Understanding patterns of pollination is important for understanding gene flow and genetic diversity of native plant populations. With climate change the interest in studying flowering phenology has dramatically increased. However, there have only been a handful of studies that have examined how flowering phenology impacts effective pollen movement. The goal of this study is to quantify how flowering synchrony and plant density affect pollination patterns in a self-incompatible prairie perennial, Echinacea angustifolia. Phenological isolation can be caused by asynchronously flowering plants. We examined how phenological isolation interacts with spatial isolation (e.g. distance to k nearest neighbor). Our study takes place in a naturalized experimental plot. In 2005 we followed the daily flowering phenology of all plants in the plot. To characterize pollination patterns, paternity was assigned to offspring using nine microsatellite loci. Candidate fathers included all 204 flowering plants in the experimental plot and twenty plants from a population 250 meters away. For each of 35 maternal plants, 30 offspring were genotyped– ten offspring each from the beginning, end, and middle of the maternal plant’s flowering phenology. We were able to assign paternity to over 80% of the offspring.
Results/Conclusions
Significantly more pollination events occurred between near neighboring plants than would be expected under random mating. Similarly, significantly more pollination events occurred between plants with high pair-wise synchrony. Surprisingly, high levels of synchrony or high density of plants did not mitigate spatial and phenological isolation. There was also a significant day of year effect in pollination distances, in that early flowering plants were more often pollinated from the population 250 meters away than were peak or late flowering plants. We used generalized linear models to predict pollination distances for a range of spatial and phenological isolation values. This demonstrated that phenological isolation affected pollination just as much as spatial isolation; and that both can lead to reproductive isolation between plants. These findings show that flowering phenology can play an important role in pollen mediated gene dispersal in a self-incompatible species. Our findings have implications especially in fragmented populations where spatial isolation is often very high, therefore phenological isolation can have an even greater impact. We also discuss of our findings in regards to climate change as many species’ flowering phenologies are being altered.
