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On The Big Challenges of a Small Shrub: Ecological Genetics of Salix herbacea L
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Plant Ecology and Evolution.
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The response of plants to climate change is among the main questions in ecology and evolution. Faced with changing conditions, populations may respond by adapting, going extinct or migrating. Fine-scale environmental variation offers a unique mosaic to explore these alternatives. In this thesis, I used ecological surveys, field experiments and molecular methods to study the range of possible responses at a very local scale in the alpine dwarf willow Salix herbacea L. Since gene flow may impact the potential for adaptation and migration, I first explored whether phenological divergence driven by snowmelt patterns impacts gene flow. I found that sites with late snowmelt work as sinks of the genetic diversity, as compared to sites with early snowmelt. I also used a combined approach that looked at the selection, heritability and genomic architecture of ecologically-relevant traits, as well as genomic divergence across the snowmelt mosaic. In this way, I was able to understand which genomic regions may relate to phenological, growth and fitness traits, and which regions in the genome harbor genetic variation associated with late- and early- snowmelt sites. I found that most of the genomic divergence driven by snowmelt is novel and is localized in few regions. Also, Salix herbacea has a strong female bias. Sex bias may matter for adaptation to climate change because different sexes of many dioecious species differ in several functions that may fluctuate with changing conditions. I found that the bias is uniform across environments and is already present at seeds and seedlings. A polygenic sex determination system together with transmission distortion may be maintaining the bias. Overall, fast-evolving microhabitat-driven genomic divergence and, at the same time, genetically-based trait variation at a larger scale may play a role for the ability of S. herbacea to persist in diverse and variable conditions.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2015. , 37 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1288
Keyword [en]
Fine-scale environmental variation, migration, adaptation, snowmelt timing
National Category
Botany
Research subject
Biology
Identifiers
URN: urn:nbn:se:uu:diva-262239ISBN: 978-91-554-9337-0 (print)OAI: oai:DiVA.org:uu-262239DiVA: diva2:852917
Public defence
2015-10-28, Zootissalen, Evolutionsbiologiskt centrum (EBC), Norbyvägen 18, Uppsala, 13:00 (English)
Opponent
Supervisors
Projects
SNSF Sinergia Salix
Available from: 2015-10-07 Created: 2015-09-10 Last updated: 2015-11-23Bibliographically approved
List of papers
1. Small-scale patterns in snowmelt timing affect gene flow and the distribution of genetic diversity in the alpine dwarf shrub Salix herbacea
Open this publication in new window or tab >>Small-scale patterns in snowmelt timing affect gene flow and the distribution of genetic diversity in the alpine dwarf shrub Salix herbacea
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2014 (English)In: Heredity, ISSN 0018-067X, E-ISSN 1365-2540, Vol. 113, no 3, 233-239 p.Article in journal (Refereed) Published
Abstract [en]

Current threats to biodiversity, such as climate change, are thought to alter the within-species genetic diversity among microhabitats in highly heterogeneous alpine environments. Assessing the spatial organization and dynamics of genetic diversity within species can help to predict the responses of organisms to environmental change. In this study, we evaluated whether small-scale heterogeneity in snowmelt timing restricts gene flow between microhabitats in the common long-lived dwarf shrub Salix herbacea L. We surveyed 273 genets across 12 early-and late-snowmelt sites (that is, ridges and snowbeds) in the Swiss Alps for phenological variation over 2 years and for genetic variation using seven SSR markers. Phenological differentiation triggered by differences in snowmelt timing did not correlate with genetic differentiation between microhabitats. On the contrary, extensive gene flow appeared to occur between microhabitats and slightly less extensively among adjacent mountains. However, ridges exhibited significantly lower levels of genetic diversity than snowbeds, and patterns of effective population size (Ne) and migration (Nem) between microhabitats were strongly asymmetric, with ridges acting as sources and snowbeds as sinks. As no recent genetic bottlenecks were detected in the studied sites, this asymmetry is likely to reflect current metapopulation dynamics of the species dominated by gene flow via seeds rather than ancient re-colonization after the last glacial period. Overall, our results suggest that seed dispersal prevents snowmelt-driven genetic isolation, and snowbeds act as sinks of genetic diversity. We discuss the consequences of such small-scale variation in gene flow and diversity levels for population responses to climate change.

National Category
Genetics Ecology
Identifiers
urn:nbn:se:uu:diva-232992 (URN)10.1038/hdy.2014.19 (DOI)000341087900006 ()
Available from: 2014-10-13 Created: 2014-09-29 Last updated: 2017-12-05Bibliographically approved
2. Evolutionary potential in the Alpine: trait heritabilities and performance variation of the dwarf willow Salix herbacea from different elevations and microhabitats
Open this publication in new window or tab >>Evolutionary potential in the Alpine: trait heritabilities and performance variation of the dwarf willow Salix herbacea from different elevations and microhabitats
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2016 (English)In: Ecology and Evolution, ISSN 2045-7758, E-ISSN 2045-7758, Vol. 6, no 12, 3940-3952 p.Article in journal (Refereed) Published
Abstract [en]

Alpine ecosystems are seriously threatened by climate change. One of the key mechanisms by which plants can adapt to changing environmental conditions is through evolutionary change. However, we still know little about the evolutionary potential in wild populations of long-lived alpine plants. Here, we investigated heritabilities of phenological traits, leaf size, and performance traits in natural populations of the long-lived alpine dwarf shrub Salix herbacea using relatedness estimates inferred from SSR (Simple Sequence Repeat) markers. Salix herbacea occurs in early-and late-snowmelt microhabitats (ridges and snowbeds), and we assessed how performance consequences of phenological traits and leaf size differ between these microhabitats in order to infer potential for evolutionary responses. Salix herbacea showed low, but significant, heritabilities of leaf size, clonal and sexual reproduction, and moderate heritabilities of phenological traits. In both microhabitats, we found that larger leaves, longer intervals between snowmelt and leaf expansion, and longer GDD (growing-degree days) until leaf expansion resulted in a stronger increase in the number of stems (clonal reproduction). In snowbeds, clonal reproduction increased with a shorter GDD until flowering, while the opposite was found on ridges. Furthermore, the proportion of flowering stems increased with GDD until flowering in both microhabitats. Our results suggest that the presence of significant heritable variation in morphology and phenology might help S. herbacea to adapt to changing environmental conditions. However, it remains to be seen if the rate of such an evolutionary response can keep pace with the rapid rate of climate change.

Keyword
Adaptive evolution; alpine ecosystem; animal model; long-lived plants; snowmelt microhabitats; SSR markers
National Category
Botany
Identifiers
urn:nbn:se:uu:diva-262237 (URN)10.1002/ece3.2171 (DOI)000379342900008 ()
Available from: 2015-09-10 Created: 2015-09-10 Last updated: 2017-12-05Bibliographically approved
3. Genome-wide patterns of microhabitat-driven divergence in the alpine dwarf shrub Salix herbacea L.
Open this publication in new window or tab >>Genome-wide patterns of microhabitat-driven divergence in the alpine dwarf shrub Salix herbacea L.
(English)Manuscript (preprint) (Other academic)
National Category
Botany
Identifiers
urn:nbn:se:uu:diva-262229 (URN)
Available from: 2015-09-10 Created: 2015-09-10 Last updated: 2015-11-23
4. Maintenance of female-bias in a polygenic sex determination system is consistent with genomic conflict
Open this publication in new window or tab >>Maintenance of female-bias in a polygenic sex determination system is consistent with genomic conflict
(English)Manuscript (preprint) (Other academic)
National Category
Botany
Identifiers
urn:nbn:se:uu:diva-262230 (URN)
Available from: 2015-09-10 Created: 2015-09-10 Last updated: 2015-11-23

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