Dans le cadre de mes recherches, je m'intéresse à la relation qui unit la variation, qui est la matière première de l'évolution, à la sélection, qui en est le moteur. Je m'intéresse notamment à l'organisation naturelle de cette variation, qu'elle soit neutre (marqueurs moléculaires) et permette d'élucider les traits de vie de l'espèce étudiéee, ou de sa richesse (dans le cadre des questions liées aux ressources génétiques) ou qu'elle soit responsable d'une modification du phénotype.
Dans ce dernier cas, je suis en particulier intéressé par l'impact de la sélection sur l'organisation de la variation et sur une plus grande échelle, de la diversité. En effet, le facteur d'ordre dans l'évolution est loin d'avoir révélé son effet sur la dynamique évolutive: le paradoxe entre l'aspect fluctuant de la sélection naturelle et la création de tendances évolutives sur le long terme reste d'actualité, surtout en ce qui concerne la mise en place des adaptations complexes. D'un autre coté, l'influence liée aux contraintes exercées sur la réalisation des phénotypes au cours du développement commence à peine à révéler son impact sur l'évolution des organismes. Enfin, on ignore encore comment réagissent les populations soumises a des régimes sélectifs qui opposent des polymorphismes bénéfiques, ce qui impacte également la structure même des génomes.
Mon approche reste avant tout marquée par l'empiricisme, les méthodes basées sur l'observation naturelle et/ou en complément d'expérimentations et de test d'hypothèses, que ce soit à un niveau d'intégration local (populations naturelles et expérimentales) ou à un niveau plus global (historique et phylogénétique).
Ashman, T-L; Penet, L. Direct and indirect effects of a sex-biased antagonist on male and female fertility: consequences for reproductive trait evolution in gender dimorphic plant. American Naturalist (in press). Abstract - Ask for a reprint
Penet, L; Nadot, S; Ressayre, A; Forchioni, A; Dreyer, L; Gouyon, PH. 2005. Multiple developmental pathways leading to a single morph: Monosulcate pollen (examples from the Asparagales). Annals Of Botany 95 (2): 331-343. Abstract - Ask for a reprint
Elias, M; Penet, L; Vindry, P; McKey, D; Panaud, O; Robert, T. 2001. Unmanaged sexual reproduction and the dynamics of genetic diversity of a vegetatively propagated crop plant, cassava (Manihot esculenta Crantz), in a traditional farming system. Molecular Ecology 10 (8): 1895-1907. Abstract - Ask for a reprint<--
Ashman, T-L; Penet, L. Direct and indirect effects of a sex-biased antagonist on male and female fertility: consequences for reproductive trait evolution in gender dimorphic plant. American Naturalist (in press).
Gender dimorphic plants are often subject to sex-differential enemy attack, but whether and how this contributes to trait evolution is unknown. To address this gap, we first documented the spatio-temporal prevalence of sex-biased weevil damage in a gynodioecious strawberry. We then conducted path analysis to evaluate the direct and indirect pathways for weevils to affect female and male fertility and to mediate selection in two experimental gardens. Direct effects of weevils significantly reduced fertility and mediated selection on reproductive traits, even in the non-preferred sex (females). Weevils significantly reduced floral display size in hermaphrodites in both gardens, and this translated into a substantial negative indirect effect on male fertility in the garden where the pathway to fertility via display was stronger. Such a result suggests that indirect effects of weevils can contribute to selection in hermaphrodites, which gain the majority of their fitness via male function. Our results also indicate that weevils can play a large role, often larger than that of pollinators, in shaping reproductive phenotype in wild strawberry, and thus raise the intriguing possibility that antagonists may be drivers in the evolution of sexual dimorphism. Finally, our results support the view that mutualists, antagonists and the abiotic environment should be considered when attempting to understand reproductive trait evolution in gender dimorphic species. <<<
Nadot, S; Forchioni, A; Penet, L; Sannier, J; Ressayre, A. 2006. Links between early pollen development and aperture pattern in monocots. Protoplasma 228 (1-3): 55-64.
Although the pollen grains produced in monocots are predominantly monosulcate (or monoporate), other aperture types are also found within this taxonomic group, such as the trichotomosulcate, inaperturate, zonaperturate, di-, or triaperturate types. The aperture pattern is determined during the young-tetrad stage of pollen development and it is known that some features of microsporogenesis can constrain the aperture type. For example, trichotomosulcate pollen is always associated with simultaneous cytokinesis, a condition considered as derived in the monocots. Our observations of the microsporogenesis pathway in a range of monocot species show that this pathway is surprisingly variable. Our results, however preliminary, reveal that variation in microsporogenesis concerns not only cytokinesis but also callose deposition among the microspores and shape of the tetrads. The role played by these features in aperture pattern determination is discussed. <<<
Penet, L; Nadot, S; Ressayre, A; Forchioni, A; Dreyer, L; Gouyon, PH. 2005. Multiple developmental pathways leading to a single morph: Monosulcate pollen (examples from the Asparagales). Annals Of Botany 95 (2): 331-343.
Background and Aims Early developmental events in microsporogenesis are known to play a role in pollen morphology: variation in cytokinesis type, cell wall formation, tetrad shape and aperture polarity are responsible for pollen aperture patterning. Despite the existence of other morphologies. monosulcate pollen is one of the most common aperture types in monocots. and is also considered as the ancestral condition in this group. It is knows to occur from either a successive or a simultaneous cytokinesis. In the present study, the developmental sequence of microsporogenesis is investigated in several species of Asparagales that produce such monosulcate pollen. representing most families of this important monocot clade. Methods The developmental pathway of microsporogenesis was investigated using light transmission and epifluorescence microscopy for all species studied. Confocal microscopy was used to confirm centripetal cell plat formation. Key Results Microsporogenesis is diverse in Asparagales. and most variation is generally found between families. It is confirmed that the whole higher Asparagales clade has a very conserved microsporogenesis. with a successive cytokinesis and centrifugal cell plate formation. Centripetal cell wall formation is described in Tecophilaeaceae and Iridaceae, a feature that had so far only been reported for eudicots. Conclusions Monosulcate pollen can be obtained from several developmental pathways, leading thus to homoplasy in the monosulcate character state. Monosulcate pollen should not therefore be considered as the ancestral state unless it is produced through the ancestral developmental pathway. The question about the ancestral developmental pathway leading to monosulcy remains open. <<<
Elias, M; Penet, L; Vindry, P; McKey, D; Panaud, O; Robert, T. 2001. Unmanaged sexual reproduction and the dynamics of genetic diversity of a vegetatively propagated crop plant, cassava (Manihot esculenta Crantz), in a traditional farming system. Molecular Ecology 10 (8): 1895-1907.
Occurrence of intervarietal or interspecific natural crosses has been reported for many crop plants in traditional farming systems, underlining the potential importance of this source of genetic exchange for the dynamics of genetic diversity of crop plants. In this study, we use microsatellite loci to investigate the role of volunteer seedlings (plants originating from unmanaged sexual reproduction) in the dynamics of genetic diversity of cassava (Manihot esculenta Crantz), a vegetatively propagated crop, in a traditional farming system in Guyana. A previous field study showed that farmers incorporate such plants into the germplasm for vegetative propagation, and that many of them are likely to be assigned by farmers to recognized varieties. Under strict vegetative propagation clonality of varieties is expected. The high proportion of polyclonal varieties observed suggests that incorporation of seedlings into the germplasm for propagation is a frequent event. The molecular variability assessed with microsatellite markers shows that there is high differentiation among heterozygous varieties, whereas populations of seedlings do not depart from the proportions expected under Hardy-Weinberg assumptions. Assignment of seedlings to a recognized variety on the basis of morphological similarity greatly increases genetic diversity within the variety. We argue that recombination and gene flow play a major role in the dynamics of genetic diversity of cassava in traditional farming systems. Documenting unmanaged sexual reproduction and its genetic consequences is a prerequisite for defining strategies of in situ conservation of crop plant genetic resources. <<<