A leading-edge scenario in the phylogeography and evolutionary history of East Asian insular Taxus in Taiwan and the Philippines

TL;DR

This study explores the evolutionary history of Taxus yew trees in Taiwan and the Philippines, revealing genetic differences and migration patterns between island and mainland populations.

Contribution

The study provides new insights into the genetic divergence and migration history of Taxus phytonii in East Asian islands.

Findings

Taiwanese and Philippine Taxus phytonii lineages are genetically distinct from each other and continental relatives.

Taiwanese T. phytonii originated more than 2.49 Mya, while Philippine T. phytonii originated more than 1.08 Mya.

Recent migrations from continental T. mairei to Taiwanese T. phytonii and then to Philippine T. phytonii were identified.

Abstract

The cool temperate origin of gymnosperm Taxus species in East Asia is specifically diverse and widespread. Certain lineages have managed to extend their distribution further south to subtropical and tropical islands such as Taiwan and the Philippines. To address questions including whether these insular lineages, recently identified as T. phytonii, have become genetically distinct from each other and from their continental relatives, and when and how they colonized their residing islands, we sampled over 11 populations, covering 179 Taxus individuals from Taiwan and the Philippines. Using four cpDNA and one nuclear marker, we showed in population genetic and genealogical analyses that the two insular lineages were genetically distinct from each other and also from other continental Taxus and that they represented each other’s closest relative. Estimated with the coalescent-based multi-type tree (MTT) analyses, we inferred an origin of Taiwanese T. phytonii more ancient than 2.49 Mya and that of Philippine T. phytonii more ancient than 1.08 Mya. In addition, the divergence demographic history revealed by both MTT and isolation with migration (IM) analyses indicated the presence of recent post-split migrations from a continental taxon, T. mairei, to Taiwanese T. phytonii, as well as from Taiwanese T. phytonii to Philippine T. phytonii. Overall, this study suggests Taiwan as a stepping stone through which the temperate-origin yew trees can extend their distributions to tropical regions such as the Philippines.

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