Comment les peuplements de plantes et d'insectes phytophages se façonnent mutuellement : la théorie coévolutive de la structure des peuplements

A plant community may be considered as an assemblage of species whose chemical defenses against herbivores are more or less efficient. In the same way a community of phytophagous insects can be viewed as a group of consumers which are capable either of bypassing the plants'chemical defenses, or of taking advantage of them. The inter-relations between the two communities result in an array of compromise solutions originating from the coevolution of plants and insects. The pros and cons of such a coevolutionary theory of community structure are discussed. Particular attention is given to the following points : the concept of community structure, the major categories of toxichemicals and digestibility-reducing substances involved in the « arms race » between plant producers and animal consumers, the evolutionary mechanisms implied in coevolution, the costs and benefits of the alternative adaptive strategies adopted by insect consumers (with particular emphasis on their bioenergetic implications), and the dynamic aspect of coevolution. Whereas coevolution undoubtedly plays a role in plant-insect interactions, such a role should not be overemphasized. The weil documented case of the moths living on various oak species highlights sorne obvious inconsistencies. Thus the coevolutionary theory of community structure should still be considered more as a useful working hypothesis rather than a well established fac

Le concept de niche chez les drosophiles

Deux modèles de coévolution entre des insectes et leurs plantes hôtes, les Drosophiles des Ficus en Côte-d’Ivoire et les Dro sophiles des cactus dans le désert de Sonora aux Etats-Unis, servent de base à la discussion du concept de niche. Le premier modèle est issu d’un écosystème de savanes tropicales, caractérisé par une grande richesse et une forte diversité des espèces entraî nant des concentrations d’espèces et d’importants chevauchements de niches ; le second est issu d’un écosystème désertique caracté risé par une faible richesse et une faible diversité des espèces ne provoquant qu’un chevauchement limité des niches. La niche est conçue comme l’ensemble des pressions du milieu qui s’exercent sur le pool de gènes d’une population locale dans un habitat donné en limitant l’expression de ses potentialités à un moment précis.The niche theory is discussed in the light of two coevolution ary models : the coevolution of Drosophilids and their Ficus hosts in the Afrotropical region (after Lachaise’s data) and the coevolution of cactiphilic Drosophila and their desert cactus hosts in the Ne arctic region (after Heed’s data). The former model provides species packing, wide niche overlap and resource partitioning whe reas the latter, because of a smaller species diversity, leads to a greater breeding-site separation and host-specificity. The niche is conceived as the trade-off between the selective pressures which act to limit the expression of the genetic potentialities of a deme in a definite habitat and at a given time

Patterns of nucleotide diversity at the regions encompassing the Drosophila insulin-like peptide (dilp) genes: demography vs positive selection in Drosophila melanogaster.

In Drosophila, the insulin-signaling pathway controls some life history traits, such as fertility and lifespan, and it is considered to be the main metabolic pathway involved in establishing adult body size. Several observations concerning variation in body size in the Drosophila genus are suggestive of its adaptive character. Genes encoding proteins in this pathway are, therefore, good candidates to have experienced adaptive changes and to reveal the footprint of positive selection. The Drosophila insulin-like peptides (DILPs) are the ligands that trigger the insulin-signaling cascade. In Drosophila melanogaster, there are several peptides that are structurally similar to the single mammalian insulin peptide. The footprint of recent adaptive changes on nucleotide variation can be unveiled through the analysis of polymorphism and divergence. With this aim, we have surveyed nucleotide sequence variation at the dilp1-7 genes in a natural population of D. melanogaster. The comparison of polymorphism in D. melanogaster and divergence from D. simulans at different functional classes of the dilp genes provided no evidence of adaptive protein evolution after the split of the D. melanogaster and D. simulans lineages. However, our survey of polymorphism at the dilp gene regions of D. melanogaster has provided some evidence for the action of positive selection at or near these genes. The regions encompassing the dilp1-4 genes and the dilp6 gene stand out as likely affected by recent adaptive events

Le concept de niche chez les Drosophiles

The niche theory is discussed in the light of two coevolution ary models : the coevolution of Drosophilids and their Ficus hosts in the Afrotropical region (after Lachaise’s data) and the coevolution of cactiphilic Drosophila and their desert cactus hosts in the Nearctic region (after Heed’s data). The former model provides species packing, wide niche overlap and resource partitioning whereas the latter, because of a smaller species diversity, leads to a greater breeding-site separation and host-specificity. The niche is conceived as the trade-off between the selective pressures which act to limit the expression of the genetic potentialities of a deme in a definite habitat and at a given time.Deux modèles de coévolution entre des insectes et leurs plantes hôtes, les Drosophiles des Ficus en Côte-d’Ivoire et les Drosophiles des cactus dans le désert de Sonora aux Etats-Unis, servent de base à la discussion du concept de niche. Le premier modèle est issu d’un écosystème de savanes tropicales, caractérisé par une grande richesse et une forte diversité des espèces entraînant des concentrations d’espèces et d’importants chevauchements de niches ; le second est issu d’un écosystème désertique caractérisé par une faible richesse et une faible diversité des espèces ne provoquant qu’un chevauchement limité des niches. La niche est conçue comme l’ensemble des pressions du milieu qui s’exercent sur le pool de gènes d’une population locale dans un habitat donné en limitant l’expression de ses potentialités à un moment précis.Lachaise Daniel. Le concept de niche chez les Drosophiles. In: La Terre et La Vie, Revue d'Histoire naturelle, tome 33, n°3, 1979. pp. 425-456

Comment les peuplements de plantes et d’insectes phytophages se façonnent mutuellement : la théorie coévolutive de la structure des peuplements

A plant community may be considered as an assemblage of species whose chemical defenses against herbivores are more or less efficient. In the same way a community of phytophagous insects can be viewed as a group of consumers which are capable either of bypassing the plants’ chemical defenses, or of taking advantage of them. The inter-relations between the two communities result in an array of compromise solutions originating from the coevolution of plants and insects. The pros and cons of such a coevolutionary theory of community structure are discussed. Particular attention is given to the following points : the concept of community structure, the major categories of toxiche-micals and digestibility-reducing substances involved in the «arms race» between plant producers and animal consumers, the evolutionary mechanisms implied in coevolution, the costs and benefits of the alternative adaptive strategies adopted by insect consumers (with particular emphasis on their bioenergetic implications), and the dynamic aspect of coevolution. Whereas coevolution undoubtedly plays a role in plant-insect interactions, such a role should not be overemphasized. The well documented case of the moths living on various oak species highlights some obvious inconsistencies. Thus the coevolutionary theory of community structure should still be considered more as a useful working hypothesis rather than a well established fact.Lachaise Daniel. Comment les peuplements de plantes et d’insectes phytophages se façonnent mutuellement : la théorie coévolutive de la structure des peuplements. In: Revue d'Écologie (La Terre et La Vie), tome 36, n°4, 1982. pp. 481-537

Le peuplement d'Insectes en forêt de Taï (Côte d'Ivoire)

Couturier Guy, Lachaise Daniel. Le peuplement d'Insectes en forêt de Taï (Côte d'Ivoire). In: Bulletin de la Société entomologique de France, volume 87 (9-10), Novembre-décembre 1982. pp. 384-388

The sperm roller: a modified testicular duct linked to giant sperm transport within the male reproductive tract

International audienc

Data from: Inter-island divergence within Drosophila mauritiana, a species of the D. simulans complex: past history and/or speciation in progress?

Speciation with gene flow may be more common than generally thought making detailed understanding of the extent and pattern of genetic divergence between geographically isolated populations useful. Species of the Drosophila simulans complex provide a good model for speciation and evolutionary studies; understanding their population genetic structure will increase our understanding of the context in which speciation has occurred. Here we describe the genetic diversity and the genetic differentiation, at mitochondrial and nuclear loci, of two distant populations of D. mauritiana (Mauritius and Rodrigues Islands). We surveyed the two populations for their mitochondrial types, eight nuclear genes and 18 microsatellite loci. A new mitochondrial type is fixed in the Rodrigues population of D. mauritiana. The two populations are highly differentiated, their divergence appears relatively ancient (100,000 years) compared to the origin of the species, around 0.25 MYA, and they exhibit very limited gene flow. However, they have similar levels of divergence from their sibling, D. simulans. Both nuclear genes and microsatellites revealed contrasting demographic histories between the two populations; expansion for the Mauritius population and stable population size for the Rodrigues Island population. The pronounced geographic structure discovered within D. mauritiana in addition to the low amount of genetic exchange between those two island populations is significant for understanding how the genetic structuring of the species contributes to its evolutionary history, and clearly merits further attention in the broad context of speciation

An extended scaled equation for the temperature dependence of the surface tension of pure compounds inferred from an analysis of experimental data

International audienceWe have made a literature survey and performed a critical analysis of the available experimental surface tension data for the most volatile compounds in petroleum fluids: nitrogen, methane, ethane, propane, i-butane, n-butane, n-pentane, n-hexane, n-heptane and n-octane. Including the selected data with those for oxygen, xenon, krypton and those obtained recently for 16 partially halogenated hydrocarbons (refrigerants), we propose the following extended scaled equation to represent the surface tension of these substances:σ=kTc(NAVc)2/3(4 .35+4.14ω)t1.26(1+0.19t0.5-0.25t)where t=1-T/Tc is reduced temperature, k, NA, Vc, and ω are the Boltzmann constant, Avogadro number, the critical volume and the acentric factor, respectively. This equation, which only differs slightly from that proposed by Schmidt et al. [J.W. Schmidt, E. Carrillo-Nava, M.R. Moldover, Fluid Phase Equilibria 122 (1996) 187-206] for refrigerants, yields values for σ within 3.5% of the experimental values for all these compounds. Available data for other compounds (refrigerants) are in agreement with this relation; in the light of that we also examine some compounds (carbon dioxide and argon) for which there exist conflicting datasets