Westram, Anja MISTA ; Faria, Rui; Johannesson, Kerstin; Butlin, Roger
Combining hybrid zone analysis with genomic data is a promising approach to understanding the genomic basis of adaptive divergence. It allows for the identification of genomic regions underlying barriers to gene flow. It also provides insights into spatial patterns of allele frequency change, informing about the interplay between environmental factors, dispersal and selection. However, when only a single hybrid zone is analysed, it is difficult to separate patterns generated by selection from those resulting from chance. Therefore, it is beneficial to look for repeatable patterns across replicate hybrid zones in the same system. We applied this approach to the marine snail Littorina saxatilis, which contains two ecotypes, adapted to wave-exposed rocks vs. high-predation boulder fields. The existence of numerous hybrid zones between ecotypes offered the opportunity to test for the repeatability of genomic architectures and spatial patterns of divergence. We sampled and phenotyped snails from seven replicate hybrid zones on the Swedish west coast and genotyped them for thousands of single nucleotide polymorphisms. Shell shape and size showed parallel clines across all zones. Many genomic regions showing steep clines and/or high differentiation were shared among hybrid zones, consistent with a common evolutionary history and extensive gene flow between zones, and supporting the importance of these regions for divergence. In particular, we found that several large putative inversions contribute to divergence in all locations. Additionally, we found evidence for consistent displacement of clines from the boulder–rock transition. Our results demonstrate patterns of spatial variation that would not be accessible without continuous spatial sampling, a large genomic data set and replicate hybrid zones.
We thank everyone who helped with fieldwork, snail processing and DNA extractions, particularly Laura Brettell, Mårten Duvetorp, Juan Galindo, Anne-Lise Liabot, Mark Ravinet, Irena Senčić and Zuzanna Zagrodzka. We are also grateful to Edinburgh Genomics for library preparation and sequencing, to Stuart Baird and Mark Ravinet for helpful discussions, and to three anonymous reviewers for their constructive comments. This work was supported by the Natural Environment Research Council (NE/K014021/1), the European Research Council (AdG-693030-BARRIERS), Swedish Research Councils Formas and Vetenskapsrådet through a Linnaeus grant to the Centre for Marine Evolutionary Biology (217-2008-1719), the European Regional Development Fund (POCI-01-0145-FEDER-030628), and the Fundação para a iência e a Tecnologia, Portugal (PTDC/BIA-EVL/ 30628/2017). A.M.W. and R.F. were funded by the European Union’s Horizon 2020 research and innovation programme under Marie Skłodowska-Curie grant agreements no. 754411/797747 and no. 706376, respectively.
Westram AM, Faria R, Johannesson K, Butlin R. Using replicate hybrid zones to understand the genomic basis of adaptive divergence. Molecular Ecology. 2021;30(15):3797-3814. doi:10.1111/mec.15861
Westram, A. M., Faria, R., Johannesson, K., & Butlin, R. (2021). Using replicate hybrid zones to understand the genomic basis of adaptive divergence. Molecular Ecology. Wiley. https://doi.org/10.1111/mec.15861
Westram, Anja M, Rui Faria, Kerstin Johannesson, and Roger Butlin. “Using Replicate Hybrid Zones to Understand the Genomic Basis of Adaptive Divergence.” Molecular Ecology. Wiley, 2021. https://doi.org/10.1111/mec.15861.
A. M. Westram, R. Faria, K. Johannesson, and R. Butlin, “Using replicate hybrid zones to understand the genomic basis of adaptive divergence,” Molecular Ecology, vol. 30, no. 15. Wiley, pp. 3797–3814, 2021.
Westram AM, Faria R, Johannesson K, Butlin R. 2021. Using replicate hybrid zones to understand the genomic basis of adaptive divergence. Molecular Ecology. 30(15), 3797–3814.
Westram, Anja M., et al. “Using Replicate Hybrid Zones to Understand the Genomic Basis of Adaptive Divergence.” Molecular Ecology, vol. 30, no. 15, Wiley, 2021, pp. 3797–814, doi:10.1111/mec.15861.
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