A study of genetic differentiation and hybridization among oak species with divergent ecological and evolutionary profiles [Elektronische Ressource] / by Charalambos Neophytou
Description
AstudyofgeneticdifferentiationandhybridizationamongoakspecieswithdivergentecologicalandevolutionaryprofilesThesissubmittedinpartialfulfilmentoftherequirementsofthedegreeDoctorrer.nat.oftheFacultyofForestandEnvironmentalSciences,Albert"Ludwigs"UniversitätFreiburgimBreisgau,GermanybyCharalambosNeophytouFreiburgimBreisgau,Germany2010 DeanofFaculty: Prof.Dr.JürgenBauhusSupervisor: Prof.Dr.SiegfriedFinkSecondReviewer: Assoc.Prof.Dr.FilipposA.AravanopoulosDateofthesis’defence:December8,2010 Tableof contents1.Introduction ...............................................................................................................................1 2.Objectivesandhypotheses.......................................................................................................32.1.InterspecificandgeographicgeneticdifferentiationpatternswithinandbetweenQuercus petraea(Matt.)Liebl.and Q. roburL.basedondatafromnaturalstandsgrowingunderdrasticallydiverseenvironmentalconditionsandpossessingdifferentevolutionaryhistories................................................................................................................32.
Informations
| Publié par | albert-ludwigs-universitat_freiburg |
| Publié le | 01 janvier 2010 |
| Nombre de lectures | 6 |
| Langue | English |
Extrait
A study of genetic differentiation and hybridization among oak species with divergent ecological and evolutionary profiles Thesis submitted in partial fulfilment of the requirements of the degree Doctor rer. nat. of the Faculty of Forest and Environmental Sciences, Albert"Ludwigs"Universität Freiburg im Breisgau, Germany by Charalambos Neophytou Freiburg im Breisgau, Germany 2010
Dean of Faculty: Prof. Dr. Jürgen Bauhus Supervisor: Prof. Dr. Siegfried Fink Second Reviewer: Assoc. Prof. Dr. Filippos A. Aravanopoulos Date of thesis’ defence: December 8, 2010
Table of contents 1. Introduction ............................................................................................................................... 1 2. Objectives and hypotheses....................................................................................................... 3 2.1. Interspecific and geographic genetic differentiation patterns within and between (Matt.) Liebl. and L. based on data from natural stands growing under drastically diverse environmental conditions and possessing different evolutionary histories................................................................................................................ 3 2.2. Patterns of genetic differentiation and hybridization between Poech and 3L. in the insular environment of Cyprus.............................................................. 2.2.1. Interspecific and intraspecific genetic differentiation between and 4: a large scale and multipopulation approach................................................... 2.2.2. Hybridization dynamics between and : genetic analysis of adult trees and progenies in a mixed stand ....................................................................... 4 2.3. Evolutionary conservation of the used microsatellite loci and phylogenetic relationships among the study species ................................................................................... 5 3. Literature review ........................................................................................................................ 6 3.1. Phylogeny of the genus ................. 6in Europe and the Mediterranean Basin 3.2. Differentiation, hybridization and evolution in oaks.................................................... 7 3.2.1. The use of morphological traits ............................................................................... 8 3.2.2. The use of molecular markers .................................................................................. 9 3.3. and in Europe: Species distribution and ecological requirements. ....................................................................................................................................................10 3.3.1. (Matt.) Liebl .....................................................................................10 3.3.2. L. ..........................................................................................................11 3.3.3. Differentiation and hybridization between and ............1 .......1 3.4. , and ssp.in Cyprus: Species distribution and ecological requirements. ............................................................................14 3.4.1. ................14...... ........................................................................ce.h oP 3.4.2. ......................................................................................1.5. ....... L......... 3.4.3. ssp.A. Kern .......................................................................15 3.4.4. Differentiation and hybridization between and ............61.. 4. Accomplished research ...........................................................................................................18 4.1. Detecting interspecific and geographic differentiation in two interfertile oak species ( (Matt.) Liebl. and L.) using small sets of microsatellite markers (Manuscript I) ...........................................................................................................18 4.1.1. Methodology .............................................................................................................18 4.1.2. Results and discussion .............................................................................................18 4.1.3. Conclusion.................................................................................................................20 4.2. Interfertile oaks in an island environment. I. Contrasting patterns of nuclear and chloroplast DNA differentiation between and in Cyprus (Manuscript II).........................................................................................................................20 4.2.1. Methodology .............................................................................................................20 4.2.2. Results and discussion .............................................................................................21 4.2.3. Conclusion.................................................................................................................21
4.3. Interfertile oaks in an island environment. II. Limited hybridization between Poech and L. in a mixed stand (Manuscript III)....................22 4.3.1. Methodology .............................................................................................................22 4.3.2. Results and discussion .............................................................................................22 4.3.3. Conclusion.................................................................................................................23 4.4. Conservation of nuclear SSR loci reveals high affinity of ssp. veneris A. Kern (Fagaceae) to section Robur (Manuscript IV)........................................23 4.4.1. Methodology .............................................................................................................23 4.4.2. Results and discussion .............................................................................................24 4.4.3. Conclusion.................................................................................................................24 4.5. Phylogenetic relationships among the study species based on chloroplast DNA haplotypes.................................................................................................................................25 4.5.1. Methodology .............................................................................................................25 4.5.2. Results and discussion .............................................................................................25 4.5.3. Conclusions...............................................................................................................26 5. General discussion...................................................................................................................28 6. Conclusions and outlook........................................................................................................34 7. Summary ...................................................................................................................................37 8. Zusammenfassung...................................................................................................................39 9. Περίληψη...................................................................................................................................42 10. References ..............................................................................................................................45 11. Acknowledgments .................................................................................................................56 12. Publications ............................................................................................................................58
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1. Introduction Oaks (L.) constitute one of the most species"rich genera of the northern hemisphere (Frodin 2004). They occupy a wide distribution range covering large parts of Europe, North America, the Mediterranean Basin and Asia spreading southwest to Columbia in South America and southeast to Indonesia. Consisting of 300"500 species (Camus 1934, Manos et al. 1999), they are a dominant element in a great variety of ecosystems ranging from Mediterranean sclerophyllous communities to temperate deciduous forests and tropical mountainous plant communities (Axelrod 1983). Numerous species, subspecies and varieties present a multiplicity of climatic, edaphic and photoperiodic adaptations. Besides their high taxonomic complexity, oaks are characterized by especially high levels of hybridization. Numerous records of intermediate forms arise from studies of both fossilized and living species (Palmer 1948, Stebbins 1950, Rushton 1993). In Europe, the genus is widely present and forms large forests in a wide ecological spectrum. Two important taxonomic groups, the sections Quercus and Cerris are represented with more than 30 species (Denk and Grimm 2010). The widespread deciduous species and (section Quercus) predominate in several landscapes across the continent and play an important economical role as a valuable source of wood (Aas 2008a, Aas 2008b). A series of other deciduous species occupy diverse habitats with their centres of diversity mainly being the three main peninsulas of the Mediterranean part of Europe (the Iberian, the Italian and the Balkan Peninsulas; Roloff et al. 2008). Evergreen sclerophyllous oaks are a significant element of Mediterranean sclerophyllous communities and are adapted to the particular environmental conditions there (e.g. prolonged summer drought and fire; Mooney and Dunn 1970). Besides species with large distribution ranges and broad ecological amplitudes, several other oak taxa are geographically restricted and show a high specificity of habitat like the endemic , which is confined to the igneous rock formations of the Troodos Mountains in Cyprus (Knopf 2008). In the light of a rapid climate change, a significant worldwide shift of climatic zones is expected over the next years. The reaction of tree species consists in three main alternative strategies: adaptation, migration or extinction (Savolainen et al. 2007, Aitken et al. 2008). Species with wide ecological amplitudes are expected to shift their distribution ranges northwards, but also to occupy additional habitats within their current growing areas, due to retreat of other more demanding species. Species with more restricted habitats may be more vulnerable to extinction. On the other hand, a shift of the ecological zones northwards may offer new niches for these species (Lindner et al. 2010). Given the rapidity of global warming, fast migratory responses are needed for the species to cope with climatic changes. A facilitated gene flow of preadapted alleles (assisted migration) or even a species transfer from warmer climates may be required in the effort to cope with environmental changes (Aitken et al. 2008). The significant role of interbreeding in the evolution of genus has been increasingly recognized since the middle of the last century (Stebbins 1950, Muller 1952, Burger 1975, Van Valen 1976). Studies of hybridization in oaks contributed to a reconsideration of the biological species concept, which requires reproductive isolation among species (Mayr 1942). Empirical and scientific observations documented in a large body of literature support the notion that interbreeding amongstspecies is not an
1. Introduction
2 occasional phenomenon, but an active evolutionary mechanism proceeding over generations and leading to substantial exchanges of genetic variation between different taxonomical units (Muller 1952, Stebbins 1950, Burger 1975, Van Valen 1976, Petit et al. 2004, Curtu et al. 2009). The role of interspecific gene flow as a means of adaptive variation exchange is a fascinating and challenging topic of recent and current research (Petit et al. 2004, Scotti"Saintagne et al. 2004a, Muir and Schlötterer 2005, Lexer et al. 2006, Lepais et al. 2009). Over the last decades, new tools of DNA analysis have given the opportunity to assess the genetic imprints of hybridization and have allowed tests of several evolutionary hypotheses in oaks. In the present study, species differentiation and interspecific gene flow are studied by focusing on oak species with divergent ecological and evolutionary profiles. Firstly, taxonomic and geographic genetic variation among very distinct environments are investigated in the interfertile and , two continental oak species with a large distribution range and an analogous ecological amplitude. Secondly, hybridization and differentiation are examined in the paradigm of and , two Mediterranean oak species growing in the restrictive insular environment of Cyprus and being the only potentially interfertile oaks there. Thirdly, evolutionary conservation of loci and phylogenetic relationships are resolved among the former oak species that represent two different and important sections of taxonomy. For this purpose, ssp., the third oak species of Cyprus, is additionally used forming a potential outgroup.
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2. Objectives and hypotheses 2.1. Interspecific and geographic genetic differentiation patterns within and between Quercus petraea (Matt.) Liebl. and Q. robur L. based on data from natural stands growing under drastically diverse environmental conditions and possessing different evolutionary histories The first objective of this study is to analyse interspecific and geographic patterns of genetic variation in a wide continental environment, in particular within and between and . and a broad geographic distribution possess and ecological amplitude reflecting a series of adaptations to contrasting environments. The present study especially focuses on the less studied Balkan refugial provenances through an analysis of interspecific and geographic patterns of genetic variation within and between and using a multilocus approach. Insofar evidence by suggests that only a restricted proportion of the genome accounts for interspecific differentiation between the two species, which has been attributed to directional selection affecting a limited number of genes and hitchhiked regions. On the other hand, gene flow has been suggested to play a homogenizing role in the rest of the genome (Bodénès et al. 1997, Petit et al. 2004, Scotti"Saintagne et al. 2004a). For studying both factors of differentiation – the taxonomic and the geographic – interspecific population pairs from different environments along a large scale ecological gradient are included. It is hypothesized that loci accounting for species differentiation have a consistent geographic pattern due to directional selection acting for maintenance of species identity. On the contrary, variation at the remaining loci is governed by the homogenizing effect of interspecific gene flow and by local selection. Genomic loci which vary strongly among regions, but show low interspecific differentiation at the local scale may indicate adaptations to the regional conditions, which are shared between the species due to ‘adaptive introgression’. Moreover, selectively neutral loci are expected to be less differentiated both at the interspecific and interregional level. Genetic variation among regions and between species was tested against the ‘null’ hypothesis of absence of genetic differentiation either at the taxonomic or the geographical level. 2.2. Patterns of genetic differentiation and hybridization between Q. alnifolia Poech and Q. coccifera L. in the insular environment o f Cyprus The second objective of the study is the analysis of genetic differentiation, hybridization and introgression in a restricted insular environment, in particular between and . Being phylogenetically related and forming both sympatric and pure populations in Cyprus, and present an ideal paradigm for the study of differentiation in the presence of hybridization and potential introgression in a restricted insular environment. Potential hybridization between these species and the third oak species of Cyprus, ssp., has never been reported and may not be expected as the latter species shows an affinity to another section (Meikle 1977, Schirone and Spada 2001).
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