@article{11334, abstract = {Hybridization is a common evolutionary process with multiple possible outcomes. In vertebrates, interspecific hybridization has repeatedly generated parthenogenetic hybrid species. However, it is unknown whether the generation of parthenogenetic hybrids is a rare outcome of frequent hybridization between sexual species within a genus or the typical outcome of rare hybridization events. Darevskia is a genus of rock lizards with both hybrid parthenogenetic and sexual species. Using capture sequencing, we estimate phylogenetic relationships and gene flow among the sexual species, to determine how introgressive hybridization relates to the origins of parthenogenetic hybrids. We find evidence for widespread hybridization with gene flow, both between recently diverged species and deep branches. Surprisingly, we find no signal of gene flow between parental species of the parthenogenetic hybrids, suggesting that the parental pairs were either reproductively or geographically isolated early in their divergence. The generation of parthenogenetic hybrids in Darevskia is, then, a rare outcome of the total occurrence of hybridization within the genus, but the typical outcome when specific species pairs hybridize. Our results question the conventional view that parthenogenetic lineages are generated by hybridization in a window of divergence. Instead, they suggest that some lineages possess specific properties that underpin successful parthenogenetic reproduction.}, author = {Freitas, Susana and Westram, Anja M and Schwander, Tanja and Arakelyan, Marine and Ilgaz, Çetin and Kumlutas, Yusuf and Harris, David James and Carretero, Miguel A. and Butlin, Roger K.}, issn = {1558-5646}, journal = {Evolution}, number = {5}, pages = {899--914}, publisher = {Wiley}, title = {{Parthenogenesis in Darevskia lizards: A rare outcome of common hybridization, not a common outcome of rare hybridization}}, doi = {10.1111/evo.14462}, volume = {76}, year = {2022}, } @article{9394, abstract = {Chromosomal inversions have long been recognized for their role in local adaptation. By suppressing recombination in heterozygous individuals, they can maintain coadapted gene complexes and protect them from homogenizing effects of gene flow. However, to fully understand their importance for local adaptation we need to know their influence on phenotypes under divergent selection. For this, the marine snail Littorina saxatilis provides an ideal study system. Divergent ecotypes adapted to wave action and crab predation occur in close proximity on intertidal shores with gene flow between them. Here, we used F2 individuals obtained from crosses between the ecotypes to test for associations between genomic regions and traits distinguishing the Crab‐/Wave‐adapted ecotypes including size, shape, shell thickness, and behavior. We show that most of these traits are influenced by two previously detected inversion regions that are divergent between ecotypes. We thus gain a better understanding of one important underlying mechanism responsible for the rapid and repeated formation of ecotypes: divergent selection acting on inversions. We also found that some inversions contributed to more than one trait suggesting that they may contain several loci involved in adaptation, consistent with the hypothesis that suppression of recombination within inversions facilitates differentiation in the presence of gene flow.}, author = {Koch, Eva L. and Morales, Hernán E. and Larsson, Jenny and Westram, Anja M and Faria, Rui and Lemmon, Alan R. and Lemmon, E. Moriarty and Johannesson, Kerstin and Butlin, Roger K.}, issn = {2056-3744}, journal = {Evolution Letters}, number = {3}, pages = {196--213}, publisher = {Wiley}, title = {{Genetic variation for adaptive traits is associated with polymorphic inversions in Littorina saxatilis}}, doi = {10.1002/evl3.227}, volume = {5}, year = {2021}, } @article{9470, abstract = {A key step in understanding the genetic basis of different evolutionary outcomes (e.g., adaptation) is to determine the roles played by different mutation types (e.g., SNPs, translocations and inversions). To do this we must simultaneously consider different mutation types in an evolutionary framework. Here, we propose a research framework that directly utilizes the most important characteristics of mutations, their population genetic effects, to determine their relative evolutionary significance in a given scenario. We review known population genetic effects of different mutation types and show how these may be connected to different evolutionary outcomes. We provide examples of how to implement this framework and pinpoint areas where more data, theory and synthesis are needed. Linking experimental and theoretical approaches to examine different mutation types simultaneously is a critical step towards understanding their evolutionary significance.}, author = {Berdan, Emma L. and Blanckaert, Alexandre and Slotte, Tanja and Suh, Alexander and Westram, Anja M and Fragata, Inês}, issn = {1365294X}, journal = {Molecular Ecology}, number = {12}, pages = {2710--2723}, publisher = {Wiley}, title = {{Unboxing mutations: Connecting mutation types with evolutionary consequences}}, doi = {10.1111/mec.15936}, volume = {30}, year = {2021}, } @article{7995, abstract = {When divergent populations are connected by gene flow, the establishment of complete reproductive isolation usually requires the joint action of multiple barrier effects. One example where multiple barrier effects are coupled consists of a single trait that is under divergent natural selection and also mediates assortative mating. Such multiple‐effect traits can strongly reduce gene flow. However, there are few cases where patterns of assortative mating have been described quantitatively and their impact on gene flow has been determined. Two ecotypes of the coastal marine snail, Littorina saxatilis , occur in North Atlantic rocky‐shore habitats dominated by either crab predation or wave action. There is evidence for divergent natural selection acting on size, and size‐assortative mating has previously been documented. Here, we analyze the mating pattern in L. saxatilis with respect to size in intensively sampled transects across boundaries between the habitats. We show that the mating pattern is mostly conserved between ecotypes and that it generates both assortment and directional sexual selection for small male size. Using simulations, we show that the mating pattern can contribute to reproductive isolation between ecotypes but the barrier to gene flow is likely strengthened more by sexual selection than by assortment.}, author = {Perini, Samuel and Rafajlović, Marina and Westram, Anja M and Johannesson, Kerstin and Butlin, Roger K.}, issn = {15585646}, journal = {Evolution}, number = {7}, pages = {1482--1497}, publisher = {Wiley}, title = {{Assortative mating, sexual selection, and their consequences for gene flow in Littorina}}, doi = {10.1111/evo.14027}, volume = {74}, year = {2020}, } @article{8168, abstract = {Speciation, that is, the evolution of reproductive barriers eventually leading to complete isolation, is a crucial process generating biodiversity. Recent work has contributed much to our understanding of how reproductive barriers begin to evolve, and how they are maintained in the face of gene flow. However, little is known about the transition from partial to strong reproductive isolation (RI) and the completion of speciation. We argue that the evolution of strong RI is likely to involve different processes, or new interactions among processes, compared with the evolution of the first reproductive barriers. Transition to strong RI may be brought about by changing external conditions, for example, following secondary contact. However, the increasing levels of RI themselves create opportunities for new barriers to evolve and, and interaction or coupling among barriers. These changing processes may depend on genomic architecture and leave detectable signals in the genome. We outline outstanding questions and suggest more theoretical and empirical work, considering both patterns and processes associated with strong RI, is needed to understand how speciation is completed.}, author = {Kulmuni, Jonna and Butlin, Roger K. and Lucek, Kay and Savolainen, Vincent and Westram, Anja M}, issn = {1471-2970}, journal = {Philosophical Transactions of the Royal Society. Series B: Biological sciences}, number = {1806}, publisher = {The Royal Society}, title = {{Towards the completion of speciation: The evolution of reproductive isolation beyond the first barriers}}, doi = {10.1098/rstb.2019.0528}, volume = {375}, year = {2020}, } @article{7393, abstract = {The study of parallel ecological divergence provides important clues to the operation of natural selection. Parallel divergence often occurs in heterogeneous environments with different kinds of environmental gradients in different locations, but the genomic basis underlying this process is unknown. We investigated the genomics of rapid parallel adaptation in the marine snail Littorina saxatilis in response to two independent environmental axes (crab-predation versus wave-action and low-shore versus high-shore). Using pooled whole-genome resequencing, we show that sharing of genomic regions of high differentiation between environments is generally low but increases at smaller spatial scales. We identify different shared genomic regions of divergence for each environmental axis and show that most of these regions overlap with candidate chromosomal inversions. Several inversion regions are divergent and polymorphic across many localities. We argue that chromosomal inversions could store shared variation that fuels rapid parallel adaptation to heterogeneous environments, possibly as balanced polymorphism shared by adaptive gene flow.}, author = {Morales, Hernán E. and Faria, Rui and Johannesson, Kerstin and Larsson, Tomas and Panova, Marina and Westram, Anja M and Butlin, Roger K.}, issn = {2375-2548}, journal = {Science Advances}, number = {12}, publisher = {AAAS}, title = {{Genomic architecture of parallel ecological divergence: Beyond a single environmental contrast}}, doi = {10.1126/sciadv.aav9963}, volume = {5}, year = {2019}, }