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Adjusting to the extreme: Thermal adaptation in a freshwater gastropod
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Animal ecology.
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Temperature is a ubiquitous force influencing biological processes ranging from cellular responses to life span. The thermal environment for many organisms is predicted to change with globally increasing temperatures and studies conducted in natural systems incorporating various evolutionary forces, such as gene flow, is needed. In my thesis, I investigate how snails (Radix balthica) originating from distinct geothermal environments within Lake Mývatn in northern Iceland have adapted, both genetically and phenotypically, to the respective thermal regime. Locations were classified as either cold, warm or seasonal depending on the average and variance in temperature. A high resolution spatial distribution of genetic variation within Mývatn was obtained using both neutral and outlier AFLPs. In addition, the genetic profile enabled me identify warm origin snails irrespective of geographic location in Iceland. Warm environments were often more stressful than cold or seasonal environments but snails originating from a high temperature location benefited from increased performance elsewhere. Patterns of growth were identical in both common garden and reciprocal transplant experiment; warm origin snails grew faster than both cold and seasonal origin snails. This result is in concordance with quantitative genetics models of thermal adaptation but suggesting cogradient rather than countergradient variation. Although warm origin snails generally had superior performance, survival at cold temperatures (< 12 °C) was reduced. All snails matured at similar size in the common garden experiment but cold origin snails were observed to mature later and lay fewer eggs. Also, snails had a common optimum for growth rate at 20 °C irrespective of thermal origin. This is arguably the reason why snails were observed to have a common thermal preference. Interestingly, warm origin snails had a reduced tolerance to high temperatures compared to cold and seasonal origin snails which did not differ in tolerance. Putatively, natural selection has reduced a putatively unnecessary trait (high temperature tolerance in a stable thermal environment) in favour of higher growth rate and performance in warm habitats. In conclusion, the price of high performance in a warm environment was paid in terms of reduced survival at low temperatures and a potential disadvantage of reduced genetic variability.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2015. , 49 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1251
Keyword [en]
Radix balthica, Lake Mývatn, geothermal springs, thermal adaptation, isolation by environment, population structure, gene flow, cogradient variation, AFLP, thermal preference, CTmax
National Category
Biological Sciences
Research subject
Biology with specialization in Population Biology
Identifiers
URN: urn:nbn:se:uu:diva-248495ISBN: 978-91-554-9243-4 (print)OAI: oai:DiVA.org:uu-248495DiVA: diva2:801342
Public defence
2015-06-05, Zootissalen, Villavägen 9, 2tr, Uppsala, 10:00 (English)
Opponent
Supervisors
Available from: 2015-05-13 Created: 2015-03-30 Last updated: 2015-07-07
List of papers
1. AFLPs and Mitochondrial Haplotypes Reveal Local Adaptation to Extreme Thermal Environments in a Freshwater Gastropod
Open this publication in new window or tab >>AFLPs and Mitochondrial Haplotypes Reveal Local Adaptation to Extreme Thermal Environments in a Freshwater Gastropod
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2014 (English)In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 9, no 7, e101821- p.Article in journal (Refereed) Published
Abstract [en]

The way environmental variation shapes neutral and adaptive genetic variation in natural populations is a key issue in evolutionary biology. Genome scans allow the identification of the genetic basis of local adaptation without previous knowledge of genetic variation or traits under selection. Candidate loci for divergent adaptation are expected to show higher F-ST than neutral loci influenced solely by random genetic drift, migration and mutation. The comparison of spatial patterns of neutral markers and loci under selection may help disentangle the effects of gene flow, genetic drift and selection among populations living in contrasting environments. Using the gastropod Radix balthica as a system, we analyzed 376 AFLP markers and 25 mtDNA COI haplotypes for candidate loci and associations with local adaptation among contrasting thermal environments in Lake Myvatn, a volcanic lake in northern Iceland. We found that 2% of the analysed AFLP markers were under directional selection and 12% of the mitochondrial haplotypes correlated with differing thermal habitats. The genetic networks were concordant for AFLP markers and mitochondrial haplotypes, depicting distinct topologies at neutral and candidate loci. Neutral topologies were characterized by intense gene flow revealed by dense nets with edges connecting contrasting thermal habitats, whereas the connections at candidate loci were mostly restricted to populations within each thermal habitat and the number of edges decreased with temperature. Our results suggest microgeographic adaptation within Lake Myvatn and highlight the utility of genome scans in detecting adaptive divergence.

National Category
Ecology Zoology
Identifiers
urn:nbn:se:uu:diva-230100 (URN)10.1371/journal.pone.0101821 (DOI)000339040600068 ()
Available from: 2014-09-01 Created: 2014-08-19 Last updated: 2017-12-05Bibliographically approved
2. Genetic divergance and isolation by environment in geothermal populations of the common pond snail (Radix balthica)
Open this publication in new window or tab >>Genetic divergance and isolation by environment in geothermal populations of the common pond snail (Radix balthica)
(English)Manuscript (preprint) (Other academic)
Keyword
Radix balthica, AFLP, gene flow, temperature, landscape genetics
National Category
Genetics
Identifiers
urn:nbn:se:uu:diva-248493 (URN)
Available from: 2015-04-09 Created: 2015-03-30 Last updated: 2015-07-07
3. Local adaptation of gastropod life history to contrasting thermal environments in a geothermal lake
Open this publication in new window or tab >>Local adaptation of gastropod life history to contrasting thermal environments in a geothermal lake
(English)Article in journal (Refereed) Submitted
Keyword
Radix balthica, common garden, reciprocal transplant, thermal adaptation, cogradient variation
National Category
Zoology
Identifiers
urn:nbn:se:uu:diva-248492 (URN)
Available from: 2015-04-09 Created: 2015-03-30 Last updated: 2015-07-28Bibliographically approved
4. Similar temperature preference but different maximum tolerance in contrasting thermal populations of Radix balthica
Open this publication in new window or tab >>Similar temperature preference but different maximum tolerance in contrasting thermal populations of Radix balthica
(English)Manuscript (preprint) (Other academic)
National Category
Zoology
Identifiers
urn:nbn:se:uu:diva-248494 (URN)
Available from: 2015-04-09 Created: 2015-03-30 Last updated: 2015-07-07

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