Search results for "milieu"
showing 10 items of 19813 documents
Impact of eutrophication on the carbon stable-isotopic baseline of benthic invertebrates in two deep soft-water lakes
2017
International audience
Burial behaviour by dealates of the termite Pseudacanthotermes spiniger (Termitidae, Macrotermitinae) induced by chemical signals from termite corpses
2011
In order to maintain healthy colonies, termite workers dispose of the cadavers of dead nest mates by cannibalism, burial, or necrophoresis. However, when multiple reproductives found a new colony by pleometrosis, there are no worker castes at the early stages of the foundation to eliminate or isolate the corpses. In this study, we showed that in young pleometrotic colonies, reproductives of Pseudacanthotermes spiniger had the ability to perform this task. Because of the claustral conditions, and the potential inability of the dealates to feed on their own, their behaviour was restricted to the burial of the cadaver within the initial chamber. This burial behaviour, previously not reported i…
No evidence of an immune adjustment in response to a parasitoid threat in Lobesia botrana larvae.
2017
5 pages; International audience; Immune function is a key determinant of an organism's fitness, and natural insect populations are highly variable for this trait, mainly due to environmental heterogeneity and pathogen diversity. We previously reported a positive correlation between infection prevalence by parasitoids and host immunity in natural populations of the vineyard pest Lobesia botrana. Here, we tested whether this correlation reflects a plastic adjustment of host immunity in response to the local presence of parasites. To this end, we measured immunity of non-parasitized L. botrana larvae exposed, respectively, to one of the two most common species of parasitoids in vineyards, over…
Host-manipulation by parasites: towards a neuroethological approach?
2009
2 pages; International audience
Effects of mowing on fungal endophytes and arbuscular mycorrhizal fungi in subalpine grasslands
2013
International audience; In French subalpine grasslands, cessation of mowing promotes dominance of Festuca paniculata, which alters plant diversity and ecosystem functioning. One of the mechanisms underpinning such effects may be linked to simultaneous changes in the abundance of fungal symbionts such as endophytes and arbuscular mycorrhizal fungi. In field conditions, mowing reduced the abundance of the endophyte Neotyphodium sp. in leaves of F. paniculata by a factor of 6, and increased mycorrhizal densities by a factor of 15 in the soil. In greenhouse experiments, the mycorrhizal colonization of Trifolium pratense and Allium porrum increased 3- fold and 3.8- fold respectively in mown vs u…
Première contribution à l'étude des mycorhizes des îles Kerguelen
1999
Abstract Until recently mycorrhizae had not been studied in the Antarctic region. Some studies have demonstrated that mycorrhizae occur in some southern circumpolar islands. This paper gives the first results on the mycorrhizae in the Kerguelen islands (Sub-antarctic). Twenty-one plant root systems, fixed in the field, were examined microscopically in the laboratory to determine their mycorrhizal status. No ectomycorrhiza, arbutoid or ericoid were noted. Six plant species showed vesicular arbuscular mycorrhizae: Ranunculus biternatus, Galium antarcticum, Festuca erecta, Poa kerguelensis, Agrostis magellanica and Poa annua. However, the mycorrhizal status varied according to the site studied.
Historical and contemporary dynamics of adaptive differentiation in European oaks
2010
International audience
Population differentiation for adaptive traits and their underlying loci in forest trees : theoretical predictions and experimental results
2000
Population differentiation has been investigated in forest trees since provenance tests were established. A vast amount of results has accumulated in numerous reports and articles about intraspecific variation, that have been summarized in textbooks about forest genetics (Wright 1976). Provenance differences exist for almost any adaptive trait that has been measured in provenance test and for almost any species. These results contrast markedly with data based on biochemical markers as isozymes. As shown by the literature review by Hamrick et al. (1992), forest trees usually exhibit extremely low levels of differentiation for isozymes. Results derived from isozyme surveys are confirmed by ot…
Characterization of Fusarium oxysporum populations by growth parameter evaluation in microtiter plates
1997
Trophic competition for the C source is the main mechanism involved in the interaction between pathogenic and non-pathogenic populations of Fusarium oxysporum. Therefore, a phenotypical characterization based on the growth characteristics of these populations will provide classical genotypical characterizations with additionnal information of ecological significance.
Influence of nitrogen availability on seed nitrogen accumulation in pea
1999
International audience; The final seed nitrogen concentration (the ratio of seed N and dry matter content) is highly variable in pea (Pisum sativum L.) and N remobilization during seed filling may limit yield by restricting the seed filling period. This study was conducted to determine how seed N accumulation is regulated in pea. The effect of N availability and distribution on individual seed N accumulation rate at different nodes was investigated in three genotypes grown in the field and glasshouse under various levels of N fertilizer, depodding, and defoliation. The N content of vegetative plants parts (stems, leaves, podwalls) and seeds from three mainstem nodes were regularly recorded.…