Abstract:

Clonal plants reproduce asexually via clonal growth and simultaneously reproduce sexually, and the consequences of clonal growth on pollination and mating have been one of the essential questions in ecology and evolution of plant reproduction. An increasing number of studies report the effects of clonal size, architecture, genetic diversity, and floral deployments on pollinator visit and behavior. The most common view is that clonal growth produces large floral displays and therefore increases attraction to pollinators. Consequently, clonal growth may help to maximize male reproductive success by dispersing more pollen. On the other hand, geitonogamy, pollination among flowers within one individual plant, is an inevitable byproduct with an increase in clone size. More frequent geitonogamous pollination has been expected in clonal plants with large floral displays and leads to a reduction in female fitness because of inbreeding depression or pollen clogging. However, some recent theoretical and empirical studies suggest new ideas on this issue. First, the number of flowers visited by individual pollinator within a clone did not increase proportionally with clone size in clumped clonal plants, and pollinator movements within a single bout mainly occurred within ramet. The selfing component analyses based on molecular markers further evidenced that within-ramet geitonogamy was the largest contributing factor to the total geitonogamy in two clonal species. Second, the experimental study of bumblebees foraging on artificial flowers showed that when the same amount of flowers was distributed among multiple ramets, geitonogamy was not higher but in fact, lower compared with one single inflorescence. The model-based simulation suggested clonal growth could promote pollination quality without increasing geitonogamy when flowers simultaneously received and donated pollen. These studies support a novel explanation of the evolution of clonality in plants. Future studies on the pollination ecology of clonal plants may focus on the effects of clonal growth on pollinator behavior and plant mating from multiple angles. Comparative studies between clonal and non-clonal taxa or between clonal and non-clonal populations of the same species are required to evaluate the ecological and evolutionary consequences of clonal growth.

Key words: clonal architecture, clonal growth, floral deployments, geitonogamous pollination, mating system, pollinator behavior