Many subtropical plant and animal lineages exhibit a disjunct distribution in the pan-Mediterranean and East Asia (also known as “Tethyan disjunctions”). One hypothesis is that Tethyan disjunct taxa are relics of once-widespread Cenozoic paleotropical evergreen forests. Another hypothesis is that subtropical to tropical disjunctions in the Old World may have established by the Miocene through long distance dispersal, transoceanic transport, or by a combination of vicariance and dispersal.
Quercus section Ilex Loudon is an ecologically diverse lineage with about 35 species widely distributed in Mediterranean Europe, Northern Africa and the East Asian subtropics. Fossils of sectionIlex are well represented in the Cenozoic Tethyan forest flora of Europe, the Himalayas and East Asia. Therefore, the section is a model clade for investigating the timing and origins of the East Asian-Tethyan disjunction in subtropical to tropical lineages.
By coupling molecular divergence time dating, ancestral range reconstruction and morphological analysis of fossil and extant lineages of Querucs section Ilex, we found that Quercus section Ilex was widespread along the East Tethys seaway from the middle Eocene onward. The European holly oaks originated from an East Asian ancestral lineage that dispersed to Europe via the Tibet-Himalaya corridor in the Oligocene. Lowlands along the margins of the Himalayas and through an Oligocene Tibetan valley served as the dispersal route(s) for these species. Changing climates drove Miocene extinction and local adaptation of European lineages. Dispersal of Quercus section Ilex, a dominant lineage of evergreen forests in Europe and East Asia, through the Tibet-Himalaya corridor implies relative continuity of an evergreen forest belt between East Asia and the western Himalaya throughout the Oligocene, which is also supported by paleoclimatic reconstructions.
This work, performed by Plant Systematics and Evolution group of Shanghai Chenshan Plant Science Research Center, Chinese Academy of Sciences/ Shanghai Chenshan Botanical Garden, was published online on the Journal of Biogeography Plant on 10th July 2019. This work was supported by grants from the National Natural Science Foundation of China (31700174), the Southeast Asia Biodiversity Research Institute, Chinese Academy of Sciences (Y4ZK111B01) and the Shanghai Municipal Administration of Forestation and City Appearances (G172406, G182427 and G162404).
Paper title: East Asian origins of European holly oaks (Quercus section Ilex Loudon) via the Tibet-Himalaya
Figure 1. Divergence time dating, biogeographical history, and habitat evolution of Quercus section Ilex.
Figure 2. Principal component analysis (PCA) of the leaf geometry for extant and two fossils species of Quercus section Ilex.