Meeting Abstract
Polyploidy, the event of increasing nuclear chromosomes, is believed to be a significant driver of diversification among land plants. Mechanisms of chromosome number evolution include whole-genome duplication, half-genome increases (demi-polyploidy), gains or losses of single chromosomes that alter the DNA content of an organism (aneuploidy), or chromosome fission or fusion (ascending dysploidy or descending dysploidy, respectively). Considering the high variability in chromosome number transitions across multiple clades within angiosperms and the ancient genome duplication events responsible for their diversity, studies of non-model systems are necessary to close the gaps in our understanding of chromosomal evolution with respect to polyploid plants. Allium (Amaryllidaceae) is an ideal candidate for polyploid research because it is the largest genus in its family and includes numerous natural populations of diploid and polyploid species. Plants in this genus mainly occupy temperate climates in the Northern Hemisphere and include economically important ornamentals and cultivated crops such as leeks, garlic, chives, and onion varieties. Here, we present a global molecular phylogeny of Allium comprising 429 of approximately 800 species. We examined chromosomal evolution with chromEvol v. 2.0 (Glick and Mayrose, 2014) which uses likelihood-based methods for inferring the pattern of chromosome number change across a phylogeny. The ancestral base number was inferred to be n = 8, consistent with the most common haploid number of Old-World species. The best-fit model of chromosomal evolution indicated that chromosome transitions occurred through the constant gains and losses of single chromosomes as well as demi-polyploidization events, with the rate of chromosome gain events being approximately four to five times more likely to occur than half duplication and loss events.
