{"language":[{"iso":"eng"}],"license":"https://creativecommons.org/licenses/by-nc-sa/4.0/","day":"07","degree_awarded":"PhD","date_created":"2024-11-06T21:25:37Z","_id":"18515","OA_type":"gold","date_updated":"2024-12-03T13:40:38Z","file":[{"checksum":"c32cf7bc75748d9c551d8eb70178bbec","access_level":"open_access","creator":"psurendr","date_updated":"2024-11-07T10:59:29Z","success":1,"content_type":"application/pdf","file_name":"PhD_Thesis__Parvathy_071124_PDFA.pdf","file_id":"18519","relation":"main_file","date_created":"2024-11-07T10:59:29Z","file_size":37019760},{"content_type":"application/zip","date_updated":"2024-11-07T10:59:42Z","creator":"psurendr","access_level":"closed","checksum":"4417e02d54084d89e75734e18caaa96d","date_created":"2024-11-07T10:59:42Z","file_size":41198857,"relation":"source_file","file_id":"18520","file_name":"PhD Thesis- Parvathy_071124.zip"}],"author":[{"orcid":"0000-0001-6395-386X","id":"455235B8-F248-11E8-B48F-1D18A9856A87","full_name":"Surendranadh, Parvathy","first_name":"Parvathy","last_name":"Surendranadh"}],"acknowledgement":"I also acknowledge the funding agencies Marie Curie COFUND Doctoral Fellowship,\r\nAustrian Science Fund FWF (grant P32166) and ERC (grant PR1000ERC02) for financially\r\nsupporting my research over the years.","department":[{"_id":"GradSch"},{"_id":"NiBa"}],"user_id":"2DF688A6-F248-11E8-B48F-1D18A9856A87","ddc":["576"],"title":"Effect of population structure on neutral genetic variation and barriers to gene exchange","publication_status":"published","oa":1,"file_date_updated":"2024-11-07T10:59:42Z","acknowledged_ssus":[{"_id":"ScienComp"}],"oa_version":"Published Version","page":"219","corr_author":"1","month":"11","alternative_title":["ISTA Thesis"],"supervisor":[{"orcid":"0000-0002-8548-5240","first_name":"Nicholas H","full_name":"Barton, Nicholas H","last_name":"Barton","id":"4880FE40-F248-11E8-B48F-1D18A9856A87"}],"tmp":{"image":"/images/cc_by_nc_sa.png","short":"CC BY-NC-SA (4.0)","name":"Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International (CC BY-NC-SA 4.0)","legal_code_url":"https://creativecommons.org/licenses/by-nc-sa/4.0/legalcode"},"status":"public","abstract":[{"lang":"eng","text":"Understanding the role of evolutionary processes in shaping genetic variation has been a\r\nprimary goal in evolutionary genetics. In this regard, a key question is how genetically\r\ndistinct populations evolve in the face of gene flow, thereby generating genetic and\r\nphenotypic divergence and reproductive isolation (RI). This requires quantifying the role\r\nand relative contributions of prezygotic and postzygotic isolating mechanisms on the\r\nreduction of gene exchange between populations, and identifying regions in the genome\r\nthat mediate RI, which is often polygenic. Further, this needs distinguishing neutral and\r\nselected regions in the genome, and discerning how selection influences patterns of neutral\r\ndivergence.\r\nPopulation structure, defined as any deviation from panmixia, such as geographic distribution, movement and mating patterns of individuals, influences how genetic variation is\r\nstructured in space and shapes the neutral null model. Availability of large scale spatial\r\ngenomic datasets now enables us to detect signatures of population structure in genetic\r\ndata and infer population genetic parameters. Such inferences are crucial and have wide\r\napplications in biodiversity, conservation genetics, population management and medical\r\ngenetics. However, inferences are based on assumptions that do not always match the\r\ncomplex reality, thus leading to erroneous conclusions. Moreover, the role and interaction\r\nof heterogeneous population density and dispersal, which are ubiquitous in nature, has\r\nbeen challenging to study owing to their mathematical complexity. In such scenarios,\r\nfeedback between theory, data and simulations can prove to be useful.\r\nIn this thesis, I examine the effect of population structure on neutral genetic variation\r\nand barriers to gene exchange in hybridising populations, thereby bridging together the\r\nfields of spatial population genetics and speciation.\r\nDespite being a key concept in speciation, reproductive isolation (RI) lacks a quantitative\r\ndefinition and has been used and measured differently across different fields. Chapter 2\r\ngives a quantitative definition of RI, in terms of the effect of genetic differences on gene\r\nflow. We give analytical predictions for RI in a range of scenarios, in terms of effective migration rates for discrete populations and barrier strength for continuous populations.\r\nIn addition to this, we discuss current measures of RI and their limitations, and propose\r\nthe need for new measures that combine organismal and genetic perspectives of RI.\r\nIn chapter 3, I examine the combined effect of assortative mating, sexual selection\r\nand viability selection on RI. For this, we consider a polygenic ‘magic’ trait under a\r\nmainland-island model. We obtain novel theoretical predictions for molecular divergence\r\nin terms of effective migration rates, which bears a simple relationship to measurable\r\nfitness components of migrants and various early generation hybrids. We explore the\r\nconditions under which local adaptation can be maintained despite maladaptive gene flow\r\nand quantify the relative contributions of viability and sexual selection to genome-wide\r\nbarriers to gene flow.\r\nThe next two chapters of the thesis focus on a hybrid zone of Antirrhinum majus that\r\nconsist of two subspecies- the magenta flowered A. m. pseudomajus and the yellow\r\nflowered A.m. striatum. Previous studies have suggested that flower colour is target of\r\npollinator mediated selection and is influenced only by few genes. While these regions\r\nshow high genetic differentiation between the subspecies, the rest of the genome is seen\r\nto be well mixed. Chapter 4 examines the effects of heterogeneous population density\r\nand leptokurtic dispersal on isolation by distance and the distribution of heterozygosity\r\nby focusing on non-flower colour markers.\r\nChapter 5 analyses cline shapes and associations among 6 focal flower colour markers to\r\nunderstand how selection and dispersal maintain this hybrid zone. We see sharp coincident\r\nstepped clines at all loci and positive associations throughout the hybrid zone, contrary to\r\nthe expected patterns from diffusive gene flow. With a novel scheme of inferring dispersal\r\ncombined with multilocus simulations, we show that stepped clines do not reflect genetic\r\nbarriers to gene flow, but are rather a result of long-distance migration. This framework\r\nallows us to get realistic estimates gene flow and selection and shows how traditional cline\r\nanalysis may lead to inaccurate conclusions when assumptions of the theory are not met.\r\nOverall, this thesis investigates how different features of population structure leave\r\ndetectable signatures in genetic variation, namely in patterns of isolation by distance,\r\nlinkage disequilibrium and genetic divergence. It also highlights how effective migration\r\nrates provide useful way of analysing polygenic architectures and shed new light into\r\nhybrid zones. In doing so, I identify scenarios when simple models become insufficient\r\nand suggest possibe directions by combining genetic data with simulations."}],"citation":{"ieee":"P. Surendranadh, “Effect of population structure on neutral genetic variation and barriers to gene exchange,” Institute of Science and Technology Austria, 2024.","ista":"Surendranadh P. 2024. Effect of population structure on neutral genetic variation and barriers to gene exchange. Institute of Science and Technology Austria.","apa":"Surendranadh, P. (2024). <i>Effect of population structure on neutral genetic variation and barriers to gene exchange</i>. Institute of Science and Technology Austria. <a href=\"https://doi.org/10.15479/at:ista:18515\">https://doi.org/10.15479/at:ista:18515</a>","ama":"Surendranadh P. Effect of population structure on neutral genetic variation and barriers to gene exchange. 2024. doi:<a href=\"https://doi.org/10.15479/at:ista:18515\">10.15479/at:ista:18515</a>","chicago":"Surendranadh, Parvathy. “Effect of Population Structure on Neutral Genetic Variation and Barriers to Gene Exchange.” Institute of Science and Technology Austria, 2024. <a href=\"https://doi.org/10.15479/at:ista:18515\">https://doi.org/10.15479/at:ista:18515</a>.","short":"P. Surendranadh, Effect of Population Structure on Neutral Genetic Variation and Barriers to Gene Exchange, Institute of Science and Technology Austria, 2024.","mla":"Surendranadh, Parvathy. <i>Effect of Population Structure on Neutral Genetic Variation and Barriers to Gene Exchange</i>. Institute of Science and Technology Austria, 2024, doi:<a href=\"https://doi.org/10.15479/at:ista:18515\">10.15479/at:ista:18515</a>."},"doi":"10.15479/at:ista:18515","OA_place":"repository","year":"2024","type":"dissertation","publication_identifier":{"issn":["2663-337X"]},"has_accepted_license":"1","date_published":"2024-11-07T00:00:00Z","article_processing_charge":"No","project":[{"_id":"05959E1C-7A3F-11EA-A408-12923DDC885E","name":"Snapdragon Speciation","grant_number":"P32166"},{"_id":"bd6958e0-d553-11ed-ba76-86eba6a76c00","name":"Understanding the evolution of continuous genomes","grant_number":"101055327"}],"publisher":"Institute of Science and Technology Austria"}