Infection dynamics of the monogenean parasite Gyrodactylus gasterostei on sympatric and allopatric populations of the three-spined stickleback Gasterosteus aculeatus

Parasites with high host specificity maximally depend on their hosts, which should increase the likelihood of coevolution. However, coevolution requires reciprocal selection exerted by the host and the parasite, and thus a considerable level of parasite virulence. In species of the monogenean ectoparasite genus Gyrodactylus consecutive generations are confronted with a single host, which may constrain the evolution of virulence. Transmission, which is often important in the ecology of Gyrodactylus species, may have the opposite effect, but may also lead to the avoidance of coevolutionary arms races. We investigated the potential outcome of coevolution between Gyrodactylus gasterostei Gl?ser, 1974 and its host, the three-spined stickleback (Gasterosteus aculeatus L.) by determining the strength of genotype by genotype (GxG) interactions on two levels: within and between sympatric and allopatric host populations. To do so, we compared the parasite's infection dynamics on laboratory-reared sympatric (Belgian) and allopatric (German) hosts. We found that a parasite line successfully infected a range of sympatric host genotypes (represented by families), while it failed to establish on allopatric hosts. Phylogeographic studies suggest that neutral genetic divergence between the host populations cannot explain this dramatic difference. Provided that this result can be generalised towards other parasite lines, we conclude that coevolution in this host-parasite system is more likely to lead to local adaptation on the population level than to GxG interactions within populations.     

Breeding potential of Belgian landraces of leek ( Allium ampeloprasum L. var. porrum)

Western Europe is the world's greatest leek producing and consuming region. Belgium is situated in the centre of Western Europe and can be considered as a genepool of landraces of leek. Although the commercial varieties nowadays take over the successes of Belgian landraces, this paper deals with the breeding potential of the Belgian landraces. Typing the Belgian landraces was done in an observation trial together with 50 cultivars. Clustering analysis revealed that 4 of the Belgian landraces were autumn types, 2 landraces were of the early winter type and another 12 landraces were ranged with 6 commercial varieties to form the most winterhardy group of leek. For the important characteristics leaf colour and senescence resistance, the Belgian landraces were better than most of the commercial varieties. Although, for economically more important characteristics shaft length and some disease resistance they scored low. Finally, in this trial, the Belgian landraces were high yielding, especially in the late season. But also in the early season (harvest in September and November) some Belgian landraces were in the top 10 for yield. At harvest in February 9 of the 10 best yielding winterleeks were Belgian landraces. This proves that the Belgian landraces were well adapted to the soil and climate of this region. This revised version was published online in July 2006 with corrections to the Cover Date.