Breeding System Evolution and Pollination Success in the Wind-Pollinated Herb Plantago Maritima

Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 14

Breeding System Evolution and Pollination Success in the Wind-Pollinated Herb Plantago maritima

EMIL NILSSON

ACTA UNIVERSITATIS UPSALIENSIS ISSN 1651-6214 UPPSALA ISBN 91-554-6153-0 2005 urn:nbn:se:uu:diva-4790 ! " #$ %&&' #&(&& " )" "* +" , - "*

. -* %&&'* / - ) " 0 1) 2 * * #3* 3& * * 4 /. $#1''315#'61&

4 " " 4 " " , 1 " * 0 " " 4 7 8 7 ,"" " " 8 78 78 1 78 , " " " - * 4 #&3 4 7 &19&: 5*6: 8* , ; " " , " <* , " ; , <* +" " " " " " " " * " , " , " " , " " " , ," 1 , * 4 , "" , 1 " " " , ," " , " 1 * +" , , " " " 1 " 1 * 4 ; " , " , , " * +" , , " , ,"" " " < ; 1 < *

! / 1 1 , 1

" # $ " " $ " $ % &'$ $ "()*+,- $

= - . %&&'

4 . #5'#15%#3 4 /. $#1''315#'61& ( ((( 139$& 7" (>> * *> ? @ ( ((( 139$&8

! " # $ % & '

! ( ) " # * % + , + ! & '

! - . " # + + + & '

. ! / & '

. ! ( ) 0% 1 & '

Contents

Introduction...... 7 The evolution of plant breeding systems...... 8 Wind pollination...... 9 The cost of sex...... 10 The evolution of self-fertility ...... 11 Gynodioecy ...... 12 Breeding system variation in Plantago ...... 13 Aims of this thesis...... 15 Material and Methods ...... 16 Study species...... 16 Study areas ...... 18 Field estimates, fruit and seed production (I, II, III)...... 19 Plant material and controlled crosses (II, IV)...... 20 Molecular markers (V) ...... 20 Cytological investigation...... 20 Results and discussion ...... 22 Proportion of females (I)...... 22 Self-fertility (II) ...... 23 Cytology...... 24 Density dependent seed output (III) ...... 24 Genetic diversity (IV) ...... 25 General discussion ...... 26 Conclusions...... 28 Acknowledgements...... 29 Fyra män i brudkammaren och ensamma kvinnor komplicerar gulkämparnas kärleksliv ...... 30 References...... 33

Introduction

Most flowering plants are sessile organisms, destined to live wherever the seeds germinated. Being sessile is a major drawback when it comes to sex. While most free moving organisms seek out their mate prior to mating, plants require a means of transferring male gametes (pollen) between mates. Many plants accomplish this by attracting insects and manipulating their behaviour so that they will transport pollen between plants of the same species (e.g., Darwin, 1877a; Nilsson, 1998; Pellmyr, 2003). However, this plant–insect relationship is not entirely flawless. First, potential insect pollinators are not present in all plant habitats (Proctor et al., 1996), and are not entirely reliable pollen vectors in the habitats where they do occur (Kalisz et al., 2004). Second, animal pollen vectors can carry diseases capable of de- stroying the reproductive function of stricken plants (Carlsson and Elmqvist, 1992; Marr, 1997). Third, cues that attract pollinators might also attract plant herbivores (Mutikainen and Delph, 1996; Ehrlén et al. 2002). To avoid these problems, some plants rely on wind or water to transport their pollen between mates (Whitehead, 1983; Goodwillie, 1999), others are highly self- fertilizing (Jain, 1976; Hoffmann et al., 2003), and some have given up sex more or less entirely (van Dijk, 2003). However, even though asexual reproduction (Berg & Redbo-Torstensson, 1998) or self-fertilization (Kalisz et al., 2004) could provide a means of securing reproduction, most plants are adapted to increase the proportion of pollen reaching other plants, and to receive pollen from other plants (Barrett, 2002). About 70 percent of all flowering plant species are co-sexual with only hermaphrodite flowers, i.e. flowers containing both male (stamen) and female (pistil) sexual function (Yampolsky and Yampolsky, 1922). Because of the large number of pollen grains produced by single individuals, matings can potentially occur with many individuals, including the plant, and even the flower, where the pollen originates (Barrett and Harder, 1996; Barrett, 2002). Self-fertilization, however, is commonly costly for the plant as it may generate less fit offspring compared to cross-pollinated progeny (e.g., Ågren and Schemske, 1993; Husband and Schemske, 1996; Koelewijn, 2004). In fact, the separation of male and female function, whether within the same flower, within individuals, or among individuals, is a strategy believed to maximize the number of cross-fertilized progeny (Barrett, 2002). Moreover, some plants have a self-incompatibility system whereby self-pollen is recognized and rejected (Franklin-Tong and Franklin, 2003). Thus, reducing self-

7 fertilization, and maximizing cross-fertilization, reduces the risk of inbreeding depression. Furthermore, this creates high gene flow within populations, which enables outcrossing populations to maintain a high genetic diversity. This could increase the possibility for an adaptive response to changes in the biotic or abiotic environment (Falconer and Mackay, 1996; Fowler and Whitlock, 1999). Despite these benefits of outcrossing, the transition from self-incompatibility to self-fertility is a common evolutionary shift in plant mating system (Roalson and McCubbin, 2003). This makes flowering plants a suitable study system of the evolutionary significance and maintenance of sex, a highly controversial and unresolved issue in evolutionary biology.

The evolution of plant breeding systems

The earliest fossil evidence of angiosperms (flowering plants) has been dated to early Cretaceous, 125 – 115 million years before present (Friis et al., 2001). The flowers of early angiosperms were most likely hermaphroditic (Friis et al., 1999) and pollinated by insects (Friis et al., 1999; Pellmyr, 1992; Ren, 1998), but their flowers contained no nectar (Crepet et al., 1991). Instead pollen served as food for the pollinators and leftover pollen was transported between plants as the insect pollinator foraged among the flowers. Because of the negative effects associated with self-fertilization, the evolution of self-incompatibility was a major breakthrough in the history of angiosperm plants. It has been suggested that self-incompatibility evolved early in angiosperm history (Zavada, 1984), and indeed the occurrence of a gametophytic incompatibility system among several groups of eudicots (e.g., Solanaceae, Rosaceae, Scrophulariaceae and Plantaginaceae) suggests an ancient origin of self-incompatibility (Igic and Kohn, 2001). Self- incompatibility opens up for more promiscuous pollination strategies, such as wind pollination. A high number of pollen is commonly produced by wind-pollinated species (Ackerman, 2000). The high probability of self- fertilization in such species could be prevented by the rejection of self-pollen with a self-incompatibility system or a temporal or spatial separation of sex function (Culley et al., 2002). Gender dimorphism, i.e. when not all members of a population are hermaphrodite (Richards, 1997), is an interesting aspect of plant breeding systems. The sexual function of plants can be expressed as male and female on separate individuals (i.e. dioecy), as female and hermaphrodite individuals (gynodioecy) or as the unusual male and hermaphrodite individuals (androdioecy). Furthermore, the proportion of male and female flowers can vary within individuals. Approximately 19 percent of known species exhibit some kind of gender dimorphism (Yamplosky and Yampolsky, 1922); this in-

8 cludes a wide variety of gender strategies that involve various combinations of female, male and hermaphroditic flowers at the plant or population level (Barrett, 2002). The invasion of female plants into originally hermaphrodite populations is a common evolutionary pathway to more complex dimor- phisms (Charlesworth and Charlesworth, 1978). An important process in the evolution of plants is polyploidization, i.e. the multiplication of entire chromosomal complements (Ramsey and Schem- ske, 2002; Popp, 2004). Between 47 and 70 percent of flowering plants have been estimated to be descendants of polyploid ancestors (Masterson, 1994). Polyploidy creates a reproductive barrier between the plant with raised ploidy level and its progenitors, but can also have implications for breeding system evolution. First, it is thought to be common that self-incompatibility is lost following a polyploidization event (e.g., Entani et al., 1999; Miller and Vernable, 2000, but see Brunet and Liston, 2001; Mable, 2004). Second, polyploidy has been proposed to promote the evolution of gender dimorphism (Pannell et al., 2004). However, self-fertility, and gender dimorphism, can evolve without a change in ploidy level (Wallander, 2001; Dorken et al., 2002; Kondo et al., 2002; Tsukamoto et al., 2003; Busch, 2004; Thorogood et al., 2004).

Wind pollination

Wind pollination has evolved in numerous lineages of angiosperm plants, and it is found in about 18 percent of angiosperm families today (Ackerman, 2000). It is both ecologically and economically important; many the domi- nant plants of the boreal forest, savanna and temperate grasslands are pollinated by wind (Kellogg, 2001; Shantz, 1954). However, biologists have largely overlooked wind-pollination, possibly because of the aesthetic en- ticement of showy, animal pollinated plants (Barrett, 2002). The evolution of wind pollination could be favoured if animal pollinators are absent (Weller et al., 1990; Cox, 1991), spatially or temporally unreliable (Goodwillie, 1999), or if there is competition among plant species for pollinators. Wind-pollination may allow the maintenance of high levels of cross- pollination in pollinator poor environment (e.g., Dow and Ashley, 1996). Consistent with this view, wind pollination is a common pollination system in habitats where potential insect pollinators are sparse, such as grasslands, savanna, and salt-marshes (Proctor et al., 1996). Pollen from wind-pollinated plants has been found to travel tremendous distances. Tormo-Molina et al. (2001) recorded substantial airborne Plan- tago pollen concentrations several kilometres from the nearest population, and van deer Knaap (1987) recorded pollen deposition of e.g. Plantago lanceolata and P. maritima in peat on the artic islands Spitsbergen and Jan

9 Mayen, more than 500 km from nearest pollen source. This has led to the common assumption that pollen limitation of seed production is unlikely in such plants (e.g., Faegri and van der Pijl, 1966). Yet empirical estimates of successful pollen transfer are much shorter (e.g., Bos et al., 1986). White- head (1983) suggested that wind pollination is most efficient in large and dense populations, and the limited empirical evidence at hand supports this hypothesis. For example, pollen limitation has been established in one population of Plantago maritima (Dinnétz, 1997) and in areas where the clonal grass Spartina alterniflora occurs at low density (Davis et al., 2004). Thus, wind-pollinated plants might be independent of animal pollinators, but could still be pollen limited if interplant distances becomes large. This could happen during colonization, and could be an important selective agent in the evolution of mating systems in wind-pollinated plants. If self- incompatibility is lost, imprecise pollen transfer in wind-pollinated plants could generate high selfing rates. The highly bimodal distribution of outcrossing rates, with a deficit of mixed mating, could be a response to selection for either of two major mating strategies in wind-pollinated species (Vogler and Kalisz, 2001).

The cost of sex

Despite the common occurrence of sexual reproduction, evolutionary biology has so far failed to thoroughly explain its maintenance (e.g., Agrawal, 2001). Sexual reproduction occurs in a wide range of organisms, from the sharing of genetic material in bacteria, to the complex lifecycle of higher organisms with haploid-diploid generations and recombination during meio- sis. Among flowering plants, the evolution of self-fertile taxa from self- incompatible progenitors (Schoen et al., 1996; Sharma et al., 1992; Stebbins, 1970), asexual strains from sexual ancestors (van Dijk, 2003), and the evolution of dioecy in self-fertile groups (Miller and Vernable, 2000), suggests that the advantage, or cost, of sexual reproduction is spatially and temporally variable. Traditionally the cost of sex has been assessed using arguments about the reproductive contribution to future generations (i.e. fitness). First, there is a two-fold transmission advantage of the selfer. While an outcrossing individual only transmits half of its genes to its offspring, a selfer transmits all of its genes (Maynard Smith, 1978). Second, an obligate cross-fertilized plant faces the risk of not receiving enough pollen, independent of the resource status of the plant (Ashman et al., 2004). Pollen limitation is a common phe- nomenon in plant populations (Burd, 1994) and is most frequent in self- incompatible species (Larson and Barrett, 2000), suggesting that a shift in

10 mating system, from self-incompatibility to self-compatibility, can be partly driven by pollen limitation (Ashman et al., 2004). The rarity of organisms showing an ancient asexual origin (Judson and Normark, 1996) suggests that sexual reproduction is advantageous for most organisms. It is commonly believed that recombination allows for new com- bination of alleles to be presented in different individuals, and that these individuals will vary in fitness because of new beneficial allele combinations or the accumulation of deleterious mutations (Archetti, 2003). However, it has proven difficult to provide an experimental set up where these hypothe- ses can be tested. But because of the lower rate of recombination in self- fertilizing populations (Hagenblad and Nordborg, 2002), selfing populations of otherwise outcrossing plant species could provide the appropriate frame- work for approaching these problems.

The evolution of self-fertility

Self-incompatibility is a genetic mechanism in flowering plants that prevents self-fertilizations by rejecting pollen from genetically related individuals (Vieira and Charlesworth, 2002). It is a common mechanism, described in 91 out of 275 families of angiosperms (Haring et al., 1990). Despite the general success of self-incompatibility, the shift to self-fertility is common in the history of flowering plants (Stebbins, 1957, 1970; Schoen et al., 1997; Ta- lavera et al., 2001). Self-incompatibility is considered most likely to be lost in situations where pollen limitation is significant, such as during colonization, in isolated populations or at the range margin of a species’ distribution (Baker 1955; 1967; Jarne and Charlesworth, 1992; Pannell, 1997; Pannell and Barrett, 1998). The reproductive assurance provided by self-fertilization is considered the ecological driver promoting self-fertility genes to spread in a population (e.g., Cheptou, 2004). The strength of this selection is deter- mined by the magnitude of inbreeding depression and pollen limitation (Lloyd 1979; Lande and Schemske, 1985; Stebbins, 1957). A shift in life history strategy towards a more short-lived habit both lowers the cost of present reproduction on future reproduction, and could reduce the expression of late-acting inbreeding depression (Charlesworth, 1989; Morgan et al., 1997). Furthermore, while inbreeding depression commonly is treated as a constant, recent empirical evidence suggests that biotic conditions, such as the frequency and density of outcrossed conspecific plants, is of importance for the expression of inbreeding depression (e.g., Koelewijn, 1998; Cheptou et al., 2001; Cheptou and Schoen, 2003; Koelewijn, 2004). Self-fertility might be more likely to evolve under conditions where intraspecific competition is relaxed, pollen limitation severe, such as during the range expansion of a species. The inbreeding depression may be reduced in such situations,

11 and could be lowered further by several generations of low population sizes (Barrett, 1988). Once self-fertility has evolved, consequent purging of deleterious mutations can reduce the inbreeding depression among self-fertilizing lines (Crnokrak and Barrett, 2002; Lande and Schemske, 1985, see Byers and Waller, 1999 for review). Populations can become genetically depleted after periods of high selfing rates. This led Stebbins (1957) among others (e.g., Cheptou, 2004) to suggest that selfing could be an evolutionary dead end. However, as of yet, there is no thorough empirical evidence supporting this notion (Takebayashi and Morrell, 2001). Nevertheless, selfing reduces the genetic diversity within populations, and reduces the effective frequency of recombination throughout the genome (Charlesworth, 2003; Hagenblad and Nordborg, 2002; Nordborg, 2000). The evolutionary consequences of these processes are yet to be thoroughly examined. Re-evolution of self-incompatibility once self-fertility is obtained is unlikely because the re-activation of functional self-incompatibility requires more independent mutations than when it was lost (Charlesworth and Charlesworth, 1998; Takebayashi and Morell, 2001; Nasrallah et al., 2004). Self-incompatibility can be lost due to one or very few mutational events, but re-activation of self-incompatibility is much more complex (e.g., Nasral- lah et al., 2004). This is because once stabilising selection stops acting on the genes regulating self-incompatibility, secondary mutations can accumulate in these genes.

Gynodioecy

Gynodioecy i.e. the co-occurrence of females and hermaphrodites in the same population (Darwin, 1877a), is a common gender dimorphism in flowering plants. It occurs in about seven percent of angiosperm species (Yam- polsky and Yampolsky, 1922). A major question in the attempts to explain this breeding system has been whether the genetic factors maintaining this gender dimorphism are long lived, or if they are short lived and re-evolve frequently, similar to a host-pathogen system (Charlesworth, 2002). The female (i.e. male sterile) phenotype is commonly govenered by cytoplasmi- cally inherited genes, whereas specific nuclear genes can restore male fertility (Couvet et al., 1986; Kaul, 1988; Frank, 1989; Charlesworth and Laporte, 1998). Females are normally in the minority in gynodioecious species, but the proportion of females varies greatly due to the complex dynamics of the nuclear-cytoplasmatic sex determination system (e.g., Gouyon et al., 1991; Couvet et al., 1998; Bailey et al., 2003; Jacobs and Wade, 2003; Ronce and Olivieri, 2004). The theoretical models at hand for explaining the co- existence of females and hermaphrodites consider both sexual differences in

12 female fertility and the pattern of female inheritance (e.g., Lewis, 1941; De- lanny et al., 1981; Gouyon et al., 1991; Bailey et al., 2003; Jacobs and Wade, 2003). Stochastic processes and founder events can increase the overall frequency of females in gynodioecious populations. First, a lack of restorer genes in young populations may create a purely cytoplasmic inheritance of females. In such a situation, the proportion of females should increase until pollen limitation prevents any further increase in frequency (McCauley et al., 2000). Second, a mismatch between cytoplasm and restorer genes may allow for cytoplasmic inheritance of sex until the invasion of matching restorer genes, and a consequent reduction in the proportion of females (Cou- vet et al., 1986; Couvet et al., 1998; Ronce and Olivieri, 2004). However, stochastic processes and founder events could also increase the probability that females are missing altogether from a local population. Thus the evolution of nuclear-cytoplasmic gynodioecy can resemble an epidemic disease, where new male sterilizing mutants constantly sweep trough populations followed by their corresponding restorer genes (Ingvarsson and Taylor, 2002). Theoretical models predict that the maintenance of females requires a female fecundity advantage over hermaphrodites, and this has been found in most gynodioecious species (reviewed in Gouyon and Couvet, 1987). This female fecundity advantage can have two components: the reallocation of resources due to the lack of male function (Darwin, 1877a) and the higher outcrossing rate in females (Charlesworth and Charlesworth, 1978). The higher fecundity of females in self-incompatible species, such as Plantago lanceolata (van Damme 1984; van Damme and van Delden 1984), suggests that reallocation could be important for the maintenance of females. The outcrossing advantage of females, as compared to hermaphrodites where self-fertilized offspring could suffer from inbreeding depression, has been emphasized in several models of nuclear-cytoplasmic gynodioecy (e.g., Charlesworth and Charlesworth, 1978; Sakai et al., 1997). A higher female outcrossing rate, and a higher female germination rate, has been observed in Schiedea salicaria (Weller and Sakai, 2004). In contrast, inbreeding depression among hermaphrodites cannot on its own explain the female fecundity advantage in Thymus vulgaris (Thompson and Tarayre, 2000).

Breeding system variation in Plantago

A vast diversity of sexual strategies is displayed in flowering plants, and considerable amount of variation can be found within the genus Plantago (Fig. 1). The genus is, however, less diverse in terms of in pollination strategies. All species are either mostly wind pollinated, or produce cleistogamous

13 (closed) flowers (Primack, 1978; Sharma et al., 1992). The genus belongs to the family Plantaginaceae (Hoggard et al., 2003; Rønsted et al., 2002), the phylogeny of which was recently widened to include several taxa from the former Scrophulariaceae, such as Antirrhinum, Digitalis and Veronica (Olmstead et al., 2001; Albach et al., 2005). Interestingly, these newly in- cluded taxa exhibit characters highly adapted to insect pollination (e.g., Parachnowitsch and Elle, 2004), indicating that the genus Plantago originates from insect pollinated progenitors. Furthermore, even though apparently adapted to wind pollination, insect pollination has been reported in Plantago. For example, P. media is frequently visited by potential pollinators (Proctor et al., 1996), and Stelleman (1978) found syrphid fly visits to account for some seed set in P. lanceolata. Plantago has been estimated to be approximately 6 million years old, which suggests a rapid recent radiation and successful worldwide colonisation (Rønsted et al., 2002). Gynodioecy is a common sexual system in the genus Plantago and occurs in at least seven of 36 European species (van Damme, 1985). Interestingly, unlike gynodioecious species in many other families, gynodioecy co-occurs with self-incompatibility in many species of Plantago (Fig. 1).

Figure 1. The incidence of self-incompatibility and gynodioecy in some European Plantago species (van Damme 1985) and their phylogenetic interrelationship (Røn- sted et al. 2002).

14 Aims of this thesis

The general objective of this thesis was to explore the evolution and maintenance of gynodioecy and self-incompatibility in natural populations of Plan- tago maritima. I approached this problem by combining estimates of seed production from natural populations with controlled crosses and analysis of genetic variation inferred from molecular markers.

More specifically, I address the following questions:

x Is the proportion of females in gynodioecious populations higher in small populations? (I) x Can differences in population size and relative female fitness of hermaphrodites and females together explain variation in the proportion of females among populations? (I) x Are there self-compatible populations of Plantago maritima close to the northern range margin, and if so, how does self-compatibility affect the outcrossing rate? (II, V) x Are self-fertile populations polyploid? x Is seed output density-dependent in self-incompatible populations, and density independent in self-compatible populations of Plantago maritima? (III) x Is the within-population genetic diversity lower, and the among population diversity higher, in self-compatible than in self- incompatible populations? (IV, V)

15 Material and Methods

Study species

Plantago maritima L. (Plantaginaceae) in the wide sense has a broad distribution in the northern hemisphere (Hultén and Fries, 1986). However the taxonomy is somewhat confused (Ross, 1970). The North American variants are commonly placed in the subspecies californica (Hultén and Fries, 1986) or juncoides (Ross, 1970). The subspecies juncoides is said to inhabit Green- land, Iceland and even the artic coast of Norway and western Russia (Hultén and Fries, 1986), although the taxonomic status of the Norwegian and Rus- sian plants is unclear (Tutin et al., 1976). Gregor (1939) found North Ameri- can variants to be self-compatible and hermaphroditic, unlike the self- incompatible and gynodioecious European plants. Several morphologically different varieties occur in Europe, but their systematic status is not investigated (Tutin et al., 1976; Pignatti, 1982). Both subspecies serpentina, which grows in mountains areas, and P. alpina have been given species status (Tutin et al., 1976). The common chromosome number for all varieties is 2n = 12 (Tutin et al., 1976), but Gregor (1939) reported tetraploid (2n = 24) as well as diploid (2n = 12) populations of P. alpina. Even though there is a great deal of taxonomical confusion within this species and between its close relatives, the plants used in this study belong to the nominal subspecies maritima as described by Linnaeus (1755). Plantago maritima was chosen as the study species of this thesis mainly because of its gynodioecious breeding system (Ross, 1970). However, the species has other convenient features for studies of reproductive biology. It is salt tolerant (Staal et al., 1991) and is consequently common in marine habitats throughout Europe (Tutin et al., 1976). In Sweden, the species is common along the coastline, and inhabits many of the islands in the archipelagos of eastern Sweden and southwestern Finland, but becomes less frequent in the northern part of the country (Hultén, 1971). Individual rosettes are easily distinguished and vegetative propagation is rare (Dinnétz and Jer- ling, 1997). Furthermore, the seeds are easy to germinate if they are given plenty of light (Jerling, 1982).

16 Figure 2. The (A) hermaphrodite and (B) female inflorescences of two Plantago maritima plants from the Gryt archipelago in southern Sweden.

The species is predominantly self-incompatible in Europe (Ross, 1970; Dinnétz, 1996) but I have observed seed set following self-pollination in pilot studies of plants from northern Sweden and northernmost Norway. Self-incompatibility in P. maritima is likely to be a single-locus gametophytic system, similar to that of P. lanceolata (Ross, 1973). The flowers of P. maritima are arranged in a dense racemose inflorescence (Fig. 2). A single plant can produce from one up to more than a hun- dred inflorescences during one season (pers. obs.). The hermaphrodite flower possesses a long style with a hairy stigma during female phase, and four stamens with bright yellow anthers during male phase (Fig. 3). The conscious anthers can attract syrphid flies (pers. obs.) Female flowers have shorter filaments and thin brown anthers, and the morphology of female types is highly variable even though some distinct types can be recognized (Dinnétz, 1988). Typically, the stigma is longer and erect for a longer period in female flowers as compared to hermaphrodite flowers (Dinnétz, 1996).

17 A. B.

Figure 3. A detailed study of (A) a single hermaphrodite and (B) female Plantago maritima flower from the plants in Fig. 2. The hermaphrodite is in male phase, with erect anthers and a withered pistil. The female flower (B) has a large feathery pistil and rudimentary stamens by the base of the pistil.

The species is protogynous, i.e. the pistil matures before the anthers on the stamen are ripe, but the degree of protogyny is highly variable. Within a individual, the temporal separation between female and male function can vary from one to 10 days (Dinnétz, 1997). However, the variation in temporal separation of sexual function in individual flowers has not been investigated. The flowering time is highly variable among regions, with a more extended flowering time in southern plants. I have observed differences in flowering time both in the field and in plants growing in the greenhouse.

Study areas

I used seeds or plants originating from Plantago maritima populations in archipelagos on the east cost of Sweden (Gryt, Öregrund and Skeppsvik) and southwestern Finland (Korpoo; Fig. 4), except for (V) where plant material originates from Longhoughton, United Kingdom. The northern Skeppsvik archipelago is situated 880 km north of the southernmost Gryt archipelago, and is subjected to an isostatic land-uplift of about 8 mm per year. In Skeppsvik, the age of the investigated islands range from 46 to 700 years (Carlsson et al., 1990). In contrast, the land uplift is about 2 mm per year in the southern Gryt archipelago. The islands are much higher in Gryt, and the estimated age of the younger islands does not fall below 1600 years (Nils- son, 1999). The salinity of the seawater declines towards the north, with

18 brackish waters in the Gryt archipelago (~ 7‰), but virtually fresh water in the northern Skeppsvik archipelago (~ 4 ‰; Snoeijs, 1999).

Figure 4. The location of the Gryt (I, II, III, IV), Korpoo (I, IV), Öregrund (I, II, IV) and Skeppsvik (I, II, III, IV) archipelagos in Sweden and Finland.

Field estimates, fruit and seed production (I, II, III)

For each study population, I estimated the proportion of females by deter- mining the sex of 200 plants, or all plants if the population consisted of fewer than 200 flowering individuals. Plants with partially reduced male function were pooled with the hermaphrodite plants when the proportion of females was calculated. Population size was estimated as number of flowering plants. In this thesis, a population was defined as all plants on an island, or a group of plants separated by more than 50 meters to the next plants. Fruit and seed set were estimated in 30 plants per sex morph (I) or in 20 - 30 hermaphrodites (III) for each population. Plants were scored for number of inflorescences and distance to nearest pollen donor. Three inflorescences, or all inflorescences if fewer than three, were collected and stored at 4 ºC until further analysis. I estimated seed production by counting the number of flowers and fruits on each plant, counted seeds from ten ripe fruits weighed the seeds.

19 Plant material and controlled crosses (II, IV)

I germinated seeds under artificial light to obtain adult reproducing plants, for the self-compatibility experiment (II), and fresh plant material for DNA extraction (II, IV). The germination frequencies were overall high and most seeds germinated within two weeks. I cultivated plants from one population from the Gryt archipelago, and one population from the Skeppsvik archipelago, in pots filled with a commercial soil mixture (P-jord, Weibulls, Ham- menhög, Sweden). On each plant, one inflorescence was pollinated with self- pollen only, and one inflorescence received additional cross pollen from another plant of the same population. To avoid pollen contamination, each inflorescence was isolated in a transparent cellophane bag prior to, and during, treatment. The bag was removed once flowering stopped.

Molecular markers (V)

I developed five polymorphic microsatellite markers, following a modified protocol of Edwards et al. (1996), for Plantago maritima (V). This provided a valuable tool for assessing the variation in the mating system between populations (II) and the population genetic structure (IV). Microsatellite loci, i.e. fragments of DNA that vary in the number a simple DNA sequence is repeated, are often highly polymorphic and relatively easy to survey (Slat- kin, 1995). As markers, they are considered neutral and follow Mendelian inheritance (Jarne and Lagoda, 1996). In fact, microsatellites studies proved to be essential for the articles (II) and (VI) in this thesis. Several allozyme marker systems showed no variation in a population from the northern Skeppsvik archipelago. However, the allozyme systems 6PGD, IDH, PGI, PGM and GOT displayed polymorphisms in plants originating from the southern Gryt archipelago (E. Nilsson and P. J. van Dijk, unpublished results).

Cytological investigation

I used two methods to assess the chromosome number in plant material from Sweden, Spain, Portugal, USA (California) and Norway. The ploidy level of the plants was first estimated by measuring the nuclear DNA amount with a UV flow cytometer following the protocol described in Tas and van Dijk (1999). The nuclear DNA amount was corrected against Taraxacum plants of known ploidy level. Flow cytometry estimates are highly correlated to chromosome counts (Tas and van Dijk, 1999).

20 Second, chromosome numbers in cell extracts from root tips were counted manually. For chromosome counts, seeds from 10 different populations were germinated on moist filter paper. Two seedlings from each motherplant were pre-treated with 10 – 20 ml of 0.002 M 8-hydroxyquinoline for 4 – 5 hours at 4 – 5 ºC, and then fixed in vials half full with 1:3 acetic acid and ethanol (70%) for 24 hours. The seedlings were then hydrolysed in test tubes with 1M HCl for 8 – 10 minutes in a water bath of 60 ºC. Subsequently, the seedlings were cleaned with distilled water and dried on clean paper tissue. When dry, seedlings were transferred to a vial and stained in lacto-aceto-orcein for 4 – 5 hours at 20 ºC in darkness. The root tip was transferred to an objective glass where a drop of acid was added and the non-stained part of the root removed. An analysing glass was placed on the tissue and the root was squashed by gently pressing the glass with a toothpick. Finally, the numbers of chromosomes in cells undergoing the appropriate stage of mitosis were counted under a microscope.

21 Results and discussion

Proportion of females (I)

As expected under nuclear-cytoplasmic inheritance of gynodioecy, the proportion of females in populations of Plantago maritima was highly variable (I), as would be expected under the nuclear-cytoplasmic inheritance of gynodioecy. Females were more frequently missing from small populations, and the variance in sex ratio decreased with increasing population size. There was also a decrease in female frequency with increasing population size. This is consistent with the idea that a mismatch between cytoplasmic male-sterility genes and restorers may be particularly likely in small and young populations (Belhassen et al., 1991; Manicacci et al., 1996; Couvet et al., 1998; Ronce and Olivieri, 2004). The proportion of females was highest in the northernmost Skeppsvik archipelago and lowest in the southernmost Gryt archipelago (I). The proportion of females increased with the relative female fecundity, and decreased with increasing population size (Fig. 5). It thus seems plausi- ble that both selection and stochastic processes govern sex ratios in Plantago maritima. Surprisingly, ecological processes, such as pollen limitation, have received relatively little attention in both the theoretical modelling and in empirical investigations of gynodioecious species (But see Ashman, 2002, 2003; Asikainen and Mutikainen, 2003). Furthermore, the general female fecundity advantage reported in the literature is commonly estimated from greenhouse grown plants. It cannot be assumed that females would gain a similar advantage in natural populations, where pollen limitation (e.g., Ash- man, 2004) and sex-biased herbivory (Mutikatinen and Delph, 1996; Ågren et al., 1999; Ashman, 2003) could be present. Moreover, characters of reproductive success, rather than estimates of total reproductive success, have commonly been used as evidence for a female fecundity advantage, and there may be trade-offs among components of reproductive success.

22 A. B.

t = 4.81 0.15 t = -5.71 0.10 p < 0.001 0.10 p < 0.001 0.05 0.05 0.00 0.00 -0.05 -0.05 -0.10 -0.10 -0.15 Proportion of females Proportion of females Proportion -0.6 -0.2 0.2 0.4 0.6 -0.4 -0.2 0.0 0.2 0.4

Relative female fecundity Population size

Figure 5. The relationship between proportion of females, relative female fecundity 2 and population size (F2,9 = 16.8, P < 0.001, R = 0.79) among 12 populations of Plantago maritima as described by added variable plot. The plots depict (A) the relationship between proportion of females and relative female fecundity when variation in population size is accounted for, and (B) the relationship between proportion of females and population size when female frequency is accounted for.

Self-fertility (II)

Controlled crosses and genetic analysis of progeny arrays demonstrated that the Skeppsvik population of P. maritima was self-compatible and mixed- mating, while the south Swedish population was self-incompatible and predominantly outcrossing (II). Gregor (1939) has previously described North American populations as self-compatible, but this is the first evidence of self-fertile P. maritima from Europe. Gametophytic self-incompatibility is likely to be ancestral in eudicots (Igic and Kohn, 2001), and it has been shown that there is a substantial sequence homology between the Rosaceae, Solanaceae, Scrophulariaceae and Plantaginaceae (Vieira and Charlesworth, 2002). The self-incompatibility system in P. maritima is most probably gametophytic as in P. lanceolata (Ross, 1973). Thus, it is likely that similar processes are responsible for the breakdown of self-incompatibility in Plantago maritima. The breakdown of gametophytic self-incompatibility has been thoroughly investigated in the genera Lycopersicon (Kondo et al., 2003) and Petunia (Tsukamoto et al., 2003) of the Solanaceae In both Lycopersicon and Petu-

23 nia, an enzyme in the style recognizes self-pollen and rejects it. In the self- compatible Petunia axillaris ssp. axillaris from Uruguay, a modifier locus suppresses the expression of this enzyme, and thus allows self-fertilization (Tsukamoto et al., 2003). The expression of the self-incompatibility enzyme is also suppressed in self-compatible Lycopersicon, but in this species the gene transcribing the enzyme as been altered (Kondo et al., 2003).

Cytology

With one exception, the cytological studies did not indicate any deviation from the basic chromosome number 2n = 12. Spanish plants from the island of Mallorca appeared to have 2n = 20 from the flow cytometry; no visual chromosome count was preformed with this material. As this would be a deviation from a simple duplication, further investigations are required with visual confirmation of this somewhat odd chromosome number (cf. Dart et al., 2004). The chromosome number of 2n = 12 was visually confirmed for plant material from northern Norway, Sweden and Finland. Consequently, it is most probable that the plant material used in this thesis is diploid (2n = 12).

Density dependent seed output (III)

The self-incompatible populations of Plantago maritima in the Gryt archipelago displayed a dramatic decrease in seed output with distance to nearest pollen donor (III; Fig. 6). The rapid decline in seed output with distance in the Gryt populations suggests that the pollen dispersal distance is short. In contrast, seed output did not decrease with increasing distance to nearest pollen donor in the Skeppsvik archipelago, suggesting that self- fertilization provides reproductive assurance in the absence of outcrossed pollen. This suggests that hermaphrodites in the self-compatible populations may have an advantage over females during colonisation of empty habitats, as previously suggested in the theoretical models of Pannell (1997). How- ever, the high frequency of females among populations in the Skeppsvik archipelago suggests that females have some advantage over hermaphrodites, possibly by being fully outcrossed.

24 Gryt Skeppsvik y = 1.54 – 0.54 log(x) 1.2 P < 0.001, R2 = 0.62 1.2

0.8 0.8

0.4 0.4 Fruits per flower Fruits per flower 0.0 0.0 1 10 100 1000 1 10 100 1000 Mean distance to pollen donor (cm) Mean distance to pollen donor (cm)

Figure 6. The relationship between fruits per flower (arcsine square-root trans- formed) and mean distance to nearest pollen donor in Plantago maritima populations from the Gryt (N = 21) and the Skeppsvik (N = 20) archipelagos.

Genetic diversity (IV)

The genetic diversity was high in populations of Plantago maritima in southern Sweden (IV), but decreased towards the north. The northern Skeppsvik archipelago had the lowest observed heterozygosity and no pri- vate alleles. The low level of genetic diversity among and within the northern populations suggest that they have had a history of small population sizes, where periods of extensive selfing could have further reduced genetic diversity. However, only one population from the Skeppsvik archipelago have a significant deviation from Hardy-Weinberg equilibrium due to an excess of homozygotes. This suggests that most individuals are the results of outcross- ings in these populations, despite their ability to self-fertilize.

25 General discussion

I have demonstrated the occurrence of self-fertility in north Swedish populations of the otherwise predominantly outcrossing Plantago maritima. The self-fertilizing ability of these populations apparently facilitates density- independent seed production. In contrast, seed production in populations from the south Swedish Gryt archipelago showed a markedly positive density dependence. Furthermore, southern populations had a higher genetic diversity than the northern populations. The colonizing ability of self-fertile plants (Pannell and Barrett, 1998) could have accelerated the northward post-glacial expansion, but at the same time contributed to the loss of genetic diversity by the joint action of founding events and self-fertilization (Ing- varsson, 2002). Interestingly, the proportion of females in populations tends to increase towards the north and is highest in the northern Skeppsvik archipelago. The importance of self-fertility, and inbreeding depression among selfed progeny, for the maintenance of females in gynodioecious populations has been under debate (e.g., Charlesworth and Charlesworth, 1978; Gouyon et al., 1991). The joint occurrence of both self-incompatible and self-compatible gynodioecious populations of Plantago maritima makes it an interesting species for the evolution of this breeding system. The higher incidence of females among populations in the northern Skeppsvik archipelago suggests that the female reproductive succes of females relative hermaphrodites may be higher in self-compatible than in self-incompatible populations. At the same time, the occurrence of females in the southernmost Gryt archipelago demonstrates that self-fertility in hermaphrodites is by no means imperative for the evolution of gynodioecy. Theory predicts that mixed-mating, i.e. both self- and cross-fertilisations, can be adaptive if it provides reproductive assurance (Lloyd, 1992; but see Cheptou, 2004). However, inbreeding depression among selfed progeny can not be severe, and self-fertilizations should not hinder outcrossing for mixed- mating to provide reproductive assurance (Lloyd, 1992). Further studies are required to assess the amount of inbreeding depression experienced by selfed progeny in natural populations. The evolution of breeding systems is a process that alters the very funda- ment of evolution by changing the way by which gene combinations are presented for natural selection (Bell, 2005). Once self-fertility is achieved,

26 high selfing rates can evolve and with that the frequency of recombination is lowered (Hagenblad and Nordborg, 2002). Consequently, a lower number of allele variants will be presented to natural selection. The high number of allele variants produced by recombination is commonly believed to be the advantage of sexual reproduction (Archetti, 2003). However, effectively high outcrossing rates can be maintained even in self-fertile populations. First, in the case of Plantago maritima, a temporal separation between female and male function (i.e. dichogamy) would decrease the probability of selfing. Second, with severe inbreeding depression among selfed progeny, most adult plants will be the results of outcrossing even though a substantial part of the seed output stems from self-pollinations (cf. Herlihy and Eckert, 2002). Moreover, it is likely that hermaphrodites experience a high cost of reproduction if selfed seeds do not contribute to fitness (Ashman, 1994). Females, on the other hand, would avoid such a cost.

27 Conclusions

In this thesis, I have documented considerable variation in the breeding system of Plantago maritima. The sex ratio variation can be attributed to both stochastic processes and selection, because females are more abundant in populations where they set more seeds than hermaphrodites. The relative difference in seed production between females and hermaphrodites could be influenced by the breeding system of a local population. I documented the loss of self-incompatibility in a population from northern Sweden, and confirmed a functional self-incompatibility system in southern Sweden. A comparative field study was performed to evaluate the importance of this shift in breeding system in this wind-pollinated plant. Plant fecundity decreased with increasing distance to nearest pollen donor both within and among populations in the south Swedish Gryt archipelago where self- incompatibility have been confirmed. My results suggest, in accordance with the limited empirical evidence at hand, that effective pollen dispersal distance is low in wind-pollinated herbs. In contrast, plant fecundity was overall higher and was not density-dependent in the Skeppsvik archipelago in northern Sweden where controlled crosses showed that plants are self-compatible. These results are consistent with the prediction that evolution of self-fertility should reduce the density-dependence of pollination success, and has not previously been indicated in a wind-pollinated plant. I found low genetic diversity within populations from northern Sweden, which may be the result of a history of small population sizes and periods of frequent self- fertilization.

28 Acknowledgements

I thank Gerard Marsher, Swantje Löbel, Stein Are Sæther, Bengt Carlsson, Erica Torninger, Geir Løe, Jon Ågren, Magnus Larsson, Mariette Mankte- low, Åsa Nilsson and Per Toräng for reading and improving earlier versions of this thesis. Furthermore, I would like to express my gratitude to the following persons who have in some way made studies easier: J. Ågren, G. Løe, P. Toräng, M. Larsson, S. Sandring, I. Wänstrand, L. van Nieuwer- burgh, H. Stenøien, H. Rydin, R. Alexandersson, M. Mendez, B. Carlson, T. Snäll, S. Sundberg, B. Svensson, A. Nilsson, J. Alcantara, S. Karlsson, E. Rosén, E. Torninger, W. Jungskär, S. Björklund, J.M.M. van Damme, H. Koelewijn, P.J. van Dijk, M. Verduijn, M. Hale, K. Wolff, N. Abdullah, R. El-Bakatoushi, J. Richards, I. Nyberg, M. Andersson, N. Rustum, G. Nils- son, L. Nilsson, V. Vange, P. Nilsson, J. Nilsson, Å. Nilsson, M. Gaudeul, M. Heuertz, S. Gustafsson, M. Lascaux, M. Carlsson, J. Fogelqvist, A. Rudh, B. Roger, F. Söderman, J. Höglund, R. Ekblom, A. Vinnersten, P. Erixon, M. Pop, E. Wallander, S. Kalisz, S. Tonsor, S. C. H. Barrett, P. Mutikainen, L. Jerling, J. Ehrlén, M. Mildén, M. Bertilsson, G. Marsher, B. Lindgren, M. Fornbacke, S.-A. Sæther, E. Fornbacke, C. Dahlstedt, T. Tranefors, O. Fogelström, E. Larsson, S. Sjögren, J. Kjellgren, A. Johansson, T. Rosqvist, J. Ericsson, P. Eriksson, P. Jacobsson, J. Waldenström, E. Uggla, N. Mörnerud, A. Carlsson, P. Andersson, P. Samuelsson, A. Sunderlöf, A. Norman, P. Dahlin, T. Nilsson, Å. Wikberg, C. Wikberg, A. Wikberg, L. Nilsson, B. Johansson, A. Starrén, I. Starrén, B. Starrén, D. Starrén, kollek- tivet Svängdörren, The Flying Phantom and his Flaming Stars, and Dom kallar det festival. Financial support for the studies in this thesis was kindly provided by B. Lundmans fond and H. Ax:son Jonsson fond. Plants from outside Sweden, Finland and Norway used in the cytology study were kindly provided by J. M. M. van Damme (Heteren, The Netherlands) and K. Wolff (Newcastle-Upon-Tyne, United Kingdom).

29 Fyra män i brudkammaren och ensamma kvinnor komplicerar gulkämparnas kärleksliv

Få växter uppvisar en sådan variation i vägen till en lyckad befruktning som gulkämparna. Det är, kortfattat, vad jag lärt mig under mina fem år som doktorand. Eftersom jag bedrivit min forskning i Uppsala är det svårt att inte dra paralleller till stadens botaniska gigant, Carl von Linné. Hur skulle unge prästsonen Linné ha reagerat om han kände till gulkämparnas märkliga kär- leksliv? Själv samlade han in dem i sin ungdoms dagar under vandringar på Gräsö, för gulkämpar är en vanlig växt i den svenska skärgården. Han gav dem det passande vetenskapliga namnet Plantago maritima utifrån deras växtplats, "kämparna vid havet". Under min tid som doktorand har jag också samlat in gulkämpar, från Gryts skärgård i söder, vidare mot finska Skär- gårdshavet i öster och upp till Skeppsvik skärgård utanför Umeå i norr. Många gånger har jag brutit av en blomställning och tittat på de många och små blommorna. De har fyra gula ståndare och en fjäderlik pistill. Linné förde dem till klassen Tetrandria, vilket innebar, förklarade han, fyra män i samma brudkammare med en kvinna. Det finns dock en komplikation. De fyra männen och kvinnan tillhör samma individ.

En brudkammare fylld av pollen

De flesta gulkämpar är hermafroditer. Det Linné kallade ”männen” utgörs av ståndarna, växtens hanliga reproduktionsorgan som sprider pollen. De sitter i samma blomma som ”kvinnan”, eller pistillen, det honliga reproduktionsor- ganet. Inne i pistillen finns fröanlag som innehåller växtens äggceller. Vid en lyckad befruktning gror pollenkorn som fastnat på utsidan av pistillen ner till ett av fröanlagen och befruktar det, varvid ett frö kan utvecklas. Brudkam- maren står för själva blomman, som innefattar både de fyra ståndarna och pistillen, men också kronbladen och foderbladen. Hos många växter är kronbladen stora och färgglada för att locka till sig insekter som kan hjälpa till med pollineringen. Hos gulkämpar är kronbladen emellertid små och för- krympta, eftersom gulkämparna låter vinden sprida deras pollen. En blåsig dag blir brudkammaren fylld av pollen.

30 Hos de flesta växter och djur är inavel, korsning mellan närbesläktade individer, eller som i hermafroditers fall, självbefruktning, skadligt för av- komman. Både djur och växter har därför mekanismer för att undvika inavel. Många gulkämpar har ett kemiskt försvar mot självbefruktning. I pistillen finns enzym som känner igen och dödar pollen som kommer från samma individ. Jag har visat att korspollinerade gulkämpar från södra Sverige sätter tolv gånger så många frön som självpollinerade. De fyra ”männen” tjänar inte mycket på att sprida sitt pollen i sin egen brudkammare. Det måste nå längre bort! Men trots att gulkämparna sprider stora mängder pollen så är det förvånansvärt få pollenkorn som når en pistill. I min avhandling så visar jag att antalet frö per gulkämpe minskar drastiskt med ökat avstånd mellan väx- terna. En gulkämpe som står en meter från närmaste artfrände sätter inte mer än några få frön på mer än hundra blommor, medan en gulkämpe som står nära andra plantor kan få minst hundra frön på lika många blommor! Men någonting har hänt med gulkämparna längs Norrlands kust. De har tappat förmågan att döda pollen från samma individ. Pollen som sprids i den egna brudkammaren kan gro och befrukta de egna fröanlagen. Mina växthus- försök visar att självpollinerade gulkämpar från Skeppsvik skärgård utanför Umeå sätter lika mycket frö som de korspollinerade. Varför är det så? Under kolonisationen norrut efter senaste istiden kan det ha varit en fördel för gul- kämpar som stått ensamma och inte nåtts av pollen från andra plantor att kunna befrukta sig själva. Självbefruktade frön verkar vara bättre än inga frön alls. Fördelen är tillsynes uppenbar, gulkämpar i norra Sverige sätter mycket frö oberoende av hur långt det är till närmsta planta. Nackdelen bor- de vara skadliga effekter av inavel på självbefruktad avkomma. De fyra männen och kvinnan i brudkammaren har tydligen olika strategier i södra och norra Sverige!

En ensam kvinna i brudkammaren

Det finns en joker i den här sängkammarfarsen. En del av gulkämparna är enbart honor. Med Linnés språkbruk skulle man kunna säga att kvinnan är ensam i brudkammaren, för de fyra männen (ståndarna) är sterila och för- krympta. Med andra ord måste pollen alltid komma från andra hermafroditer för att de ska bli befruktade. De honliga plantorna är vanligare i norra Sveri- ge än i södra. Jag har räknat antalet honor och hermafroditer på sammanlagt över nittio öar i tre skärgårdar. I Gryts skärgård i södra Sverige är honorna ovanliga. På öar i det enorma Skärgårdshavet i Finland är honorna lite vanligare. Men i Skeppsvik skärgård utanför Umeå är honor vanligast. Hur kan det komma sig? I norra Sverige kan hermafroditerna befrukta sig själva. De får mycket frön oberoende av hur nära andra gulkämpar de står. Om de frö hermafrodi-

31 terna sätter med sig själva drabbas av inavelsdepression och bildar mindre livskraftiga plantor kan de konkurreras ut av andra gulkämpar, däribland honor. Kanske klarar sig honorna bättre genom att de alltid sätter frö med hjälp av pollen från andra gulkämpar? Jag har visat att honor är vanligare på öar där de sätter mer frön än hermafroditerna, och ovanligare där honorna sätter färre frön. Det verkar med andra ord som att honorna har en fördel under vissa omständigheter, men en nackdel i andra. Ännu så länge kan jag inte sätta fingret på vilka omständig- heter det är som gynnar honorna. Men i södra Sverige är honor inte lika van- liga. Här kan hermafroditerna inte befrukta sig själva utan är också de bero- ende av pollen från andra individer.

Skärgården – Sveriges Galapagos?

När Linné stötte på gulsporrar med fem lika långa ståndare, i stället för som normalt två par ståndare av olika längd, drog han ”en vidunderlig slutsats”, nämligen att nya arter kan uppstå inom växtvärlden. Detta frö till en evolu- tionsteori som Linné formulerade skulle ha kunnat revolutionera dåtidens syn på naturen om det fått utvecklas. Om Linné hade tittat lite närmare på sina Plantago maritima hade han säkert sett att vissa gulkämpar helt saknar män i brudkammaren. Då kanske han skulle ha drabbats av den för en dåtida prästson svåra insikten att naturen inte är konstant, utan formas av skillnader mellan olika individers förutsättningar. Men om naturen är föränderlig, vem eller vad är det då som skapar denna variation? Kanske var detta en alltför svindlande tanke för Linné som hade vigt sitt liv åt att ge alla skapelsens organismer ett namn. I stället skulle detta frö inte plockas upp förrän hundra år senare, av en annan berömd forskare, Charles Darwin. Hans teori om det naturliga urvalet tillkom under en resa till Galapagosöarna. Helt klart är dock att man inte behöver åka till Galapagosöarna för att studera evolutionen. Den svenska skärgården duger gott.

32 References

ACKERMAN, J. D. 2000. Abiotic pollen and pollination: ecological, functional, and evolutionary perspectives. Plant Systematics and Evolution 222:167-185 AGRAWAL, A. F. 2001. Sexual selection and the maintenance of sexual reproduction. Nature 411: 692- 695 ÅGREN, J., DANELL, K., ELMQVIST, T., ERICSON, L. AND J. HJÄLTÉN 1999. Sexual dimorphism and biotid interactions. In: Geber, M. A., Dawson, T. E. and Delph, L. E. (Eds.) Gender and Sexual Dimorphism in Flowering Plants. Springer-Verlag, Berlin, Germany ÅGREN, J. AND D. W. SCHEMSKE 1993. Outrossing rate and inbreeding depression in two annual monoecious herbs, Begonia hirsuta and B. semiovata. Evolution 47: 125–135 ALBCH, D. C., MEUDT, H. M. AND B. OXELMAN. 2005. Piecing together the “new” Plantaginaceae. American Journal of Botany 92: 297-315 ARCHETTI, M. 2003. A selfish origin for recombination. Journal of Theoretical Biology 223: 335-346 ASHMAN, T.-L. 1994. A dynamic perspective on the physiological cost of reproduction in plants. American Naturalist 144: 300-316 ASHMAN, T.-L. 2002. The role of herbivores in the evolution of separate sexes from hermaphroditism. Ecology 83: 1175–1184 ASHMAN, T.-L. 2003. Constraints of the evolution of males and sexual dimorphism: field estimates of genetic architecture of reproductive traits in three popoulations of gynodioecious Fragraria virgin- iana. Evolution 57: 2012-2025 ASHMAN, T.-L., KNIGHT, T. M., STEETS, J. A., AMARASEKARE, P., BURD, M., CAMPBELLl, D. R., DUDASH, M. R., JOHNSTON, M. O., MAZER, S. J., MITCHELL, R. J., MORGAN, M. T. AND W. G. WILSON 2004. Pollen limitation of plant reproduction: ecological and evolutionary causes and consequences. Ecology 85: 2408–2421 ASIKAINEN, E. AND P. MUTIKAINEN 2003. Female frequency and relative fitness of females and hermaphrodites in gynodioecious Geranium sylvaticum (Geraniaceae). American Journal of Botany 90: 226-234 BAILEY, M. F., DELPH, L. F. AND C. M. LIVELY 2003. Modeling gynodioecy: novel scenarios for maintaining polymorphism. American Naturalist 161: 762–776 BAKER, H.G. 1955. Self-compatibility and establishment after "long-distance" dispersal. Evolution 9: 347-348 BAKER, H.G. 1967. Support for baker's law - as a rule. Evolution 21: 853-856 BARRETT, S. C. H. 1988. The evolution, maintenance, and loss of self-incompatibility systems. In: Lovett Doust, J. and L. Lovett Doust (eds.) Plant reproductive ecology, patterns and strategies. Pp. 98 – 124. Oxford University Press, Oxford. BARRETT, S. C. H. 2002. The evolution of plant sexual diversity. Nature reviews 3: 274-284 BARRETT, S. C. H., HARDER, L. D. AND A. C. WORLEY 1996. The comparative biology of pollination and mating in flowering plants. Philosophical Transactions of the Royal Society of London B- Biological Sciences 351: 1271–1280 BELHASSEN, E., DOMMÉE, B., ATLAN, A., GOUYON, P. H., POMENTE, D., ASSOUAD, M. W. AND D. COUVET 1991. Complex determination of male sterility in Thymus vulgaris L.: genetic and molecular analysis. Theoretical and Applied Genetics 82: 137–143 BELL, G. 2005. The evolution of evolution. Heredity 94: 1 - 2

33 BERG, H. AND P. REDBO-TORSTENSSON 1998. Cleistogamy as a bet-hedging strategy in Oxalis acetosella, a perennial herb. Journal of Ecology 86: 491-500 BOS, M., HARMENS, H. AND K. VRIELING 1986. Gene flow in Plantago I. Gene flow and neigh- bourhood size in P. lanceolata. Heredity 56: 43-54. BREMER, K., FRIIS, E. M. AND B. BREMER 2004. Molecular phylogenetic dating of Asterid flowering plants show early Cretaceous diversification. Systematic Biology 53: 496–505 BRUNET, J. AND A. LISTON 2001. Polyploidy and gender dimorphism. Science 291:1441a. BURD, M. 1994. Bateman’s principle and plant reproduction: the role of pollen limitation in fruit and seed set. Botanical Review 60: 83-139 BUSCH, J. W. 2004. Inbreeding depression in self-incompatible and self-compatible populations of Leavenworthia alabamica. Heredity 94: 159-165 BYERS, D. L. AND D. M. WALLER 1999. Do plant populations purge their genetic load? Effects of population size and mating history on inbreeding depression. Annual Review of Ecology and Sys- tematics 30: 479-513 CARLSSON, U., ELMQVIST, T, WENNSTRÖM, A. AND L. ERICSON 1990. Infection by pathogens and population age of host plants. Journal of Ecology 78: 1094-1105 CHARLESWORTH, D. 1989. Evolution of low female fertility in plants: pollen limitation, resource allocation and genetic load. Trends in Ecology and Evolution 4: 289-292 CHARLESWORTH, D. 2002. What maintains male-sterility factors in plant populations? Heredity 89: 408-409. CHARLESWORTH, D. 2003. Effects of inbreeding on the genetic diversity of populations. Philosophi- cal Transactions of the Royal Society of London B-Biological Series 358: 1051–1070 CHARLESWORTH, B. AND D. CHARLESWORTH 1978. A model for the evolution of dioecy and gynodioecy. The American Naturalist 112: 975-997 CHARLESWORTH, B. AND D. CHARLESWORTH 1998. Some evolutionary consequences of deleterious mutations. Genetica 102/103: 3–19 CHARLESWORTH, D. AND V. LAPORTE 1998. The male-sterility polymorphism of Silene vulgaris: analysis of genetic data from two populations and comparison with Thymus vulgaris. Genetics 150: 1267–1282 CHEPTOU, P.-O. 2004. Allee effect and self-fertilization in hermaphrodites: reproductive assurance in demographically stable populations. Evolution 58: 2613-2621 CHEPTOU, P.-O., LEPART, J. AND J. ESCARRÉ 2001. Inbreeding depression under intraspecific competition in a highly outcrossing population of Crepis sancta (Asteraceae): evidence for frequency-dependent variation. American Journal of Botany 88: 1424– 1429 CHEPTOU, P.-O. AND D. J. SCHOEN 2003. Frequency-dependent inbreeding depression in Amsinckia. American Naturalist 162: 744–753 COUVET, D., BONNEMAISON, F., AND P. H. GOUYON 1986. The maintenance of females among hermaphrodites: the importance of nuclear-cytoplasmic interactions. Heredity 57: 325-330 COUVET, D., RONCE, O. AND C: GLIDDON 1998. The maintenance of nucleocytoplasmic polymorphism in a metapopulation: the case of gynodioecy. American Naturalist 152: 59-68 COX, P. A. 1991. Abiotic pollination: an evolutionary escape for animal-pollinated angiosperms. Phil. Trans. R. Soc. Lond. B 333, 217 – 224 CREPET, W. L., FRIIS, E. M. AND K. C. NIXON 1991. Fossil evidence for the evolution of biotic pollination. Philosophical Transactions of the Royal Society of London B-Biological Series 333: 187–195 CRNOKRAK, P. AND S. C. H. BARRETT 2002. Purging the genetic load: a review of the experimental evidence. Evolution 56: 2347-2358 CULLEY, T. M., WELLER, S. G. AND A. K. SAKAI 2002. The evolution of wind pollination in angiosperms. Trends in Ecology and Evolution 17: 361–369 DARWIN, C. 1877a. The various contrivances by which orchids are fertilised by insects. 2nd Ed. John Murray, London, U. K.

34 DARWIN, C. 1877b. Different forms of flowers on plants of the same species. John Murray, London, U.K. DART, S., KRON, P. AND B. K. MABLE. 2004. Characterizing polyploidy in Arabidopsis lyrata using chromosome counts and flow cytometry. Canadian Journal of botany, 82: 185-197 DAVIS, H. G., TAYLOR, C. M., LAMBRINOS, J. G. AND D. R. STRONG. 2004. Pollen limitation causes an Allee effect in a wind-pollinated invasive grass (Spartina alterniflora). Proceedings of the National Academy of Science USA 101: 13804-13807 DELANNAY, X., GOUYON, P. H. AND G. VALDEYRON 1981. Mathematical study of the evolution of gynodioecy with cytoplasmic inheritance under the effect of a nuclear restorer gene. Genetics 99: 169-181 DINNÉTZ, P. 1988. Local variation in degree of gynodioecy and protogyny in Plantago maritima. Med- delande från Botaniska Institutionen, Stockholms Universitet DINNÉTZ, P. 1996. Nuclear-cytoplasmic male sterility and population dynamics in Plantago maritima. Doctoral thesis, Stockholm University. DINNÉTZ, P. 1997. Male sterility, protogyny, and pollen-pistil interference in Plantago maritima (Plan- taginaceae), a wind-pollinated, self-incompatible perennial. American Journal of Botany 84: 1588– 1594 DINNÉTZ, P. AND L. JERLING 1997. Gynodioecy in Plantago maritima L.; no compensation for loss of male function. Acta Botanica Neerlandica 46: 193-206 DORKEN, M. E., FREIDMAN, J. AND S. C. H. BARRETT 2002. The evolution and maintenance of monoecy and dioecy in Sagittaria latifolia (Alismataceae). Evolution 56: 31 - 41 DOW, B. D. AND M. V. ASHLEY 1996. Microsatellite analysis of seed dispersal and parentage of saplings in bur oak, Quercus macrocarpa. Molecular Ecology 5: 615–627 EDWARDS, K. J., BARKER, J. H. A., DALY, A. JONES, C. AND A. KARP 1996. Microsatellite libraries enriched for several microsatellite sequences in plants. Biotechniques 20: 758-760 EHRLÉN, J., KÄCK, S. AND J. ÅGREN 2002. Pollen limitation, seed predation and scape length in Primula farinosa. OIKOS 97: 45-51 ENTANI, T., IWANO, M., SHIBA, H., TAKAYAMA, S., FUKUI, K. AND A. ISOGAI 1999. Centro- meric localization of an S-RNase gene in Petunia hybrida Vilm. Theoretical and Applied Genetics 99: 391–397 FAEGRI, K. AND L. VAN DER PIJL 1966. The principles of pollination ecology. Pergamon press, London, U.K. FALCONER, D. S. AND T. F. C. MACKAY 1996. Introduction to quantitative genetics, 4th edn. Pearson education limited, Essex, U.K. FENSTER, C. B. AND K. RITLAND 1992. Chloroplast DNA and isozyme diverstiy in two Mimulus species (Scrophulariaceae) with contrasting mating systems. American Journal of Botany 79: 1440– 1447 FRANK, S. A. 1989. The evolutionary dynamics of cytoplasmic male sterility. American Naturalist 133: 345-376 FRANKLIN-TONG, N.(V.E.) AND F. C. H. FRANKLIN 2003. Gametophytic self-incompatibility inhibits pollen tube growth using different mechanisms. Trends in Plant Science 8: 598-605 FRIIS, E. M., PEDERSEN, K. R. AND P. R. CRANE 1999. Early angiosperm diversification: the diversity of pollen associated with angiosperm reproductive structures in Early Cretaceous floras from Portugal. Annals of the Missouri Botanical Garden 86: 259-296 FRIIS, E. M., RAUNSGAARD PEDERSEN, K. AND P. R. CRANE 2001. Fossil evidence of water lilies (Nymphaeales) in the early Cretaceous. Nature 410: 357–360 FOWLER, K. AND M. C. WHITLOCK 1999. The variance in inbreeding depression and the recovery of fitness in bottlenecked populations. Proceedings of the Royal Society of Londondon B-Biological Series 266: 2061-2066 GOODWILLIE, C. 1999. Wind pollination and reproductive assurance in Linanthus parviflorus (Po- lemoniaceae), a self-incompatible annual. American Journal of Botany 86: 948–954

35 GOUYON, P.-H. AND D. COUVET 1987. A conflict between two sexes, females and hermaphrodites. In S.C. Stearns [ed.] The evolution of sex and its consequences, pp. 245-261. Birkhäuser, Basel GOUYON, P.-H., VICHOT, F. AND J. M. M. VAN DAMME 1991. Nuclear-cytoplasmic male sterility: single-point equilibria versus limit cycles. American Naturalist 137: 498–514 GREGOR, J. W. 1939. Experimental taxonomy. IV. Population differentiation in North American and European Sea plantains allied to Plantago maritima L. New Phytologist 38: 293-322 HAGENBLAD, J. AND M. NORDBORG 2002. Sequence variation and haplotype structure surrounding the flowering time locus FRI in Arabidopsis thaliana. Genetics 161: 289–298 HARING, V., GRAY, J. E., MCCLURE, B. A., ANDERSON, M. A. AND A. E. CLARKE 1990. Self- incompatibility: a self-recognition system in plants. Science 250: 937–941 HERLIHY, C. R. AND C. G. ECKERT 2002. Genetic cost of reproductive assurance in a self-fertilizing plant. Nature 416: 320-323 HOFFMANN, M. H., BREMER, M., SCHNEIDER, K., BURGER, F., STOLLE, E. AND G. MORITZ 2003. Flower visitors in a natural population of Arabidopsis thaliana. Plant Biology 5: 491 – 494 HOGGARD, R. K., KORES, P. J., MOLVRAY, M., HOGGARD, G. D. AND D. A. BROUGHTON 2003. Molecular systematics and biogeography of the amphibious genus Littorella (Plantaginaceae). American Journal of Botany 90: 429–435 HULTÉN, E. 1971. Atlas över växternas utbredning i Norden. 2nd Edition. Generalstabens litografiska anstalts förlag, Stockholm. HULTÉN, E. AND M. FRIES M. 1986. Atlas of North European vascular plants: north of the Tropic of Cancer I-III. Koeltz Scientific Books, Königstein HUSBAND, B. C. AND D. W. SCHEMSKE 1996. Evolution of the magnitude and timing of inbreeding depression in plants. Evolution 50: 54-70 IGIC, B. AND J. R. KOHN 2001. Evolutionary relationships among self-incompatibility RNases. Pro- ceedings of the National Acadademy of Science USA 98: 13167–13171 INGVARSSON, P.K. AND TAYLOR, D.R. 2002. Genealogical evidence for epidemics of selfish genes. Proceedings of the National Acadademy of Science USA 99: 11265-11269 JACOBS, M. S. AND M. J. WADE 2003. A synthetic review of the theory of gynodioecy. American Naturalist 161: 837-851 JAIN, S.K. 1976. The evolution of inbreeding in plants. Annual Review of Ecology and Systematics 7: 469–495 JARNE, P. AND D. CHARLESWORTH 1993. The evolution of the selfing rate in functionally hermaphrodite plants and animals. Annual review of Ecology and Systematics 24: 441-466. JARNE, P. AND P. J. L. LAGODA 1996. Microsatellites, from molecules to populations and back. Trends in Ecology and Evolution 11: 424–429 JERLING, L. 1982. Population dynamics of a perennial herb (Plantago maritima L.) along a distribu- tional gradient – a demographic study. Doctoral thesis, University of Stockholm, Sweden. JUDSON, O. P. AND B. B. NORMARK 1996. Ancient asexual scandals. Trends in Ecology and Evolu- tion 11: 41-46 KALISZ, S., VOGLER, D. W. AND K. M. HANLEY 2004. Context-dependent autonomous self- fertilization yields reproductive assurance and mixed mating. Nature 430: 884–887 KAUL, M. L. H. 1988. Male sterility in higher plants. Springer-Verlag, Berlin KELLOGG, E. A. 2001. Evolutionary history of the grasses. Plant Physiology 125: 1198-1205 KOELEWIJN, H. P. 1998. Effects of different levels of inbreeding on progeny fitness in Plantago coronopus. Evolution 52: 692-702 KOELEWIJN, H. P. 2004. Sibling competition, size variation and frequency-dependent outcrossing advantage in Plantago coronopus. Evolutionary Ecology 18: 51-74 KONDO, K., YAMAMOTO, M., ITASHASHI, R., SATO, T., EGASHIRA, H., HATTORI, T. AND Y. KOWYAMA Y. 2002. Insights into the evolution of self-compatibility in Lycopersicon from a study of stylar factors. Plant Journal 30: 143–153 LANDE, R. AND D. W. SCHEMSKE 1985. The evolution of self-fertilization and inbreeding depression in plants. I. Genetic models. Evolution 39: 24-40

36 LARSON, B. M. H. AND S. C. H. BARRETT 2000. A comparison of pollen limitation in flowering plants. Biological Journal of the Linnean Society 69: 503–520 LEWIS, D. 1941. Male sterility in natural populations of hermaphrodite plants. The equilibrium between females and hermaphrodites to be expected with different types of inheritance. New Phytologist 40: 56–63 LINNÉ, C. von 1755. Flora Svecica. Svensk Flora (swedish translation 1986). Forum, Stockholm LLOYD, D. G. 1975. The maintenance of gynodioecy and androdioecy in angiosperms. Genetica 45: 325-339 LLOYD, D. G. 1979. Some reproductive factors affecting the selection of self-fertilization in plants. American Naturalist 113: 67–9 LLOYD, D. G. 1992. Self- and cross-fertilization in plants. II. The selection of self-fertilization. Interna- tional Journal of Plant Sciences 153: 370-380. MABLE, B. K. 2004. Polyploidy and self-compatibility: is there an association? New Phytologist 162: 803-811 MARR, D. L. 1997. Impact of a pollinator-transmitted disease on reproduction in healthy Silene acaulis. Ecology 78: 1471–1480 MASTERSON, J. 1994. Stomatal size in fossil plants: evidence for polyploidy in majority of angiosperms. Science 264: 421–423 MANICACCI, D., COUVET, D., BELHASSEN, E., GOUYON, P.-H. AND A. ATLAIN 1996. Founder effects and sex ratio in the gynodioecious Thymus vulgaris L. Molecular Ecology 5: 63-72 MAYNARD SMITH, J. 1978. The evolution of sex. Cambridge university press, Cambridge MCCAULEY, D. E., OLSON, M. S., EMERY, S. N. AND D. R. TAYLOR 2000. Population structure influences sex ratio evolution in a gynodioecious plant. American Naturalist 155: 814-819 MILLER, J. S. AND VERNABLE, D. L. 2000. Polyploidy and the evolution of gender dimorphism in plants. Science 289: 2335–2338 MORGAN, M. T., SCHOEN, D. J. AND T. M. BATAILLON, T. M. 1997. The evolution of self- fertilization in perennials. American Naturalist 150: 618–638 MUTIKAINEN, P. AND L. E. DELPH 1996. Effects of herbivory on male reproductive success in plants. Oikos 75: 353-358 NASRALLAH, M. E., LIU, P., SHERMAN-BROYLES, S., BOGGS, N. A. AND J. B. NASRALLAH 2004. Natural variation in expression of self-incompatibility in Arabidopsis thaliana: implications for the evolution of selfing. Proceedings of the National Academy of Science USA 101: 16070- 16074 NILSSON, A. 1998. Deep flowers for long tongues. Trends in Ecology and Evolution 13: 259-260 NILSSON, E. 1999. Reduced dispersal capacity in island populations of Senecio sylvaticus L. Master thesis, Uppsala University, Sweden NORDBORG, M. 2000. Linkage disequilibrium, gene trees and selfing: an ancestral recombination graph with partial self-fertilization. Genetics 154: 923–929 OLMSTEAD, R. G., DEPAMPHILIS, C. W., WOLFE, A. D., YOUNG, N. D., ELISONS, W. J. AND P. A. REEVES 2001. Disintegration of the Scrophulariaceae. Amercian Journal of Botany 88: 348–361 PANNELL, J. 1997. The maintenance of gynodioecy and androdioecy in a metapopulation. Evolution 51: 10-20 PANNELL, J.R. AND S. C. H. BARRETT 1998. Baker's law revised: Reproductive assurance in a metapopulation. Evolution 52: 657-668 PANNELL, J. R., OBBARD, D. J. AND J. A. B. RICHARD 2004. Polyploidy and the sexual system: what can we learn from Mercurialis annua? Biological Journal of the Linnean Society 82: 547-560. PARACHNOWITSCH, A. L. AND E. ELLE 2004. Variation in sex allocation and male-female trade- offs in six populations of Collinsia parviflora (Scrophulariaceae s.l.). American Journal of Botany 91: 1200–1207 PELLMYR, O. 1992. Evolution of insect pollination and angiosperm diversification. Trends in Ecology and Evolution 7: 46-49

37 PELLMYR, O. 2003. Yuccas, yucca moths, and coevolution: a review. Annals of the Missouri Botanical Garden 90: 35-55 PIGNATTI, S. 1982. Flora d’Italia. Edagricole, Bologna. POP, M. 2004. Disentangling the reticulate history of polyploids in Silene (Caryophyllaceae). Doctoral thesis, Uppsala University, Sweden. PRIMACK, R. B. 1979. Reproductive effort in annual and perennial species of Plantago (Plantagina- ceae). The American Naturalist 114, 51 – 62 PROCTOR, M., YOE, P. AND A. LACK 1996. The Natural History of Pollination. Timber Press, Port- land, Oregon, USA. RAMSEY, J. AND D. W. SCHEMSKE 2002. Neopolyploidy in flowering plants. Annual Review of Ecology and Systematics 33: 589-639 REN, D. 1998. Flower-associated Brachycera flies as fossil evidence for Jurassic angiosperm origins. Science 280: 85-88 RICHARDS, A. J. 1997. Plant Breeding Systems. Chapman & Hall, London ROALSON, E. H. AND A. G. MCCUBBIN 2003. S-RNases and sexual incompatibility: structure, func- tions, and evolutionary perspectives. Molecular Phylogenetics and Evolution 29: 490-506 RONCE, O. AND I. OLIVIERI 2004. Life history evolution in metapopulations. In, Hanski, I. and O.E.Gaggiotti (eds.) Ecology, Genetics, and Evolution of metapopulations. Elsevier academic press, Oxford ROSS, M. D. 1970. Breeding systems in Plantago. Heredity 25: 129–133 ROSS, M. D. 1973. Inheritance of self-incompatibility in Plantago lanceolata. Heredity 30, 169-176 RØNSTED, N., CHAE, M. W., ALBACH, D. C. AND M. A. BELLO 2002. Phylogenetic relationships within Plantago (Plantaginaceae): evidence from nuclear ribosomal ITS and plastid trnL-F sequence data. Botanical Journal of the Linnean Society 139: 323-338 SAKAI, A. K., WELLER, S. G., CHEN, M.-L., CHOU, S. Y. AND C. TASANONT 1997. Evolution of gynodioecy and maintenance of females: the role of inbreeding depression, outcrossing rates, and resource allocation in Schiedea adamantis (Caryophyllaceae). Evolution 51: 724-736 SCHOEN, D. J., MORGAN, M. T. AND T. BASTILLON 1996. How does self-pollination evolve? Inferences from floral ecology and molecular genetic variation. Philosophical Transansactions of the Royal Society of London B-Biological Series 351: 1281–1290 SHANTZ, H. L. 1954. The place of grasslands in the earth's cover. Ecology 35: 143-145 SHARMA, N., KOUL, P. AND A. K. KOUL 1992. Reproductive biology of Plantago: shift from cross- to self-pollination. Annals of Botany 69: 7–11 SLATKIN, M. 1995. A measure of population subdivision based on microsatellite allele frequencies. Genetics 139: 457-462 SNOEIJS, P. 1999. Marine and brackish waters. In: Rydin, H., Snoeijs, P. and Diekmann, M. (Eds.). Swedish plant geography. Acta Phytogeographica Suecica 84, pp 169 - 186 STEBBINS, G. L. 1957. Self fertilization and population viability in the higher plants. American Natural- ist 91: 337-354 STEBBINS, G. L. 1970. Adaptive radiation of reproductive characteristics in angiosperms. I. Pollination mechanisms. Annual Review of Ecology and Systematics 1: 307-326 SHANTZ, H. L. 1954. The place of grasslands in the earth’s cover. Ecology 35: 143–145 SHARMA, N., KOUL, P. AND A. K. KOUL 1992. Genetic system of six species of Plantago (Plantagi- naceae). Plant Systematics and Evolution 181: 1-9 STAAL, M., MAATHUIS, F. J. M., ELZENGA, T. M., OVERBEEK, H. M. AND H. B. A. PRINS 1991. Na+/H+ antiport activity in tonoplast vesicles from root of the salt-tolerant Plantago maritima and the salt-sensitive Plantago media. Physiologia Plantarum 82: 179–184 STEBBINS, G. L. 1957. Self fertilization and population viability in the higher plants. American Natural- ist 41: 337-354 STELLEMAN, P. 1978. The possible role of insect visits in pollination of reputedly anemophilous plants, exemplified by Plantago lanceolata, and syrphid flies. pp. 41- 46. In A. Richards. (ed.) The pollination of flowers by insects. Linneaen Society Symposium Series Number 6. 213 pp.

38 TAKEBAYASHI, N. AND P. MORRELL 2001. Is self-fertilization an evolutionary dead end? Revisiting an old hypothesis with genetic theories and a macroevolutionary approach. American Journal of Botany 88: 1143–1150 TALAVERA, S., GIBBS, P.E., FERNÁNDEZ-PIERA AND M. A. ORTIZ-HERRERA 2001. Genetic control of self-incompatibility in Anagallis monelli (Primulaceae: Myrsinaceae). Heredity 87: 589- 597. TAS, I. C. Q. AND P. J. VAN DIJK 1999. Crosses between sexual and apomictic dandelions (Tarax- acum). I. The inheritance of apomixis. Heredity 83: 707–714 THOMPSON, J. D. AND M. TARAYRE 2000. Exploring the genetic basis and proximate causes of female fertility advantage in gynodioecious Thymus vulgaris. Evolution 54: 1510-1520 THOROGOOD, D., ARMSTEAD, I. P., TURNER, L. B., HUMPHREYS, M. O. AND M. D: HAY- WARD 2004. Identification and mode of action of self-compatibility loci in Lolium perenne L. He- redity doi:10.1038/sj.hdy.6800582 TORMO-MOLINA, R., PALACIOS, I. S., MUÑOZ, R., MUÑOS, J. T. AND A. M. CORCHERO 2001. Environmental factors affecting airborne pollen concentration in anemophilus species of Plantago. Annals of Botany 87: 1-8 TSUKAMOTO, T., ANDO, T., KOKUBUN, H., WATANABE, H., SATO, T., MASADA, M., MARCHESI, E. AND T.-H. KAO 2003. Breakdown of self-incompatibility in natural populations of Petunia axillaris caused by a modifier locus that suppresses the expression of an S-RNase gene. Sexual Plant Reproduction 15: 255-263 TUTION, T. G., HEYWOOD, V. H., BURGES, N. A., MOORE, D. M., VALENTINE, D. H., WAL- TERS, S. M. AND D. A. WEBB 1976. Flora Europaea vol. IV. Cambridge University Press, Cam- bridge VALLEJO-MARÍN, M. AND M. K. UYENOYAMA 2004. On the evolutionary costs of self- incompatibility: incomplete reproductive compensation due to pollen limitation. Evolution 58: 1924–1935 VAN DAMME, J. M. M. 1984. Gynodioecy in Plantago lanceolata L. III. Sexual reproduction and the maintenance of male steriles. Heredity 52: 77–93 VAN DAMME, J. M. M. 1985. Why are so many Plantago species gynodioecious? pp. 241-250. In: Haeck J and Woldendorp JW (Eds) Structure and Functioning of Plant Popula- tions. 2. North Holland Publ. Comp. Amsterdam VAN DAMME, J.M.M. AND W. VAN DELDEN 1984. Gynodioecy in Plantago lanceolata L. IV. Fitness components of sex types in different life cycle stages. Evolution 38: 1326-1336 VAN DER KNAAP, W. O. 1987. Long-distance transported pollen and spores on Spitsbergen and Jan Mayen. Pollen et Spores 29: 449-454 VAN DIJK, P. J. 2003. Ecological and evolutionary opportunities of apomixis: insights from Taraxacum and Chondrilla. Philosophical Transactions of the Royal Society of London B-Biological Sciences 358: 1113–1121 VIEIRA, C. P. AND D. CHARLESWORTH, D. 2002. Molecular variation at the self-incompatibility locus in natural populations of the genera Antirrhinum and Misopates. Heredity 88: 172-181 VOGLER, D. W. AND S. KALISZ 2001. Sex among the flowers: the distribution of plant mating systems. Evolution 55: 202-204 WALLANDER, E. 2001. Evolution of wind-pollination in Fraxinus (Oleaceae) – an ecophylogenetic approach. Doctoral Thesis, Göteborg University, Sweden. WELLER, S. G., SAKAI, A. K., WAGNER, W. L. AND D. R. HERBST 1990. Evolution of dioecy in Schiedea (Caryophyllaceae: Alsinoideae) in the Hawaiian islands: biogeographical and ecological factors. Systematic Botany 15: 266–276 WELLER, S. G. AND A. K. SAKAI 2004. Selfing and resource allocation in Schiedea salicaria (Caryo- phyllaceae), a gynodioecious species. Journal of Evolutionary Biology 0, 0. doi:10.1111/j.1420- 9101.2004.00835.x WHITEHEAD, D. R. 1983. Wind pollination: Some ecological and evolutionary perspectives. In, Real, L. (Ed.) Pollination Biology. Academinc Press, Inc. London

39 WILLIS, K. J. AND J. C. MCELWAIN 2002. The evolution of plants. Oxford university press, Oxford, U.K. YAMPOLSKY, C. AND H. YAMPOLSKY 1922. Distribution of sex forms in the phanerogamic flora. Bibliotheca Genetica 3: 1–62 ZAVADA, M. S. 1984. The relationship between pollen exine sculpturing and self-incompatibility mechanisms. Plant Systematics and Evolution 147: 67-78

Acta Universitatis Upsaliensis Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 14

Editor: The Dean of the Faculty of Science and Technology

A doctoral dissertation from the Faculty of Science and Technology, Uppsala University, is usually a summary of a number of papers. A few copies of the complete dissertation are kept at major Swedish research libraries, while the summary alone is distributed internationally through the series Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology. (Prior to January, 2005, the series was published under the title "Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology".)

ACTA UNIVERSITATIS Distribution: publications.uu.se UPSALIENSIS UPPSALA urn:nbn:se:uu:diva-4790 2005