The origin of the early differentiation of Ivies (Hedera L.) and the radiation of the Asian Palmate group (Araliaceae)

摘要

The Asian Palmate group is one of the four major clades of the family Araliaceae that is formed by 18 genera, including ivies (Hedera L.). The Mediterranean diversity centre and temperate affinity of ivies contrast with the inferred Asian centre of diversity of the primarily tropical and subtropical Asian Palmate group. We herein investigated the sister-group relationships of Hedera to reconstruct the evolutionary context for its origin and early diversification. Seven nuclear and plastid DNA regions were analyzed in 61 Araliaceae samples including all the 18 Asian Palmate genera. Maximum Parsimony, Maximum Likelihood and Bayesian Inference were run together with a battery of topology testing analyses constraining the expected Hedera's sister-group relationships. Additionally, Bayesian polytomy resolvability and divergence time analyses were also conducted. Genome incongruence and hard nuclear and plastid basal polytomies are detected for the Asian Palmate group where the lineage of Hedera is placed. Topology testing analyses do not allow rejecting any of the tentative sisters of Hedera. An early radiation with inter-lineage hybridization and genome doubling is suggested for the Asian Palmate group where all the seven temperate genera, including Hedera, seem to have played an important role. The radiation took placed during the Upper Cretaceous in Asia under a general cooling and the eastern Asian mountain uplift that produced new temperate environments and promoted lineage connections. This allows us to hypothesize that the origin of the Hedera lineage may fit in a temperate niche conservatism scenario where the combination of the radiation with lineage admixtures prevents us from discovering its sister-group.