Exploring the relationship between tychoparthenogenesis and inbreeding depression in the Desert Locust, Schistocerca gregaria

Tychoparthenogenesis, a form of asexual reproduction in which a small proportion of unfertilized eggs can hatch spontaneously, could be an intermediate evolutionary link in the transition from sexual to parthenogenetic reproduction. The lower fitness of tychoparthenogenetic offspring could be due to either developmental constraints or to inbreeding depression in more homozygous individuals. We tested the hypothesis that in populations where inbreeding depression has been purged, tychoparthenogenesis may be less costly. To assess this hypothesis, we compared the impact of inbreeding and parthenogenetic treatments on eight life-history traits (five measuring inbreeding depression and three measuring inbreeding avoidance) in four laboratory populations of the desert locust, Schistocerca gregaria, with contrasted demographic histories. Overall, we found no clear relationship between the population history (illustrated by the levels of genetic diversity or inbreeding) and inbreeding depression, or between inbreeding depression and parthenogenetic capacity. First, there was a general lack of inbreeding depression in every population, except in two populations for two traits. This pattern could not be explained by the purging of inbreeding load in the studied populations. Second, we observed large differences between populations in their capacity to reproduce through tychoparthenogenesis. Only the oldest laboratory population successfully produced parthenogenetic offspring. However, the level of inbreeding depression did not explain the differences in parthenogenetic success between all studied populations. Differences in development constraints may arise driven by random and selective processes between populations. (Résumé d'auteur

Représentation discursive des pairs et ethos dans les arrêts de la Cour de cassation française

The French Cour de cassation is located at the apex of the judicial pyramid. The court is responsiblefor verifying the conformity of decisions to the law. Despite the dominance of this pre-discursive ethos,the organ is not exempt from justifying its decisions, which are strategically made to be read at thehearing, and then published. From a discursive approach, it will be shown that argumentation in thosejudicial decisions is based on the distribution of roles, which influences the relationships between theCour and the judges. The discursive representation of judicial organs reveals a discursive routinelinked to the situation of enunciation marked by the judicial ritual. The representation of relationshipsand rigid staging give us information about the discursive image of the Cour and its ethos, which isparticularly relevant for its persuasive strategy.La Cour de cassation de Francia se sitúa en la cúspide de la jerarquía judicial. Es el órgano responsable de verificar la conformidad de las decisiones a la ley. Su ethos previo es dominante, pero esta imagen social no la exime de argumentar sus sentencias, estratégicamente compuestas con vista a ser leídas para la audiencia y publicadas posteriormente. Desde una perspectiva discursiva, mostramos que la argumentación vehiculada por las sentencias se basa, entre otros, en la asignación de roles que determina la relación entre los jueces y la Cour. La inscripción en cadencia de los órganos judiciales obedece a ritos discursivos, reflejo de una situación de enunciación marcada por la impronta del ritual judicial. La manifestación de las relaciones con los jueces así como la rígida puesta en escena que conlleva, nos informan sobre la imagen discursiva de la Cour, su ethos, cuya construcción participa también de la estrategia de persuasión.La Cour de cassation française se situe au sommet de la hiérarchie judiciaire. C’est l’organisme chargé de vérifier la conformité des décisions au droit. Son ethos préalable est dominant mais cette image sociale d’elle-même ne la soustrait pas à l’obligation de motiver ses arrêts, stratégiquement composés pour la lecture à l’audience et leur postérieure publication. Depuis une perspective discursive, l’on montre que l’argumentation véhiculée par les arrêts se fonde notamment sur l’attribution des rôles qui imprègne les relations entre les pairs et la Cour. L’inscription cadencée des instances obéit à des rites discursifs qui sont autant de traces d’une situation d’énonciation marquée sous le sceau du rituel judiciaire. La manifestation des rapports aux pairs, ainsi que la mise en scène rigide dans laquelle elle s’exerce, nous renseignent sur l’image discursive de la Cour, son ethos, dont la construction participe également de l’entreprise de persuasion

Correlation between parasite prevalence and adult size in a trematode-mollusc system: evidence for evolutionary gigantism in the freshwater snail Galba truncatula?

The snail-trematode host-parasite system has been widely studied, as trematodes are known to greatly influence the fitness of their hosts. Indeed, during their development, the trematodes castrate the snail and one possible consequence of infection is gigantism of the snail. Snail gigantism is usually investigated experimentally by comparing the size of healthy and artificially infected snails. Here, I focused on naturally infected populations in order to investigate if snails submitted to trematode pressure have evolved specific life-history traits to respond to the parasite prevalence in their natural population. To this end, I estimated the correlations between measures of size (obtained from healthy laboratory individuals originating from populations) and the parasite prevalence at the population level. I found that the adult size of populations was positively correlated with population prevalence, an indication that gigantism might be operating. Moreover, I found a positive relation between growth and fecundity in healthy populations, while no such trade off was found in highly parasitized populations, suggesting that there may be a cost in fecundity to this gigantis

Création et quasi-disparition du vignoble de Haute-Loue

Pourquoi et comment un vignoble s'est-il implanté et développé dans la Haute vallée de la Loue ? Pourquoi et comment a-t-il quasiment disparu ? Pourquoi et comment a-t-il été reconstitué en partie récemment ? Telles sont les questions auxquelles l'auteur s'efforce de répondre. La renaissance du vignoble de Haute-Loue au cours des dernières décennies sera abordée dans un prochain numéro