Effects of complex life cycles on genetic diversity: cyclical parthenogenesis.

Neutral patterns of population genetic diversity in species with complex life cycles are difficult to anticipate. Cyclical parthenogenesis (CP), in which organisms undergo several rounds of clonal reproduction followed by a sexual event, is one such life cycle. Many species, including crop pests (aphids), human parasites (trematodes) or models used in evolutionary science (Daphnia), are cyclical parthenogens. It is therefore crucial to understand the impact of such a life cycle on neutral genetic diversity. In this paper, we describe distributions of genetic diversity under conditions of CP with various clonal phase lengths. Using a Markov chain model of CP for a single locus and individual-based simulations for two loci, our analysis first demonstrates that strong departures from full sexuality are observed after only a few generations of clonality. The convergence towards predictions made under conditions of full clonality during the clonal phase depends on the balance between mutations and genetic drift. Second, the sexual event of CP usually resets the genetic diversity at a single locus towards predictions made under full sexuality. However, this single recombination event is insufficient to reshuffle gametic phases towards full-sexuality predictions. Finally, for similar levels of clonality, CP and acyclic partial clonality (wherein a fixed proportion of individuals are clonally produced within each generation) differentially affect the distribution of genetic diversity. Overall, this work provides solid predictions of neutral genetic diversity that may serve as a null model in detecting the action of common evolutionary or demographic processes in cyclical parthenogens (for example, selection or bottlenecks).

Zonal shear and super-rotation in a magnetized spherical Couette-flow experiment.

We present measurements performed in a spherical shell filled with liquid sodium, where a 74-mm-radius inner sphere is rotated while a 210-mm-radius outer sphere is at rest. The inner sphere holds a dipolar magnetic field and acts as a magnetic propeller when rotated. In this experimental setup called "Derviche Tourneur Sodium" (DTS), direct measurements of the velocity are performed by ultrasonic Doppler velocimetry. Differences in electric potential and the induced magnetic field are also measured to characterize the magnetohydrodynamic flow. Rotation frequencies of the inner sphere are varied between -30 Hz and +30 Hz, the magnetic Reynolds number based on measured sodium velocities and on the shell radius reaching to about 33. We have investigated the mean axisymmetric part of the flow, which consists of differential rotation. Strong super-rotation of the fluid with respect to the rotating inner sphere is directly measured. It is found that the organization of the mean flow does not change much throughout the entire range of parameters covered by our experiment. The direct measurements of zonal velocity give a nice illustration of Ferraro's law of isorotation in the vicinity of the inner sphere, where magnetic forces dominate inertial ones. The transition from a Ferraro regime in the interior to a geostrophic regime, where inertial forces predominate, in the outer regions has been well documented. It takes place where the local Elsasser number is about 1. A quantitative agreement with nonlinear numerical simulations is obtained when keeping the same Elsasser number. The experiments also reveal a region that violates Ferraro's law just above the inner sphere.

A branching process, its application in biology: influence of demographic parameters on the social structure in mammal groups.

Branching processes are widely used in biology. This theoretical tool is used in cell dynamics, epidemics and population dynamics. In population dynamics, branching processes are mainly used to access extinction probabilities of populations, groups or families, with the Galton-Watson branching process. Many mammal species live in socially-structured groups, and the smallest units of these groups are lineages (or families) of kin-related individuals. In many primate species, these lineages are matrilines, as females remain in their natal groups most of the time, whereas males generally disperse. Lineage parameters, such as numbers of matrilines, size of each matriline and average degree of relatedness, could strongly influence the genetic composition of groups. Evidence indicates that division along matrilines could induce substantial differentiation among fission groups. Here, we develop a novel mathematical model based on the branching process theory describing demographic dynamics of groups. The main result of this model is an explicit analytical expression of the joint distribution of numbers of lineages and sizes of socially-structured groups. We investigated the influence of parameters such as natality and mortality on the outcome of the process, including extinction probability. Finally, we discuss this theoretical result with respect to biological significance.

Gingival coverage of denuded root surfaces. An historical review of four surgical procedures.

A review of four distinct surgical procedures, designed to provide coverage of denuded root surfaces resulting from gingival recession, is presented. Each procedure is supported by photographs illustrating the surgical technique for each. Principles yielding a high degree of predictability, applied to appropriately diagnosed and selected cases are reviewed.

[Esthetics in periodontal surgery: description and discussion of an incision and suture technic]. / L'esthétique en chirurgie parodontale: description et discussion d'une technique d'incision et de suture.

One of the main aspects from a patient's standpoint regarding periodontal therapy is esthetics; the clinician who wants to control the disease by pocket elimination may underestimate this fact. This article describes a conservative surgical approach and a type of modified vertical mattress suture which allows repositioning of soft tissues to a preoperative level. A discussion follows on how such a conservative approach respects the philosophy of modern periodontal therapy.

[Study of statistical test connections in non-orthogonal analysis of variance]. / Etude des liaisons statistiques de tests en analyse de variance non orthogonale.

In the Analysis of Variance, we quite often split up the model to test different hypotheses about the model. However, when we analyse the results, we must not forget that the statistics used for the tests are not stochastically independent, either for an orthogonal design, because the test statistics have the same denominator, or for non-orthogonal design. In the latter case, test statistics have not only the same denominator but also not-independent numerators. The links between test statistics have been studied for orthogonal designs (Dall'Aglio, 1962) and for symmetrical Incomplete Block Design (Ballas and Webster, 1966). We shall give here results for the general case of the Analysis of Variance, treat more particularly the case of the Incomplete Block Design and show the joint distribution of two test statistics and, more simply, their correlation coefficient.

[Lumbar epidural veins. Normal radioanatomy (author's transl)]. / Les veines lombaires épidurales. Radio-anatomie normale

Epidural venous system of the human corps are injected by a fortacryl-minium mixture then dissected with detail. These study confirms existence of two longitudinal venous plexus: one anterior and internal, one another anterior and external. There is no posterior longitudinal venous plexus.

[Lumbar epidural veins (anatomic study apropos of 31 cases)]. / Les veines épidurales lombaires (etude anatomique à propos de 31 cas).

Using 31 corrosion preparations with fortacryl-minium, a new systematization of lumbar internal vertebral veins is suggested. The classical posterior longitudinal vein was not found. An anterior-lateral venous flow, composed of an anterior-internal venous canal and of an anterior-external venous canal was described. These venous canals jointly progress along internal face of the pedicle and leave a wider space between them in front of the exit foramina, to allow the passage of roots. The authors then study the transversal veins, the junction of the lumbar column with the sacral column and veins of the exit foramina.

Cavum veli interpositi. Roentgen anatomy - pathology and physiology.

158 pneumoencephalographies of infants less than 2 years old were examined and 53 of them had a large cavum veli interpositi. A neuroradiological description of this cistern is given and a comparison made with injected anatomical specimens. A statistical comparison with 105 pneumoencephalographies without a cavum veli interpositi does not shown any correlation between the presence of this cistern and pathological conditions. This investigation indicates that a large cavum veli interpositi in the newborn has no relation to hydrocephalus or cerebral atrophy. The younger the child, the more frequent is the presence of this cistern, especially under eight months of age.

[Anatomo-radiological study of the spinal venous system of the lumbo-sacral junction]. / Contribution à l'étude anatomo-radiologique du système veineux rachidien de la jonction lombo-sacrée

Transfemoral ascending lumbar catheterization of the epidural veins is a new radiological method in lumbar disk disease. The technique and interpretation of the venogram offer some problems: Origin of ascending lumbar vein and internal vertebral venous structures are variable. The authors use 11 corrosion preparations and 18 venograms for the study of the ascending lumbar vein and internal vertebral venous system.