PLANT POLYPLOIDY AND POLLINATION: FLORAL TRAITS AND INSECT VISITS TO DIPLOID AND TETRAPLOID HEUCHERA GROSSULARIIFOLIA

In many polyploid species, polyploids often have different suites of floral traits and different flowering times than their diploid progenitor species. We hypothesized that such differences in floral traits in polyploids may subsequently affect their interactions with pollinating and other insect visitors. We measured floral morphology and flowering phenology in 14 populations of diploid and autotetraploid Heuchera grossulariifolia Rydb. (Saxifragaceae), determined if repeated evolution of independent polyploid lineages resulted in differentiation in floral morphology among those lineages, and ascertained if there was a consistent pattern of differentiation among genetically similar diploid and autotetraploid populations. In addition, we evaluated the differences in suites of floral visitors within a natural community where diploids and autotetraploids occur sympatrically. Overall, flowers of autotetraploid plants were larger and shaped differently than those of diploids, had a different flowering phenology than that of diploids, and attracted different suites of floral visitors. In comparison with flowers of diploids, tetraploid floral morphology varied widely from pronounced differences between cytotypes in some populations to similar flower shapes and sizes between ploidal levels in other populations. Observations of floral visitors to diploids and autotetraploids in a natural sympatric population demonstrated that the cytotypes had different suites of floral visitors and six of the 15 common visitors preferentially visited one ploidy more frequently. Moreover, we also found that floral morphology differed among independent autotetraploid origins, but there was no consistent pattern of differentiation between genetically similar diploid and autotetraploid populations. Hence, the results suggest that the process of polyploidization creates the potential for attraction of different suites of floral visitors. Multiple origins of polyploidy also presents the opportunity for new or different plant-insect interactions among independent polyploid lineages. These differences in turn may affect patterns of gene flow between diploids and polyploids and also among plants of independent polyploid origin. Polyploidy, therefore, may result in a geographic mosaic of interspecific interactions across a species' range, contributing to diversification in both plant and insect groups.