François Bretagnolle

Evolutionary consequences of diploid-polyploid hybrid zones in wild species.

Hybrid zones between cytotypes with different ploidy levels are particularly interesting for studying the ecology and the evolution of reproductive interactions between closely related taxa. Diploid-polyploid hybrid zones differ fundamentally from those between diploids in that they reflect certain conditions that are characteristic of the early stage of polyploid establishment, and allow tests of hypotheses relating to the dynamics and evolution of polyploid complexes. Recent theoretical and empirical studies have provided important data on the evolution of isolating mechanisms in diploid-polyploid contact zones, but have also shown that introgression might counteract the evolution of isolating mechanisms.

Adaptive divergence for a fitness-related trait among invasive Ambrosia artemisiifolia populations in France

The impact of natural selection on the adaptive divergence of invasive populations can be assessed by testing the null hypothesis that the extent of quantitative genetic differentiation (QST) would be similar to that of neutral molecular differentiation (FST). Using eight microsatellite loci and a common garden approach, we compared QST and FST among ten populations of an invasive species Ambrosia artemisiifolia (common ragweed) in France. In a common garden study with varying water and nutrient levels, we measured QST for five traits (height, total biomass, reproductive allocation, above‐ to belowground biomass ratio, and days to flowering). Although low FST indicated weak genetic structure and strong gene flow among populations, we found significant diversifying selection (QSTu2003>u2003FST)u2003for reproductive allocation that may be closely related to fitness. It suggests that abiotic conditions may have exerted selection pressure on A. artemisiifolia populations to differentiate adaptively, such that populations at higher altitude or latitude evolved greater reproductive allocation. As previous studies indicate multiple introductions from various source populations of A. artemisiifolia in North America, our results suggest thatu2003the admixture of introduced populations may have increased genetic diversity and additive genetic variance, and in turn, promotedu2003the rapid evolution and adaptation of this invasive species.

Anthropogenic disturbance and habitat differentiation between sexual diploid and apomictic triploid Taraxacum sect. Ruderalia.

Co-occurrence of sexual diploid and apomictic triploidTaraxacum sectionRuderalia has been reported frequently. Many suggestions have been put forward with respect to the existence of an ecological differentiation between the cytotypes. In a study of 116Ruderalia populations in the area around Neuchâtel (Switzerland) such a habitat differentiation has been proven. Large differences in the diploid/triploid ratio have been found between different field types. Adjacent fields of different types sometimes had significantly different cytotype ratios. In a canonical correspondence analysis significant vegetation differences were found between fields with mainly diploidRuderalia and fields with mainly triploidRuderalia. Two environmental indicators were significantly positively correlated with ploidy levels, altitude with diploids, and the percentage of therophytes in a vegetation with triploids. The percentage of therophytes is thought to be an indicator of the amount of disturbance due to human activities. At lower altitudes, the diploid/triploid ratio is largely determined by the amount of disturbance. Highly-disturbed fields contain mainly triploids whereas relatively stable fields contain mainly diploids. At higher altitudes there are mainly diploids. The presence of triploidTaraxacum sect.Ruderalia in the region around Neuchâtel appears to be the result of the high amount of human activities of the last few hundred years. Whether the triploid presence is due to immigration or to local formation from diploids is yet unknown.

[Ragweed (Ambrosia artemisiifolia L.): expansion history of a "biological pollutant" in France].

In France, common ragweed (Ambrosia artemisiifolia L.) is an invasive species, which most probably originates from North America. This plant is responsible for human health problems as the pollen causes allergic rhinitis and seasonal asthma; in addition, it engenders agronomical problems as the efficient herbicide treatments are few. Consequently, various departments of the Rhône-Alpes region set up eradication programs for common ragweed. The species is distributed over a large range of ecological environments (road margins, embankments, river beds) and does not seem to be dependent on soil properties. Its ability to occupy different environments varies with the geographic location. Common ragweed was cultivated in botanical gardens during the XVIIIth century but seems to have arrived in France in seed lots during the XIXth century. It therefore began its invasion as a crop weed. Because of its late emergence date (late March), common ragweed is most frequently found in spring crops as well as during the inter-crop season. Its natural dispersal mechanisms are rudimentary; its seeds are probably dispersed mostly during the transport of material (soil, gravel, compost...), irrigation and especially via harvest combines. The development history of this species in France is scarcely known. The examination of herbarium collections helped to partially reconstruct the history of the species. According to the first results, the species arrived in several locations and at different dates in France. However, common ragweed spread most successfully in the Lyons region because of reasons still unknown.

L’ambroisie : Chronique de l’extension d’un « polluant biologique » en France

L’ambroisie à feuilles d’armoise (Ambrosia artemisiifolia L.) est une astéracée originaire du continent américain. Citée parmi les espèces envahissantes [1], son extension en France semble récente, mais les problèmes de santé publique posés par son expansion géographique sont de plus en plus inquiétants [2]. Naturalisée en France au milieu du XIXe siècle, elle est restée relativement peu connue des allergologues jusqu’au milieu des années 1960. En 1966, R. Touraine et al. [3] détaillent son rôle dans un certain nombre de pollinoses de la région lyonnaise et signalent les risques pour la santé publique de son extension géographique. En effet, le pollen de l’ambroisie est à l’origine de très fortes allergies (pollinose, rhinite saisonnière) dont les symptômes sont, par ordre décroissant de fréquence, des rhinites, des conjonctivites, de l’asthme et, plus rarement, de l’eczéma et de l’urticaire [4]. Localisée principalement dans la région Rhône-Alpes, elle est considérée comme un véritable « polluant biologique » et fait l’objet d’arrêtés d’éradication dans plusieurs départements (Rhône, Drôme, Vaucluse, Ardèche1...). Des campagnes d’arrachage sont même organisées depuis plusieurs années par le Conseil Régional Rhône-Alpes pour limiter les émissions de pollen. Biologie et écologie de la plante

Écologie, distribution et morphologie comparées des nivéoles de Nice (Acis nicaeensis) et de Fabre (Acis fabrei), Alliaceae endémiques des Alpes maritimes et et de la Nesque (Vaucluse)

Abstract Acis nicaeensis and A. fabrei are two endemic geophytes from the Maritime Alps and the Vaucluse (Nesque basin) respectively. The aims of this study are to establish the distinctive morphological characters between the two snowflakes, to examine the chorology and the demography of the populations, in addition with the evaluation of their ecological requirements. Among the most discriminating characters, leaf width, stigma—anther separation, number of internal tepal veins and diameter of the epigynous disk are the most useful. Thirty—six existing populations have been censused for A. nicaeensis occuring in ecological conditions ranging from thermophilous mattoral to xerophilous grasslands with annual or perennial species. The four known populations of A. fabrei are found on rocky grasslands in clearings. The different factors threatening the two snowflakes are discussed.