Detailed position: CNRS Researcher
Laboratoire Écologie, Systématique, Évolution
Bât. 362, rue du Doyen André Guinier
91405 Orsay Cedex
Tel: +33 (0)1 69 15 57 01
Fax: +33 (0)1 69 15 73 53
Email: jean-michel.guillon (at) u-psud.fr
Environmental Sex Determination in Equisetum : mechanisms and evolutionary significance.
In some animal and vegetal species, the sex ratio (proportion of males in the offspring) varies with the environment. A theoretical model (Charnov and Bull 1977, Bull 1981) makes prediction about (i) the conditions favouring the evolution of this pattern, and (ii) the expected sex ratio bias. In short, when male and female fitness react differently to the variation of the environment, natural selection favours the expression of the sex that benefits more from the local environment. In this case, it may be advantageous for the individual to determine its sex according to the environment in which it develops (Environmental Sex Determination: ESD). A typical example of ESD is found in turtles where the incubation temperature of the egg determines the sex of the developing embryo (Temperature-dependent Sex Determination: TSD).?I began to investigate ESD with horsetails (Equisetum).
My work first consisted in describing how sex determination in gametophytes could be modified in vitro by external factors such as light intensity or the presence of sugars in the growth medium (Guillon and Raquin 2002). Then, I examined whether the theory of Charnov and Bull could provide an explanation for the observed pattern: Did light favoured female sex expression because females benefited more than males from higher light intensity? Results obtained did not support this hypothesis, so that I got interested in dispersal as a factor potentially able to modify the evolution of sex ratio.
Dispersal and sex ratio evolution in a heterogeneous environment.
The analysis of a model based on sex biased dispersal (Guillon, Julliard and Leturque 2006) showed that habitat-dependent biased sex ratios are evolutionarily stable when there is a difference between pollen and seed dispersal rates, or between male gametes and spore dispersal rates in the case of lower plants. However, the results of this model failed to provide an explanation for the pattern of sex expression in Equisetum.?To get a better understanding of the evolution of ESD in Equisetum, I reconstructed the phylogeny of the genus by using chloroplastic genes that are known to be maternally inherited (Guillon and Raquin 2000). The resulting phylogeny questioned the monophyly of the two accepted subgenera (Guillon 2004, 2007).
A spatially explicit model takes into account dispersal in a more realistic way, by studying the effect of dispersal distance on the convergence stable strategy of sex ratio (Guillon and Bottein 2011). Another theoretical model investigates the interaction between the selective force described by Charnov and Bull and those resulting from sex biased dispersal (Guillon 2016).
Another study aims at identifying the conditions required for the evolution of sex-biased dispersal by introducing temporal variation of habitat quality. Our results show that the dispersal strategy can be sex-biased when male dispersal occurs before fertilization and female dispersal occurs after fertilization. When dispersal rates can be habitat-dependent, the selected strategies are the ones leading to a distribution of individuals that matches the expected amount of resources available in different habitat (Aguilée, de Villemereuil and Guillon 2015).
Temperature-dependent Sex Determination in reptiles : consequences and evolutionary significance.
During his PhD thesis, Vincent Hulin studied the influence of nest site selection on the evolution of temperature-dependent sex determination (TSD) in turtles. A simulated turtle population with natal philopatry shows a biased sex ratio at the evolutionary equilibrium: more males are produced in environments characterized by a low incubation success, and more females are produced in environments characterized by a high incubation success; This result provides a new perspective on the evolution of TSD in reptiles, especially in turtles (Hulin and Guillon 2007). Several hypotheses will be tested, using a new phylogeny of turtles (Guillon, Guéry, Hulin and Girondot 2012). Other results show a relation between sex ratios in natural nests and the transitional range of temperature for TSD (Hulin, Delmas, Girondot, Godfrey and Guillon 2009), and evaluate the potential effects of global warming on sex ratios of turtles (Hulin, Grondot, Godfrey et Guillon 2008).
|Depuis 1998||CR1 CNRS au Laboratoire Evolution et Systématique de l’Université Paris 11|
|1993-1997||CR2 CNRS au Laboratoire de Biochimie de l’Ecole Polytechnique|
|1989-1992||Doctorat en Biologie à l’Ecole Polytechnique : Approche Enzymologique et Génétique du Rôle de la Formylation N-terminale dans le Démarrage de la Traduction chez les Bactéries|
|1987-1988||DEA Bases Fondamentales de l’Oncogénèse à l’Université Paris 11|
|1986-1987||Agrégation de Biochimie-Génie Biologique|
|1984-1988||Elève à l’Ecole Normale Supérieure De Cachan (Section Biochimie)|
Girondot M, Guillon J-M (2018)-The w-value : an alternative to t- and Chi-2 tests.Journal of Biostatistics & Biometrics,1:1-3
Schmitt E, Guillon J-M, Meinnel T, Mechulam Y, Dardel F & Blanquet S. (1996)-Molecular recognition governing the initiation of translation in Escherichia coli.A review. Biochimie ,78:543-554
Meinnel T, Guillon J-M, Mechulam Y & Blanquet S. (1993)-Escherichia coli fmt gene for methionyl-tRNAMetf formyltransferase escapes metabolic control. Journal of Bacteriology ,175:993-1000
Meinnel T, Guillon J-M, Mechulam Y & Blanquet S. (1993)-Structure et activité biologique: l\’exemple des acides ribonucléiques de transfert dans la traduction du message génétique en protéine. Revue Scientifique et Technique de la Défense ,20:165-172
Guillon J-M (1992)-Approche enzymologique et génétique du rôle de la formylation N-terminale dans le démarrage de la traduction chez les bactéries. Thèse de Doctorat de l’Ecole Polytechnique,134p
Guillon J-M, Mechulam Y, Schmitter J-M, Blanquet S & Fayat G. (1992)-Disruption of the gene for Met-tRNAMetf formyltransferase severely impairs the growth of Escherichia coli. Journal of Bacteriology ,174:4294-4301
Guillon J-M, Meinnel T, Mechulam Y, Lazennec C, Blanquet S & Fayat G. (1992)-Nucleotides of tRNA governing the specificity of Escherichia coli methionyl-tRNAMetf formyltransferase. Journal of Molecular Biology ,224:359-367