Uncovering the consequences of co-flowering and pollinator sharing: Effects of local community context on pollen transfer dynamics, female reproductive success and floral evolution in Mimulus guttatus.

摘要

While plant-pollinator interactions commonly take place within a larger community context, studies of plants and their pollinators have typically focused on pair-wise interactions. Co-flowering species whithin multi-species communities may influence pollinator foraging decisions and hence plant reproductive success and floral evolution. For instance, plants growing in highly diverse areas may be more pollen limited than plants in species-poor areas due to the high levels of pollinator competition and interspecific pollen transfer. As a result, stronger selection pressures can also be expected in highly diverse areas in order to increase the quantity and/or quality of pollen reaching conspecific stigmas. However, how plant community composition contributes to the severity of pollen limitation, what the potential underlying mechanisms are and how selection on floral traits changes with increasing community diversity is still unclear. In this study I use Mimulus guttatus as a model system to evaluate the effect of local co-flowering community context on quantity and quality aspects of pollen limitation, pollen transfer dynamics, heterospecific pollen effects and selection processes in high and low diversity areas. I show that the relative contribution of pollen quantity and quality limitation to overall pollen limitation of reproductive success depends on the co-flowering community context in which M. guttatus exists. I further uncover heterospecific pollen receipt as a potential mechanism underlying decreased reproductive success in highly diverse areas by showing that complex interactions among multiple heterospecific pollen donors can exacerbate its effects and that heterospecific pollen receipt can have an even greater detrimental effect on self compared to outcross conspecific pollen. Finally, I show that co-flowering community context can be an important driver of selection that promotes floral trait differentiation among populations, in the case of M. guttatus in flower longevity. By combining observational, experimental, field and greenhouse approaches, this study extends our knowledge of the processes underlying insufficient pollination in natural communities, reveals new complexities in our understanding of heterospecific pollen effects and advances our understanding of the community properties shaping the evolutionary dynamics of constituent populations.