Date Published: February 7, 2019
Publisher: Public Library of Science
Author(s): Yanfen Zhao, Borong Pan, Mingli Zhang, Tzen-Yuh Chiang.
Tugarinovia (Family Asteraceae) is a monotypic genus. It’s sole species, Tugarinovia mongolica Iljin, is distributed in the northern part of Inner Mongolia, with one additional variety, Tugarinovia mongolica var ovatifolia, which is distributed in the southern part of Inner Mongolia. The species has a limited geographical range and declining populations. To understand the phylogeographic structure of T. mongolica, we sequenced two chloroplast DNA regions (psbA-trnH and psbK-psbI) from 219 individuals of 16 populations, and investigated the genetic variation and phylogeographic patterns of T. mongolica. The results identified a total of 17 (H1-H17) chloroplast haplotypes. There were no haplotypes shared between the northern (T. mongolica) and southern groups (T. mongolica var. ovatifolia), and they formed two distinct lineages. The regional split was also supported by AMOVA and BEAST analyses. AMOVA showed the main variation that occurred between the two geographic groups. The time of divergence of the two groups can be dated to the early Pleistocene epoch, when climate fluctuations most likely resulted in the allopatric divergence of T. mongolica. The formation of the desert blocked genetic flow and enhanced the divergence of the northern and southern groups. Our results indicate that the genetic differences between T. mongolica and T. mongolica var. ovatifolia are consistent with previously proposed morphological differences. We speculate that the dry, cold climate and the expansion of the desert during the Quaternary resulted in the currently observed distribution of extant populations of T. mongolica. In the northern group, the populations Chuanjinsumu, Wuliji and Yingen displayed the highest genetic diversity and should be given priority protection. The southern group showed a higher genetic drift (FST = 1, GST = 1), and the inbreeding load (HS = 0) required protection for each population. Our results propose that the protection of T. mongolica should be implemented through in situ and ex situ conservation practices to increase the effective population size and genetic diversity.
In recent years, phylogeographic studies of the arid region of Northwest China have increased and mainly focus on the impact of the Quaternary climate fluctuations on species’ phylogeographic patterns [1–3]. An increasing number of studies have shown that the deserts have an impact on the genetic structure and phylogeographic pattern of species, causing the speciation and population differentiation of many desert species [1, 4–6]. Evidence from pollen records indicates that ice sheets did not appear in arid Northwest China during the Quaternary . However, glacial and interglacial cycles affected the evolutionary processes of species in this region [1, 8–10], through allopatric divergence [2, 11], range fragmentation, and regional range expansion [12, 13]. Additionally, the uplift of the Tibetan Plateau and global Pleistocene cooling promoted the formation and subsequent evolution of the desert [14, 15]. Several previous studies have shown that the increased aridification and desert expansion led to the speciation, habitat fragmentation, and diversification of desert plant species, as well as the distribution of montane plants on both sides of the desert [1, 2, 4, 16]. In addition, the desert zone acted as a geographical barrier that hindered gene flow among populations, which led to high genetic diversity among the populations and low genetic diversity within populations in arid Northwest China [4, 5, 16, 17]. However, few researchers have investigated the effects of desert formation on the evolutionary process of regional species in this arid region.