Refugia and phylogeography of Taiwania in East Asia

Abstract

Aim The East Asia endemic Taiwania cryptomerioides Hayata is an iconic and relictual monotypic conifer whose main extant populations are now restricted to the Yunnan-Myanmar border, northern Vietnam and Taiwan. It has also been reported from several localities in Guizhou, Hubei and Fujian Provinces, China. Its fossil record indicates that, while it was more widely distributed in the Northern Hemisphere and grew under a range of different ecological conditions, it has remained almost unchanged in its morphology for over 100 Myr. We investigate whether these remaining extant, disjunct populations have diverged genetically; when such a divergence may have occurred; and which, if any, of the extant populations exhibit refugial characteristics.Location East Asia.Methods Sequences of five chloroplast DNA markers (petG-trnP, trnH-psbA, trnV-trnM, trnC-ycf6 and trnL-trnF) from all extant populations of T. cryptomerioides were analysed to reveal their phylogeography. Molecular clock models with fossil calibrations were used to estimate divergence times between extant populations.Results Extremely low nucleotide diversity was found in the overall population (p = 0.00077) with only nine haplotypes distinguished. The mainland Asia populations share one major ancestral haplotype. The insular populations in Taiwan all possess a unique haplotype with at least an eight-mutational-step difference to the mainland Asia haplotype. Molecular clock estimations demonstrated that the mean divergence time between the predominant insular population haplotype and the mainland Asia haplotype occurred at c. 3.23-3.41 Ma, followed by a split into Vietnamese and Yunnan-Myanmar populations (c. 1.0-1.39 Ma).Main conclusions Strong genetic differentiation exists between insular (Taiwan) and mainland Asia populations. The split between insular and mainland haplotypes can be dated back to the end of the Pliocene. The Yunnan-Myanmar border area, northern Vietnam and Taiwan are identified here as potential refugia for T. cryptomerioides. Other populations in mainland China are unlikely to be the result of historical fragmentation and their origins require further investigation.

Chloroplast DNA phylogeographic analysis reveals significant spatial genetic structure of the relictual tree Davidia involucrata (Davidiaceae)

“…All the analyzed populations of D. involucrata in this study contained a single haplotype except for one population (HH) containing two haplotypes. The high frequency of populations containing a single haplotype is similar to C. japonica (Li et al 2008), J. mandshurica (Bai et al 2010), Taiwania cryptomerioides (Chou et al 2011) and Cercidiphyllum japonicum (Qi et al 2012). As a relict tree species, D. involucrata is expected to harbor high levels of diversity in the non-recombining cytoplasmic genome, due to the long evolutionary history (Chiang and Schaal 1999;Huang et al 2001).…”

“…The gene diversity is also much higher than that in most of the East Asian conifers where cpDNA markers have been used (Gao et al 2007;Chou et al 2011). On the contrary, the withinpopulation gene diversity (H S = 0.017) is extremely low.…”

Phylogeography of Quercus glauca (Fagaceae), a dominant tree of East Asian subtropical evergreen forests, based on three chloroplast DNA interspace sequences

“…7.41 Ma) (Liu et al 2014), which also follow a similar timeline of haplotype divergence in the late Pliocene. A different study on the relict tree Taiwania cryptomerioides from the subtropics estimated a crown age divergence time of 3.4-3.2 Ma (Chou et al 2011), which is later than other woody genera studied, but still in the Neogene. The similar lineage divergence patterns exhibited by different plant taxa confirm that the evolutionary history of these Neogene taxa in subtropical Asia was impacted by pre-Quaternary climatic or/and geological events.…”

“…These multiple refugia have been proposed as hotspots for biodiversity conservation. However, phylogeographic studies conducted on plant species in this region are limited, and most were restricted to either narrow geographical regions (e.g., Japanese-Taiwan archipelagos; Hsieh et al 2013;Kono et al 2012;Nakamura et al 2010) or focused on endangered species with few populations (Chou et al 2011;Gao et al 2007;Gong et al 2008b;Wang et al 2009). Recent phylogeographic studies on two sympatric beeches (Fagus lucida and Fagus longipetiolata) in subtropical China (Zhang et al 2013) and on the Tertiary genus Cercidiphyllum (Qi et al 2012) in warm-temperate deciduous forests of East Asia suggest that pre-Quaternary events (at the Miocene/Pliocene boundary) are associated with the early divergence of the species and haplotypes of both genera.…”

Explaining the distribution of breeding and dispersal syndromes in conifers

“…In the Northern Hemisphere, for example, a number of extant genera underwent significant range contraction, and possibly species extinction, during the Neogene (e.g. Cathaya, Pseudolarix, Taiwania [35,36]), but these groups appear to have been monoecious with dry cones. The current distribution of the dry-dioecy trait combination, on the other hand, is more likely to have been directly influenced by extinction.…”