The Role of Allotriploidy in the Evolution of Meconopsis (Papaveraceae): A Preliminary Study of Ancient Polyploid and Hybrid Speciation

Abstract

Also known as the Himalayan Poppy, Meconopsis is a genus of herbaceous plants growing only in the high elevation habits of the Himalaya and its adjacent plateau and mountain areas. The genus exhibits high morphological and ecological diversity, but the major causes of divergence in Meconopsis have not previously been studied. Our recent revised taxonomic classification, based on a molecular phylogeny, divided the genus into four monophyletic sections. Because chromosome number varies among these sections and our previous phylogenetic analyses revealed extensive incongruence between the recovered nrITS and cpDNA trees, possibly due to ancient hybridization, this study focused on evaluating the potential role of ancient polyploidization and hybridization in Meconopsis' evolutionary history. Our investigation based on the results of reconstructed ancestral chromosome numbers using a Maximum Likelihood method implemented in chromEvol showed that two extant Meconopsis sections (sect. Grandes and sect. Primulinae) shared a triploid ancestor. We further examined the pattern of hybridization in Meconopsis by reconstructing a nuclear marker GAPDH (glyceraldehyde 3-phosphate dehydrogenase gene) network. The result, along with morphological, phylogenetic, and cytological evidence, all point to a hybrid nature of the triploid ancestor. Based on the resultant GAPDH network, an ancient reticulate evolution scenario in Meconopsis is proposed. Overall, this preliminary study shows how an ancient triploid event promoted polyploid evolution in Meconopsis and also exemplifies how allotriploidization and successive polyploidization played an important role in diversification of the genus.