Dispersal strategy of cyst nematodes (Heterodera arenaria) in the plant root zone of mobile dunes and consequences for emergence, survival and reproductive success

Root-feeding nematodes may play an important role in generating spatial and temporal variation in natural plant communities, but little is known about the performance of the nematodes in the plant root zone. We studied the emergence, survival and reproductive success of the cyst nematode Heterodera arenaria , a root feeding-specialist that occurs in mobile dunes. The host plants of H. arenaria are buried regularly by windblown sand to which the plants respond by upward clonal expansion. As a consequence, the nematodes have to migrate upwards in the soil profile to find new roots for feeding and reproduction, however, not all juveniles migrate. We tested the hypothesis that the offspring from migrated individuals would perform better than from individuals that remained behind and discuss the advantage of this dualistic behavior. The individual performance of the cyst nematodes was better when their juveniles migrated to the new root layer. In the field, in the new root layer the cysts had more eggs and juveniles than cysts collected from the 1-year-old root layer. Under controlled conditions, cysts from the new root layer released their first juveniles faster than cysts from the 1-year-old root layer. However, the juveniles that do not migrate might be crucial for the persistence of the population. In the past decade in two extremely dry years, we could not find cysts in the new root layer. Apparently, summer drought constrains cyst formation, so that the cysts produced in the older root layers serve as a reservoir for the population. Such reservoirs could become more important when climate change will result in increased incidence of summer droughts.