Abstract
Both classical and recent studies suggest that chromosomal inversion polymorphisms are important in adaptation and speciation. However, biases in discovery and reporting of inversions make it difficult to assess their prevalence and biological importance. Here, we use an approach based on linkage disequilibrium among markers genotyped for samples collected across a transect between contrasting habitats to detect chromosomal rearrangements de novo. We report 17 polymorphic rearrangements in a single locality for the coastal marine snail, Littorina saxatilis. Patterns of diversity in the field and of recombination in controlled crosses provide strong evidence that at least the majority of these rearrangements are inversions. Most show clinal changes in frequency between habitats, suggestive of divergent selection, but only one appears to be fixed for different arrangements in the two habitats. Consistent with widespread evidence for balancing selection on inversion polymorphisms, we argue that a combination of heterosis and divergent selection can explain the observed patterns and should be considered in other systems spanning environmental gradients.
Highlights
The potential roles of chromosomal rearrangements in adaptation and speciation have been investigated almost since their discovery, approximately a century ago (Dobzhansky, 1970; Sturtevant, 1926, 1938)
When speciation requires the build‐up of associations among traits involved in reproductive isolation in the face of gene flow
Work emphasized the impact of chromosomal inversions on adaptation and speciation (Dobzhansky, 1970; Sturtevant, 1926, 1938) but, subsequently, structural rearrangements received less attention, despite some prominent exceptions (e.g., Balanyà, Huey, Gilchrist, & Serra, 2009; Coluzzi, Sabatini, della Torre, Di Deco, & Petrarca, 2002)
Summary
The potential roles of chromosomal rearrangements in adaptation and speciation have been investigated almost since their discovery, approximately a century ago (Dobzhansky, 1970; Sturtevant, 1926, 1938) Their contributions to these processes remained poorly understood until attention was given to their effects on re‐ combination, especially the suppression of recombination in hetero‐ zygotes (Faria & Navarro, 2010; Rieseberg, 2001; Trickett & Butlin, 1994). | 1376 genetic architectures that suppress recombination between loci in‐ volved in these traits are likely to evolve (Smadja & Butlin, 2011) This is the case for chromosomal rearrangements, including inver‐ sions, translocations and fusions/fissions. A predic‐ tion underlying these different roles is that, in the presence of gene flow, inversions will tend to be enriched for barrier loci
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