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Parallel Evolution Despite Low Genetic Diversity in Three-Spined Stickleback

Show simple item record 2021-06-03T04:47:14Z 2021-06-03T04:47:14Z 2021-06-03
dc.title Parallel Evolution Despite Low Genetic Diversity in Three-Spined Stickleback en
ethesis.faculty Bio- ja ympäristötieteellinen tiedekunta fi
ethesis.faculty Faculty of Biological and Environmental Sciences en
ethesis.faculty Bio- och miljövetenskapliga fakulteten sv
ethesis.faculty.URI Helsingin yliopisto fi University of Helsinki en Helsingfors universitet sv
dct.creator Coll Costa, Carla Jr
dct.issued 2021
dct.language.ISO639-2 eng
dct.abstract The three-spined stickleback (Gasterosteus aculeatus) is a model organism for studies of parallel evolution in the wild; marine stickleback populations have repeatedly colonized and successfully adapted to different brackish and freshwater habitats. During Pleistocene glaciations, three-spined stickleback populations inhabiting high-latitude areas of Europe were eradicated, whereas populations residing in (or moving to) the south persisted in refugia. After the retreat of the ice sheets covering northern Europe, the high-latitude areas became recolonized by migration from south, and hence, today’s northern European populations are relatively young. Population genetic studies of European three-spined sticklebacks have usually been conducted at high-latitude areas where freshwater populations are typically less than 10.000 years old. Few studies have focused on southern populations, where more of the ancestral diversity is likely to reside. These studies have utilized a limited number of microsatellite markers and mtDNA sequence fragments, whereas studies of southern populations focusing on genome-wide diversity, in particular from the edge of the southern distribution limit in the Iberian Peninsula, are still missing. Here, I wanted to cover this gap in knowledge by carrying out an empirical and statistical study with RAD-seq data from southern and northern European populations of three-spined stickleback. The main aims of this study were two-fold. First, to investigate whether the southern European freshwater populations of the three-spined stickleback – which currently lack or have limited connection to ancestral marine populations carrying most of the standing genetic variation (SGV) – have lost genetic diversity due to population bottlenecks and inbreeding as compared to their northern European counterparts. Second, to compare the degree of genetic parallelism in southern vs. northern European populations in genomic regions which have been shown to be consistently associated with freshwater colonization in earlier studies. Under the assumption that the lack of continued access to SGV in the ancestral marine population reduces the likelihood of parallel evolution, I hypothesized that the degree of genetic parallelism in genomic regions subject to positive selection in freshwater environments is lower in the southern than in northern European populations. However, if a reduction in genetic diversity and/or cessation of gene flow between southern European freshwater and marine populations occurred following freshwater adaptation, the opposite pattern could be expected. I paid particular attention to chromosomal inversions associated with marine-freshwater adaptations identified in previous studies. The results confirmed my expectation of reduced genetic diversity in southern as compared to northern European stickleback populations. On the other hand, and contrary to what I expected, analysis of clusters of global parallelism involved in freshwater adaptation revealed that southern European populations exhibit a higher degree of genetic parallelism in response to freshwater colonisation than those from northern Europe. This suggests that the loss of genetic diversity in southern populations has occurred after they had adapted to freshwater environments, explaining the high degree of genetic parallelism in spite of the current low levels of genetic diversity. In addition, it could be that selection pressures in south are more homogenous than in north, which would also explain the higher degree of genetic parallelism observed in southern Europe. The findings presented here, challenge the current paradigm that parallel evolution is unlikely in populations with low genetic diversity and that have experienced recent bottlenecks. en
dct.subject adaptation en
dct.subject Gasterosteus aculeatus en
dct.subject genetic diversity en
dct.subject parallel evolution en
dct.subject standing genetic variation en
dct.language en
ethesis.language englanti fi
ethesis.language English en
ethesis.language engelska sv
ethesis.supervisor Momigliano, Paolo
ethesis.supervisor Merilä, Juha
ethesis.thesistype pro gradu -tutkielmat fi
ethesis.thesistype master's thesis en
ethesis.thesistype pro gradu-avhandlingar sv
dct.identifier.ethesis E-thesisID:7971de8d-8e08-429d-b2c0-38f26fc7c5c1
ethesis-internal.timestamp.reviewStep 2021-04-21 07:55:06:603
ethesis.principalprofessor Seppä, Perttu
ethesis.principalprofessor Pietiäinen, Hannu
dct.identifier.urn URN:NBN:fi:hulib-202106032469
dc.type.dcmitype Text
ethesis.facultystudyline ei opintosuuntaa fi
ethesis.facultystudyline no specialization en
ethesis.facultystudyline ingen studieinriktning sv
ethesis.mastersdegreeprogram Ekologian ja evoluutiobiologian maisteriohjelma fi
ethesis.mastersdegreeprogram Master's Programme in Ecology and Evolutionary Biology en
ethesis.mastersdegreeprogram Magisterprogrammet i ekologi och evolutionsbiologi sv

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