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Van Belleghem SM, Baquero M, Papa R, Salazar C, McMillan WO, Counterman BA, Jiggins CD, Martin SH. Patterns of Z chromosome divergence among Heliconius species highlight the importance of historical demography. Mol Ecol 2018; 27:3852-3872. [PMID: 29569384 PMCID: PMC6151167 DOI: 10.1111/mec.14560] [Citation(s) in RCA: 43] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2017] [Revised: 02/14/2018] [Accepted: 02/20/2018] [Indexed: 12/31/2022]
Abstract
Sex chromosomes are disproportionately involved in reproductive isolation and adaptation. In support of such a “large‐X” effect, genome scans between recently diverged populations and species pairs often identify distinct patterns of divergence on the sex chromosome compared to autosomes. When measures of divergence between populations are higher on the sex chromosome compared to autosomes, such patterns could be interpreted as evidence for faster divergence on the sex chromosome, that is “faster‐X”, barriers to gene flow on the sex chromosome. However, demographic changes can strongly skew divergence estimates and are not always taken into consideration. We used 224 whole‐genome sequences representing 36 populations from two Heliconius butterfly clades (H. erato and H. melpomene) to explore patterns of Z chromosome divergence. We show that increased divergence compared to equilibrium expectations can in many cases be explained by demographic change. Among Heliconius erato populations, for instance, population size increase in the ancestral population can explain increased absolute divergence measures on the Z chromosome compared to the autosomes, as a result of increased ancestral Z chromosome genetic diversity. Nonetheless, we do identify increased divergence on the Z chromosome relative to the autosomes in parapatric or sympatric species comparisons that imply postzygotic reproductive barriers. Using simulations, we show that this is consistent with reduced gene flow on the Z chromosome, perhaps due to greater accumulation of incompatibilities. Our work demonstrates the importance of taking demography into account to interpret patterns of divergence on the Z chromosome, but nonetheless provides evidence to support the Z chromosome as a strong barrier to gene flow in incipient Heliconius butterfly species.
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Affiliation(s)
- Steven M Van Belleghem
- Department of Zoology, University of Cambridge, Cambridge, UK.,Department of Biological Sciences, Mississippi State University, Mississippi State, MS, USA.,Department of Biology, Center for Applied Tropical Ecology and Conservation, University of Puerto Rico, Rio Piedras, Puerto Rico.,Smithsonian Tropical Research Institute, Apartado, Panamá, Panama
| | - Margarita Baquero
- Department of Biological Sciences, Mississippi State University, Mississippi State, MS, USA
| | - Riccardo Papa
- Department of Biology, Center for Applied Tropical Ecology and Conservation, University of Puerto Rico, Rio Piedras, Puerto Rico
| | - Camilo Salazar
- Biology Program, Faculty of Natural Sciences and Mathematics, Universidad del Rosario, Carrera, Bogota, Colombia
| | - W Owen McMillan
- Smithsonian Tropical Research Institute, Apartado, Panamá, Panama
| | - Brian A Counterman
- Department of Biological Sciences, Mississippi State University, Mississippi State, MS, USA
| | - Chris D Jiggins
- Department of Zoology, University of Cambridge, Cambridge, UK
| | - Simon H Martin
- Department of Zoology, University of Cambridge, Cambridge, UK
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Nadeau NJ, Kawakami T. Population Genomics of Speciation and Admixture. POPULATION GENOMICS 2018. [DOI: 10.1007/13836_2018_24] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
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Martin SH, Jiggins CD. Interpreting the genomic landscape of introgression. Curr Opin Genet Dev 2017; 47:69-74. [PMID: 28923541 DOI: 10.1016/j.gde.2017.08.007] [Citation(s) in RCA: 106] [Impact Index Per Article: 15.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2017] [Revised: 08/28/2017] [Accepted: 08/31/2017] [Indexed: 11/17/2022]
Abstract
Introgression, the transfer of genetic material between species through hybridisation, occurs in many taxa and has important consequences. Genomic studies allow us to characterise the landscape of introgression across the genome, shedding light on both its adaptive benefits and the incompatibilities that help to maintain species barriers. Studies taking a genome-wide view suggest that adaptive introgression may be common, but that introgressed variation between many species is selected against throughout much of the genome. Confounding factors can complicate interpretations from these data, and computational simulations have proved vital to illustrate expected patterns under different scenarios. Future developments will move beyond correlative evidence to explicit models that account for how selection and genetic drift influence introgressed variation.
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Affiliation(s)
- Simon H Martin
- Department of Zoology, University of Cambridge, Cambridge CB2 3EJ, United Kingdom.
| | - Chris D Jiggins
- Department of Zoology, University of Cambridge, Cambridge CB2 3EJ, United Kingdom
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