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Herbivory, phenotypic variation, and reproductive barriers in fucoids
Stockholm University, Faculty of Science, Department of Botany.
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Along the shores of the Northern hemisphere Fucus (Phaeophyceae) species are a prominent presence, providing substrate, shelter, and food for many species. Fucus evanescens, a non-indigenous species (NIS) in Sweden, and F. radicans, a recently described species that so far has only been found inside the species poor Baltic Sea, are the focus of this thesis.

Interactions with enemies (e.g. predators, herbivores, parasites) have been shown to play a role in the success of NIS. The low consumption of Fucus evanescens by the generalist gastropod Littorina littorea in Sweden was found to depend on high levels of chemical defense in the introduced population, not the failure of the herbivore to recognize F. evanescens as suitable food.

A survey of the relative abundance of F. radicans and F. vesiculosus and the most common associated fauna along the Swedish Bothnian Sea coast showed that F. radicans and F. vesiculosus are equally abundant throughout the range of F. radicans. The most common associated fauna were found to be more abundant on F. radicans compared to F. vesiculosus.  In Sweden, where F. radicans had lower levels of defense chemicals than F. vesiculosus, F. radicans was grazed more than F. vesiculosus in bioassays. This could, together with other factors, influence the range of F. radicans.

Fucus radicans and F. vesiculosus are closely related, recently separated, and growing sympatrically, therefore, possible reproductive barriers between F. radicans and F. vesiculosus were studied. In Estonia F. radicans and F. vesiculosus reproduces at different times of the year. No such clear reproductive barrier was found between the two species in Sweden where they reproduce at the same time and fertilization success and germling survival were the same for hybrids as for F. vesiculosus.

Since the high clonality of F. radicans means that the gentic diversity in F. radicans populations is low I investigated how genetic diversity translates to phenotypic diversity in nine traits. Phlorotannin levels, recovery after desiccation, and recovery after freezing showed inherited variation, while the other six traits showed no variation related to genetic diversity. Phenotypic variation in populations of F. radicans will be higher in populations with higher genetic diversity and this might be beneficial to the community.

Place, publisher, year, edition, pages
Stockholm: Department of Botany, Stockholm University , 2012. , 49 p.
Keyword [en]
Non-indigenous species, Enemy Release Hypothesis, Asexual reproduction, Phlorotannins, Distribution
National Category
Ecology
Research subject
Plant Ecology
Identifiers
URN: urn:nbn:se:su:diva-79481ISBN: 978-91-7447-538-8 (print)OAI: oai:DiVA.org:su-79481DiVA: diva2:549818
Public defence
2012-10-11, föreläsningssalen, Botaniska institutionen, Lilla Frescativägen 5, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 3: Accepted.

Available from: 2012-09-19 Created: 2012-09-04 Last updated: 2012-09-06Bibliographically approved
List of papers
1. Grazing and geographic range of the Baltic seaweed Fucus radicans (Phaeophyceae)
Open this publication in new window or tab >>Grazing and geographic range of the Baltic seaweed Fucus radicans (Phaeophyceae)
2012 (English)In: Marine Biology Research, ISSN 1745-1000, E-ISSN 1745-1019, Vol. 8, no 4, 322-330 p.Article in journal (Refereed) Published
Abstract [en]

The range of the recently described seaweed Fucus radicans is limited to the Bothnian Sea and the northern Baltic Sea while the range of the sympatric Fucus vesiculosus extends outside the Baltic Sea. Here we present results from a survey of the distribution and relative abundance of F. radicans and F. vesiculosus and abundance of associated herbivores along the range of F. radicans in Sweden. Both Fucus species were equally common. Herbivores were found in significantly higher numbers on F. radicans. The range of the herbivore Idotea balthica overlaps the southern range of F. radicans and is known to decrease the abundance of fucoids through grazing. We therefore hypothesized that if I. balthica has a preference for F. radicans it could affect the range of F. radicans. To test the preference of I. balthica we performed a bioassay where it had a choice between F. radicans and F. vesiculosus. Another bioassay was performed with the most common herbivore in our survey, Gammarus spp. Both herbivores consumed significantly more F. radicans than F. vesiculosus. Our results indicate that grazing may be an important factor in limiting the southern range of F. radicans along the Swedish coast.

Keyword
The Baltic Sea, Idotea balthica, phlorotannin, distribution, growth rate
National Category
Botany Ecology
Research subject
Plant Ecology
Identifiers
urn:nbn:se:su:diva-79567 (URN)10.1080/17451000.2011.637565 (DOI)000302439700002 ()
Available from: 2012-09-06 Created: 2012-09-06 Last updated: 2017-12-07Bibliographically approved
2. Higher resistance to herbivory in introduced compared to native populations of a seaweed
Open this publication in new window or tab >>Higher resistance to herbivory in introduced compared to native populations of a seaweed
2010 (English)In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 164, no 3, 833-840 p.Article in journal (Refereed) Published
Abstract [en]

Non-indigenous species (NIS) are important components of global change, and in order to manage such species it is important to understand which factors affect their success. Interactions with enemies in the new range have been shown to be important for the outcome of introductions, but thus far most studies on NIS-enemy interactions have considered only specialist herbivores in terrestrial systems. Here we present the results from the first biogeographic study that compares herbivore resistance between populations in the native and new region of a non-indigenous seaweed. We show that low consumption of the non-indigenous seaweed by a generalist herbivore is caused by higher chemical defence levels and herbivore resistance in the new range-and not by the failure of the herbivore to recognise the non-indigenous seaweed as a suitable host. Since most seaweed-herbivore interactions are dominated by generalist herbivores, this pattern could be common in marine communities. Our results also reveal that traits used to predict the invasive potential of species, such as their resistance to enemies, can change during the invasion process, but not always in the way predicted by dominant theories.

Keyword
Non-indigenous species, Enemy release, Generalist grazer, Fucus evanescens, Littorina littorea
National Category
Botany Ecology
Research subject
Plant Ecology
Identifiers
urn:nbn:se:su:diva-49552 (URN)10.1007/s00442-010-1767-1 (DOI)000283097900024 ()
Available from: 2010-12-15 Created: 2010-12-15 Last updated: 2017-12-11Bibliographically approved
3. Reproduction and reproductive isolation in Fucus radicans (Phaeophyceae)
Open this publication in new window or tab >>Reproduction and reproductive isolation in Fucus radicans (Phaeophyceae)
(English)In: Marine Biology Research, ISSN 1745-1000, E-ISSN 1745-1019Article in journal (Refereed) Accepted
Abstract [en]

Recent morphological and genetic studies show that Fucus radicans is a separate species from the sympatric F. vesiculosus. Fucus radicans recently diverged from F. vesiculosus in the Baltic Sea where populations grow in mixed stands. Thus, strong reproductive barriers are expected to be in place to prevent introgression. The seasonal timing of reproduction of the two species in Estonia was shown to be different, likely forming an effective pre-zygotic reproductive barrier. In Sweden, however, no such temporal difference was found. We artificially crossed Swedish F. radicans and F. vesiculosus to identify other potential reproductive barriers. Fertilization success and survival was equally high within and between species in the artificial crossings, suggesting no early post-zygote barriers. Both species recruit new thalli both sexually and asexually, but F. radicans is generally more asexual than F. vesiculosus. By studying their reproductive efforts we found that Swedish F. radicans allocates more resources to adventitious branches than to gamete production compared to F. radicans in Estonia and F. vesiculosus in both Sweden and Estonia. This indicates that Swedish F. radicans has an asexual reproductive strategy while Estonian F. radicans and F. vesiculosus have sexual reproductive strategies.

Keyword
Fucus vesiculosus, hybridization, reproductive effort, asexual reproduction, sexual reproduction
National Category
Botany Ecology
Research subject
Plant Ecology
Identifiers
urn:nbn:se:su:diva-79477 (URN)
Funder
Formas
Available from: 2012-09-04 Created: 2012-09-04 Last updated: 2017-12-07Bibliographically approved
4. Phenotypic variation in sexually and asexually recruited individuals of the Baltic Sea endemic macroalga Fucus radicans: in the field and after growth in a common-garden
Open this publication in new window or tab >>Phenotypic variation in sexually and asexually recruited individuals of the Baltic Sea endemic macroalga Fucus radicans: in the field and after growth in a common-garden
Show others...
2012 (English)In: BMC Ecology, ISSN 1472-6785, E-ISSN 1472-6785, Vol. 12, 2- p.Article in journal (Refereed) Published
Abstract [en]

BACKGROUND: Most species of brown macroalgae recruit exclusively sexually. However, Fucus radicans, a dominant species in the northern Baltic Sea, recruits new attached thalli both sexually and asexually. The level of asexual recruitment varies among populations from complete sexual recruitment to almost (> 90%) monoclonal populations. If phenotypic traits have substantial inherited variation, low levels of sexual activity will decrease population variation in these traits, which may affect function and resilience of the species. We assessed the level of inherited variation in nine phenotypic traits by comparing variation within and among three monoclonal groups and one group of unique multilocus genotypes (MLGs) sampled in the wild.

RESULTS: Of the nine phenotypic traits, recovery after freezing, recovery after desiccation, and phlorotannin content showed substantial inherited variation, that is, phenotypic variation in these traits were to a large extend genetically determined. In contrast, variation in six other phenotypic traits (growth rate, palatability to isopod grazers, thallus width, distance between dichotomies, water content after desiccation and photochemical yield under ambient conditions) did not show significant signals of genetic variation at the power of analyses used in the study. Averaged over all nine traits, phenotypic variation within monoclonal groups was only 68% of the variation within the group of different MLGs showing that genotype diversity does affect the overall level of phenotypic variation in this species.

CONCLUSIONS: Our result indicates that, in general, phenotypic diversity in populations of Fucus radicans increases with increased multilocus genotype (MLG) diversity, but effects are specific for individual traits. In the light of Fucus radicans being a foundation species of the northern Baltic Sea, we propose that increased MLG diversity (leading to increased trait variation) will promote ecosystem function and resilience in areas where F. radicans is common, but this suggestion needs experimental support.

Keyword
Phenotypic traits, Inherited varitaion, Foundation species, Ecosystem function
National Category
Botany Ecology
Research subject
Plant Ecology
Identifiers
urn:nbn:se:su:diva-79475 (URN)10.1186/1472-6785-12-2 (DOI)000303159100001 ()22356775 (PubMedID)
Available from: 2012-09-05 Created: 2012-09-04 Last updated: 2017-12-07Bibliographically approved

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