Jessica Grochowski

Cytotype distribution and evidence for local adaptation to drought of a polyploid goldenrod across a climate gradient in Minnesota

Polyploidy, the possession of more than two complete sets of chromosomes, is extremely common in plants and is thought to have played a large role in their evolutionary diversification with 47% to 80% of the angiosperms having polyploid origins. The high incidence of polyploidy indicates that it may have important adaptive significance. Empirical studies of polyploid plants have shown morphological, physiological, and developmental differences in relation to their diploid progenitors, which putatively increases their ecological tolerance, such as survival during drought. I conducted research on a known polyploid goldenrod, Solidago altissima, to: 1) characterize cytotype distribution in prairie and forest biomes and across a precipitation gradient in Minnesota, and 2) to test for local adaptation to drought stress. The ploidy level of plants sampled from 15 populations was determined by flow cytometry and confirmed with root tip squashes. To test for local adaptation to drought stress, prairie and forest plants of known ploidy levels were grown in a common garden and subjected to a drought treatment. The results show both prairie and forest populations contain diploids, tetraploids, and hexaploids, with the hexaploids having higher frequencies in the prairie, indicating that polyploidy may be contributing to the evolutionary diversification of the species. However, differences in precipitation alone did not significantly influence the cytotype frequencies. The drought experiment showed that prairie plants are more drought-tolerant that forest plants but the three ploidy levels within populations are equally well-adapted to differences in water availability. In contrast to many other species, there are no measurable differences between the ploidy levels in either biome, termed cryptic polyploidy.