The Reproductive Ecology of Diploid and Tetraploid Galax urceolata

Abstract

Polyploidy is common in nature, particularly among plants, and is often associated with significant morphological, ecological, and evolutionary change. These changes may contribute to prezygotic and postzygotic isolation between cytotypes; therefore, polyploidy is commonly thought to lead to speciation. Recent work suggests prezygotic mechanisms may be more important in determining isolation than postzygotic mechanisms. We compared the reproductive ecology of populations of diploid and tetraploid Galax to assess the potential for gene flow between the cytotypes. Galax urceolata is native to the southern Appalachian Mountains and is a natural polyploid series with diploid, triploid, and autotetraploid individuals occurring in uniform and mixed-cytotype populations. We found the temporal peak of flower production in tetraploids slightly preceded that of diploids; however, the overall distributions of flowering phenologies were similar. Hymenoptera and Diptera were the most common floral visitors and diploids were visited slightly more often than tetraploids; however, there were no differences between cytotypes in terms of the taxonomic composition of their floral visitors. Seed production is likely pollen limited, but again this does not differ between cytotypes. While tetraploids produced more flowers than diploids, there was no difference in fruit production. Finally, our data suggest that Galax urceolata is self-incompatible. In sum we found few differences in the reproductive ecology of diploid and tetraploid Galax, which when combined with obligate outcrossing increases the potential for gene flow between cytotypes and reduces the likelihood of differentiation.