Correlated evolution of mating strategy and inbreeding depression within and among populations of the hermaphroditic snail Physa acuta

Inbreeding depression is one of the main forces opposing the evolution of self-fertilization. Of central importance is the hypothesis that inbreeding depression and selfing coevolve antagonistically, generating either low selfing rate and high inbreeding depression or vice versa. However, there is limited evidence for this coevolution within species. We investigated this topic in the hermaphroditic snail Physa acuta. In this species, isolated individuals delay the onset of egg laying compared to individuals having access to mates. Longer delays (''waiting times'') indicate more intense selfing avoidance. We measured inbreeding depression and waiting time in a large quantitative-genetic experiment (281 outbred families derived from 26 natural populations). We observed large genetic variance for both traits and a strong positive genetic covariance between them, most of which resided within rather than among populations. It means that, within populations, individuals with higher mutation load avoided selfing more strongly on average. This genetic covariance may result from pleiotropy and/or linkage disequilibrium. Whatever its genetic architecture, the fact it emerges specifically when individuals are deprived of mates suggests it is not fortuitous and rather reflects the action of natural selection. We conclude that a diversity of mating strategies can arise within populations subjected to variation in inbreeding depression.

Symmetry-breaking in cumulative measures of shapes of polymer models.

Using numerical simulations we investigate shapes of random equilateral open and closed chains, one of the simplest models of freely fluctuating polymers in a solution. We are interested in the 3D density distribution of the modeled polymers where the polymers have been aligned with respect to their three principal axes of inertia. This type of approach was pioneered by Theodorou and Suter in 1985. While individual configurations of the modeled polymers are almost always nonsymmetric, the approach of Theodorou and Suter results in cumulative shapes that are highly symmetric. By taking advantage of asymmetries within the individual configurations, we modify the procedure of aligning independent configurations in a way that shows their asymmetry. This approach reveals, for example, that the 3D density distribution for linear polymers has a bean shape predicted theoretically by Kuhn. The symmetry-breaking approach reveals complementary information to the traditional, symmetrical, 3D density distributions originally introduced by Theodorou and Suter.

Latitudinal patterns in plant defense: evolution of cardenolides, their toxicity and induction following herbivory.

Attempts over the past 50 years to explain variation in the abundance, distribution and diversity of plant secondary compounds gave rise to theories of plant defense. Remarkably, few phylogenetically robust tests of these long-standing theories have been conducted. Using >50 species of milkweed (Asclepias spp.), we show that variation among plant species in the induction of toxic cardenolides is explained by latitude, with higher inducibility evolving more frequently at lower latitudes. We also found that: (1) the production of cardenolides showed positive-correlated evolution with the diversity of cardenolides, (2) greater cardenolide investment by a species is accompanied by an increase in an estimate of toxicity (measured as chemical polarity) and (3) instead of trading off, constitutive and induced cardenolides were positively correlated. Analyses of root and shoot cardenolides showed concordant patterns. Thus, milkweed species from lower latitudes are better defended with higher inducibility, greater diversity and added toxicity of cardenolides.

U-Pb and Ar-Ar geochronological data from the Pelagonian basement in Evia (Greece): geodynamic implications for the evolution of Paleotethys

High precision U-Pb zircon and Ar-40/Ar-39 mica geochronological data on metagranodiorites, metagranites and mica schists from north and central Evia island (Greece) are presented in this study. U-Pb zircon ages range from 308 to 1912 Ma, and indicate a prolonged magmatic activity in Late Carboniferous. Proterozoic ages represent inherited cores within younger crystals. Muscovite Ar-40/Ar-39 plateau ages of 288 to 297 Ma are interpreted as cooling ages of the magmatic bodies and metamorphic host rocks in upper greenschist to epidote-amphibolite metamorphic conditions. The multistage magmatism had a duration between 308 and 319 hla but some older intrusions, as well as metamorphic events, cannot be excluded. Geochemical analyses and zircon typology indicate calc-alkaline affinities for the granites of central Evia and alkaline to calc-alkaline characteristics for the metagranodiorites from the northern part of the island. The new data point towards the SE continuation, in Evia and the Cyclades, of a Variscan continental crust already recognised in northern Greece (Pelagonian basement). The Late Carboniferous magmatism is viewed as a result of northward subduction of the Paleotethys under the Eurasian margin.

Characterization of the rice PHO1 gene family reveals a key role for OsPHO1;2 in phosphate homeostasis and the evolution of a distinct clade in dicotyledons.

Phosphate homeostasis was studied in a monocotyledonous model plant through the characterization of the PHO1 gene family in rice (Oryza sativa). Bioinformatics and phylogenetic analysis showed that the rice genome has three PHO1 homologs, which cluster with the Arabidopsis (Arabidopsis thaliana) AtPHO1 and AtPHO1;H1, the only two genes known to be involved in root-to-shoot transfer of phosphate. In contrast to the Arabidopsis PHO1 gene family, all three rice PHO1 genes have a cis-natural antisense transcript located at the 5 ' end of the genes. Strand-specific quantitative reverse transcription-PCR analyses revealed distinct patterns of expression for sense and antisense transcripts for all three genes, both at the level of tissue expression and in response to nutrient stress. The most abundantly expressed gene was OsPHO1;2 in the roots, for both sense and antisense transcripts. However, while the OsPHO1;2 sense transcript was relatively stable under various nutrient deficiencies, the antisense transcript was highly induced by inorganic phosphate (Pi) deficiency. Characterization of Ospho1;1 and Ospho1;2 insertion mutants revealed that only Ospho1;2 mutants had defects in Pi homeostasis, namely strong reduction in Pi transfer from root to shoot, which was accompanied by low-shoot and high-root Pi. Our data identify OsPHO1;2 as playing a key role in the transfer of Pi from roots to shoots in rice, and indicate that this gene could be regulated by its cis-natural antisense transcripts. Furthermore, phylogenetic analysis of PHO1 homologs in monocotyledons and dicotyledons revealed the emergence of a distinct clade of PHO1 genes in dicotyledons, which include members having roles other than long-distance Pi transport.

Cumulative risk factors for adolescent alcohol misuse and its perceived consequences among 16 to 20 year old adolescents in Switzerland

Rapport de synthèse : OBJECTIF: évaluer l'impact cumulatif des facteurs individuels et environnementaux associés au mésusage d'alcool chez les adolescents et leurs corrélations avec ses conséquences perçues. METHODE : enquête scolaire transversale d'un échantillon représentatif de la population nationale, incluant 7548 apprentis et élèves ayant terminé l'école obligatoire âgés de 16 à 20 ans, en Suisse, en 2002. Le mésusage de l'alcool est fondé sur les réponses aux questions portant sur la fréquence 1) de sa consommation, 2) des épisodes d'ivresse et 3) de la conduite d'un véhicule sous son emprise. RÉSULTATS : quinze facteurs de risque significatifs ont été identifiés pour les adolescents des deux sexes. Un score individuel de facteurs de risques cumulés a été calculé en les additionnant. L'association entre ce score et la probabilité d'être engagé dans le mésusage d'alcool s'est révélée hautement significative et dose dépendante (p<0.001). Une proportion importante des adolescents rapporte des conséquences subjectives néfastes liées à leur consommation d'alcool. Il existe une corrélation linéaire (p<0.001) entre le score de facteurs de risque et la proportion d'adolescents rapportant des problèmes liés à la consommation d'alcool tels que mauvaises performances scolaires, comportements à risque, problèmes relationnels et comportements sexuels à risques. CONCLUSION : les facteurs de risque du mésusage d'alcool chez les adolescents sont cumulatifs et peuvent être synthétisés par un score individuel corrélé à la tendance à ce mésusage. La relation linéaire de ce score avec des problèmes subjectifs consécutifs à ce mésusage est un indicateur supplémentaire de sa validité.