More recently explored research topics include the evolution of dispersal characteristics in stress imposing environments, among which fragmentation. Seed characteristics are maternally controlled but influence both the dispersal capacity and the probability of successful establishment of the offspring. Mother plants experiencing stressful conditions can be expected to show an adaptive plastic response towards producing more seeds with a higher dispersal capacity, since this will result in a higher probability of escaping the stress imposing environment by increasing the colonization capacity of the offspring. On the other hand, stress is often associated with a shortage of resources, which may result in a constrained resource allocation to reproduction. Seed characteristics of individuals in stressful conditions will hence be determined by the balance between on the one hand the genetic ability of the plant to respond plastically through increasing colonization capacity and on the other hand resource constraints on reproduction and adaptive plasticity. A first test of this hypothesis was executed on Senecio jacobaea. This species is able to delay flowering and to regrow the next year when an individual is severely defoliated by caterpillars of Tyria jacobaea. Secondarily infected individuals, infected during two consecutive years, can be expected to show a more sensitive plastic reaction in seed characteristics towards higher offspring colonization capacity, since they experienced herbivory stress during two consecutive years, but repeated defoliation may also cause resource limitations constraining reproduction. We related seed characteristics, such as seed size, pappus length and the number of heavy and light seeds in a flowerhead, of primarily and secondarily infected individuals of Senecio jacobaea with the level of caterpillar herbivory stress. Although primary infection itself did not affect seed characteristics, pappus length was positively and the number of heavy seeds was negatively correlated with the degree of infection, which indicates that only severe infection causes a plastic reaction, at the cost of the production of heavy seeds. In contrast, secondarily infected individuals had a smaller pappus and heavy seeds and pappus length decreased with increasing infection level, indicating the importance of resource constraints. Only primarily infected individuals had the ability to react plastically towards a higher dispersal capacity and resource constraints mainly determined seed characteristic of individuals that experienced herbivory stress during two consecutive years. The same research questions are currently tested on populations of Aster tripolium.
reproduction capacity, dispersal capacity, adaptive plasticity
created:2011-12-14 14:18:59 UTC, source:web