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Immunogenetic variation along the latitudinal gradient in Scandinavian anuran species: Evolutionary processes, demography and infection
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Animal ecology.
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The evolutionary and demographic processes affecting how genetic variation is partitioned and distributed over large geographical scales is of fundamental importance for our understanding of how organisms may adapt to their environments. Northern peripheral populations generally have lower genetic variation and individuals in these populations may therefore face difficulties adapting to their local environment. At northern latitudes lack of genetic variation could be detrimental in face of newly emerging diseases as a result of anthropogenic actions and warmer climate in these areas. In this thesis, I explore genetic variation and the contemporary evolutionary processes affecting genes involved in the adaptive immune defense (Major Histocompatibility Complex; MHC) and the innate immune defense (AMP; Antimicrobial Peptides) over a large geographical gradient in anuran species (paper I, II and IV). I study signatures of historical selection on the MHC class II exon 2 and AMP (Temporin, Brevinin and Palustrin) sequences in the Signal Peptide and the Acidic Propiece domains (paper II and III). Finally, I investigate potential associations between specific MHC class II exon 2 alleles and a chytrid fungus infection (Bd) in common toads (Bufo bufo) (paper IV). The results reveal that genetic variation of MHC class II exon 2 decreases towards northern latitudes in R. arvalis and B. bufo and have been shaped by complex evolutionary processes (drift, selection, migration) affected by different demographic scenarios. On the other hand, AMP nucleotide variation is divergent among geographical areas, but there is no clear geographical pattern along the same gradient, suggesting diversifying selection as the main force shaping genetic variation. Finally, I found an effect of two specific MHC class II exon 2 alleles on survival in juvenile B. bufo when infected with Bd. In summary, my thesis unravels the complex patterns shaping genetic diversity at large scales. My results may guide conservation practices aiming to prevent amphibian mass mortality events on-going all over the world.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2019. , p. 45
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1811
National Category
Evolutionary Biology
Research subject
Biology; Biology with specialization in Evolutionary Genetics
Identifiers
URN: urn:nbn:se:uu:diva-382092ISBN: 978-91-513-0662-9 (print)OAI: oai:DiVA.org:uu-382092DiVA, id: diva2:1305943
Public defence
2019-06-14, Zootisalen, Norbyvägen 14-18, Uppsala, 13:00 (English)
Opponent
Supervisors
Funder
Swedish Research Council Formas, 146400178Swedish Research Council, 621-2013-4503Available from: 2019-05-22 Created: 2019-04-20 Last updated: 2019-06-17
List of papers
1. Drift, selection, or migration?: Processes affecting genetic differentiation and variation along a latitudinal gradient in an amphibian
Open this publication in new window or tab >>Drift, selection, or migration?: Processes affecting genetic differentiation and variation along a latitudinal gradient in an amphibian
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2017 (English)In: BMC Evolutionary Biology, ISSN 1471-2148, E-ISSN 1471-2148, Vol. 17, article id 189Article in journal (Refereed) Published
Abstract [en]

Background: Past events like fluctuations in population size and post-glacial colonization processes may influence the relative importance of genetic drift, migration and selection when determining the present day patterns of genetic variation. We disentangle how drift, selection and migration shape neutral and adaptive genetic variation in 12 moor frog populations along a 1700 km latitudinal gradient. We studied genetic differentiation and variation at a MHC exon II locus and a set of 18 microsatellites. Results: Using outlier analyses, we identified the MHC II exon 2 (corresponding to the beta-2 domain) locus and one microsatellite locus (RCO8640) to be subject to diversifying selection, while five microsatellite loci showed signals of stabilizing selection among populations. STRUCTURE and DAPC analyses on the neutral microsatellites assigned populations to a northern and a southern cluster, reflecting two different post-glacial colonization routes found in previous studies. Genetic variation overall was lower in the northern cluster. The signature of selection on MHC exon II was weaker in the northern cluster, possibly as a consequence of smaller and more fragmented populations. Conclusion: Our results show that historical demographic processes combined with selection and drift have led to a complex pattern of differentiation along the gradient where some loci are more divergent among populations than predicted from drift expectations due to diversifying selection, while other loci are more uniform among populations due to stabilizing selection. Importantly, both overall and MHC genetic variation are lower at northern latitudes. Due to lower evolutionary potential, the low genetic variation in northern populations may increase the risk of extinction when confronted with emerging pathogens and climate change.

Keywords
Genetic drift, Natural selection, Major histocompatibility complex, Microsatellites, Outlier tests, Rana arvalis
National Category
Evolutionary Biology
Identifiers
urn:nbn:se:uu:diva-332660 (URN)10.1186/s12862-017-1022-z (DOI)000407567900003 ()
Funder
Swedish Research Council Formas, 146,400,178Swedish Research Council, 621-2013-4503
Available from: 2017-10-31 Created: 2017-10-31 Last updated: 2019-04-20Bibliographically approved
2. Contrasting patterns of AMP nucleotide and peptide variation along a latitudinal gradient in two frog species
Open this publication in new window or tab >>Contrasting patterns of AMP nucleotide and peptide variation along a latitudinal gradient in two frog species
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(English)Manuscript (preprint) (Other academic)
National Category
Evolutionary Biology
Identifiers
urn:nbn:se:uu:diva-382091 (URN)
Available from: 2019-04-20 Created: 2019-04-20 Last updated: 2019-04-20
3. Signatures of historical selection on MHC reveal different selection patterns in the moor frog (Rana arvalis)
Open this publication in new window or tab >>Signatures of historical selection on MHC reveal different selection patterns in the moor frog (Rana arvalis)
2018 (English)In: Immunogenetics, ISSN 0093-7711, E-ISSN 1432-1211, Vol. 70, no 7, p. 477-484Article in journal (Refereed) Published
Abstract [en]

MHC genes are key components in disease resistance and an excellent system for studying selection acting on genetic variation in natural populations. Current patterns of variation in MHC genes are likely to be influenced by past and ongoing selection as well as demographic fluctuations in population size such as those imposed by post-glacial recolonization processes. Here, we investigated signatures of historical selection and demography on an MHC class II gene in 12 moor frog populations along a 1700-km latitudinal gradient. Sequences were obtained from 207 individuals and consecutively assigned into two different clusters (northern and southern clusters, respectively) in concordance with a previously described dual post-glacial colonization route. Selection analyses comparing the relative rates of non-synonymous to synonymous substitutions (dN/dS) suggested evidence of different selection patterns in the northern and the southern clusters, with divergent selection prevailing in the south but uniform positive selection predominating in the north. Also, models of codon evolution revealed considerable differences in the strength of selection: The southern cluster appeared to be under strong selection while the northern cluster showed moderate signs of selection. Our results indicate that the MHC alleles in the north diverged from southern MHC alleles as a result of differential selection patterns.

National Category
Evolutionary Biology
Identifiers
urn:nbn:se:uu:diva-341392 (URN)10.1007/s00251-017-1051-1 (DOI)000435594000006 ()29387920 (PubMedID)
Funder
Swedish Research Council Formas, 215-2014-594Swedish Research Council, 621-2013-4503
Available from: 2018-02-07 Created: 2018-02-07 Last updated: 2019-04-20Bibliographically approved
4. Latitudinal MHC variation and haplotype associated differential survival in response to experimental infection of two strains of Bd-GPL in common toads
Open this publication in new window or tab >>Latitudinal MHC variation and haplotype associated differential survival in response to experimental infection of two strains of Bd-GPL in common toads
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(English)Manuscript (preprint) (Other academic)
National Category
Evolutionary Biology
Identifiers
urn:nbn:se:uu:diva-382090 (URN)10.1101/597559 (DOI)
Available from: 2019-04-20 Created: 2019-04-20 Last updated: 2019-11-12

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