Abstract
(Sub-project to 838.06.110) One aspect of Environmental Risk Assessments (ERA) of transgenic crops involves the introduction of the transgene in natural environments through outcrossing with a wild relative or through the establishment of feral populations. This necessitates an assessment of the likelihood of an expansion of hybrid/feral plants carrying the transgene as well as the associated and potentially adverse effects on the ecosystem. Two types of scenarios can be envisaged: hybrid/feral plants carrying the transgene spread in habitats where hybrids or feral plants already occur, or they also invade novel habitats. The latter could be due to a transgene that increases the abiotic stress tolerance of its carrier. The potential chain of events that follows and may lead to adverse effects could be very different for these two situations. Effects of a local spread of feral/hybrid plants could result from a major shift in their frequency, for instance, from being a relatively rare to a dominant component of the system, or due to a new trait or substance introduced to the system. This could result in the disappearance of other, competing species from the system, and quantitative changes in the functional diversity of the ecosystem. However, if plants invade new habitats they will encounter species they have never met before, and they may also introduce other species (pathogens, herbivores, pollinators) to the recipient system. This suggests that this may lead to qualitative effects on ecosystem diversity and functioning. In both scenarios fundamental ecological questions need to be addressed: To what extent is the role of a species unique in the functioning of the ecosystem and for the species it interacts with? What limits the current margins of a species? distribution and what attributes make that species become invasive? What are the consequences of an invasion for the ecosystem? We aim to study the potential effects of a change in the presence of hybrid/feral plants by a combined experimental and theoretical approach. Our experimental systems are (i) hybrids between crop and wild lettuce (Lactuca sativa and L. serriola, resp.) as a model for crop/wild hybridisation, and (ii) Brassica napus as a model feral system. We specifically focus on abiotic stress related to salinity and drought: (i) new GM races are being developed with increased drought/salt tolerance; (ii) non-GM material varying in salt/drought tolerance is available so that the scientific questions can be adequately addressed - no GM material will be used in the experiments; (iii) extensive data is available on their occurrence in (semi-)natural habitats in the Netherlands. We shall use three types of manipulations: changes to the local densities of plants, establishing new populations within and outside the current ecological range, and creating experimental populations in ?oases? where they are not exposed to the stress of the surrounding environment. We focus on the following potential hazards associated with the expansion of the plants: Are other species (e.g., competitors) reduced in their presence, and thereby in danger of disappearing? Do specific diseases or herbivores increase to levels beyond the baseline, or are they introduced to new environments? Is pollinator behaviour affected, leading to reduced seed set of other species and potentially their demise? Is there a decrease in the functional diversity of the ecosystem or in its dynamics/stability? Note, however, that not all changes are necessarily detrimental for a system. The theoretical approach aims to analyse the limits of the species? current ecological distributions by means of data analysis and modelling. The main goal is to determine if drought/salt stress tolerance is an important factor limiting the current distribution of the focal plants. If so, increased stress tolerance may cause an invasion outside the current distribution range, and other habitats that may be colonized. We will test if it is feasible to predict such changes, and to identify potential habitats that could be susceptible to invasions.
Netherlands