Sympatric Speciation in Baltic Sea Fucus Populations

Sympatric speciation in Baltic Sea Fucus populations

Is vegetative reproduction the key for evolution of F. radicans ?

by Dan Tiderman

Plants & Ecology

Plant Ecology 2009/7 Department of Botany Stockholm University Sympatric speciation in Baltic Sea Fucus populations

Is vegetative reproduction the key for evolution of F. radicans ?

by Dan Tiderman

Supervisors: Helena Forslund and Lena Kautsky

Plants & Ecology

Plant Ecology 2009/7 Department of Botany Stockholm University

Plants & Ecology

Plant Ecology Department of Botany Stockholm University S-106 91 Stockholm Sweden

© Plant Ecology ISSN 1651-9248 Printed by Solna Printcenter Cover: Adventitious branch from Fucus radicans. Photo by Dan Tiderman. Summary Speciation processes are a disputed area of research, and subjected to constant review and adjustment. The theories of allopatric speciation that are focusing on isolation mechanisms as the dominating force for speciation have been regarded as the main path for speciation, but have recently been challenged by several studies indicating different modes of sympatric speciation. Few of these studies have concerned plants, but a recent identification of the Baltic Sea seaweed Fucus radicans have highlighted a situation of probable sympatric speciation under some intricate circumstances. The complex history and environment of the brackish Baltic Sea area, and the predominant vegetative reproduction strategy of Swedish F. radicans raises several questions. The evolutionary forces present while F. radicans arguably split from the sympatric populations of Fucus vesiculosus seems ambiguous in several ways and the evolutionary history is difficult to access. To improve the insight of the domain, a comparative test of Swedish F. radicans abilities for vegetative reproduction was performed with the aim to possibly find the forces trigging the emergence of F. radicans and the factors restricting the current spatial occurrence of this species. Adventitious branches from four different categories of origin/species from Swedish and Estonian F. vesiculosus and F. radicans respectively were compared in a controlled experimental setup to evaluate possible adaptations towards vegetative reproduction.

The results indicate that the vegetatively reproducing Swedish F. radicans have adapted to develop more extensive branching and some other morphological traits possibly linked to nutrient uptake. The observed differences in morphology, the vegetative reproduction strategy, and the adaptations revealed in this study are proposed to be linked to the northern boundary of the fundamental niche of these two closely related Fucus species, where the low salinity environment probably is restricting the success of sexual reproduction. However, other factors than the reproductive strategy could as well have been triggering the emergence of F. radicans. When trying to explain the evolutionary history of F. radicans several scenarios such as polyploidy or relict populations may be suggested as the source for the emergence of F. radicans in the Baltic Sea. Those are briefly presented and discussed as alternative explanations, but the complexity of the ecologically related adaptations needs further both genetic and ecological studies.

Sammanfattning Artbildningsprocesser är ett omtvistat forskningsområde som ständigt är föremål för uppdateringar och justeringar. De alloptriska artbildningsteorierna som grundar sig på teorier om att olika former av isolering mellan populationer är den avgörande faktorn för artbildning har länge varit dominerande. Men de har på senare tid utmanats av studier som påvisat olika typer av sympatrisk artbildning. Få av dessa studier har emellertid baserats på växtstudier, men en nyligen identifierad tångart i Östersjön har lyft fram ett fall av trolig sympatrisk artbildning under något speciella förhållanden. Den komplicerade evolutionära historien och miljön i Östersjöns brackvattenmiljö, samt den huvudsakligen vegetativa reproduktionsstrategin hos de svenska populationerna av den nyligen identifierade arten Fucus radicans, lyfter fram ett flertal frågeställningar. De evolutionära drivkrafterna som verkat då F. radicans förmodat uppstått ur Fucus vesiculosus kan uppfattas som mångtydiga på många sätt och den evolutionära utvecklingen är svår att överblicka. För att skapa mer förståelse inom området, gjordes en jämförande studie av svensk F. radicans förmåga till vegetativ förökning med syftet att om möjligt belysa de drivkrafter som legat bakom uppkomsten av F. radicans samt vilka faktorer som reglerar artens nuvarande utbredning. Adventivgrenar från fyra kategorier av art/ursprung med svensk och estnisk F. radicans respektive F. vesiculosus jämfördes i en kontrollerad försöksmiljö för att utvärdera möjliga anpassningar mot vegetativ reproduktion.

Resultaten påvisar att den vegetativt reproducerande svenska F. radicans har anpassat sig genom ett mer förgrenat växtsätt samt andra morphologiska egenskaper som möjligen är förknippade med näringsupptag. De observerade morfologiska skillnaderna, den vegetativa reproduktionsstrategin och anpassningarna som påvisas i denna studie föreslås vara kopplade till den nordliga utbredningsgränsen för de två nära besläktade Fucus arterna där den låga salthalten förmodligen begränsar framgången av sexuell förökning. Det kan emellertid finnas fler orsaker än reproduktionsstrategier som legat bakom uppkomsten av F. radicans i Östersjön. Dessa alternativa förklaringar är översiktligt presenterade och diskuterade. Komplexiteten av dessa ekologiskt betingade anpassningar visar på behov av fler studier, både inom de genetiska och ekologiska forskningsområdena.

Introduction The emergence of new species were long exclusively regarded as the result of genetic drift in subpopulations separated by some kind of geographic barrier, and the resulting differentiated populations where commonly classified as separate species if reproductive isolation had occurred (Mayr 1963; Dobhansky 1970). The definition of species were later on suggested to comprise populations with uniting attributes such as reproductive period, anatomy and reproductive behaviour (Templeton 1989; Paterson 1985). This definition included vegetative reproducing species which were not considered by the definition of reproductive isolation. Another view of the species concept is the phylogenetic approach (Cracraft 1983), where species are regarded as populations with a common ancestor and with some new characters possible to diagnose. Most of these species theories are compromised in that they do not account for the ever present and ambiguous processes of hybridisation and the situation of constant ongoing evolutionary processes. This is still an uncomfortable vagueness in the speciation concepts and was remarked by Buffon already in the 1800th century (Sörman 2007).

Using a simplified spatial approach, speciation can be separated in to allopatric speciation where isolation factors are the keys and into sympatric speciation, where speciation occurs without any apparent isolation between populations. The traditional, and still largely dominating speciation theories that are based on reproductive isolation all fall into the category of allopatric speciation where the antagonistic forces of spatially dependent adaptation and gene flow makes up the key mechanism of the evolutionary process. The sympatric speciation theory is more recent and suggests that in some circumstances speciation can occur in populations without the presence of separating barriers, typically in recently colonized or isolated areas that offer a variety of new niches (Schliewen et al. 2001). An important mechanism in plants but also known in some animals, are speciation by polyploidy, where characters can change in relative short periods by chromosome multiplication. Polyploidy is also suggested to be one of the predominant modes of sympatric speciation in plants due to the large effects on gene regulation (Otto & Whitton 2000).

Several studies have demonstrated sympatric speciation and some examples are: differentiating to host plant adaptation in flies (Feder et al. 1988), adaptation to different patterns for sexual selection in African cichlids (Schliewen et al. 2001), and adaptive niche separation in salmons (Lu & Bernatchez 1999). In plants, however some of these adaptive

5 forces do not seem applicable due to the sessile life strategies in plants which inhibit active choosing among patchy micro niches and are excluding the impact from active mating. However recent studies indicates that sympatric speciation has occurred in the Baltic Sea seaweed, Fucus radicans (L. Bergström et L. Kautsky sp. nov.). The species has arguably descended from Fucus vesiculosus (L.) (Pereyra et al. 2009) and has recently attracted attention, as new research has revealed that this dwarf morph is to be regarded as a species of its own (Bergström et al. 2005).

The scene of this sympatric speciation, the Baltic Sea, is the largest brackish water body in the world and is intriguing as a scene for speciation processes for several reasons. The longitudinal extension makes for a varying range of climatic environments. The restricted influx of marine water to the southwest in conjunction with abundant freshwater supplies from the northern parts results in a consecutive salinity gradient increasing southwards. The young and complex evolutionary history of approximately 8000 years since the last glaciations (Björk 1995) entails a flora and fauna in transformation (Kautsky et al. 1992; Johannesson & André 2006). The brackish environment generally present a challenging environment, optimal neither for organisms from marine or freshwater origin. The composition of the inhabitants today (Sommer et al. 2008; Schmölke 2008) indicates that the majority of the current marine species immigrated during the marine Littorina Sea period. The marine organisms in the area have since then been going through an intensive adaptation and extinction phase (Johannesson & André 2006) in a sequence of successive transformation of the environment towards freshwater conditions.

The fucoids F. radicans and F. vesiculosus are the only structural large, long-lived macroalgal species in the Bothnian Sea where they form the canopy along bedrock and gravel shores making an important foundation for the ecological communities present (Wikström & Kautsky 2007, Kautsky et al. 1992). Fucus radicans have been found in the Bothnian Sea, and along the Estonian coast (Bergström et al. 2005; Pereyra et al. 2009). Findings of the species in the Gulf of Finland are difficult to assess due to uncertainties regarding the wide range of morphological variance found, which is not yet genetically resolved. Just like F. vesiculosus the Estonian populations of F. radicans are sexually reproducing. Contrary to this, the F. radicans populations in the Bothnian Sea are predominantly reproducing vegetatively (Bergström et al. 2005; Tatarenkov et al. 2005) growing adventitious branches that fall off to generate new clonal individuals (Tatarenkov et al. 2005). This situation of regional vegetative

6 reproduction may cause low genetic variation and may consequently lead towards long term restriction in adaption capabilities. This could possibly make the clonal populations vulnerable to long term changes in the environment (Spielman et al. 2004).

The situation of an apparent sympatric speciation into the current clonal populations raises several questions. Why and how did the speciation occur and why are clonal F. radicans populations successful in the Bothnian Sea and especially in the northern parts where studies indicate that it is relatively more abundant (Forslund 2009a). Could the vegetative reproduction actually be the key for the emergence of F. radicans ? One possible explanation is that vegetative reproduction is more effective due to the limited efficiency of sexual reproduction in low salinity environments, where osmosis mechanisms restrict the success and survival of the eggs released (Serrão et al. 1996; Serrão et al. 1999). This could possibly explain why the vegetatively reproducing F. radicans has evolved in this area, at the margin of the fundamental niche for fucoids. Also, other factors in these marginal areas could be of importance as environmental stress factors probably are restricting F. vesiculosus in more ways than just reproduction, thus possibly relieving some of the overall competitive pressure for F. radicans (Johannesson & André 2006).

One prerequisite for F. radicans to be superior to F. vesiculosus regarding vegetative reproduction is that some new traits enhancing this reproduction strategy have been acquired. I tested the hypothesis that clonal Fucus populations should use more resources for vegetative reproduction than sexually reproducing Fucus populations by counting the number of advent- tious branches per biomass in plants of both F. vesiculosus and F. radicans from two regions.

The extent, and establishment of released adventitious branches are hypothesised to be more critical to F. radicans with a reduced ability to establish by sexually produced zygotes. In the sexually reproducing populations, adventitious branches could possibly serve primary as free floating individuals improving the ability for long range spreading (Ingólfsson 1995) and thus be assumed to be of less importance. I tested the establishment ability of adventitious branches by growing adventitious branches from Estonian and Swedish F. radicans and F. vesiculosus respectively on a substrate while examining the extent of rhizoid development and comparing the ability to adhere to the substrate.

The following hypothesis where also defined: Adventitious branches from F. radicans have more cryptostomata than does F. vesiculosus. The rationale for this is that the narrower thallus in F. radicans (Bergström et al. 2005) allows for less nutrient uptake, which should be compensated by a higher density of cryptostomata provided with hyaline hairs possibly serving as a expanded surface for nutrient uptake (Deboer & Whoriskey 1983). This was tested by counting the cryptostomata in adventitious branches from the two species, grown in the same environmental conditions.

Material & Methods Study species The macroalgae F. radicans, and F. vesiculosus are two of the three known fucoids in the Baltic Sea. They are both canopy forming in shallow waters and on hard substrate bottoms. As all fucoids they are perennial and produce one type of diploid thallus. Fucus radicans differs from F. vesiculosus morphologically in having a more shrubbery appearance, being smaller in size and slimmer in the dimensions. It also lacks the vesicles present in F. vesiculosus. Though being dioecious as is F. vesiculosus, the Bothnian Sea populations of F. radicans is predominantly vegetative reproducing (Tatarenkov et al. 2005), while the Estonian populations of F. radicans seems to reproduce predominantly sexually like F. vesiculosus (H. Forslund pers. comm.). The adventitious branches growing from the thallus are the main source for vegetative reproduction in both F. radicans and F. vesiculosus. These branches can remain on the thallus extending the branching or detach to serve as propagules for new individuals. If the rhizoids originating from the base of the adventitious branches, find a suitable substratum, the branch has the possibility to attach and establish a new sessile plant (Tatarenkov et al. 2005).

Study sites and sampling Individuals from four different combinations of population sites and species where used for the study. Swedish and Estonian F. radicans and Swedish and Estonian F. vesiculosus. The Swedish individuals of both F. radicans and F. vesiculosus where collected in Öregrund the 24th of April and the Estonian plants at Ösel on the 1st of Maj. The plants where transported in cool and humid conditions and placed in tanks after 1-2 days and subsequently accommodated on the bottom of shallow water open cisterns for a period of 7-8 weeks at the Askö marine laboratory. The cisterns where supplied by continuous incoming sea water with an approximate temperature of 14ºC and 6.5 ‰ salinity and natural light. From each of the

8 site/species combinations, 10 plants and a couple of reserve plants where randomly picked. It should be noted that in collecting the Estonian samples of F. vesiculosus some plants where short in adventitious branches. In these cases a new plant where randomly choosen. Also notably is that the Estonian samples of F. vesiculosus by visual impression where in slightly worse condition than the other categories sampled. The number of adventitious branches for each plant where counted and the plants where weighted wet after surplus water was removed. Ten adventitious branches of 2-5mm in size were detached from each sample plant and located on granite discs of 35mm diameter. The discs were encircled by a cylindrical mesh net of 40mm height attached to the discs perimeter by aquarium silicone. The net served as a restricting barrier in case of turbulence or accidental movements of the samples. The samples were placed in a temperature of 15ºC inside oblong plastic containers of approximately 80 liter and a water depth of 75mm. The system was continuously fed by sea water in an approximately rate of 30 l/h with a temperature of 14ºC. The sample discs where randomly orientated 35 mm below the surface in the drain end of the container. The water were mixed by air feeding stones in the tap end of the container causing slight surface undulations in the drain end. Illumination of 3200 Kelvin color temperature were present for 18 hours/day with an intensity of 87 µmol s-¹ m² at surface level. Gentle cleaning of the mesh net were executed at an interval of 4 weeks approximately. After 11 weeks the adventitious branch samples were examined visually using magnification equipment. The observations made were: occurrence of rhizoids, if rhizoids where attaching to the disc, the amount of growth and the cross section shape of the thallus, if cryptostomata were present and the amount observed. The observations were either boolean or ordered classifications based on definitions as follows:

Definitions and classification for observations: Occurrence of rhizoids – rhizoids visible or not visible Rhizoids attached to the substrate – The base of the branch steadily attached by rhizoids and not detached by a slightly movement of the branch in the upper part. The amount of growth –  No apparent growth  Limited growth, less than or equal to 50%  Substantial growth, more than 50% Cross section shape of main body –  Circular: width less or equal to 2x the height  Elliptical: width more than 2x, but less or equal to 3x the height  Flattened: width more than 3x the height Amount of cryptostomata –  No/few: Not visible or less than 4  Normal :4 or more

Statistical analyses of the number of adventitious branches were made using one-way ANOVA. Occurrence of rhizoid and cryptostomata were analysed by Fisher's Exact Test and the growth and cross section shape were analyzed by chi-square methods. All analyses were made using R version 2.9.0 (R Development Core Team 2009).

Results Number of adventitious branches The vegetative reproducing Swedish F. radicans had significantly more adventitious branches than the sexually producing categories (F4, 45 = 86.26, p < 0.001,). Swedish F. vesiculosus also showed significant more branches than the Estonian counterpart. (F4, 45 = 86.26, p < 0.01).

Figure 1 Number of adventitious branches per g measured wet weight in plants from the four combinations of species/origin. Error bars show confidence interval (n= 10)

Rhizoid development by the adventitious branches Very few of the adventitious branches developed rhizoids. The results showed no differences between categories (p = 0.34). Only 7 of the total number of branches used(450) where firmly attached to the platter.

Figure 2 The percentage of adventitious branches that developed rhizoids showed no significant differencies between the origin/species combinations [ n = 100(Swedish F. radicans); 120(Estonian F. radicans); 120(Swedish F. vesiculosus); 110(Estonian F. vesiculosus) ]

The overall thallus growth and the cross section shape The Estonian F. radicans had the highest general growth rate with 88% having substantial growth, (χ² = 120.6; df=6; p<0.001). In the samples of Swedish F. radicans, no single adventitious branch were classified as having substantial growth (Fig 3). The two different categories of F. radicans showed generally a growth pattern with rounded cross sections, whereas the Swedish F. vesiculosus were generally elliptical, (χ² = 432.2; df=6; p<0.001). The most flattened growth pattern were found in Estonian F. vesiculosus where 54% had a flat cross section and 38% where elliptical (Fig. 4).

Figure 3 The relative amount of growth for each Fucus category divided into the 3 classifications defined. (n=100,120,120,110 respectively).

Figure 4 A comparison of the cross section shapes for each Fucus category divided into different flatness classifications of the thallus. (n=100,120,120,110 respectively).

The amount of Cryptostomata Although F. vesiculosus developed less cryptostomata overall than did F. radicans, different patterns were found depending on the origin. In Sweden F. vesiculosus had more cryptostomata than F. radicans (p < 0.01) but in Estonia the species-cryptostomata relation was reversed (Fig. 5).

Figure 5 The results indicate that F. radicans in Estonia had slightly more samples with a higher amount of cryptostomata compared to the F. vesiculosus populations, but with the opposite relation found in the populations originating from Sweden (n=100,120,120,110 respectively)

Discussion The results from this study shows that the vegetative reproducing Swedish F. radicans had significantly more adventitious branches than the predominantly sexually reproducing populations of F. vesiculosus and the F. radicans population originating from Estonia. In line with the hypothesis stipulated, this could indicate that Swedish F. radicans are allocating more resources into producing vegetative propagules for new individuals instead of investing efforts in producing sexual gametes. This could imply that the extent of branch development in Swedish F. radicans may be a result of adaption towards an amount of branch development that brings a reproductive advantage in the special circumstances of the Bothnian Sea. Presuming that the majority of adventitious branches produced are not departed from the source plant and thus brings a more shrubby morphological overall appearance, a second interpretation of the results is possible. Traits such as extensive branching could potentially be an advantage in the prevailing conditions by extending the surface area for nutrient uptake while still keeping an overall size. The more compact morphology could make the plant less vulnerable to external factors like ice scouring or limitations in nutrient resources. The extended nutrient uptake capabilities could also imply that the improved vegetative reproductive abilities could be a secondary effect and may be the result of an initial morphological adaption towards extended surface area. Whether or not any of these adaptive forces were initially driving the adaption towards a more extensive branching is not clear, but the advan- tages from both of these consequences may be crucial for the fitness of Swedish F. radicans.

One question arising when analysing the amounts of branching is if the morphological differences are a case of adaption or plasticity. In the case of the two F. radicans populations, plasticity could not be excluded due to the fact that the spatially split populations initially had different environmental conditions, even if the recent environment have been the same. This would however imply that the plasticity is a trait unique for F. radicans because I) the results comparing the two different sympatric Fucus species from the Swedish coast also show clear difference in the amount of branching, II) the spatially split F. vesiculosus population does not show the same obvious difference in branching as the F. radicans populations.

The test of rhizoid development under artificial conditions showed less overall growth of rhizoids than expected and no species/origin combination produced more rhizoids than the others. As shown by the results the overall growth of the adventitious branches were not low in general. This signs of a basically sound environmental living conditions should

14 consequently rule out the environment to be the cause for the generally meagre rhizoid development and leads to the suspicion that some key environmental factors controlling rhizoid growth have been poorly understood, and that the trigger inducing rhizoid development is still to be found. A previous studie (Tatarenkov et al. 2005) has shown significant differences between the rhizoid development in F. radicans and F. vesiculosus and a more extensive rhizoid development overall. If further studies are to be performed, preparatory work is needed to examine the environmental factors trigging the growth of rhizoids, provided such factors are to be found. The success rate of vegetative propagules in natural conditions is another issue of interest for understanding the dynamics of the evolutionary pathways, this is an area largely yet to be investigated.

To try to answer the question if the vegetative reproduction is the key to the emergence of sympatric Fucus populations in the Bothnian Sea, it is appropriate to monitor alternative reasons for the current spatial presence of F. radicans. That is, what are F. radicans merits in this particular environment compared to its larger sibling species F. vesiculosus? If no restricting environmental factors are present it is generally a good idea to maximize the available resources and grow big, as this will enhance the competitive ability in several ways, as for example suppression of competition or greater reproductive ability. On the other hand if resources become sparser, predation increases, different forms of environmental stress factors are present, a bigger body may not be the best solution and could possibly backlash due to difficulties at maintaining the more abundant biomass and coping with temporary harsher conditions. This generally mean that for F. radicans there may be more benefits than reproductive advantage alone to favor the species in the northern Bothnia Sea which is constituting one of the margins of the fundamental niche for Fucus species. Some environmental factors for further studies are the physiological impact of regional variations in seasonal salinity due to river outwash in the north, or the consequences from ice scouring and the effects of the more extended periods of permanent sea ice in the north.

A puzzling situation is the presence of F. radicans in Estonia. In this area where F. radicans reproduces sexually the benefits of vegetative reproduction or the possible impact of stress factors areas are not that obvious. One possible reason for the presence here (L. Kautsky pers. comm.) is that the sea bed is constituted by coarse gravel over finer sediments. This may be prohibiting the larger F. vesiculosus from reaching reproductive size. The cause for this could be that plants of greater size, as F. vesiculosus, established on the relative fine sized gravel is

15 easier moved away by currents or wave action. This is then possibly a lesser problem for the more slender built F. radicans.

Comparing the two Estonian Fucus species, F. radicans had slightly more cryptostomata than F. vesiculosus. With the former species having a relatively slimmer thallus cross section, more cryptostomata and thus more hyaline hairs for nutrient uptake could be a way of compensating for the relative lesser thallus surface area. However it should be noted that the greater amount of cryptostomata in this study could be an effect of the overall greater growth noted in the Estonian F. vesiculosus samples. There could also be a lesser need for surface area in F. radicans due to the geometric laws stating that a smaller body possesses a greater surface area to volume quota. Contrary to the Estonian populations the Swedish F. radicans showed less cryptostomata than the Swedish F. vesiculosus. This is opposing the nutrient theory proposed for the Estonian populations but could be a logic consequence of the comparably more shrubby appearance and more extensive branching in Swedish F. radicans compared to the Estonian counterpart. This shrubbiness could serve as an alternative mean of extending the surface area.

Then why do not the Swedish populations use the same strategy with more cryptostomata as the Estonian populations? The reasons could be twofold. Firstly the branching could serve a vital secondary purpose as extended capacity for vegetative reproduction in the northern low salinity environment generally hampering sexual reproduction ( Serrão et al. 1996; Serrão et al. 1999). Secondary, it could be a way of improving the durability against herbivores by minimizing the hyaline hairs otherwise needed and possibly attractive for herbivores. The latter would also be in line with the proposal by Forslund (2009b) that Swedish F. radicans has lower levels of chemical defense than F. vesiculosus which consequently could imply that F. radicans are more vulnerable to herbivores. By concatenating the results from this study and the previous discussion of evolutionary forces, a web can be constructed illustrating the suggested interacting factors and thus possibly explaining the spatial occurrence of Fucus radicans in the Baltic Sea (Fig 6). In comparing the ability for nutrient uptake in F. radicans to sympatric populations of F. vesiculosus, it is possible to propose that F. radicans could be using an alternative strategy for extending the surface area. This strategy may be well suited to the Bothnian Gulf with implications for reproductive success in the north and to herbivore defense abilities in the south thus delimiting the population to the current spatial range.

Figure 6 Comparing the ability for nutrient uptake in F. radicans to sympatric populations of F. vesiculosus with the Estonian population to the right and the Swedish to the left, the ability of F. vesiculosus are used as a reference level on the line indicating the necessary level of nutrient uptake ability. Divergent abilities from this norm is represented by arrows indicating traits that are positive(up) or negative(down). Attached are miniatures of the results from this study, supporting the claims for the deviations in nutrient uptake ability. To the far left are some proposed derived consequences of the nutrient deviations influencing the spatial occurrence of the Swedish F. radicans. These traits are suggested to have implications for reproductive success in the north and to herbivore defense abilities in the south thus limiting the population to the current spatial range.

In contemplating some scenarios describing the sympatric speciation process and especially emphasizing the impact from the vegetative reproduction strategy used by Swedish F. radicans, it is probable that a few clonal individuals of F. radicans have succeeded in populating vast spatial areas (Tatarenkov et al. 2005). This could have been made possible through exploiting this alternative reproduction strategy and by doing so tweaking the rules of speciation. This alternative path is realized by effectively displacing sexual reproduction as the common framework for the speciation processes and thus minimizing the counteracting forces of hybridization. Maybe these resulting populations are to be regarded as a transitional form in a temporary abnormal evolutionary situation, with clonal individuals exploiting a temporary marginal environment to make improved clonal abilities to prosper in a timeframe

17 of limited endurance. The longevity of the genetically restricted populations of clonal F. radicans will ultimately give the answer.

Even if we are witnessing a turmoil of ongoing speciation processes beginning after the deglaciation about 8000 years ago, it would be extraordinary to imagine a rapid speciation with these type of adaption’s realized in a very short time space, even as short as 400 years as proposed in models by Pereyra et al.(2008) based on microsatellite markers. The parallels to this would be few worldwide and the tendency for F. radicans populations to emerge in some different areas of the Baltic Sea under slightly different environmental conditions showing such minor morphological differences is amazing. Although somewhat improbable there is a possibility that convergent evolution has occurred in the geographically separated areas of the Bothnian Sea and of Ösel. Somewhat more probable is an initial evolution in one area and subsequent spreading and readapting into another. Maybe clonality in the Swedish/Finnish population is such a secondary trait recently emerging. The high heterozygosity found among clonal populations (Johanson 2008) could support this. If this trait of clonality commonly known in marginal areas is indeed a recent evolution we can expect further loss of sexual reproductive abilities in the future, based on indications that environmental suppression of sexual recruitment may lead towards sterility (Eckert 2002). Provided these populations of F. radicans emerged suddenly and maybe even separately, some traits already inherent may suddenly have prospered perhaps due to a change in the environmental conditions. One possibility is that a suppressed relict population of F. radicans has been present in the Baltic Sea. Another possible scenario supported by the fast and simultaneous evolution of the F. radicans populations and the morphologic relationship between F. vesiculosus and F. radicans is polyploidy. If a species resembling F. radicans once was the now extinct ancestor to the current F. vesiculosus we could maybe be witnessing a retreat from polyploidy triggered by the prevailing environmental conditions. Regardless the specific history, the evolutionary history of F. radicans is probably a scenario consisting of a mix of punctuated equilibrium phases and intermediate gradualism where the former pattern have been realized through evolutionary opportunism in situations of sudden environmental changes.

To conclude the experiences from this study, several adaptations of possible importance are found in the Swedish populations of F. radicans. These adaptations are: the more extensive branching, the vegetative reproduction, the possibly adapted levels of cryptostomata, and the morphological traits general to F. radicans. It would probably be unwise to view these adaptions as singular individual traits, but instead as a web of intricate combined and coordinated adaptations resulting in populations well suited to the very special marginal environment of the Bothnian Sea. It is not obvious that vegetative reproduction ability is the key for the evolution of Fucus radicans, but regardless of whether the clonality was an original trait and a key for the speciation to occur, or was a secondary adaption and maybe ultimately an evolutionary dead end, it is very likely to have been of great importance for the species present success in the Bothnian Sea.

Acknowledgements Many thanks for the general support to the Plant Ecology people in the department of Botany at the University of Stockholm. Also thanks to the staff at the Askö Marine Laboratories for facilitating the practical parts of this work. Very special thanks to my supervisors Helena Forslund and Lena Kautsky for sharing their knowledge and supporting me with invaluable guidance and advice.

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Serien Plants & Ecology (ISSN 1651-9248) har tidigare haft namnen "Meddelanden från Växtekologiska avdelningen, Botaniska institutionen, Stockholms Universitet" nummer 1978:1 – 1993:1 samt "Växtekologi". (ISSN 1400-9501) nummer 1994:1 – 2003:3.

Följande publikationer ingår i utgivningen:

1978:1 Liljelund, Lars-Erik: Kompendium i matematik för ekologer. 1978:2 Carlsson, Lars: Vegetationen på Littejåkkadeltat vid Sitasjaure, Lule Lappmark. 1978:3 Tapper, Per-Göran: Den maritima lövskogen i Stockholms skärgård. 1978:4: Forsse, Erik: Vegetationskartans användbarhet vid detaljplanering av fritidsbebyggelse. 1978:5 Bråvander, Lars-Gunnar och Engelmark, Thorbjörn: Botaniska studier vid Porjusselets och St. Lulevattens stränder i samband med regleringen 1974. 1979:1 Engström, Peter: Tillväxt, sulfatupptag och omsättning av cellmaterial hos pelagiska saltvattensbakterier. 1979:2 Eriksson, Sonja: Vegetationsutvecklingen i Husby-Långhundra de senaste tvåhundra åren. 1979:3 Bråvander, Lars-Gunnar: Vegetation och flora i övre Teusadalen och vid Auta- och Sitjasjaure; Norra Lule Lappmark. En översiktlig inventering med anledning av områdets exploatering för vattenkraftsändamål i Ritsemprojektet. 1979:4 Liljelund, Lars-Erik, Emanuelsson, Urban, Florgård, C. och Hofman-Bang, Vilhelm: Kunskapsöversikt och forskningsbehov rörande mekanisk påverkan på mark och vegetation. 1979:5 Reinhard, Ylva: Avloppsinfiltration - ett försök till konsekvensbeskrivning. 1980:1 Telenius, Anders och Torstensson, Peter: Populationsstudie på Spergularia marina och Spergularia media. I Frödimorfism och reproduktion. 1980:2 Hilding, Tuija: Populationsstudier på Spergularia marina och Spergularia media. II Resursallokering och mortalitet. 1980:3 Eriksson, Ove: Reproduktion och vegetativ spridning hos Potentilla anserina L. 1981:1 Eriksson, Torsten: Aspekter på färgvariation hos Dactylorhiza sambucina. 1983:1 Blom, Göran: Undersökningar av lertäkter i Färentuna, Ekerö kommun. 1984:1 Jerling, Ingemar: Kalkning som motåtgärd till försurningen och dess effekter på blåbär, Vaccinium myrtillus. 1986:1 Svanberg, Kerstin: En studie av grusbräckans (Saxifraga tridactylites) demografi. 1986:2 Nyberg, Hans: Förändringar i träd- och buskskiktets sammansättning i ädellövskogen på Tullgarnsnäset 1960-1983. 1987:1 Edenholm, Krister: Undersökningar av vegetationspåverkan av vildsvinsbök i Tullgarnsområdet. 1987:2 Nilsson, Thomas: Variation i fröstorlek och tillväxthastighet inom släktet Veronica. 1988:1 Ehrlén, Johan: Fröproduktion hos vårärt (Lathyrus vernus L.). - Begränsningar och reglering. 1988:2 Dinnétz, Patrik: Local variation in degree of gynodioecy and protogyny in Plantago maritima. 1988:3 Blom, Göran och Wincent, Helena: Effekter of kalkning på ängsvegetation. 1989:1 Eriksson, Pia: Täthetsreglering i Littoralvegetation. 1989:2 Kalvas, Arja: Jämförande studier av Fucus-populationer från Östersjön och västkusten. 1990:1 Kiviniemi, Katariina: Groddplantsetablering och spridning hos smultron, Fragaria vesca. 1990:2 Idestam-Almquist, Jerker: Transplantationsförsök med Borstnate.

1992:1 Malm, Torleif: Allokemisk påverkan från mucus hos åtta bruna makroalger på epifytiska alger. 1992:2 Pontis, Cristina: Om groddknoppar och tandrötter. Funderingar kring en klonal växt: Dentaria bulbifera. 1992:3 Agartz, Susanne: Optimal utkorsning hos Primula farinosa. 1992:4 Berglund, Anita: Ekologiska effekter av en parasitsvamp - Uromyces lineolatus på Glaux maritima (Strandkrypa). 1992:5 Ehn, Maria: Distribution and tetrasporophytes in populations of Chondrus crispus Stackhouse (Gigartinaceae, Rhodophyta) on the west coast of Sweden. 1992:6 Peterson, Torbjörn: Mollusc herbivory. 1993:1 Klásterská-Hedenberg, Martina: The influence of pH, N:P ratio and zooplankton on the phytoplanctic composition in hypertrophic ponds in the Trebon-region, Czech Republic. 1994:1 Fröborg, Heléne: Pollination and seed set in Vaccinium and Andromeda. 1994:2 Eriksson, Åsa: Makrofossilanalys av förekomst och populationsdynamik hos Najas flexilis i Sörmland. 1994:3 Klee, Irene: Effekter av kvävetillförsel på 6 vanliga arter i gran- och tallskog. 1995:1 Holm, Martin: Beståndshistorik - vad 492 träd på Fagerön i Uppland kan berätta. 1995:2 Löfgren, Anders: Distribution patterns and population structure of an economically important Amazon palm, Jessenia bataua (Mart.) Burret ssp. bataua in Bolivia. 1995:3 Norberg, Ylva: Morphological variation in the reduced, free floating Fucus vesiculosus, in the Baltic Proper. 1995:4 Hylander, Kristoffer & Hylander, Eva: Mount Zuquala - an upland forest of Ethiopia. Floristic inventory and analysis of the state of conservation. 1996:1 Eriksson, Åsa: Plant species composition and diversity in semi-natural grasslands - with special emphasis on effects of mycorrhiza. 1996:2 Kalvas, Arja: Morphological variation and reproduction in Fucus vesiculosus L. populations. 1996:3 Andersson, Regina: Fågelspridda frukter kemiska och morfologiska egenskaper i relation till fåglarnas val av frukter. 1996:4 Lindgren, Åsa: Restpopulationer, nykolonisation och diversitet hos växter i naturbetesmarker i sörmländsk skogsbygd. 1996:5 Kiviniemi, Katariina: The ecological and evolutionary significance of the early life cycle stages in plants, with special emphasis on seed dispersal. 1996:7 Franzén, Daniel: Fältskiktsförändringar i ädellövskog på Fagerön, Uppland, beroende på igenväxning av gran och skogsavverkning. 1997:1 Wicksell, Maria: Flowering synchronization in the Ericaceae and the Empetraceae. 1997:2 Bolmgren, Kjell: A study of asynchrony in phenology - with a little help from Frangula alnus. 1997:3 Kiviniemi, Katariina: A study of seed dispersal and recruitment of plants in a fragmented habitat. 1997:4 Jakobsson, Anna: Fecundity and abundance - a comparative study of grassland species. 1997:5 Löfgren, Per: Population dynamics and the influence of disturbance in the Carline Thistle, Carlina vulgaris. 1998:1 Mattsson, Birgitta: The stress concept, exemplified by low salinity and other stress factors in aquatic systems. 1998:2 Forsslund, Annika & Koffman, Anna: Species diversity of lichens on decaying wood - A comparison between old-growth and managed forest.

1998:3 Eriksson, Åsa: Recruitment processes, site history and abundance patterns of plants in semi-natural grasslands. 1998:4 Fröborg, Heléne: Biotic interactions in the recruitment phase of forest field layer plants. 1998:5 Löfgren, Anders: Spatial and temporal structure of genetic variation in plants. 1998:6 Holmén Bränn, Kristina: Limitations of recruitment in Trifolium repens. 1999:1 Mattsson, Birgitta: Salinity effects on different life cycle stages in Baltic and North Sea Fucus vesiculosus L. 1999:2 Johannessen, Åse: Factors influencing vascular epiphyte composition in a lower montane rain forest in Ecuador. An inventory with aspects of altitudinal distribution, moisture, dispersal and pollination. 1999:3 Fröborg, Heléne: Seedling recruitment in forest field layer plants: seed production, herbivory and local species dynamics. 1999:4 Franzén, Daniel: Processes determining plant species richness at different scales - examplified by grassland studies. 1999:5 Malm, Torleif: Factors regulating distribution patterns of fucoid seaweeds. A comparison between marine tidal and brackish atidal environments. 1999:6 Iversen, Therese: Flowering dynamics of the tropical tree Jacquinia nervosa. 1999:7 Isæus, Martin: Structuring factors for Fucus vesiculosus L. in Stockholm south archipelago - a GIS application. 1999:8 Lannek, Joakim: Förändringar i vegetation och flora på öar i Norrtälje skärgård. 2000:1 Jakobsson, Anna: Explaining differences in geographic range size, with focus on dispersal and speciation. 2000:2 Jakobsson, Anna: Comparative studies of colonisation ability and abundance in semi-natural grassland and deciduous forest. 2000:3 Franzén, Daniel: Aspects of pattern, process and function of species richness in Swedish seminatural grasslands. 2000:4 Öster, Mathias: The effects of habitat fragmentation on reproduction and population structure in Ranunculus bulbosus. 2001:1 Lindborg, Regina: Projecting extinction risks in plants in a conservation context. 2001:2 Lindgren, Åsa: Herbivory effects at different levels of plant organisation; the individual and the community. 2001:3 Lindborg, Regina: Forecasting the fate of plant species exposed to land use change. 2001:4 Bertilsson, Maria: Effects of habitat fragmentation on fitness components. 2001:5 Ryberg, Britta: Sustainability aspects on Oleoresin extraction from Dipterocarpus alatus. 2001:6 Dahlgren, Stefan: Undersökning av fem havsvikar i Bergkvara skärgård, östra egentliga Östersjön. 2001:7 Moen, Jon; Angerbjörn, Anders; Dinnetz, Patrik & Eriksson Ove: Biodiversitet i fjällen ovan trädgränsen: Bakgrund och kunskapsläge. 2001:8 Vanhoenacker, Didrik: To be short or long. Floral and inflorescence traits of Bird`s eye primrose Primula farinose, and interactions with pollinators and a seed predator. 2001:9 Wikström, Sofia: Plant invasions: are they possible to predict? 2001:10 von Zeipel, Hugo: Metapopulations and plant fitness in a titrophic system – seed predation and population structure in Actaea spicata L. vary with population size. 2001:11 Forsén, Britt: Survival of Hordelymus europaéus and Bromus benekenii in a deciduous forest under influence of forest management. 2001:12 Hedin, Elisabeth: Bedömningsgrunder för restaurering av lövängsrester i Norrtälje kommun.

2002:1 Dahlgren, Stefan & Kautsky, Lena: Distribution and recent changes in benthic macrovegetation in the Baltic Sea basins. – A literature review. 2002:2 Wikström, Sofia: Invasion history of Fucus evanescens C. Ag. in the Baltic Sea region and effects on the native biota. 2002:3 Janson, Emma: The effect of fragment size and isolation on the abundance of Viola tricolor in semi-natural grasslands. 2002:4 Bertilsson, Maria: Population persistance and individual fitness in Vicia pisiformis: the effects of habitat quality, population size and isolation. 2002:5 Hedman, Irja: Hävdhistorik och artrikedom av kärlväxter i ängs- och hagmarker på Singö, Fogdö och norra Väddö. 2002:6 Karlsson, Ann: Analys av florans förändring under de senaste hundra åren, ett successionsförlopp i Norrtälje kommuns skärgård. 2002:7 Isæus, Martin: Factors affecting the large and small scale distribution of fucoids in the Baltic Sea. 2003:1 Anagrius, Malin: Plant distribution patterns in an urban environment, Södermalm, Stockholm. 2003:2 Persson, Christin: Artantal och abundans av lavar på askstammar – jämförelse mellan betade och igenvuxna lövängsrester. 2003:3 Isæus, Martin: Wave impact on macroalgal communities. 2003:4 Jansson-Ask, Kristina: Betydelsen av pollen, resurser och ljustillgång för reproduktiv framgång hos Storrams, Polygonatum multiflorum. 2003:5 Sundblad, Göran: Using GIS to simulate and examine effects of wave exposure on submerged macrophyte vegetation. 2004:1 Strindell, Magnus: Abundansförändringar hos kärlväxter i ädellövskog – en jämförelse av skötselåtgärder. 2004:2 Dahlgren, Johan P: Are metapopulation dynamics important for aquatic plants? 2004:3 Wahlstrand, Anna: Predicting the occurrence of Zostera marina in bays in the Stockholm archipelago,northern Baltic proper. 2004:4 Råberg, Sonja: Competition from filamentous algae on Fucus vesiculosus – negative effects and the implications on biodiversity of associated flora and fauna. 2004:5 Smaaland, John: Effects of phosphorous load by water run-off on submersed plant communities in shallow bays in the Stockholm archipelago. 2004:6 Ramula Satu: Covariation among life history traits: implications for plant population dynamics. 2004:7 Ramula, Satu: Population viability analysis for plants: Optimizing work effort and the precision of estimates. 2004:8 Niklasson, Camilla: Effects of nutrient content and polybrominated phenols on the reproduction of Idotea baltica and Gammarus ssp. 2004:9 Lönnberg, Karin: Flowering phenology and distribution in fleshy fruited plants. 2004:10 Almlöf, Anette: Miljöfaktorers inverkan på bladmossor i Fagersjöskogen, Farsta, Stockholm. 2005:1 Hult, Anna: Factors affecting plant species composition on shores - A study made in the Stockholm archipelago, Sweden. 2005:2 Vanhoenacker, Didrik: The evolutionary pollination ecology of Primula farinosa. 2005:3 von Zeipel, Hugo: The plant-animal interactions of Actea spicata in relation to spatial context. 2005:4 Arvanitis, Leena T.: Butterfly seed predation. 2005:5 Öster, Mathias: Landscape effects on plant species diversity – a case study of Antennaria dioica. 2005:6 Boalt, Elin: Ecosystem effects of large grazing herbivores: the role of nitrogen.

2005:7 Ohlson, Helena: The influence of landscape history, connectivity and area on species diversity in semi-natural grasslands. 2005:8 Schmalholz, Martin: Patterns of variation in abundance and fecundity in the endangered grassland annual Euphrasia rostkovia ssp. Fennica. 2005:9 Knutsson, Linda: Do ants select for larger seeds in Melampyrum nemorosum? 2006:1 Forslund, Helena: A comparison of resistance to herbivory between one exotic and one native population of the brown alga Fucus evanescens. 2006:2 Nordqvist, Johanna: Effects of Ceratophyllum demersum L. on lake phytoplankton composition. 2006:3 Lönnberg, Karin: Recruitment patterns, community assembly, and the evolution of seed size. 2006:4 Mellbrand, Kajsa: Food webs across the waterline - Effects of marine subsidies on coastal predators and ecosystems. 2006:5 Enskog, Maria: Effects of eutrophication and marine subsidies on terrestrial invertebrates and plants. 2006:6 Dahlgren, Johan: Responses of forest herbs to the environment. 2006:7 Aggemyr, Elsa: The influence of landscape, field size and shape on plant species diversity in grazed former arable fields. 2006:8 Hedlund, Kristina: Flodkräftor (Astacus astacus) i Bornsjön, en omnivors påverkan på växter och snäckor. 2007:1 Eriksson, Ove: Naturbetesmarkernas växter- ekologi, artrikedom och bevarandebiologi. 2007:2 Schmalholz, Martin: The occurrence and ecological role of refugia at different spatial scales in a dynamic world. 2007:3 Vikström, Lina: Effects of local and regional variables on the flora in the former semi-natural grasslands on Wäsby Golf club’s course. 2007:4 Hansen, Joakim: The role of submersed angiosperms and charophytes for aquatic fauna communities. 2007:5 Johansson, Lena: Population dynamics of Gentianella campestris, effects of grassland management, soil conditions and the history of the landscape 2007:6 von Euler, Tove: Sex related colour polymorphism in Antennaria dioica. 2007:7 Mellbrand, Kajsa: Bechcombers, landlubbers and able seemen: Effects of marine subsidies on the roles of arthropod predators in coastal food webs. 2007:8 Hansen, Joakim: Distribution patterns of macroinvertebrates in vegetated, shallow, soft-bottom bays of the Baltic Sea. 2007:9 Axemar, Hanna: An experimental study of plant habitat choices by macroinvertebrates in brackish soft-bottom bays. 2007:10 Johnson, Samuel: The response of bryophytes to wildfire- to what extent do they survive in-situ? 2007:11 Kolb, Gundula: The effects of cormorants on population dynamics and food web structure on their nesting islands. 2007:12 Honkakangas, Jessica: Spring succession on shallow rocky shores in northern Baltic proper. 2008:1 Gunnarsson, Karl: Påverkas Fucus radicans utbredning av Idotea baltica? 2008:2 Fjäder, Mathilda: Anlagda våtmarker i odlingslandskap- Hur påverkas kärlväxternas diversitet? 2008:3 Schmalholz, Martin: Succession in boreal bryophyte communities – the role of microtopography and post-harvest bottlenecks. 2008:4 Jokinen, Kirsi: Recolonization patterns of boreal forest vegetation following a severe flash flood.

2008:5 Sagerman, Josefin: Effects of macrophyte morphology on the invertebrate fauna in the Baltic Sea. 2009:1 Andersson, Petter: Quantitative aspects of plant-insect interaction in fragmented landscapes – the role of insect search behaviour. 2009:2 Kolb, Gundula: The effects of cormorants on the plant-arthropod food web on their nesting islands. 2009:3 Johansson, Veronika: Functional traits and remnant populations in abandoned semi-natural grasslands. 2009: 4 König, Malin: Phenotypic selection on flowering phenology and herbivory in Cardamine amara. 2009:5 Forslund, Helena: Grazing and the geographical range of seaweeds – The introduced Fucus evanescens and the newly described Fucus radicans. 2009:6 von Euler, Tove: Local adaptation and life history differentiation in plant populations.