Reproductive isolation in a three‐way contact zone

Contact zones between divergent forms within a species provide insight into the role of gene flow in adaptation and speciation. Previous work has focused on contact zones involving only two divergent forms, but in nature, many more than two populations may overlap simultaneously and experience gene...

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Bibliographic Details
Published in:Molecular ecology 2024-03, Vol.33 (5), p.e17275-n/a
Main Authors: Dean, Laura L., Whiting, James R., Jones, Felicity C., MacColl, Andrew D. C.
Format: Article
Language:English
Subjects:
adaptation
Chromosome Inversion
Chromosomes
contact zone
Divergence
Gene expression
Gene flow
Genetic Speciation
Genetics, Population
Genome
Genomic analysis
Genomics
Humans
hybrid
Hybridization
Hybridization, Genetic
Hybrids
introgression
Inversions
Populations
Reproductive Isolation
Saline water
Speciation
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Summary:Contact zones between divergent forms within a species provide insight into the role of gene flow in adaptation and speciation. Previous work has focused on contact zones involving only two divergent forms, but in nature, many more than two populations may overlap simultaneously and experience gene flow. Patterns of introgression in wild populations are, therefore, likely much more complicated than is often assumed. We begin to address this gap in current knowledge by investigating patterns of divergence and introgression across a complex natural contact zone. We use phenotypic and genomic data to confirm the existence of a three‐way contact zone among divergent freshwater resident, saltwater resident and saltwater migratory three‐spined stickleback (Gasterosteus aculeatus) on the island of North Uist, Scottish Western Isles. We find evidence for hybridization, mostly between saltwater resident and saltwater migratory forms. Despite hybridization, genomic analyses reveal pairwise islands of divergence between all forms that are maintained across the contact zone. Genomic cline analyses also provide evidence for selection and/or hybrid incompatibilities in divergent regions. Divergent genomic regions occur across multiple chromosomes and involve many known adaptive loci and several chromosomal inversions. We also identify distinct immune gene expression profiles between forms, but no evidence for transgressive expression in hybrids. Our results suggest that reproductive isolation is maintained in this three‐way contact zone, despite some hybridization, and that reduced recombination in chromosomal inversions may play an important role in maintaining this isolation.
ISSN:0962-1083
1365-294X
DOI:10.1111/mec.17275