Experimental evidence of a triadic resonance of plane inertial waves in a rotating fluid

Plane inertial waves are generated using a wavemaker, made of oscillating stacked plates, in a rotating water tank. Using particle image velocimetry, we observe that, after a transient, the primary plane wave is subject to a subharmonic instability and excites two secondary plane waves. The measured frequencies and wavevectors of these secondary waves are in quantitative agreement with the predictions of the triadic resonance mechanism. The secondary wavevectors are found systematically more normal to the rotation axis than the primary wavevector: this feature illustrates the basic mechanism at the origin of the energy transfers towards slow, quasi two-dimensional, motions in rotating turbulence.Comment: to appear in Physics of Fluid

Le connoisseurship et ses révisions méthodologiques

Les questions qui animent cet échange trouvent leur point de départ dans les discussions sur le connoisseurship à l’occasion de l’atelier conjoint Clark Art Institute et INHA, qui s’est tenu à Williamstown en août 2008. Ces dernières ont conduit à revenir sur la rhétorique et le langage du connoisseurship, son historiographie en lien avec l’histoire de la photographie et aujourd’hui avec les nouvelles technologies, ainsi que sa dette envers la notion d’auteur et comment le choix de ses objets..

Natural infection by the protozoan Leptomonas wallacei impacts the morphology, physiology, reproduction, and lifespan of the insect Oncopeltus fasciatus

Trypanosomatids are protozoan parasites that infect thousands of globally dispersed hosts, potentially affecting their physiology. Several species of trypanosomatids are commonly found in phytophagous insects. Leptomonas wallacei is a gut-restricted insect trypanosomatid only retrieved from Oncopeltus fasciatus. The insects get infected by coprophagy and transovum transmission of L. wallacei cysts. The main goal of the present study was to investigate the effects of a natural infection by L. wallacei on the hemipteran insect O. fasciatus, by comparing infected and uninfected individuals in a controlled environment. The L. wallacei-infected individuals showed reduced lifespan and morphological alterations. Also, we demonstrated a higher infection burden in females than in males. The infection caused by L. wallacei reduced host reproductive fitness by negatively impacting egg load, oviposition, and eclosion, and promoting an increase in egg reabsorption. Moreover, we associated the egg reabsorption observed in infected females, with a decrease in the intersex gene expression. Finally, we suggest alterations in population dynamics induced by L. wallacei infection using a mathematical model. Collectively, our findings demonstrated that L. wallacei infection negatively affected the physiology of O. fasciatus, which suggests that L. wallacei potentially has a vast ecological impact on host population growth

Infestations parasitaires multiples (polyparasitisme) chez les mammifères sauvages (approche comparative des déterminants et des impacts évolutifs)

Même si la majorité des études théoriques ou empiriques se sont essentiellement focalisées sur des interactions impliquant un seul hôte et un seul parasite, le polyparasitisme est la règle en milieu naturel chez les mammifères.Les déterminants potentiels de la richesse parasitaire (nombre d'espèces de parasites hébergés par un hôte), mais aussi les possibles impacts de ces multiples espèces de parasites sur les hôtes sont encore largement méconnus. En effet, les nombreuses études préexistantes sur les déterminants ont souvent été réalisées dans un cadre conceptuel trop étroit avec des données souvent restreintes à certaines zones faunistiques. Nous avons donc étendu les données et reconsidéré certains déterminants classiques (tels la latitude, la taille du groupe ou encore la taille du domaine vital pour l'ensemble des mammifères).Nous en avons également proposé de nouveaux, tels la socialité chez les rongeurs ou la nature des gîtes chez les chauves souris. Les travaux relatifs aux impacts de la diversité en tant que telle sont par contre peu nombreux et récents. Nous avons donc tenté de les appréhender à différents niveaux (immunité, métabolisme et traits de vie). En établissant les effets cumulatifs des infestations multiples, tels une augmentation de l'investissement immun ou du métabolisme basal, notre travail renforce l'idée récente et encore largement sous estimée que la diversité parasitaire puisse être un facteur de pression par elle-même sur les hôtes.Despite most sudies related to host- parasite relationships have focused on single host /single parasite systems, polyparasitism (i.e.multiple parasitic infestations or polyparasitism) is the law in natural systems at individual, populational or species level. Importantly however, may open questions arise from the reality of polyparasitism. Among them, those related to the potential impacts of parasitic diversity per se but also to the determinants of this parasitic diversity need to be furtfher explored. Infortunately, studies related to the impacts or coinfectiosn are still scarce. Moreover, the numerous available investigations of determinants may have largely suffered from a too narrow conceptual framework, leading to erroneous or naive predictrions. Focusing on macroparasites and using comparative phylogenetic approach across wild mammal species, we have then reinvestigated the determinants of parasitic diversity, notably revisiting classical determinants such as group size home range size or latitude but also exploring understudied ones such as roosting ecology of bats or sociality of rodents. The impacts of parasitic diversity have mainly been approached in our study by focusing on mammals' responses at immune, metabolic or life history trait levels. We have then found strong support for cumulative effects of polyparasitism at metabolic and immune levelsMONTPELLIER-BU Sciences (341722106) / SudocSudocFranceF

Transmission ecology of rodent-borne diseases: New frontiers

International audienceRodents are recognized reservoir hosts for many human zoonotic pathogens. The current trends resulting from anthropocene defaunation suggest that in the future they, along with other small mammals, are likely to become the dominant mammals in almost all human‐modified environments. Recent intricate studies on bat‐borne emerging diseases have highlighted that many gaps exist in our understanding of the zoonotic transmission of rodent‐borne pathogens. This has emphasized the need for scientists interested in rodent‐borne diseases to integrate rodent ecology into their analysis of rodent‐borne pathogen transmission in order to identify in more detail the mechanisms of spillover and chains of transmission. Further studies are required to better understand the true impact of rodent abundance and the importance of pathogen sharing and circulation in multi‐host– multi‐pathogen communities. We also need to explore in more depth the roles of generalist and abundant species as the potential links between pathogen‐sharing, co‐infections and disease transmission

4 5 HELMINTHS COMMUNITIES OF AN INTRODUCED HARE (LEPUS GRANATENSIS) AND A NATIVE HARE (LEPUS EUROPAEUS) IN SOUTHERN

ABSTRACT We investigated the parasite communities of introduced Iberian hares (Lepus granatensis) and native European hares (Lepus europaeus) in southern France, were Iberian hares were introduced locally 20 yr ago as a game animal. Parasite communities of sypatric populations of the two hare species and of allopatric populations of European hares were compared. Iberian hares in France harbored a depauperate community of parasites, relative to population in its native habitat in Spain. European hares in areas of sympatry also were infected by Nematodiroides zembrae, which normally infects Iberian hares on their native range