From pollen dispersal to pollen-mediated gene flow - or how to calculate the probability of pollination from pollen dispersal data

Turku

2008

S. 17

Unselbständiges Werk

200149019

Pollen-mediated gene flow in cultivated plants and trees has become an attractive scientific subject in a variety of disciplines. Main applications are the risk analysis of GMOs and conservation plans for threatened plant species, but it facilitated also our basic understanding of evolutionary and ecological processes. The methods for a quantification of gene flow can be roughly divided into two categories; first, estimations of gene flow via genetic markers such as paternity analysis, TwoGener analysis or classical Fst-approaches; and secondly, estimations of pollen dispersal via aerobiological analysis or modeling of pollen flow. The methods of the first category, also referred to as effective or realized gene flow have the drawback that we see only the result of a long chain of different processes, such as pollen production, pollen emission, pollen dispersal, pollination, compatibility, fruit development etc. Since all these processes can be affected by the external drivers we are interested in, e.g. fragmentation, management practices or climate conditions, it is hard to disentangle which driver really affects which process. The second category, also referred to as potential gene flow, has the disadvantage that the physical sampling procedures have a low representativity and that successful gene flow can hardly be derived from the physical pollen dispersal. In the present paper, I introduce a new approach to derive measures of successful gene flow from data of physical pollen dispersal on the landscape level. Therefore, I analyzed the ratio between the settled pollen quantities and the number of receptive female flowers. My analysis shows, that the total number of pollinated ovules and the probability of successful gene flow depend on the quantity of settled pollen and on the number of female flowers in the settling area of the pollen. Pollen dispersal was simulated with the mesoscale meteorological model METRAS in which biological functions for pollen emission and viabllity have been integrated. Following these results, approximately 1000 pollen/m2 deposited downstream of the oak stand in a distance of 25 km, and Iower amounts of pollen deposited up to 100 km away. These values of pollen deposition lay within the range of published field studies. Depending on the pollen production of the stand, the analysis of simulated pollen dispersal indicates successful gene flow at very low frequencies up to 100 kilometers downstream of the pollen source. Given a high female flower production, in a distance of 70 km about 1 pollinated flowers/m2 can be expected and 0.3 pollinated flowers/m2 in a distance of 110 km. In the direct surrounding of the stand, the probability of pollination ranges from 50 to 100 %. Sensitivity analysis with the total annual pollen production as variable parameter demonstrates that an increase of pollen production increases in particular the pollination close to the emitting stand. The present approach allows to link local gene flow studies based on genetic markers with landscape wide estimates of potential gene flow. Thus, it facilitates our understanding of factors that shape contemporary gene flow on the landscape level.