CHAPTER 2 Habitat Differentiation Between
Total Page：16
File Type：pdf, Size：1020Kb
Research Collection Doctoral Thesis Ecological significance of ploidy level of native and invasive populations of Solidago gigantea Author(s): Schlaepfer, Daniel Rodolphe Publication Date: 2008 Permanent Link: https://doi.org/10.3929/ethz-a-005691046 Rights / License: In Copyright - Non-Commercial Use Permitted This page was generated automatically upon download from the ETH Zurich Research Collection. For more information please consult the Terms of use. ETH Library Diss. ETH No. 17677 %COLOGICALSIGNIFICANCEOFPLOIDYLEVELOFNATIVEANDINVASIVEPOPULATIONSOF Ecological$ISS%4(.O significance of ploidy level of native and invasive populations of %COLOGICALSIGNIFICANCEOFPLOIDYLEVELOF NATIVEANDINVASIVEPOPULATIONSOFSolidago gigantea 3OLIDAGOGIGANTEA 3OLIDAGOGIGANTEA $ANIEL23CHLAEPFER $ANIEL2ODOLPHE3CHLAEPFER Daniel Rodolphe Schlaepfer 2008 Diss. ETH No. 17677 Ec o l o g i c a l Sign i ficancE o f Pl o i d y lE v E l o f na t i v E a n d in v a S i v E Po P u l a t i o n S o f So l i d a g o g i g a n t e a A dissertation submitted to ETH ZURICH for the degree of Doctor of Sciences presented by Daniel Rodolphe Schlaepfer Dipl. Umwelt-Natw. ETH born 17th January 1977 citizen of Montreux VD and Rehetobel AR accepted on the recommendation of Prof. Peter J. Edwards, examiner Dr. Regula Billeter, co-examiner Prof. Heinz Müller-Schärer, co-examiner 2008 CONTENTS Summary 1 Zusammenfassung 3 General introduction 7 Chapter 1 25 Cytogeography of Solidago gigantea (Asteraceae) and its invasive ploidy level Chapter 2 65 Habitat differentiation between native ploidy levels and invasive tetraploids of Solidago gigantea (Asteraceae) Chapter 3 87 Ploidy-level precise common garden with native and invasive Solidago gigantea (Asteraceae): differences in clonal growth and nutrient responses indicate colonization success of tetraploids Chapter 4 113 Phylogeography of native ploidy levels and invasive tetraploids of Solidago gigantea (Asteraceae) General conclusions 145 Acknowledgements 153 Curriculum Vitae 155 Summary SUMMARY 1. Invasive alien species can be valuable model systems to gain new insights into evolutionary, biogeographic and ecological processes. Recent research has stressed the importance of genetic change and variation in making populations of some plant species invasive, but the significance of polyploidy needs further research. Although profound consequences of polyploidy for gene expression, physiology and ecology have been described in detail, it is not understood why polyploidy is particularly common among invasive alien plant species. The adoption of a comparative biogeographic approach, comparing populations from the invasive with those from the native range, can reveal factors influencing the invasion success. However, inadequate knowledge of the ecology of a species in its native range often impedes progress towards understanding why it becomes invasive. This project uses Solidago gigantea Aiton (Asteraceae) as model species to investigate these issues; in its native range in North America, the species occurs in three ploidy levels—diploids, tetraploids, and hexaploids—and it is invasive in a wide range of habitats over large parts of Europe. By studying the ecology and genetics of ploidy levels in the native and the invasive range, using a comparative biogeographic approach, I aimed to improve our understanding of the significance that polyploidy plays in biological invasions. 2. The distribution of ploidy levels of S. gigantea in North America, Europe and East Asia was mapped based on locations with ploidy level data gathered from field surveys, collaborators and a literature review. North American populations on the eastern side of the Appalachian Mountains and also in southern Ontario and Québec are diploid. Tetraploids are found in eastern North America as far west as Missouri; hexaploids occur in mid-western North America, westwards from Manitoba to the Rocky Mountains. Strong geographic separation among ploidy levels was found, and populations with mixed ploidy were rare. In Europe and East Asia, only tetraploid plants were detected. Further comparisons between native and introduced populations need to account for ploidy level. 3. In a field survey, habitat conditions of populations ofS. gigantea in the native and invasive ranges were measured and environmental envelopes were constructed based upon a dataset of locations of known ploidy level. At a more local scale, the most consistent difference between diploids and tetraploids was that diploids were calcifuge whereas tetraploids were indifferent to soil calcium. An incompatible habitat template is unlikely to be the main reason why diploids do not occur in the invasive range, although some differences were found between habitat conditions in the invasive and the native range. More relevant is the fact that tetraploids of S. gigantea were successful colonizers in North America, extending their range well beyond that 1 Summary occupied by their diploid progenitors. Therefore, a pre-disposition for successful spreading is proposed to be linked to the tetraploid status. 4. In a common garden experiment, diploid and tetraploid S. gigantea were grown under high and low nutrient and calcium treatments. The results revealed large differences in life history between ploidy levels but less so between native and invasive tetraploids. Diploid plants had higher specific leaf area and leaf nutrient concentrations than native tetraploids, but tetraploids produced many more shoots and rhizomes. Diploids grew less well when calcium was present, whereas tetraploids were not affected, reflecting the known habitat differences of the ploidy levels in the field. European plants were less likely to flower and produced smaller capitulescences than North American tetraploids, but biomass production, and numbers of shoots and rhizomes did not differ. These results suggest that the same traits that made tetraploids successful in North America, e.g. higher colonization ability and wider habitat tolerance than diploids, may have predisposed tetraploids to becoming successful invaders. 5. For a phylogeographic analysis, parts of chloroplast intergenic spacer DNA from native and invasive populations of S. gigantea were sequenced. Inheritance of chloroplasts was confirmed to be maternal. In North America, significant differentiation among regions, private haplotypes, and isolation by distance were detected. The haplotype network was shallow, with one tetraploid-only star-shaped structure that was successful in colonization. The data suggest that tetraploids have formed several times in North America. Haplotype number and diversity were lower in European populations than in the native range, and evidence was found that four haplotypes were introduced to Europe from two source areas, New England and the Southern Appalachian Mts. Despite lowered diversity in the invasive range, the process of invasive spread is comparable to the spread of successful tetraploid lineages in the native range. 6. This project is the first to investigate the ecology and genetics of ploidy levels in the native range of S. gigantea and to consider how ploidy level influences the invasion potential of the species. I conclude that the ploidy levels differ markedly in habitat requirements, niche width and the distribution of genetic diversity. However, the most important difference is in the development of the rhizome system and hence presumably in the ability of ploidy levels to colonize and spread. I argue that the invasive potential of S. gigantea was probably not acquired through adaptation after introduction but through the formation of polyploids in the native range. Overall, this project has furnished evidence that polyploidy in S. gigantea does matter ecologically; and it seems probable that polyploidy also plays a significant role in biological invasions more generally. 2 Zusammenfassung ZUSAMMENFASSUNG 1. Invasive gebietsfremde Arten können ausgezeichnete Studienobjekte sein, um neue Erkenntnisse über evolutive, biogeographische und ökologische Prozesse zu gewinnen. Insbesondere wurde kürzlich erkannt, wie wichtig genetische Veränderung und Variation sind, um die Ursachen von biologischen Invasionsprozessen besser zu verstehen, jedoch ist mehr Forschung über die Bedeutung von Polyploidie nötig. Unklar ist zum Beispiel, weshalb Polyploidie so häufig in invasiven gebietsfremden Pflanzenarten vorkommt, obwohl verschiedentlich beschrieben worden ist, dass Polyploidie die Genexpression, die Physiologie und die Ökologie von Pflanzen stark verändern kann. Gerade um solche Faktoren zu bestimmen, die den Erfolg von biologischen Invasionen ursächlich beeinflussen, ist der vergleichende biogeographische Ansatz geeignet. Mangelndes Wissen über die Ökologie von invasiven Arten in ihrem ursprünglichen Gebiet verhindert jedoch häufig ein besseres Verständnis von Invasionsprozessen. Dieses Projekt wählte die Art Solidago gigantea Aiton (Asteraceae) als Untersuchungsobjekt. Diese Art kommt in ihrem ursprünglichen Verbreitungsgebiet in Nordamerika in drei Ploidiestufen vor, nämlich als diploide, tetraploide und hexaploide Individuen. In Europa ist sie invasiv in verschiedenen Habitaten und weitverbreitet. Durch Untersuchungen über die Ökologie und die Genetik der verschiedener Ploidiestufen dieser Art in einem vergleichenden biogeographischer Ansatz versuchte ich, unser Verständnis für die Bedeutung zu vertiefen, die die Polyploidie in biologischen Invasionsprozessen hat. 2. Die Verbreitung der Ploidiestufen von S. gigantea wurde sowohl