General discussion

Abstract

The study of secondary pollen presentation is the study of attributes involved in pollination success. These attributes could promote pollination success of two kinds. The first kind is achieved by leaving more progeny: genotypes giving more pollen should leave a greater number of progeny than those producing less pollen (i.e. the fitness of these genotypes is higher). Secondary pollen presentation is not concerned with increasing pollen supply but it would have the same effect if it ensured that a greater proportion of the pollen that is produced reaches receptive, compatible stigmas. The second kind is achieved by leaving progeny of better quality; this improves the fitness of the next generation. It depends on exercising a choice of mates, but in plants the scope for mate-choice is limited. However, the fitness of the next generation might be improved if, as a male, a plant can sample a genetically widened range of females, and this might be achieved by spreading pollen more widely in space and/or time. Some forms of secondary pollen presentation could have this effect. In either case, we have to look at the processes of pollen removal and pollen transfer, and these operate mainly through the individual flower, though not infrequently attributes promoting pollination success will be found in the inflorescence and sometimes in the form of the whole plant. Secondary pollen presentation takes effect through the individual flower.