Genetics and Ecology of Natural Populations

Genetics and ecology of natural populations

Elisabeth Lundqvist

Umeå 2002

Division of Genetics / Department of Molecular Biology Umeå University SE-901 87 Umeå Sweden

AKADEMISK AVHANDLING

Som med vederbörligt tillstånd av rektorsämbetet vid Umeå Universitet för erhållande av filosofie doktorsexamen i genetik kommer att offentligen försvaras fredagen den 27 september, kl 13.00 i sal KB3 Bl, KBC-huset

Examinator: Docent Åsa Rasmuson-Lestander

Opponent: Docent Ulf Lagercrantz, Inst. för växtbiologi, SLU, Uppsala Organisation Document name Umeå University DOCTORAL DISSERTATION Department of Molecular Biology / Division of Genetics SE-901 87 Umeå, Sweden

Author Date of issue Elisabeth Lundqvist September 2002

Title Genetics and ecology of natural populations

Abstract

I have studied the genetic variation of single species using morphological variation and enzyme electrophoresis. I have striven to understand the interaction between the breeding structure and the ecology of the species in relation to the community, in which it lives. The work was done in the county of Västerbotten, northern Sweden. In the Skeppsvik archipelago I have studied the population structure of Silene dioica: ecotypic variation in other populations. I have also studied the genetic diversity of Angelica archangelica, Bistorta vivipara, Viscaria alpina and the earthworm Eiseniella tetraedra along the free-flowing Vindel and Sävar Rivers and the regulated Urne River. The island populations of S. dioica are subdivided into several breeding units and levels of differentiation among subpopulations within islands were about twice as high as among islands. Restricted seed and pollen dispersal creates patches made up of related individuals that may diverge as a result of drift. Frequent seed and pollen dispersal occurs among islands and they will receive the same alleles. This may explain the pattern of differentiation observed. In contrast, the patches within islands may be founded by only a few individuals. * S. dioica exhibits morphological differentiation in vegetative and floral characters between serpentine, cold spring, rich forest and coastal habitats. There was no association between genetic and geographical distance or between genetic distance and habitat. Serpentine and cold spring, which represented the most extreme habitats were also most differentiated. Populations of S. dioica are subject to herbivory; predation may exert a selective pressure on vegetative characters. A number of selective forces such as pollinators and fungal parasites act on reproductive characters. Assuming that water dispersal is important I tested several hypotheses to explain patterns of genetic diversity expected to be exhibited by riparian organisms along free-flowing and regulated rivers. I show that dispersal, distribution and breeding structure are important determinants of the evolution of the riparian flora. Patterns of genetic diversity may be exhibited at many spatial scales, e.g. among entire rivers, and between types of riverbanks within a river reach. Populations must be sampled at a spatial scale relevant to the hypothesis to be tested.

Key words Angelica archangelica, Bistorta vivipara, Viscaria alpina,Eiseniella tetraedra, ecotypes, hydrochory, genetic differentiation, clone diversity, genetic patterns, riparian

Language ISBN Number of pages English 91-7305-286-8 148

Signature Date 2002-05-27 <1 Genetics and ecology of natural populations

Elisabeth Lundqvist

Umeå 2002

Division of Genetics / Department of Molecular Biology Umeå University SE-901 87 Umeå Sweden

AKADEMISK AVHANDLING

Examinator: Docent Åsa Rasmuson-Lestander

Author Date of issue Elisabeth Lundqvist September 2002

Title Genetics and ecology of natural populations

Abstract

I have studied the genetic variation of single species using morphological variation and enzyme electrophoresis. I have striven to understand the interaction between the breeding structure and the ecology of the species in relation to the community, in which it lives. The work was done in the county of Västerbotten, northern Sweden. In the Skeppsvik archipelago I have studied the population structure of Silene dioica: ecotypic variation in other populations. I have also studied the genetic diversity of Angelica archangelica, Bistorta vivipara, Viscaria alpina and the earthworm Eiseniella tetraedro along the free-flowing Vindel and Sävar Rivers and the regulated Urne River. The island populations of S. dioica are subdivided into several breeding units and levels of differentiation among subpopulations within islands were about twice as high as among islands. Restricted seed and pollen dispersal creates patches made up of related individuals that may diverge as a result of drift. Frequent seed and pollen dispersal occurs among islands and they will receive the same alleles. This may explain the pattern of differentiation observed. In contrast, the patches within islands may be founded by only a few individuals. S. dioica exhibits morphological differentiation in vegetative and floral characters between serpentine, cold spring, rich forest and coastal habitats. There was no association between genetic and geographical distance or between genetic distance and habitat. Serpentine and cold spring, which represented the most extreme habitats were also most differentiated. Populations of S. dioica are subject to herbivory; predation may exert a selective pressure on vegetative characters. A number of selective forces such as pollinators and fungal parasites act on reproductive characters. Assuming that water dispersal is important I tested several hypotheses to explain patterns of genetic diversity expected to be exhibited by riparian organisms along free-flowing and regulated rivers. I show that dispersal, distribution and breeding structure are important determinants of the evolution of the riparian flora. Patterns of genetic diversity may be exhibited at many spatial scales, e.g. among entire rivers, and between types of riverbanks within a river reach. Populations must be sampled at a spatial scale relevant to the hypothesis to be tested.

Key words Angelica archangelica, Bistorta vivipara, Viscaria alpina,Eiseniella tetraedro, ecotypes, hydrochory, genetic differentiation, clone diversity, genetic patterns, riparian

Language ISBN Number of pages English 91-7305-286-8 148

Signature Date 2002-05-27 To my family

ISBN 91-7305-286-8 © Elisabeth Lundqvist, 2002

Printed by: Solfjädern Offset AB Cover drawing by Veronica Lundqvist

CONTENTS

LIST OF PAPERS...... 1 INTRODUCTION...... 2 Genetic variation in natural populations ...... 3 Genetic structure of natural populations ...... 3 Genetic adaptation in natural populations...... 4 Human impact of natural populations ...... 5 The aims of this thesis...... 7 The plants and the worm ...... 7 The populations and rivers ...... 9 SUMMARY OF THE PAPERS...... 12 Paper 1 ...... 12 Paper II ...... 12 Paper III...... 13 Paper IV ...... 14 Paper V...... 15 DISCUSSION...... 16 Genetic structure and morphology of S. dioica...... 16 Genetic variation and patterns in riparian corridors ...... 18 ACKNOWLEDGEMENTS...... 20 REFERENCES...... 20 Acknowledgements...... 27 References...... 29 LIST OF PAPERS

This thesis is a summary of the following papers, which will be referred to by their Roman numerals:

I. Giles, B. E., Lundqvist, E. and Goudet, J. 1998. Restricted gene flow and subpopulation differentiation in Silene dioica. Heredity, 80: 715-723.

II. Lundqvist, E. and Puu, M. Ecotypic variation in Silene dioica (Caryophyllacae). Submitted manuscript.

III. Lundqvist, E. and Andersson, E. 2001. Genetic diversity in populations of plants with different breeding and dispersal strategies in a free-flowing boreal river system. Hereditas, 135: 75-83.

IV. Terhivuo, J. Lundqvist, E. and Saura, A. 2002. Clone diversity of Eiseniella tetraedra (Lumbricidae: Oligochaeta) along regulated and free-flowing boreal rivers. Ecography in press.

V. Genetic patterns of riparian plants and animals in river corridors. Submitted manuscript.

Papers I, III and IV are reproduced with due permission from the publishers

1 INTRODUCTION

Ecological genetics is a combination of population genetics and ecology (Ford 1964). At the level of populations this combination implies that the Hardy-Weinberg law is supplemented with an exponential or logistic component that defines the environmental pressure that prevents an unlimited growth of the population. The father of ecological genetics is Göte

Turesson (1922); or following Olof Langlet (1971), the entire field is at least two hundred years old.

Ford was a zoologist, while Turesson and Langlet were botanists. I may stress this difference, since populations of animals and plants differ greatly from each other. An animal moves about and can freely choose its habitat and mating partner. A plant has no choice: it has to try to live at the place, where the seed or propagule once has fallen. The breeding systems of plants vary extensively beginning from complete self-incompatibility (where the pollen will never grow on the stigma of the mother plant) through self-compatibility (that allows cross-fertilization) to obligate selfing. How these different alternatives are realized, depends on the density of the population, the placement of stamens and stigmas in relation to each other (and whether they are located on the same or different individuals), whether the stamens and stigmas function at the same time as well as on pollinators and competition between pollen grains.

Plants have also many mechanisms of asexual reproduction and the seeds can develop without fertilization; these mechanisms are collectively called apomixis. Apomixis is in general associated with polyploidy (Asker and Jerling 1992). All the above parameters are influenced by genetic and environmental factors. The very immobility of plants makes them ideal material in the study of the genetic effects of environmental heterogeneity.

2 Genetic variation in natural populations

Genetic variation is defined as the amount of allelic diversity present at a number of loci and the relative frequency of these alleles. This is an important characterization of populations since the evolutionary potential of a species is a function of the amount of its genetic variation. According to Fisher's Fundamental Theorem of Natural Selection the rate of increase in fitness of a species at any time is equal to its genetic variance in fitness at that time

(Fisher 1930). Ford (e.g. 1964) defined genetic polymorphism as follows: “Genetic polymorphism is the occurrence together in the same locality of two or more discontinuous forms of a species in such proportions that the rarest of them cannot be maintained merely by recurrent mutation”. This definition excludes geographic races as well as continuously ranging morphological characters that are determined by multiple loci. The definition is curious since it also includes selection as the factor underlying the phenomenon. This notwithstanding, the discovery of protein gel electrophoresis gave a new set of tools for detecting genetic variability within species. This method is still the method of choice in studies concerning the genetic structure of plant populations, but it has been supplemented with molecular tools such as microsatellites (e.g. Karhu 2001).

Genetic structure o f natural populations

Genetic variation may be structured within and among different populations as well as at several hierarchical levels. Genetic structure results from the joint action of mutation, migration, selection and drift and these selective forces operate within the historical and biological context of each species. Gene flow may strongly influence the patterns of genetic differentiation (Slatkin 1985). There are a variety of ecological variables that affect the

3 genetic structure within and among populations (Loveless and Hamrick 1984). Factors

affecting reproduction and dispersal are considered to be particularly important (Jain 1975).

F-statistics measure the reduction in heterozygosity expected with random mating at

any level of population hierarchy in comparison to another, more inclusive level of hierarchy.

This gives an indication of population differentiation, as it allows a comparison of the overall

effect of population substructure. F-statistics can be used to partition the genetic

differentiation of populations. Mean total diversity F it,mean within-population F is and among-population F st are commonly used measures of population substructuring at different levels of hierarchy (Wright 1969,1978).

Genetic adaptation in natural populations

Olof Langlet (1971) wished to stress that genetic adaptation to climate has been subject to scientific study for a long time. Forest tree provenances had been tested in central Europe so that Duhamel du Monceau wrote the first treatise in 1755 on pine provenances. From this time onwards we have a continuous series of scientific papers that shows how plants are adapted to local conditions (Linhart and Grant 1996). The genetics underlying this adaptive response was understood much later (e.g. Baur 1914). In the beginning of the last century Turesson (1922,

1925) coined the ecotype concept. This concept became a basic unit of biosystematics

(Stebbins 1950). Ecotype is an ecological unit that is formed within a species as a reaction of the genotype to a given environment (Fig 1).

Fig. 1. Ecotypes of Silene diocia. The ones on the left descend from seeds collected at Finse, Hardanger Vidde at an altitude of 1000 m. The ones on the right come from Sognefjord on the coast in Norway. Both was grown in greenhouse in Berlin (modified from Baur 1914).

4 Turesson studied several plant species; the red campion, Silene dioica, among them. The ecotype concept is uncontroversial as such, but it has been somewhat of a hindrance in understanding the genetic variation within a species in relation to environmental change. To give an example, cline, that is a continuous variation in relation to a changing environment along a transect (photoperiod, growing season, temperature etc.), cannot easily be accommodated within the ecotype concept. To give an example, Langlet (1971) had found clear-cut continuous variation in his studies on pines; he did not see ecotypes anywhere.

Human impact of natural populations

“Ecologists traditionally have sought to study pristine ecosystems to try to get

at the workings of nature without the confounding influences of human

activity. But that approach is collapsing in the wake of scientist’s realization

that there are no places left on Earth that don’t fall under humanity’s shadow”

(Gallagher and Carpenter 1997).

Humans affect the natural environment in about all ecosystems of the world (e.g Goudie

2000). Much of this is deep down in prehistory, like the destruction of the megafauna of

Australia, the Americas and Madagascar. The moa were still around when the Dutch came to

New Zealand: at the same time the last dodos of Mauritius were gone. Later all kinds

European or whatever animals or plants were let loose in Australia or New Zealand. The consequences were apparent to Darwin when he wrote the “Origin of species”. Already he pointed out that oceanic island biota are, in particular, vulnerable.

The habitats of most plant and animal species are patchily distributed across the terrestrial landscape. This fragmentation of the landscape is most apparent where the human impact has been greatest such as the agricultural areas in e.g. Europe. In northern Europe

5 energy production has modified the boreal ecosystem dramatically in that rivers and riparian

zones have borne the brunt of this energy production (Petts 1984). Today most largest river

systems in Europe and North America are affected by flow regulation and fragmentation by

dams (Dynesius and Nilsson 1994).

Many studies have shown that species composition of rivers change as a consequence

of this disruption (Nilsson et al. 1991, Nilsson and Jansson 1995, Jansson et al. 2000ab,

Merrit and Cooper 2000). With few exceptions riparian zones (Fig. 2) are more species rich than upland ecosystems as shown for plants (Nilsson and Jansson 1995) and animals (Naiman

and Décamps 1997). Riparian zones perform several functions e.g. as a corridor for dispersal

(Naiman et al. 1993). Andersson (1999) has shown experimentally the importance of hydrochory (dispersal by water) in shaping the riparian flora. Seeds floating in water contribute to a continuous gene flow and give rise to large population sizes (Edwards et al.

1994). Dams and impoundments may profoundly reduce this gene flow, promoting differentiation among populations and reduce population sizes leading to depleted gene pools.

Fig. 2. The zonation of the vegetation making up the riparian zone of the free-flowing Vindel

River. Modified from Jansson (2000).

6 THE AIMS OF THE THESIS

In this thesis I have studied patterns of genetic variation of single species within natural populations. I have quantified the genetic variation using morphological and enzyme electrophoresis as well as conducted studies in different ecological settings. My goal has been to understand the interaction between the underlying genetic composition and the ecology of both the single species and the community of which it belong.

I have striven:

• to estimate the size of breeding units of Silene dioica and to study the differentiation at

different levels (Paper I).

• to study the morphological response of Silene dioica to different environments

(Paper II).

• to assess the genetic diversity and population structure in populations of three plants in

a free-flowing river system (Paper III).

• to assess the clone diversity of a lumbricid along a regulated and a free-flowing river

(Paper IV).

• to study different genetic and clonal patterns in river corridors (Paper V)

THE PLANTS AND THE WORM

S. dioica (L.) Clairv. (Caryophyllaceae) (Papers I and II) has a wide distribution in northern and central Europe (Jalas and Suominen 1986). In northern Sweden S. dioica is native on the

7 shores of the Gulf of Bothnia where it is a member of primary succession as well as along the

large rivers and in the Scandes (Jonsell 2001). S. dioica grows in fertile and often disturbed

habitats such as sub alpine tall-herb meadows and screes (Jonsell 2001) as well as on

serpentine soils (Westerbergh and Saura 1992). S. dioica may also grow in rich coniferous

and deciduoud woods on mesic to slightly moist ground with running water. It is also a weed

found along roadsides and cultivated areas.

S. dioica is a perennial diploid with heteromorphic sex chromosomes, with females being XX and males being XY. In northern Sweden, the plants have an average life span of 5-

10 years (Carlsson 1995); they start to flower at an age of 2-3 years. S. dioica has a persistent

seed bank (Roberts 1986) and depending on disturbance level the seed bank vary in size

(Matlack 1987). The seeds are dispersed passively: they are shaken out by wind or animals. S. dioica is pollinated by bumblebees, syrphids, muscids (Westerbergh and Saura 1994) and lepidopterans (Knuth 1898, Jürgens et al. (1996).

Bistorta vivipara (Polygonaceae) (Papers III and V) is a circumpolar plant that is common in arctic and alpine habitats. It grows in the north in most kind of woodless habitats and in herb-rich forests (Karlsson 2000). It is perennial and individual plants can be long- lived, up to 26 years (Law et al. 1983). B. vivipara is polyploid, with a variable chromosome number (Löve and Löve 1975). It produces bulbils (asexual propagules) in the lower part of the inflorescences and has in the upper part protandrous flowers. B. vivipara does not produce runners and reproduces in northernmost Europe exclusively by bulbils (Söyrinki 1939).

Viscaria alpina (Caryophyllaceae) (Papers III and V) has an amphi-Atlantic subarctic- alpine distribution and is widespread in Fennoscandia. The plant is a diploid, short-lived perennial herb (Wesenberg 2001). In the lowland, localities are found mainly along rivers and lakes. V alpina is hermaphroditic, often protandric and it is pollinated by insects. Seed dispersal is passive; seeds remain in the capsule until wind, rain, snow or animals shake them

8 out. V. alpina has a limited vegetative reproduction by rejuvenating the rosettes (Nagy and

Proctor 1996, Wesenberg 2001).

Angelica archangelica (Apiaceae) (Papers III and V) has an amphi-Atlantic subarctic and alpine distribution. It is diploid, perennial, short-lived herb (Ojala 1986) that dies after flowering. In northern Europe the life span is from two to four years (Ojala 1985). The hermaphroditic flowers are strongly protandric and the main pollinators are bees and flies

(Knuth 1898).

Eiseniella tetraedra (Lumbricidae) (Papers IV and V) is a parthenogenetic oligochaete that is tetraploid in northern Europe. It can be found in waterlogged habitats such as shores of lakes and rivers but also in the brackish water along the coasts of the Baltic Sea (Terhivuo

1988). They are small earthworms that reproduce through laying resistant cocoons that can be carried by water (Schwert and Dance 1979). The individual worms are short-lived, attaining at most an age of one and a half years (Sims and Gerard 1985).

THE POPULATIONS AND RIVERS

The size of the breeding units of S. dioica (Paper I) was determined in the Skeppsvik

Archipelago (Fig. 3) in northern Sweden. Here new islands are continuously formed through land upheaval (Ericson and Wallentinus, 1979). The islands differ in age and stage of primary succession and, accordingly, S. dioica populations follow the succession. The islands (Paper I,

Fig. 1) that we chose were in similar successional stage, had continuous distribution of S. dioica individuals and were located in the same area of the archipelago.

In the morphological study of S. dioica (Paper II) I investigated populations situated in the county of Västerbotten in northern Sweden (Fig. 3). The populations varied in the

9 following parameters; size (estimated number of adult individuals), maximum age (the time

since the retreat of the Scandinavian ice sheet at the close of the Weichsel glaciation or, for

populations 6 through 8, the retreat of the Baltic Sea because of land upheaval), altitude,

habitat and degree of isolation (i.e. distance to nearest population) (II, Table 1).

In the riparian studies (Papers III, IV and V) the localities were situated along the

Urne, Vindel and Sävar Rivers (Fig. 3). The Vindel and Urne Rivers run parallel from the

Scandes Mountain to the joint confluence at Vännäs before they empy into the Gulf of

Bothnia. Both rivers have a catchment area of about 13 000 km2. The free-flowing Vindel

River has large natural seasonal fluctuations in water flow and level. The water level variation ranges up to 6 m and is normally lowest during August -September and highest during the

spring flood (May-June). Water flow ranges from a minimum mean of 15 mV1 to a maximum

mean of 1660 m3s_1at the confluence with the Urne River. The natural discharge for Urne

River at this confluence varied from 72 mV1 up to 1800 mV1.

Following regulation Urne River consists of a stair-stepped series of storage reservoirs and run-of-river impoundments (IV, Fig. 2). As a consequence the discharge at the confluence with Vindel River is reduced and varies now between 0 and 918 mVl (Jansson et al. 2000a).

The free-flowing Sävar River is 145 km long with a catchment area of 1165 km2 and has a water discharge at its mouth that ranges annually between 1 and 160 mV1 (Nilsson et al.

1991). The riparian vegetations in Vindel and Sävar Rivers are distinctly zoned (Fig. 2) while the vegetation along the Urne River is concentrated in a narrow strip at the high water level in reservoirs and impoundments.

10 Fig. 3. Sampling localities of material studied in this thesis, Black stars on the insert map (lower right) show die islands, where the Si iene dioica populations studied in Paper I grow. Open stars on the main map show the location of 5. dioica populations studied in the ecotype part (Paper 11). The left inserì rnap shows the location of Bistorta vivipara, Viscaria alpina and .Angelica ■archangelica populations studied in Paper III and the circles on the main map show where the Eiseniella tetraedro populations studied in Paper IV come from.

11 SUMMARY OF PAPERS I-V

(I). Restricted gene flow and subpopulation differentiation in Silene dioica.

This study was done to estimate the size of the breeding units of Silene dioica on four closely

situated island populations in the Skeppsvik Archipelago in northern Sweden (Fig. 3). In

addition, we studied the population structure within and between islands. We sampled material from ten S. dioica individuals from a total of 100 patches. The patches were circles with an area of 0.2 m2. The size and shape were chosen based on the result from a study I had conducted on one single island (Lundqvist 1994). F-statistics based on nine polymorphic allozyme loci show that plants on single islands are divided into many small breeding units that range in size between 0.2 m2 and 6 m2. The hierarchical analyses showed that level of differentiation among patches within islands were about twice as high as among islands. We concluded that restricted seed and pollen dispersal creates patches made up of related individuals. Since F il (the correlation of genes within individuals relative to the island) is positive this family structure alone cannot explain the positive F pl (the correlation of genes within patches relative to the island), drift is needed as an additional explanation.

(II). Ecotypic variation in Silene dioica (Caryophyllacae).

To evaluate the effects of environmental heterogeneity on Silene dioica we studied the morphological differentiation in vegetative and reproductive (floral) characters, and the onset of reproduction in a greenhouse experiment. We sampled seeds from eight populations in northern Sweden (Fig. 3). The populations represented four different habitats: serpentine, cold spring, rich forest and coast. We calculated the genetic distance among populations from data

12 based on enzyme allele frequencies derived from the offspring grown in the greenhouse. The

resulting dendrogram showed that there was no association between genetic and geographic

distances and that the genetic distance and habitat were not associated either. We grouped the

populations into four groups each representing a different habitat. The results show that the

most differentiated groups represented the most extreme habitats i.e. serpentine and cold

spring. A number of selective forces such as pollinators and the sterilising smut fungus

Microbotryum violaceum may act on reproductive characters. It seems that these selective

forces may act in a mosaic fashion over small geographic areas. The cold spring populations

had a delayed onset of reproduction in comparison with the other habitat groups.

(III). Genetic diversity in populations of plants with different breeding and dispersal

strategies in a free-flowing boreal river system.

In order to find riparian plants that can be used for study the genetic effects of hydrochory we

studied the genetic diversity of three plants: Angelica archangelica, Bistorta vivipara and

Viscaria alpina. The plants were chosen in that they should be riparian and found mainly or

exclusively in the riparian corridor. The study was made in the free-flowing boreal Vindel

River system in northern Sweden (Fig. 3). The plants have different reproductive strategies;

A. archangelica is an insect pollinated outbreeder, V. alpina has a mixed mating system while

B. vivipara is apomictic. The propagules of these plants differ in floating capacity; seeds of A. archangelica may float for over a year, while the propagules (seeds and bulbils, respectively) of V. alpina and B. vivipara float for less than two days. We assessed enzyme gene diversity with starch gel electrophoresis. B. vivipara had high level of clonal diversity with D values

(Simpson’s index) ranging between 0.78 and 0.99. However, only a few clones were shared between localities, which made similarity comparisons impossible. The mean heterozygosity

13 (He) based on six polymorphic loci over all populations of V. alpina was 0.15. We found that

F it (0.44), F st (0.39) and Fis (0.08) all differed significantly from zero indicating a deficiency of heterozygotes and a high degree of differentiation between populations. A dendrogram (III,

Fig. 5) shows that there was no association between genetic and geographical distances. The enzyme phenotype diversity of A. archangelica was found to increase downstream indicating efficient seed dispersal by water

(IV). Clone diversity of Eiseniella tetraedro, (Lumbricidae: Oligochaeta) along regulated and free-flowing boreal rivers.

In this paper we extended the work on genetic diversity of riparian species to include the parthenogenetic and polyploid earthworm Eiseniella tetraedra. We included two major rivers, one free and the other regulated in order to investigate the effects of regulation on genetic diversity. The study was conducted along the free-flowing Vindel River, the regulated Urne

River (that flows parallel to the Vindel River) and the lower course of the small free-flowing

Sävar River in northern Sweden (Fig. 3). We identified the clones on the basis of overall enzyme phenotypes that were detected using starch gel electrophoresis. The results show that clone pool diversity and similarity are higher along the Vindel River than along Urne River.

We concluded that the twenty major dams that have harnessed the Urne River have also effectively stopped clone dispersal by water. We found that clone diversity is highest at the joint river mouth of the two major rivers. The clone diversity found at the lower course of the small Sävar River was of the same magnitude. Results from two consecutive years show that clone turnover between years is high and that there are more clones present than we succeed to sample in a single year. There was no evidence for parallel adaptation of clones along the two major rivers.

14 (V). Genetic patterns of riparian plants and animals in river corridors.

We put forward seven hypotheses that predict patterns of genetic and clonal diversity within and among populations of riparian plants and animals. The hypotheses are based on the assumption that dispersal by water is important in riparian corridors. We tested the hypotheses using our own data from papers III and IV, as well as data from the literature. Hypothesis I predicts that genetic diversity within populations should increase downstream as populations may receive propagules from an increasingly large area. Alternatively, the genetic diversity may be higher along the middle reaches of rivers and decrease towards the mouth due to unstable riparian sedimentary soils of the riparian zones along the lower reaches that limit establishment. We found support for the former alternative with the data of A. archangelica

(Paper III), as well as from three studies in the literature (Durka 1999, Akimoto et al. 1998,

Russell et al. 1999). Hypothesis II predicts that riparian zones that are effective traps of floating material have high diversity. We found support for this hypothesis with the data of B. vivipara (Paper III) that had the clone diversity tied to water flow velocity and was highest along turbulent reaches. Hypothesis III predicts that riparian populations should be genetically more similar to each other than populations occupying other habitats if waters dispersal is more effective than other dispersal modes. The combined results of V. alpina from our paper

III and that of Sjöberg (1999) as well as the data of Ritland (1988) support this hypothesis. In addition, the clone diversity of E. tetraedro (Paper IV) was higher at the river mouths in all rivers in comparison with non-river mouth seashore populations (Terhivuo and Saura 1996,

1997). Hypotheses IV and V predict that natural dispersal barriers (lakes) and dams will restrict water dispersal. Hypothesis VI predicts that free-flowing rivers have higher diversity than regulated ones. We found no support for hypothesis IV. Both diversity and similarity of

E. tetraedro (Paper IV) were higher in the free-flowing Vindel River than along the regulated

15 Urne River. In addition, Durka (1999) and Lascoux et al. (1996) obtained similar results

supporting our hypothesis V and VI. Our last hypothesis (VII) predicts that the genetic

diversity should be higher in large than in small rivers, because populations in large rivers

may receive propagules from a larger area. We found no support for this hypothesis.

DISCUSSION

Genetic structure and morphology o f S. dioica

We found that island populations of S. dioica are subdivided into several breeding units with

estimated sizes that lie between 0.2 m2 and 6 m2 (Paper I). This result agrees with my previous results from the same area (Lundqvist 1994). Even though S. dioica is an obligate outbreeder it clearly can differentiate on a small spatial scale. In fact, significant differentiation has been estimated to occur over much smaller scale with breeding unit sizes that range between 0.2 m2 and 0.8 m2 (Lundqvist unpublished). We put forward (Paper I) two hypotheses to explain this differentiation. The first assumes restricted seed and pollen dispersal and random mating within local populations and thus local populations may diverge due to genetic drift. The other assumes that seed dispersal is more restricted than pollen dispersal and therefore family groups may establish at the colonisation within the local populations and persist over generations as a combined consequence from female offspring continue to disperse most seeds within the same local and seeds emerging from the seed bank.

Our results are consistent with both scenarios.

McCauley (1994) found that differentiation in Silene latifolia (a close relative to

S. dioica) estimated from chloroplast markers was significantly higher than the one of nuclear markers. Organelle markers show uniparental inheritance in contrast to biparentially inherited

16 nuclear markers. In most plants chloroplast genomes are inherited maternally, biparentally in some and paternally in several gymnosperms while mitochondrial genomes are in general inherited maternally (Avise 1994 and references therein). As a consequence of these different modes of inheritance the extent of gene flow for these markers will differ between populations (Birky et al. 1989). A set of molecular markers located in the mitochondrial or chloroplast genome in combination with nuclear markers would show the relative contribution of pollen and seed to the gene flow among populations (Ennos 1994). In addition, the X and Y chromosomes of S. dioica provide an opportunity to further elucidate this gene flow by using paternally inherited markers.

We found that the amount of differentiation among patches within islands was greater than among islands. This contradicts the usual expectation that genetic differences increase with geographic distances (Wright 1978, Slatkin 1993). Frequent seed and pollen dispersal occurs among islands and these will thus receive the same alleles. This may explain the pattern of differentiation that we have observed. In contrast, the patches within islands may be founded by only a few individuals.

We have shown that populations of S. dioica have become significantly differentiated in phenology and morphology but also that patterns of differentiation vary among characters

(Paper II). Plant height, thickness of leaves and number of hair on leaves all differed significantly among habitats (II, Table 4). The short growing form of S. dioica found on serpentine may be explained by a number of factors. Heavy metal content of the soils e.g. nickel can per se inhibit growth (Robertson 1992). The habitat is also dry and exposed and is often deficient of plant nutrients (Brooks 1987). This harsh habitat may also explain that the serpentine form has thicker leaves as a strategy against desiccation. Serpentine and cold spring individuals had less hair than in the other habitats. The genetics underlying this response is, in part, known (Westerbergh and Nyberg 1995). They showed that snails feed

17 preferentially on hairless plants and exert a selective pressure in maintaining hairiness in S.

dioica; on serpentine this selection is relaxed. Likewise, we have not observed any snails in the cold spring area. Aronsson (1999) has considered that the hairless variety smithii is

critically endangered and that dramatic measures should be taken to protect that unique form.

I should question the wisdom of protecting ecotypes.

We found significant differences in floral characters representing flower size and characters important for pollination as well as in the onset of reproduction (II, Table 6). The corolla was shortest in the males growing in the cold spring populations. Westerbergh and

Saura (1995) have shown that isolated populations of S. dioica like these cold spring ones are predominately pollinated by muscid and syrphid flies. The flies are small and sit mostly on the flowers but may penetrate the tube for nectar. Whether this would exert a pressure to reduce the corolla tube length remains untested. The individuals from the cold spring started the flowering two to three weeks later than from the other populations. In this extreme habitat with a mean summer temperature of 7.2 C° (Hoffsten and Malmqvist 2000) this late flowering is likely caused by a cold microclimate.

The rosettes of S. dioica can be divided; one may obtain plants with the same genotype. When these clones are transplanted in different habitats one can get a measure of phenotypic plasticity. Plants are characterized by plasticity. This means that plants have an open way of growing; competitors may regulate this open pattern in a very defined way.

Genetic variation and patterns in riparian corridors

We found that the three plants, B. vivipara, V. alpina and A. archangelica surveyed along the

Vindel River all had sufficiently high genetic diversity to be used in studies concerning dispersal by water (Paper III). This was also the case for the clonal earthworm E. tetraedra

18 that we studied along the Vindel and Ume Rivers (Paper IV). We used the data from these

two papers (III and IV) and data from the literature to test the hypotheses that we had put

forward in paper V.

A. archangelica and E. tetredra have propagules that float well. The former shows an

increased genetic diversity downstream; the latter had high clonal diversity in the headwaters,

lower in the middle reaches and highest at the river mouths. We did not sample

A. archangelica along the whole river; additional sampling should therefore, complement this

study.

The clonal diversity of B. vivipara (with short-floating diaspores) was tied to the type

of riverbank; riparian zones that trap efficiently floating material have high diversity.

Including more sampling sites at these different riverbank types may strengthen our result;

one should also include other species with short-floating diaspores.

We found evidence that riparian populations are more similar to each other than populations in other habitats. This suggests that hydrochory is more efficient than other

modes of dispersal. A plant with a broad ecological niche and wide geographic distribution will be useful in studies concerning dispersal with water along rivers versus dispersal across

other habitats; in other words, dispersal in one dimension versus two dimension.

We found no evidence that lakes act as barriers for propagule dispersal, which was the

case for dams in regulated rivers. Extending our study on plants (Paper III) to include a regulated river would be the next logical step. It was evident that genetic diversity was lower in regulated rivers in comparison with free-flowing rivers (Paper IV, Lascoux et al. 1996,

Durka 1999). One should further extend these studies to include more rivers; both free-

flowing and regulated, one should also include more species.

We have literature on dispersal ability like the studies of Romell (1954); we also have distribution maps of vascular plants (Hultén 1971, Jalas and Suominen 1986, Jonsell (Flora

19 Nordica, in progress)). The latter monograph contains also information on the breeding

system. Dispersal, distribution and breeding structure are important determinants of the future

evolution of the riparian flora. Patterns of genetic diversity may be exhibited at many spatial

scales, e.g. among entire rivers, and between types of riverbanks within a river reach.

Populations must be sampled at a spatial scale relevant to the hypothesis to be tested.

ACKNOWLEDGEMENTS

I thank Anssi Saura for contributing and commenting on this introductory chapter. The work in this thesis was made possible by financial support from the The Swedish Council for

Forestry and Agricultural Sciences (through a grant to Barbara Giles), The Swiss National

Science Foundation (through Grant no. 31-42443.95 to Jerome Goudet), The Swedish Natural

Research Council (through grants to Anssi Saura, Elisabeth Lundqvist and Barbara Giles, respectively), Kempe Foundation (through a grant to Elisabet Andersson) and grants to

Elisabeth Lundqvist from Sven and Lilly Lawskis Foundation for Natural Sciences, Nilsson-

Ehles Foundation, Ruth and Gunnar Björkmans Foundation and Kempe Foundation.

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26 A cknowledgements

Three things I believe I had to learn in this life, that is patience, self-control and the value of a higher academic education (or rather the price of a fancy fishing-hat). I think I have accomplished them all. I quote (freely translated) “The university is a hierarchical, elitist and a patriarchal organisation” (Jansson 2000). A quale loco (pro Nazareth) potest aliquid boni esse? (John 1:46). And yet here one may find wonderful people.

My thesis would never been finished without support and help from others, those I would like to thank here, as well as, those that have made my PhD time pleasant. In order of appearance: My beloved parents. Marianne and Ove you have given me a good base to stand on for coping with life. Without your support I would never, as a single mother, managed to study and finally end up with this thesis. My sister Lotta, with whom I have so much fun but also the one I can share all my problems with. Lotta, now, finally, I will have time to do all the fun we have planned. My grandma, an outstanding wonderful woman that has given me a strong faith and is a proof that there exists true Christians. (Min mormor, en enastående underbar kvinna som har gett mig en sån stark tro till så mycket och är ett bevis att det finns sanna Kristna). Uncle Stig, who still after more than 40 years has his niece like a tail whenever fishing is going on. My brother Tomas, my living doll at the age of eight. With him

I share my big interest, fishing. We have had some memorable fishing tours like when I got a catfish and he didn’t (and when I got a bigger cod, and coalfish, pike, perch ). He is also an excellent person having around whenever one gets lost in an elevator.

Children are not only a measure of reproductive success; they are the joy of life.

Veronica, my oldest and also my personal shrink. Imagine now how much time that I will have available for doing such recreation trips to exotic places like Oulu. Therese, I’m still waiting for you collecting the bet you won. You made the fieldwork very memorable. Kim, my daughter, you most of all know how much this thesis have cost. Hurry now and turn 19 so

27 that we can be that you told. Robin, my youngest, it really warms the heart of the auntie to

have you in the boat swinging big pikes and pearch with your fishing rod.

Nicke, I love when you call me in the middle of the night, you are solid and I am harmonic. Erke I have now built new stairs in my cottage; you dare to visit again. Katarina, that I shared some heavy grinding with; no doubt we got affected by that, at least you fighting with imaginary numbers. Stefan, thanks for persuading me to join the club; the thoughts of my own purple Harley with a log on the petrol tank have kept the spirit up this last year.

Margit, my friend and neighbour, thanks for everything.

Gunnar, you made me feel so welcome as a new PhD student, introduced me to such nice activities like Helmer and Rutger. You always encouraged me, not for mention, taught me useful things like Ingo’s famous combination. I know that you will share my happiness for finally finishing my thesis. Göran, thanks for all the help you have given me during these years. I have really missed your loud happy voice since you left.

Anssi, my supervisor that once inherited me, for good and bad. I am very grateful for your support. I will bring with me many funny and wise expressions that you have taught me

(and not for mention all the English corrections). A number of PhD students have been at the department, I would like to thank them for the fun we have had. The Ancient Ones, Katalin,

Stefan, Anna and Janne; the Old One, Doris, thanks for the support you have given me; the

Young Ones, Anna, Jesper, Markus, Pelle, Sa, Magnus and Malin. Anna, you have made

Monday mornings so more pleasant. Pelle, thanks for all the computer help. Magnus, it was really fun attending a conference with you. Anna, Pelle and Magnus, the three of you really know how to make a party. Sa, you have been such a good friend, it has been really nice sharing the girls’ room with you. Astrid, you were my room mate for so many years, thanks for always being a good friend and all the laboratory help you gave me. Karin, thanks for all the support you have given me and for always had time to listen to whatever problem I have

28 had. Kerstin, thanks for the help you gave me with the molecular work. We also do share the fun interest in cats and club activities. Helena, thanks for keeping track of all kinds of papers.

I thank Gunilla, Åsa, Marianne and Maggan that all have contributed to make this time pleasant.

All the PhD students in the departments of zoology and botany; to mention a few, Åsa,

Åsa, Eva, Jens, Ronny, Ulla, Ann (post doc) Tina, the Bug Queen from my hometown,

Richard, Micke......

The highlight of my PhD time was in Oulu, Finland. Outi, thanks for letting me join your group. Helmi, Meija, Päivi, Mona, Claus, Vladimir, Robert, Rosario, Hannele, Soile and

Nina you all made me feel so welcome. Auli, I guess you will comment my thesis by saying; well done, good on ya, I could see it coming. Sami, my excellent supervisor in the laboratory; thanks for that you introduced me to the cultural life in Oulu, like concert with shouting men, heavy pool playing, culinary restaurants visits, Finnish dancing, hot night clubs, and all the picturesque pubs with delicacies like tar drams.

I thank my mother, grandma and niece Veronica for all the nice drawings. And if I should have forgotten someone in my acknowledgements is not because I have forgot, I just have bad memory.

References

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Thesis, Dept. Ecol. Env. Sci. University of Umeå, Sweden.

God, The, (undated). The Bible - John 1:46.