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

Abstract

Abstract.-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 ploidallevels 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 auto tetraploid origins, but there was no consistent pattern of differentiation between genetically similar diploid and auto tetraploid 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. The evolution of polyploidy has played a major role in the creation and maintenance of plant biodiversity (e.g., Thompson and Lumaret 1992;Soltis andSoltis 1993, 1995;Song et al. 1995;Goldblatt and Takei 1997). About one-half of all angiosperm species are thought to have polyploids in their lineages (Stebbins 1971;Averett 1980;DeWet 1980;Levin 1983;Masterson 1994), and within polyploid species, multiple origins of polyploidy are considered the rule ; reviewed in Soltis and Soltis 1993). The success of many polyploid taxa has been associated with numerous changes that may differentiate them from their diploid ancestors. For example, poly...

Habitat differentiation, hybridization and gene flow patterns in mixed populations of diploid and autotetraploid Dactylorhiza maculata s.l. (Orchidaceae)

“…Adaptive strategies are needed for establishment and persistence of new polyploids. Such strategies include apomixis (Hedrén et al 2000), self-pollination (Levin 1975), pollinator shift (Segraves and Thompson 1999) and habitat differentiation (Felber-Girard et al 1996). However, even though the literature on polyploidy is comprehensive there are relatively few studies that focus on the ecological aspects of polyploidization (Soltis et al 2003).…”

Polyploidy and ecological adaptation in wild yarrow

“…This hypothesis, however, has not been tested rigorously. Ecological studies have traditionally focused on simple comparisons of diploids and naturally occurring polyploids that diverged in the distant past (15)(16)(17)(18)(19)(20). This approach confounds phenotypic differences caused by polyploidy with those caused by genic changes arising since the time of polyploid formation (21-23).…”

Ecological Factors Influencing Tetraploid Speciation in Snow Buttercups (Ranunculus Adoneus): Niche Differentiation and Tetraploid Establishment

“…Barriers to intercytotype mating based on pollinator behavior and phenological shifts have been documented (Segraves and Thompson 1999;Husband 2000). However, there are few detailed examinations of the role habitat differentiation may play in the establishment of new tetraploids.…”

“…Minority tetraploid plants can avoid reproductive costs through selfing (Levin 1975), changes to flowering time that reduce phenological overlap with diploid plants (Lewis 1976;Segraves and Thompson 1999), or shifts in floral morphology that alter pollinator preferences or constancy (Husband 2000). Spatial isolation can likewise lead to prezygotic reproductive isolation.…”