Viability and sunlight sensitivity of oak pollen and its implications for pollen-mediated gene flow

Abstract

Pollen-mediated gene flow and the male reproductive success of wind-pollinated trees depend on the initial viability of the pollen and the changes that occur in its viability during transport in the atmosphere. The viability of Quercus robur pollen was determined before and during exposure to sunlight by in vitro germination and the fluorescein diacetate reaction (FCR) in 2002 and 2003, respectively. These experiments allowed us to calculate initial pollen viability and pollen sensitivity to sunlight. The germination test revealed a lower initial pollen viability (25–65%) than the FCR (53–92%). Following 9.5 h of irradiation the viability was reduced to 75–100% as determined by the in vitro germination test or to 40–70% as determined by the FCR. The actual values of initial pollen viability and pollen sensitivity to sunlight were used to define a range of values for modelling pollen dispersal using the mesoscale meteorological model METRAS. The deposition patterns of viable pollen varied by as much as a factor of 14 by changing the viability parameters in the range of the observed values. This suggests significant differences in male reproductive success. Variations in initial pollen viability have stronger effects on the gene-flow pattern than do variations in pollen sensitivity to sunlight. In particular, pollen distribution throughout the local environment is shaped by the initial pollen viability, while pollen sensitivity to sunlight mainly influences long-distance pollen dispersal.