The present thesis elucidates facts about a prominent steppe plant’s evolutionary history (i.e., geographic origin, migration route, distribution of genealogical lineages and polyploidization events) and contemporary population divergence (i.e., genetic diversity and differentiation, impacts of abiotic and biotic factors). Artemisia frigida has been chosen as the target species, with Mongolia as the focus study region. Because A. frigida is widely distributed in the both New and Old Worlds, it was a suitable candidate for the phylogeographic study. Moreover, because of its dominance in many communities in Mongolian steppes and tolerance for cold, drought and mechanical disturbances (grazing), evaluating the effect of environmental factors and grazing pressures on its population genetics was profitable. The overall goal of this thesis was to assess the effects of paleo- and current climate, and land use changes on the distribution of A. frigida’s genealogical lineages and genetic variations.
The thesis is divided into two main parts: (i) Chapter 3 focuses on Phylogeography. Within this, section 3.3 depicts a study on the phylogeography of A. frigida, covering samples from its distributional range across the northern hemisphere. The study resulted in Asia being the species’ main origination and diversification center, and the species spread northwards to the Russian Far East and eventually crossed the Bering Strait to North America. Among four geographical regions sampled, seven genetic lineages were found, with Middle Asia having the most diverse populations. According to our phylogenetic analysis, two populations of Kazakhstan in Middle Asia represented the most likely ancestral diploids, and subsequent polyploidization events have occurred on several occasions independently. The observed phylogeographic patterns of the species showed that paleoclimate, especially glaciation events of the Quaternary has predominantly affected species’ current distribution, along with the expansion and contraction of the Eurasian steppe.
The second part (Chapter 4) is dedicated to Population genetics to reveal the effects of the current climate and land use on population genetic variation. Three studies were conducted at local and regional levels, focusing on Mongolia. The first study (Section 4.1- review of local literature) was done to offer background information about Mongolian steppes, and the effects of climate and grazing on the steppe vegetation. As a result, steppe vegetation responded to grazing in different ways, depending on the interplay of local environmental factors. In particular, an overall negative effect of grazing was found in desert, dry and high mountain steppes, but no or even positive effects in meadow and mountain steppes. The study highlighted the importance of the interaction effect of local environmental conditions and grazing in Mongolian steppe vegetation. The second study (Section 4.2) employed large scale climatic gradient and local scale grazing gradients to assess the effects of grazing and environmental factors on the population genetics of A. frigida. Precipitation gradient covered 110 – 300mm difference of mean annual precipitation from central to southern Mongolia. While three levels of grazing gradient, such as heavy, moderate, and least grazed sites were examined. According to the study, grazing in overall, had no substantial effect on the genetic diversity of A. frigida, while environmental factors, i.e., summer precipitation and soil phosphorous content, promoted high genetic diversity. Genetic differentiation among populations across large climatic gradients was extremely low, suggesting the existence of considerable gene flow among populations across the steppes of Mongolia. The third study (Section 4.3) employed grazing exclosures to evaluate the genuine effects of grazing. Because Mongolia has a long-term nomadic pastoralism history, and grazing of large herbivores is already an integral part of the steppe vegetation. Thus, we utilized reference site fences along the Trans-Mongolian Railway (TMR), where fences have been built and maintained since 1955, resulting in over 60 years of grazing exclusion. In addition, we supplemented this with data from Hustai National Park (HNP), where three fences were established in 2003. As a result, we found a significant positive impact of grazing on the genetic diversity of A. frigida, implying that a certain level of grazing is beneficial for the species. While no grazing effect on the population genetic differentiation was detected, but climatic and soil variables strongly influenced population genetic structure.
In summary, this thesis provided an in-depth investigation of the phylogeography and population genetics of the species A. frigida, which can stand as an exemplar for other Eurasian steppe species. Paleoclimate had largely shaped the current distribution pattern of the species, while contemporary climate and environmental heterogeneity promoted species’ polyploidization and genetic variation. Grazing by large herbivores showed no detrimental effect, or even a positive impact on the genetic diversity of A. frigida. Artemisia frigida populations in Mongolia are thus apparently genetically ‘healthy’, in spite of pervasive grazing in the region. Climate variables and environmental heterogeneity had a substantial impact on the species’ both genetic diversity and differentiation, indicating its higher sensibility to climate change than to land use change. The findings of the thesis could be valuable in understanding species genetic variation under global land use and climate changes.:Summary 4
List of Abbreviations 6
Chapter 1. Introduction 8
Chapter 2. Material and methods 10
2.1. Study region: Mongolian steppe 10
2.2. Focus species: Artemisia frigida Willd. 11
2.3. Molecular markers 12
Chapter 3. Phylogeography 13
3.1. Eurasian steppe and its evolutionary history 13
3.2. Artemisia L. (Asteraceae) as model plant for phylogeography 16
3.3. A case study: Phylogeography of Artemisia frigida Willd. 19
Chapter 4. Plant population genetics under changing climate and grazing……. 40
4.1. Climate – grazing interactions in Mongolian steppe 41
4.2. Climate – grazing interactions on plant population genetics 59
4.3. Effect of grazing exclusion on plant populations genetics 83
Chapter 5. Overarching synthesis and discussion 101
5.1. Molecular markers: pros and cons 102
5.2. A review of phylogeographical studies on Eurasian steppe plants 104
5.3. A review on plant population genetic studies in Mongolia 109
5.4. Outlook 113
Acknowledgements 114
References 115
Curriculum vitae 137
Confirmation 143
| Identifer | oai:union.ndltd.org:DRESDEN/oai:qucosa:de:qucosa:82370 |
| Date | 22 November 2022 |
| Creators | Khurelpurev, Oyundelger |
| Contributors | Wesche, Karsten, Ritz, Christiane M., Technische Universität Dresden |
| Source Sets | Hochschulschriftenserver (HSSS) der SLUB Dresden |
| Language | English |
| Detected Language | English |
| Type | info:eu-repo/semantics/publishedVersion, doc-type:doctoralThesis, info:eu-repo/semantics/doctoralThesis, doc-type:Text |
| Rights | info:eu-repo/semantics/openAccess |
| Relation | https://doi.org/10.1007/s10592-021-01375-w, https://doi.org/10.1111/jeb.13960, https://doi.org/10.3389/fevo.2021.703220, info:eu-repo/grantAgreement/German Ministry for Science and Education/BioTip scheme/01LC1820C//MoreStep project |
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