Biomedical subjects

Bernard Godelle

Publications and source records attributed to Bernard Godelle.

5 recordsLinked to original sources

PubMed2003

Effect of native Xenorhabdus on the fitness of their Steinernema hosts: contrasting types of interaction.

Steinernema species are entomopathogenic nematodes. They are symbiotically associated with Enterobacteriaceae of the genus Xenorhabdus. These nematode-bacteria symbioses are extremely diversified and constitute an important new model in ecology and evolution to investigate symbioses between microbes and invertebrates. However, no study has so far adequately evaluated either the outcome of the interactions or the obligate nature of interactions in different Steinernema species in the same way. Studying three different species of Steinernema, we showed that symbiotic nematodes are always fitter than aposymbiotic ones. Nevertheless, we revealed contrasting types of interaction in terms of outcome and obligate nature of the interaction. Bacterial analyses showed that nematode species differed dramatically in the number of symbiotic Xenorhabdus they carried. We suggested that when the interaction appeared more facultative for a nematode species, the nematodes carried fewer Xenorhabdus cells than strongly dependent worm species. Thus, the symbiont transmission appeared to become more efficient as the relationship between the nematode and the bacteria became tighter.

Animals↗

PubMed2003

Amplification of Nicotiana sylvestris mitochondrial subgenomes is under nuclear control and is associated with phenotypic changes.

We have previously shown the presence in a Nicotiana sylvestris protoplast-derived plant of both a nuclear mutation conferring male sterility (ms4) and a mtDNA reorganisation, named U, characterised by the amplification of substoichiometric mtDNA fragments generated by recombination in the parent T mtDNA. Here we show by physical mapping that the recombining repeats are in direct orientation, thus generating two subgenomes both of which are amplified in the U organisation to the detriment of the parent molecule, and are maintained through sexual reproduction. The nuclear ms4 mutation is likely to have play a role in the shift in mitochondrial molecule equilibrium, as higher levels of recombinant fragments were present in protoplast-derived T calli carrying the ms4 allele than in wild type calli or leaves. The MS4 gene could then lead to conflictual situation. However, subgenomic molecules were counter-selected during the regeneration process, suggesting the existence of different selective pressures in differentiated and non-differentiated cells. The U organisation is associated with higher stem height and late flowering, characters that may not be neutral from a selection point of view. The U equilibrium is an unusual example of sudden mtDNA reorganisation, without obvious differences in genetic information and with only a limited phenotypic impact.

Cell Nucleus↗

PubMed2003

Within-host parasite dynamics, emerging trade-off, and evolution of virulence with immune system.

Virulence is an evolutionary paradox because parasites never benefit from their host's death. The adaptive explanation of virulence is classically based upon the existence of physiological constraints that create a trade-off between parasites' epidemiological traits (virulence, transmissibility, and clearance). Here we develop an epidemiological model where infections are dynamic processes and we demonstrate how these dynamics generate a trade-off between emerging epidemiological parameters. We then study how host's immune strength modifies this trade-off and hence influences virulence evolution. We found that in acute infections, where parasites are engaged in a race with immune cells, immunity restrains more the duration of the infection than its intensity. As a consequence parasites evolve to provoke more virulent but shorter infections in strongly immunized hosts.

Biological Evolution↗

PubMed2002

Aperture pattern ontogeny in angiosperms.

Pollen grains display a wide range of variation in aperture number and arrangement (pattern) in angiosperms. Apertures are well-defined areas of the pollen wall surface that permit pollen tube germination. For low aperture numbers, aperture patterns are characteristic of the major taxonomic divisions of angiosperms. This paper presents a developmental model that explains most of the aperture patterns that are recorded in angiosperms. It is based on the analysis of the different events that occur during meiosis and lead to microspore differentiation. It demonstrates that variation occurring during meiosis in angiosperms is sufficient to produce the core morphological set of the most commonly observed pollen morphologies.

Cell Division↗

PubMed2002

Evolution of mutualism between globeflowers and their pollinating flies.

Plant/seed-eater pollinators mutualisms involve a plant pollinated by an insect whose larvae develop by eating a fraction of host-plant seeds. The outcome of the interaction therefore depends on the number of ovules fertilized by adult visits and the number of seeds destroyed by larvae. Among the very few cases of such mutualisms reported so far is the globeflower-globeflower flies mutualism, which is unique in that it involves several congeneric fly species (Chiastocheta genus) coexisting within a single host-plant species, Trollius europaeus. These species exhibit contrasted oviposition behaviors resulting in a more or less beneficial outcome for the plant. We designed an adaptive dynamics model to investigate how morphological traits of globeflower could affect the evolution of oviposition in its pollinating flies. Three fly traits (flower age at oviposition, clutch size and the level of avoidance of already parasitized flowers) and one plant trait (closed or open corolla) were examined. Whatever the shape of the flower, evolutionary branching occurs between early and late ovipositing flies, driven by strong competition among larvae within a fruit. Once this branching occurred, the closed shape of the corolla is likely to offer a better protection to eggs of early but not of late ovipositing flies. The difference in egg survival results in higher competition among early larvae and thus selects for decreased clutch size in early flies. This can be seen as a first step in the evolution of a mutualistic behavior. The prediction of our model fits field observations of fly behavior, giving theoretical support to the hypothesis of fly sympatric speciation within its host plant. Moreover, flower closed globe shape can be positively selected in globeflowers as it results in a reduction of parasitism strength. This last evolution therefore leads to a stable mutualism between globeflowers and globeflower flies.

Animals↗