This paper reports on different observations and experiments examining the role of ants in the seed dispersal of the rare and endemic species Centaurea corymbosa. Direct observations of seed manipulation by ants in natural populations showed that dispersal distances are very limited, and many ants did not disperse seeds at all. Cafeteria experiments failed to demonstrate: (i) that the elaiosome represents the attractive part of the achene; and (ii) that seeds of Euphorbia characias, a common species occurring in the same habitat, are more attractive than achenes of C. corymbosa despite a 10-fold difference in elaiosome size. However, ants show a foraging behavior to collect seeds of C. corymbosa because seed removal is greater at the foot of a fruiting plant than further away. Experiments in controlled conditions were also carried out to investigate the secondary benefits of seed manipulation by ants. Two independent experiments showed that, in contrast to many other myrmecochorous species, elaiosome removal decreases germination rate. Finally, the effects of burial at low depth (2 cm) on seed emergence are limited; however, as ants rarely move seeds to their nest, this secondary benefit of myrmecochory is unlikely. Therefore, it can be concluded that the functional role of an elaiosome in this species is not evident. However, ants clearly contribute to seed dispersal in C. corymbosa.

Banane: Le prix moyen est en progression sensible par rapport au niveau deja relativement soutenu de l'an passe, malgre une qualite assez mediocre d'une part significative des fruits antillais. Le recul assez marque des apports (en particulier en provenance d'Afrique et des zones dollar) et une demande dynamique durant les deux premieres decades permettent d'expliquer cette bonne performance. Avocat: La performance est une nouvelle fois tres mauvaise. La reprise enregistree en toute fin de mois ne peut compenser le niveau extremement bas des prix durant les deux premieres decades. En effet, la demande s'est de nouveau montree extremement decevante durant cette periode, face a une offre israelienne soutenue et dispersee. Orange: Meme si le marche reste satisfaisant (progression des ventes et des prix), fevrier marque une rupture dans l'excellente dynamique qui durait depuis decembre. En effet, la brutale degradation de la qualite des Navel/Naveline a eu un fort impact negatif sur une consommation deja fragilisee par des temperatures relativement superieures a la normale. Cette situation a pese sur le marche des autres varietes proposees. Pomelo: La performance est globalement satisfaisante, puisque prix et volumes progressent sensiblement malgre la traditionnelle baisse d'activite de fevrier. Toutefois, si le marche est reste equilibre pour les operateurs turcs et israeliens grâce a une reduction de leurs apports, le resultat est plus contraste pour la Floride. Des apports plus soutenus ont conduit les importateurs de cette origine a elargir leur fourchette de prix. Petits agrumes: Comme d'habitude, l'interet pour les petits agrumes s'est nettement amoindri en fevrier. Toutefois, le bilan est satisfaisant, puisque volumes et prix sont revenus a un niveau moyen, apres le fort deficit d'offre de l'an passe. En effet, le changement de varietes, intervenu en milieu de mois, a permis de rattraper la mauvaise performance realisee la premiere quinzaine en raison de problemes qualitatifs. (Resume d'auteur)

In Crepis sancta (Asteraceae), achenes produced in the periphery of the flower head have reduced dispersal ability and are larger than achenes produced in the centre of the head, which disperse farther. The proportion of central achenes produced by a single individual represents the potential dispersal rate of its progeny. Seed variation in dispersal ability may be important where there is spatio-temporal variability of habitats, but its evolutionary significance mainly depends on the heritability of the relative proportions of each achene morph. However, the number of peripheral achenes in a capitulum, and that of involucral bracts are suggested to depend on the number of parastichies, a canalized character. From a diallel cross design, phenotypic variance for several capitulum traits was partitioned among six variance components, including the additive variance. The phenotypic values of some head traits reflected the expected frequency due to ontogeny, in particular the number of involucral bracts. Yet, this character also had a significant heritability, suggesting that variation around the mode of the distribution was not only due to developmental noise. The additive variance for number of peripheral and central achenes was not significantly different from zero. In contrast, their respective proportion had a narrow sense heritability greater than 0.20. The present results suggest that the percentage of central achenes per individual, and thus the potential dispersal rate in Crepis sancta, is under quantitative genetic control, and could undergo microevolutionary changes in natural populations.