GENETIC-VARIATION AND PHENOTYPIC PLASTICITY OF POLLEN RELEASE AND CAPTURE HEIGHT IN PLANTAGO-LANCEOLATA

1. In the protogynous wind-pollinated herb Plantago lanceolata, the scape elongates during flowering, so that receptive stigmas are produced at lower heights than mature anthers. To investigate the potential impact of scape height on reproductive success through male and female function, we examined the effect of pollen release and capture height on the amount and distance of pollen dispersed to microscope slides in a wind tunnel experiment. 2. The amount of pollen dispersed to slides increased significantly with release height. In contrast, the amount of pollen captured decreased with increasing receptor height, suggesting that the heights of anthers and stigmas may be subject to disruptive selection. The amount and distance of pollen dispersed also depended upon the difference between source and capture heights. 3. A greenhouse experiment revealed significant variation among P. lanceolata genotypes in height, of stigma initiation, height of anther initiation, and temporal separation of these two events. However, significant genetic variation could not be detected for the difference in height between anther and stigma initiation within plants. The genotype mean correlation between male and female flowering heights was strongly positive. These results suggest that evolutionary response to disruptive selection on height of pollen capture and release may be physiologically or genetically constrained, and that within-population variation in scape height may lead to trade-offs in reproductive success through male and female function. 4. Height of male and female flowering increased significantly when plants were exposed to lateral shade simulating neighbouring vegetation. Thus, plastic response to environmental variation may not only influence individual fitness through female and male reproductive success but also affect patterns of gene dispersal and population structure in P. lanceolata.