Pollen performance and male fitness in an anemophilous, monoecious tree, Betula pendula
Betula pendula Roth clones were examined to study the relationship between pollen grain size and pollen tube growth rate and pollen and seed performance. Two hypotheses were tested: (i) pollen donors with larger pollen grains have faster growing pollen tubes and (ii) maternal plants produce more seeds when inflorescences have been pollinated by pollen from donors with fast pollen tube growth. Pollen from 15 plants was collected, and pollen grain sizes and pollen tube growth rates were studied in vitro. Eight maternal clones were pollinated by pollen from seven paternal clones, pollen tube growth rates of the pollen donors were measured on each maternal plant, and the number and mass of the resulting seeds were analysed. There was no correlation between pollen grain size and pollen tube growth rate in vitro. Also, there was no relationship between pollen tube growth rate and the number of produced or aborted seeds. Thus, the hypothesis that larger pollen grains would have longer pollen tubes was not supported by the present study. The results of the present study do not support the idea that pollen donors with fast pollen tube growth should sire more and better seeds.Key words: Betula pendula, female choice, nonrandom abortion, pollen competition, sexual selection.