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Väitekirja elektrooniline versioon ei sisalda publikatsioone, Taimed varieeruvad üle terve oma levila silmapaistvalt morfoloogiliselt, geneetiliselt ning kohastumuste poolest. Esiteks seab populatsioonidevaheline geograafiline kaugus füüsilised piirangud geenide vahetamiseks ja teisalt mõjutavad populatsioone eri piirkondades erinevad ökoloogilised tegurid ning keskkonnatingimused, mis võivad viia liigisisese geograafilise eristumiseni. Teisalt on nad võimelised omavahel ristuma (hübridiseeruma), mis ulatusliku geenivahetuse tagajärjel võib viia regionaalse sarnasuseni. Doktoritöös uurisime lähedaselt suguluses olevate kollase tarna (Carex flava) ja ojatarna (C. viridula) morfoloogilist ja geneetilist eristumist kolmes klimaatiliselt erinevas regioonis: Eestis, Šveitsi lauskmaal ja Šveitsi Alpides. Uuritud tarnad erinevad populatsioonide suuruse ja levila ulatuse poolest, mis teoorias põhjustab erinevat regionaalse eristumise mustrit. Sellest tulenevalt, oli minu doktoritöö peamiseks eesmärgiks tuvastada, kas ojatarn oma katkendliku leviku ja väikeste populatsioonidega on regioonide vahel rohkem eristunud kui kollane tarn, kes on laialdasema levikuga ja suuremate populatsioonidega. Teisalt on võimalik, et ristumine mõjutab nende liikide evolutsiooni. Uuringu eesmärkide täitmiseks, teostasime morfoloogilise ja geneetilise analüüsi ning ümberistutuskatse kolme eelpool mainitud regiooni vahel. Tulemused näitavad, et plastilisus, geneetiline varieeruvus ja genotüübi-keskkonna koosmõju on oluliselt mõjutanud mõlema tarna ja nende hübriidi regionaalset eristumist, kuid eristumine on mõnevõrra tugevam ojatarnal. Leidsime, et nii looduslikes populatsioonides kui ka ühisaedades erinesid kollane ja ojatarn üksteisest suurema osa morfoloogiliste tunnuste poolest oluliselt. Geneetiline analüüs toetas tarnadevahelist erinevust, kuid näitas ka geenivahetust. Seega ei ole liikidevaheline hübridiseerumine ei ole nii ulatuslik, et takistada ojatarna regionaalset eristumist. Kollase tarna ja ojatarna morfoloogilise ja geneetilise varieeruvuse kombineeritud uuring ning vastastikune ümberistutuskatse võimaldas teha mitmeid olulisi järeldusi uuritud taksonite morfoloogilise varieeruvuse, geneetilise mitmekesisuse, geneetilise eristumise ja kohastumuse kohta ning hinnata hübridiseerumise mõju laialdasema ja katkendlikuma levikuga taksonitel. See doktoritöö on oluline panus hübridiseeruvate liikide geograafilise eristumise mõistmiseks, mis on eriti tähtis globaalsete muutuste uuringutes ja looduskaitses., Plants experience different climatic and environmental conditions in different locations of their distribution areas. This can lead to different growth between populations. Moreover, populations may adapt to their local conditions. Plants of closely related plant species may also hybridize, i.e. cross between species, which may result in increased similarity. Less common species are expected to show stronger differences between regions and populations than more common species because random processes are more likely to affect the smaller populations of less common species. On the other hand, if two species hybridize with each other, they may also show similar differences between regions. We asked whether regional differences were larger in the less common sedge species Carex viridula than in the more common C. flava. We also tested whether regional differences between Estonia and lowland and highland Switzerland are mainly environmentally determined or also have a genetic basis. We assessed regional differences in morphological, size-related and floral traits in 43 populations in the field, and we studied molecular genetic differentiation. Moreover, we grew plants of all populations in three common gardens, one in each study region, which enabled us to test whether differences between species and regions are genetic, and whether plants are adapted to the environmental conditions of the home region. We found clear morphological and genetic differences between the two hybridizing species indicating that C. flava and C. viridula are indeed separate species. Nevertheless, we also found hybridization between the two and backcrossing of hybrids with the two species, which may contribute to their considerable morphological similarity. We further found that environmental effects, genetic differences and genetic differences in the expression of environmental effects all contributed to regional differences and that these differences were more pronounced in the less common C. viridula than in C. flava. This thesis contributes to understanding geographic differences in hybridizing species. This is an understudied field, which is important, however, for understanding species responses to global change and for plant conservation.

Phenotypic variation may be genetically determined or reflect phenotypic plasticity. More common plants are expected to be less differentiated between and within regions and more adapted than less common ones. However, such differences might not develop in hybridizing species which cannot evolve completely independently. We collected 311 genets of Carex flava, 215 of C. viridula and 46 of their hybrid C. × subviridula from 42 natural populations in cold temperate Estonia, mild temperate Lowland Switzerland and alpine Highland Switzerland. Three plantlets from each genet were planted to three experimental gardens, one in each region. We measured survival, growth, reproduction and morphological traits. The experimental transplants showed strong plasticity and grew smallest in the alpine garden. The less common C. viridula was slightly more differentiated between regions of origin than the more common C. flava and the hybrid. However, this depended on the experimental garden. Significant origin-by-garden-by-taxon and taxon-by-garden interactions suggest differential adaptation among populations and taxa. Regional differed from non-regional plants in several traits indicating both adaptations and, especially for C. viridula, maladaptations to the home regions. For C. flava, plant seed production was higher when mean annual temperature and precipitation were more similar between population of origin and garden, suggesting local adaptation to climate. Hybrids were intermediate between parental taxa or more similar to one of them, which was retained across gardens. We conclude that plasticity, genetic variation and genotype–environment interactions all contributed to regional differentiation of the closely related species. Hybridization did not completely align evolutionary patterns, and the less common species showed slightly more genetic differentiation between populations and more maladapted traits than the more common one.

Rarer species are expected to show stronger geographic differentiation than more common species. However, if rare species hybridize with common species, differentiation may be quite similar between the two due to genetic admixing via backcrossing. We studied morphological differentiation of plants of 21 natural populations of the more common Carex flava, 16 of the less common Carex viridula and 6 of their hybrids from 27 sites in three climatically different regions, Estonia, Lowland Switzerland and Highland Switzerland. Univariate ANOVA and multivariate principal component analysis of 14 morphological characters, describing both vegetative and reproductive characters, allowed to clearly distinguish C. flava from C. viridula. Carex viridula populations showed stronger regional variation than C. flava. Hybrids had both intermediate and transgressive characters in Switzerland and Estonia. On average, hybrids from Lowland Switzerland were more similar to Swiss C. flava than to C. viridula, while hybrids from Estonia were morphologically intermediate between plants of Estonian populations of the parental species. The results suggest that within-region genetic admixing between species has limited potential to lead to region-specific similarity between species, at least in our model system of the C. flava complex. We conclude that C. flava and C. viridula are clearly distinct species and that, despite hybridization, geographic differentiation is more pronounced in the less common C. viridula than in C. flava.