Formation d'éléments reproducteurs endogènes chez <i>Histriculus similis</i> (Ciliophora Hypotrichida)

Dans ce travail, nous décrivons la formation d'éléments reproducteurs endogènes chez le Cilié Histriculus similis. Nous donnons également le schéma de son cyle vital complet. Parallelement à la reproduction classique par bipartition, il existe aussi un autre mode de reproduction asexuel chez certaines espèces de ce groupe

The curse of taxonomic uncertainty in biogeographical studies of free-living terrestrial protists: a case study of testate amoebae from Amsterdam Island

Abstract: Aim A current debate in microbial biogeography contrasts two views concerning the distribution of free-living microorganisms. The first view assumes a ubiquitous distribution, while the second assumes that at least some species have limited geographical distributions. We tested for limited geographical distributions by identifying testate amoebae morphospecies from an extremely remote oceanic island where the potential for endemism is high. Location Amsterdam Island, Indian Ocean. Methods Sixty moss and water samples collected from the top of the volcano to the lowland were investigated for their testate amoeba content. Due to taxonomic uncertainties among the Argynnia (Nebela) dentistoma species complex (including A. antarctica), we also performed light and scanning electron microscopy investigations on the shell ultrastructure and biometric analyses on several specimens of this taxon. Results We identified a total of 43 testate amoeba taxa belonging to 15 genera. Only four testate amoeba taxa had previously been recorded on this island. Testate amoeba communities of Amsterdam Island are dominated by cosmopolitan ubiquitous euglyphid taxa such as Trinema lineare, Assulina muscorum and Corythion dubium. The length and width ranges for Argynnia dentistoma on Amsterdam Island overlap with other records of this species and of A. antarctica, suggesting that A. antarctica is not a distinct taxon. Main conclusions Although Amsterdam Island is among the most remote islands in the world, an extensive inventory of testate amoeba morphospecies provided no clear evidence for endemism. On the one hand, our detailed morphometric analysis of the A. dentistoma complex revealed that A. antarctica, a morphospecies previously suggested to display endemism, cannot be confidently distinguished from the cosmopolitan morphospecies A. dentistoma. On the other hand, five morphotaxa could not be identified with certainty and might represent new species, potentially with limited distribution. These examples illustrate how taxonomic uncertainties undermine biogeographical studies of testate amoebae. In order to allow better interpretation of morphology-based testate amoeba distribution data, an assessment of genetic diversity among and within morphotaxa in relation to geographical distance for some common testate amoebae should be given high priority

Acidification of Forest Soil in Russia: 1893-Present

It is commonly believed that fine texture soils developed on carbonateparent material are well buffered from possible acidification. There areno data, however, documenting resistance of such soils to acidicdeposition exposure on a time scale longer than 30-40 years.In this paper we employed a rare opportunity of directly testinglong-term buffering capacity of 19th century forest soils developedon calcareous silt loam. A comparison of chemical analysis of archivedsoils with modern soils collected from the same locations ~100 yearslater indicate varying degrees of acidification of forest soils in taiga andthe forest steppe regions. Reforestation and increases in precipitationcontributed to acidification, as well as acidic deposition. The acidificationof forest soil was detected through decreases in soil pH, and changesin concentrations of exchangeable calcium and aluminum, whichcorresponded with changes in communities of soil microfauna. Althoughacidification was found at all 3 locations that were analyzed, the trendsin soil chemistry were greatest where the highest loading of acidicdeposition had taken place