---
OA_place: publisher
OA_type: gold
_id: '18515'
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."
acknowledged_ssus:
- _id: ScienComp
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."
alternative_title:
- ISTA Thesis
article_processing_charge: No
author:
- first_name: Parvathy
  full_name: Surendranadh, Parvathy
  id: 455235B8-F248-11E8-B48F-1D18A9856A87
  last_name: Surendranadh
  orcid: 0000-0001-6395-386X
citation:
  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>
  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>
  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>.
  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.
  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>.
  short: P. Surendranadh, Effect of Population Structure on Neutral Genetic Variation
    and Barriers to Gene Exchange, Institute of Science and Technology Austria, 2024.
corr_author: '1'
date_created: 2024-11-06T21:25:37Z
date_published: 2024-11-07T00:00:00Z
date_updated: 2026-04-07T12:56:52Z
day: '07'
ddc:
- '576'
degree_awarded: PhD
department:
- _id: GradSch
- _id: NiBa
doi: 10.15479/at:ista:18515
file:
- access_level: open_access
  checksum: c32cf7bc75748d9c551d8eb70178bbec
  content_type: application/pdf
  creator: psurendr
  date_created: 2024-11-07T10:59:29Z
  date_updated: 2024-11-07T10:59:29Z
  file_id: '18519'
  file_name: PhD_Thesis__Parvathy_071124_PDFA.pdf
  file_size: 37019760
  relation: main_file
  success: 1
- access_level: closed
  checksum: 4417e02d54084d89e75734e18caaa96d
  content_type: application/zip
  creator: psurendr
  date_created: 2024-11-07T10:59:42Z
  date_updated: 2024-11-07T10:59:42Z
  file_id: '18520'
  file_name: PhD Thesis- Parvathy_071124.zip
  file_size: 41198857
  relation: source_file
file_date_updated: 2024-11-07T10:59:42Z
has_accepted_license: '1'
language:
- iso: eng
license: https://creativecommons.org/licenses/by-nc-sa/4.0/
month: '11'
oa: 1
oa_version: Published Version
page: '219'
project:
- _id: 05959E1C-7A3F-11EA-A408-12923DDC885E
  grant_number: P32166
  name: Snapdragon Speciation
- _id: bd6958e0-d553-11ed-ba76-86eba6a76c00
  grant_number: '101055327'
  name: Understanding the evolution of continuous genomes
publication_identifier:
  issn:
  - 2663-337X
publication_status: published
publisher: Institute of Science and Technology Austria
status: public
supervisor:
- first_name: Nicholas H
  full_name: Barton, Nicholas H
  id: 4880FE40-F248-11E8-B48F-1D18A9856A87
  last_name: Barton
  orcid: 0000-0002-8548-5240
title: Effect of population structure on neutral genetic variation and barriers to
  gene exchange
tmp:
  image: /images/cc_by_nc_sa.png
  legal_code_url: https://creativecommons.org/licenses/by-nc-sa/4.0/legalcode
  name: Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International (CC
    BY-NC-SA 4.0)
  short: CC BY-NC-SA (4.0)
type: dissertation
user_id: ba8df636-2132-11f1-aed0-ed93e2281fdd
year: '2024'
...