Competition and facilitation among fungal plant parasites affect their life-history traits

Multi-infections may result in either competitive exclusion or coexistence on the same host of pathogen genotypes belonging to the same or different species. Epidemiological consequences of multiple infections, particularly how the development and transmission of a pathogen can be modified by the presence of another pathogen, are well documented. However, understanding how life history strategies of each pathogen modulate co-infection outcomes remains quite elusive. To analyze how co-infection drives changes in life history traits and affects co-existence in epidemic pathogens, we infected detached pea stipules with two fungal species, Peyronellaea pinodes and Phoma medicaginis var. pinodella (considering two strains per species), part of the ascochyta blight complex but presenting different life history strategies. All pairwise combinations (including self-pairs) between two strains of each species were tested. Strains were inoculated simultaneously, but apart from one another on the stipule. For each strain, four life history traits were measured: incubation period, necrosis area six days after inoculation, latent period and offspring production. Results show that, in co-infection, when resources are highly allocated to lesion development, the time between inoculation and the appearance of reproduction structures (latent period) and offspring production decreased, and vice-versa relative to single infections. The direction and/or magnitude of these responses to co-infection depend on the co-infecting strains. Moreover, these changes were always higher in self-pairs than in mixed co-infections. These results suggest facilitation between co-infecting strains, resulting in the selection of an intermediate level of virulence (here measured as the lesion development) at the expense of pathogen offspring production. This strategy allows the development and reproduction of each co-infecting strain when sharing limited resources. However, the direction and strength of these life history traits variations in co-infection depend on the life history strategy of the co-infecting strains, with a clear difference between ‘opportunists', ‘scavengers' and ‘pioneer colonisers'.     

Spatial patterns of species and plant traits in response to 20 years of grazing exclusion in subalpine grassland communities

Question: Does long‐term grazing exclusion affect spatial patterns of canopy height, plant species and traits in subalpine grassland communities? Are spatial patterns of species and traits similarly affected by grazing exclusion? Are changes in spatial patterns of species associated with changes in species abundances? Location: Subalpine grasslands, Vercors and Oisans Mountains, Alps (France). Methods: Spatial sampling of vegetation and measurements of plant traits were carried out within nine pairs of grazed and ungrazed 10 m × 10‐m plots in three species‐rich communities with different productivities. We estimated within‐plot spatial patterns of canopy height, species and aggregated trait values by measuring the extent (or patch size) and intensity of spatial dependence with Moran's I. Abundance‐weighted averages for species patch size and intensity of spatial dependence were calculated across all species per plot and across species per life form. Such measures derived from analysis of spatial dependence were considered spatial traits. Results: Response of spatial patterns to grazing exclusion was only detected in patch size, whereas intensity of spatial dependence was not affected. Changes in spatial patterns were community‐dependent because spatial traits based on patch size of canopy height and species increased following grazing exclusion only in the less productive community. Unexpectedly, changes in spatial patterns of species did not support changes in spatial patterns of trait values. Abundances and patch sizes of several life forms were significantly affected by grazing exclusion. However, at the scale investigated, changes in abundance of life forms did not correspond to changes in their spatial patterns and vice versa. Conclusion: In species‐rich communities, grazing alters spatial spread of species (i.e. patch size) rather than intra‐specific aggregation (i.e. intensity of spatial dependence). Results revealed possible mechanisms of species spatial reorganisation that are independent of abundance variation. Therefore, it is important to consider changes in spatial patterns in addition to changes in mean values of vegetation features when assessing impacts of grazing management.     

Detecting the footprint of changing atmospheric nitrogen deposition loads on acid grasslands in the context of climate change

Although atmospheric nitrogen (N) deposition and climate changes are both recognized as major components of global change, their interaction at ecosystem level is less well understood. A stratified resampling approach was used to investigate the potential impact of changing levels of atmospheric nitrogen deposition and climate change on species composition of nutrient‐poor acid grasslands within the French Atlantic Domain (FAD). The study was based on a comparison, over a period of 25 years, of 162 past and present vegetation records assigned to the species‐rich Nardus grasslands and distributed in regional community types (CTs). Similarly, the characterization of N deposition and climate was stratified according to (i) past (1980–1990) and present (1995–2005) periods, and (ii) FAD and CT scales. Despite the relatively short time span between sampling periods, significant N deposition and climate changes were detected as well as vegetation changes. Correspondence analysis showed that the relative importance of N deposition and climate in explaining vegetation changes depended on the spatial scale of investigation (FAD vs. local CTs) and the CT. At the FAD scale, the increase of annual mean temperature and decrease of water availability were clearly related to the changes in floristic composition. At the local scale, the most stable CT experienced no significant climate change and a stable load of N deposition, whereas the CTs characterized by the largest floristic changes were associated with dramatic climate changes and moderate loads in both oxidized and reduced N deposition. Despite the narrow gradient of deposition investigated, N deposition was related to significant grassland community changes, depending on the region, i.e. climate context, and on whether N deposition was in the oxidized or reduced form. Our results suggest that N deposition drives grassland composition at the local scale, in interaction with climate, whereas climate changes remain the predominant driver at the FAD scale.     

Archaea as emerging organisms in complex human microbiomes

In this work, we review the state of knowledge of Archaea associated with the human microbiome. These prokaryotes, initially discovered in extreme environments, were named Archaea because these environments were thought to be the most primitive on Earth. Further research revealed that this terminology is misleading because these organisms were later found in various non-extreme environments, including the human host. Further examination of the human microbiome has enabled the isolation of three archaeal species, Methanobrevibacter smithii, Methanosphaera stadtmanae and Methanobrevibacter oralis, which are associated with oral, intestinal and vaginal mucosae in humans. Moreover, molecular studies including metagenomic analyses detected DNA sequences indicative of the presence of additional methanogenic and non-methanogenic Archaea in the human intestinal tract. All three culturable Archaea are strict anaerobes, although their potential role in human diseases remains to be established. Future research aims to detect and culture additional human mucosa-associated Archaea and to look for their presence in additional human tissues, to establish their role in human infections involving complex flora.     

Misregulated alternative splicing of BIN1 is associated with T tubule alterations and muscle weakness in myotonic dystrophy

Myotonic dystrophy is the most common muscular dystrophy in adults and the first recognized example of an RNA-mediated disease. Congenital myotonic dystrophy (CDM1) and myotonic dystrophy of type 1 (DM1) or of type 2 (DM2) are caused by the expression of mutant RNAs containing expanded CUG or CCUG repeats, respectively. These mutant RNAs sequester the splicing regulator Muscleblind-like-1 (MBNL1), resulting in specific misregulation of the alternative splicing of other pre-mRNAs. We found that alternative splicing of the bridging integrator-1 (BIN1) pre-mRNA is altered in skeletal muscle samples of people with CDM1, DM1 and DM2. BIN1 is involved in tubular invaginations of membranes and is required for the biogenesis of muscle T tubules, which are specialized skeletal muscle membrane structures essential for excitation-contraction coupling. Mutations in the BIN1 gene cause centronuclear myopathy, which shares some histopathological features with myotonic dystrophy. We found that MBNL1 binds the BIN1 pre-mRNA and regulates its alternative splicing. BIN1 missplicing results in expression of an inactive form of BIN1 lacking phosphatidylinositol 5-phosphate-binding and membrane-tubulating activities. Consistent with a defect of BIN1, muscle T tubules are altered in people with myotonic dystrophy, and membrane structures are restored upon expression of the normal splicing form of BIN1 in muscle cells of such individuals. Finally, reproducing BIN1 splicing alteration in mice is sufficient to promote T tubule alterations and muscle weakness, a predominant feature of myotonic dystrophy.     

Development of metrics based on fish body size and species traits to assess European coldwater streams

During the last decade multimetric indices (MMIs) have been greatly improved by the use of appropriate criteria to define reference conditions and by the use of statistical analysis to select a consistent set of metrics. Among the large number of MMIs developed to assess the ecological status of streams based on fish communities, the emphasis was mainly put on warmwater assemblages. When compared with warmwater fish assemblages, coldwater assemblages present depauperate faunas with a limited suit of traits. Thus, very often the number of metrics used to compute MMIs for coldwater streams is lower than for warmwaters. The objective of this study was to develop new metrics specific to European coldwater assemblages that integrate both the species traits and the body size of fish. Indeed, whereas the use of size or age classes has been highly advocated for developing MMIs, it remains largely underrepresented. Therefore, we used eight biological and ecological traits to characterize species and two size classes: small and large individuals. Among the 96 metrics tested, four were successfully related to environmental gradients and three displayed a significant response to anthropogenic pressures: the number of small rheophilous individuals, the number of small oxygen-intolerant individuals, and the number of small-habitat-intolerant individuals. These results demonstrate that metrics based on size classes could be used in the development of MMIs for coldwater streams and more generally for low-species rivers.     

A New Coral Carbonic Anhydrase in Stylophora pistillata

Scleractinian corals are of particular interest due to their ability to establish an intracellular mutualistic symbiosis with phototrophic dinoflagellates and to deposit high rates of calcium carbonate in their skeleton. Carbonic anhydrases have been shown to play a crucial role in both processes. In this study, we report the molecular cloning and characterization of a novel α-CA in the coral Stylophora pistillata. This enzyme shares homologies with the human isoform CA II and is referred to as STPCA-2. STPCA-2 is 35.2 kDa and possesses all key amino acids for catalytic activity. With a ratio between catalytic and Michaelis constants (k(cat)/K(m)) of 8.3.10(7) M(-1) s(-1) is considered as highly active. Owing to its intracellular localisation in the oral endoderm and in the aboral tissue, we propose that STPCA-2 is involved in pH regulation and/or inorganic carbon delivery to symbiont and calcification.