Abstract
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.
Highlights
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 [1,2,3]
We found that the optimal population grouping pattern of K = 2 was optimal: (1) populations 1–10 belonged to the northern group (T. mongolica), and (2) populations 11–16 belonged to the southern group (T. mongolica var. ovatifolia)
We found that the divergence time between the northern group (T. mongolica) and southern group (T. mongolica var. ovatifolia), which was determined from the BEAST analysis, occurred at 2.4976 (95%HPD: 1.2094–4.2318) Mya (Fig 4), during the early Pleistocene epoch
Summary
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 [1,2,3]. 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]. Few researchers have investigated the effects of desert formation on the evolutionary process of regional species in this arid region
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