana. In simulations with moderate logging, typical for French Guiana, with large cutting diameter (>60 cm diameter) and long cutting cycles (65 years), the two species V. americana and Sextonia rubra were not able to recover their initial stock at the end of the rotation period, with a large decrease in the number of individuals and in basal area. Under a more intensive logging system (cutting diameter >45 cm diameter, cutting cycles of 30 years) that is common practice in the Brazilian Amazon, only Symphonia globulifera showed no negative impact. Generally, the differences between the genetic parameters in the control scenarios without logging and the logging scenarios were surprisingly small. The main reasons for this were the overlapping of generations and the effective dispersal ability of gene vectors in all species, which guarantee relative homogeneity of the genetic structure in different age classes. Nevertheless, decreasing the population size by logging reduced the number of genotypes and caused higher genetic distances between the original population and the population at the end of the logging cycles. Sensitivity analysis showed that genetic changes in the logging scenarios were principally determined by the growth, densities and cutting diameter of each species, and only to a very small extent by the reproductive system including factors such as pollen and seed dispersal and flowering phenology.     

Errors in repeated measurements of soil water content in pots using a ThetaProbe

Abstract. The accuracy of a ThetaProbe (Delta-T Devices Ltd, UK) to obtain repeated measures of soil water content in pot plants was tested. This alternative to balance determinations led to a large underestimation of water content, varying from 12.2 to 21.8% of the total water content, depending on soil type.