Mechanisms of Adaptive Divergence and Speciation in Littorina saxatilis: Integrating Knowledge from Ecology and Genetics with New Data Emerging from Genomic Studies

Johannesson, Kerstin; Butlin, Roger K.; Panova, Marina; Westram, Anja M.

doi:10.1007/13836_2017_6

Cited by 28 publications

(22 citation statements)

References 95 publications

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“…Chromosomal inversions have frequently been implicated in promoting range expansions. For example, this has been empirically observed in species such as threespine stickleback (Gasteroseteus aculeatus; Jones et al 2012), yellow monkeyflower (Mimulus guttatus; Lowry and Willis 2010), rough periwinkle (Littorina saxatilis; Johannesson et al 2017;Westram et al 2018;Faria et al 2019) and red imported fire ant (Solenopsis invicta; Tsutsui and Suarez 2003;Wang et al 2013). Our results that are pertinent to reduced recombination in general, are likely to also be applicable to inversions.…”

Section: Discussionsupporting

confidence: 71%

The effect of genetic architecture and selfing on the capacity of a population to expand its range

Eriksson

Rafajlović

2020

Preprint

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Previous theoretical work on range expansions over heterogeneous environments showed that there is a critical environmental gradient where range expansion stops. For populations with freely recombining loci underlying the trait under selection (hereafter adaptive loci), the critical gradient in one-dimensional habitats depends on the fitness cost of dispersal, and the strength of selection relative to genetic drift. Here, we extend the previous work in two directions and ask: What is the role of the genetic architecture of adaptive loci during range expansions? And what effect does the ability of selfing have on range expansions? To answer these questions, we use computer simulations. We demonstrate that, while reduced recombination rates between adaptive loci slow down range expansions due to poor purging of locally deleterious alleles at the expansion front, they may also allow a species to occupy a greater range. In fact, for some parameter values, we find that a population with freely recombining adaptive loci experiences global extinction, whereas reduced recombination rates allow for a successful expansion over a wide geographic range. In addition, we find that allowance of selfing may improve the ability of populations to expand their ranges. We discuss the mechanisms underlying these results.

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Section: Discussionsupporting

confidence: 71%

The effect of genetic architecture and selfing on the capacity of a population to expand its range

Eriksson

Rafajlović

2020

Preprint

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“…In addition to learning more about speciation between these taxa, our new understanding highlights Littorina as a model for understanding how different forces influence the evolution of reproductive isolation. To date, most studies of speciation in L. saxatilis have focused on the parallel evolution of RI between locally adapted 'crab' and 'wave' ecotypes due to divergent selection in different areas of the intertidal zone [17,18,20,33,34]. Patterns of molecular and phenotypic variation suggest that the strength of the barrier between the ecotypes varies among locations, suggesting that there may be a continuum of RI in this system.…”

Section: Conclusion Broader Implications!and Next Stepsmentioning

confidence: 99%

The evolution of strong reproductive isolation between sympatric intertidal snails

Stankowski

Westram

Zagrodzka

et al. 2020

Phil. Trans. R. Soc. B

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The evolution of strong reproductive isolation (RI) is fundamental to the origins and maintenance of biological diversity, especially in situations where geographical distributions of taxa broadly overlap. But what is the history behind strong barriers currently acting in sympatry? Using whole-genome sequencing and single nucleotide polymorphism genotyping, we inferred (i) the evolutionary relationships, (ii) the strength of RI, and (iii) the demographic history of divergence between two broadly sympatric taxa of intertidal snail. Despite being cryptic, based on external morphology, Littorina arcana and Littorina saxatilis differ in their mode of female reproduction (egg-laying versus brooding), which may generate a strong post-zygotic barrier. We show that egg-laying and brooding snails are closely related, but genetically distinct. Genotyping of 3092 snails from three locations failed to recover any recent hybrid or backcrossed individuals, confirming that RI is strong. There was, however, evidence for a very low level of asymmetrical introgression, suggesting that isolation remains incomplete. The presence of strong, asymmetrical RI was further supported by demographic analysis of these populations. Although the taxa are currently broadly sympatric, demographic modelling suggests that they initially diverged during a short period of geographical separation involving very low gene flow. Our study suggests that some geographical separation may kick-start the evolution of strong RI, facilitating subsequent coexistence of taxa in sympatry. The strength of RI needed to achieve sympatry and the subsequent effect of sympatry on RI remain open questions. This article is part of the theme issue ‘Towards the completion of speciation: the evolution of reproductive isolation beyond the first barriers'.

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“…However, several studies have documented that divergent selection also has a large contribution to speciation processes (Schluter 2000;Dieckmann et al 2004;Coyne and Orr 2004), for example, in cichlid fishes in African and central American lakes (e.g., Kocher 2004), or the marine snail Littorina saxatilis Olivi, 1792 (Johannesson et al 2017). Interestingly, the role of selection in Southern Ocean speciation processes has rarely been addressed.…”

Section: Introductionmentioning

confidence: 99%

Analyzing drivers of speciation in the Southern Ocean using the sea spider species complex Colossendeis megalonyx as a test case

et al. 2020

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Colossendeis megalonyx Hoek, 1881 has the broadest distribution of all sea spiders in the Southern Ocean. Previous studies have detected several evolutionarily young lineages within this taxon and interpreted them as a result of allopatric speciation in a few shelf refuges during glacial maxima. However, alternative scenarios such as ecological speciation in sympatry have rarely been considered or tested. Here, we generated the most extensive genomic and morphometric data set on the C. megalonyx species complex to (i) comprehensively describe species diversity, (ii) explore intraspecific connectivity between populations located around Antarctica, and (iii) systematically test for positive selection indicative of adaptive speciation. We successfully applied a target hybrid enrichment approach and recovered all 1607 genes targeted. Phylogenomic analysis was consistent with previous findings and, moreover, increased the resolution of branching within lineages. We found specimens of phylogenetically well-separated lineages occurring in sympatry to be genetically distinct from each other and gene flow between geographically separated populations of the same lineages to be restricted. Evidence for positive selection was found for four genes associated with structural and neuronal functions. Hence, there is an indication for positive selection in the C. megalonyx species complex, yet its specific contribution to the speciation process remains to be explored further. Finally, morphometric analyses revealed multiple significant differences between lineages, but a clear separation proved difficult. Our study highlights the relevance of positive selection as a potential driver for speciation in the Southern Ocean.

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Mechanisms of Adaptive Divergence and Speciation in Littorina saxatilis: Integrating Knowledge from Ecology and Genetics with New Data Emerging from Genomic Studies

Cited by 28 publications

References 95 publications

The effect of genetic architecture and selfing on the capacity of a population to expand its range

The effect of genetic architecture and selfing on the capacity of a population to expand its range

The evolution of strong reproductive isolation between sympatric intertidal snails

Analyzing drivers of speciation in the Southern Ocean using the sea spider species complex Colossendeis megalonyx as a test case

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