Evolution of Reproductive Traits and Implications for Adaptation and Diversification in the Yam Genus Dioscorea L.

Abstract

Dioscorea is a pantropical monocotyledonous genus encompassing several well-known tuber crops and medicinal plants. It possesses remarkable morphological diversity, especially in reproductive characteristics, which are suggested to play important roles in species adaptation and diversification. Yet there have been few studies that consider the evolutionary pattern followed by these characters in this genus. In this study, the phylogenetic relationships among Chinese yams were reconstructed from five chloroplast and two mitochondrial DNA sequences. The evolutionary histories of bulbil possession, inflorescence architecture, the color of the male flowers and the degree of male flower opening were reconstructed. The results suggested that yam bulbils evolved after the divergence between D. sect. Testudinaria and other species of Dioscorea except for in D. sect. Stenophora and D. sect. Apodostemon. The evolutionary trend in the degree of male flower opening ranged from fully open to nearly closed. Male flowers with dark colors and panicles were shown to be derived in Dioscorea. These characteristics were found to be closely associated with the reproductive patterns and pollinating mechanisms of the Dioscorea species. The findings also shed light on the systematic relationships within this genus.