Many plant species exhibit substantial variation in genomic traits among individuals, including genome size, chromosome number, and genome copy number (ploidy). Eastern spring beauty (Claytonia virginica), an eastern North American spring wildflower, is one such species. Examples of variation in genome attributes correlating with plant size, floral attributes, and phenology have been documented across various plant species. We assessed a group of diploid and triploid C. virginica individuals in an Indiana forest to address two primary questions: In what ways do individuals of different ploidy levels differ in phenotype? Do individuals of different ploidy levels reproduce together, and if not, what is their barrier to reproduction? We measured the ploidy of approximately fifty individuals across this location and found that diploid and triploid individuals were naturally partitioned into different areas of their shared location. Of these, we assessed six diploid and six triploid individuals repeatedly, approximately every four days from the time of first flower to last fruit set, creating growth and reproductive curves from measures of leaf/flower size and reproductive stage. Concurrently, we sampled four random quadrats of the diploid and triploid areas during each visit and performed the same measurements on included individuals as on focal individuals.
Results/Conclusions
Triploid plants had significantly greater leaf width, shorter leaf length, and greater petal width than diploid plants. Triploid plants began flowering three weeks after the emergence of the first diploid flower; however, due to a shortened duration of flowering, triploid individuals collectively reached peak flowering (when the number of open flowers was greatest) eight days after diploid individuals collectively reached peak flowering. Despite the delay, diploid and triploid individuals overlapped in duration of open flowers by 1.5 weeks. Throughout the duration of flowering, we observed visitations by potential pollinators (bees, flies) and found no discernible difference in the type of visitors that diploid and triploid plants attracted (preference for the larger petals of triploids). Across our initial and follow-up surveys, we found no evidence that diploid and triploid plants interbred (e.g. individuals of hybrid ploidy, which theoretically would be produced upon interbreeding). Following this observation, we conclude that diploid and triploid individuals do differ in certain phenotypic attributes but not ones that likely impede their ability to reproduce with one another. We propose that the evident lack of inter-ploidy reproduction among what appears to be one large population is most likely due to gametic/genomic incompatibility between meta-populations separated by ploidy.