I urval från Stockholms universitets publikationsdatabas

• Genetic monitoring reveals two sympatric brown trout populations in a small mountain lake

  Anna Palmé, Linda Laikre, Nils Ryman.

  It is contentious to what extent sympatric speciation represents a general and taxonomically widespread phenomenon. Documenting the occurrence of multiple, genetically distinct populations within areas lacking barriers to gene flow can increase our understanding of this type of speciation, because such populations are expected to represent the first steps of sympatric speciation. We analyzed the genetic relationships among over 4000 brown trout (Salmo trutta) collected during 19 sampling years from a series of small mountain lakes in northern Scandinavia. Our results clearly indicate the presence of two sympatric populations within these lakes. The populations are characterized by a high degree of genetic divergence coupled with a lack of apparent phenotypic dichotomy. The differentiation pattern appears stable over the two decades monitored, and the exchange of individuals between the two populations appears small. The existence of sympatric populations characterized by substantial genetic divergence may be a much more common phenomenon than anticipated, but difficult to detect in situations where morphological or ecological differentiation is missing. Larger samples than typically collected in a single sampling effort may be needed for revealing situations of sympatry, and for reliable estimation of the number of populations.

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• Temporally stable, weak genetic structuring in brackish water northern pike (Esox lucius) in the Baltic Sea indicates a contrasting divergence pattern relative to freshwater populations

  Lovisa Wennerström (et al.).

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• Parallel adaptive evolution of geographically distant herring populations on both sides of the North Atlantic Ocean

  2017. Sangeet Lamichhaney (et al.). Proceedings of the National Academy of Sciences of the United States of America 114 (17), E3452-E3461

  Artikel

  Atlantic herring is an excellent species for studying the genetic basis of adaptation in geographically distant populations because of its characteristically large population sizes and low genetic drift. In this study we compared whole-genome resequencing data of Atlantic herring populations from both sides of the Atlantic Ocean. An important finding was the very low degree of genetic differentiation among geographically distant populations (fixation index = 0.026), suggesting lack of reproductive isolation across the ocean. This feature of the Atlantic herring facilitates the detection of genetic factors affecting adaptation because of the sharp contrast between loci showing genetic differentiation resulting from natural selection and the low background noise resulting from genetic drift. We show that genetic factors associated with timing of reproduction are shared between genetically distinct and geographically distant populations. The genes for thyroid-stimulating hormone receptor (TSHR), the SOX11 transcription factor (SOX11), calmodulin (CALM), and estrogen receptor 2 (ESR2A), all with a significant role in reproductive biology, were among the loci that showed the most consistent association with spawning time throughout the species range. In fact, the same two SNPs located at the 5' end of TSHR showed the most significant association with spawning time in both the east and west Atlantic. We also identified unexpected haplotype sharing between spring-spawning oceanic herring and autumn-spawning populations across the Atlantic Ocean and the Baltic Sea. The genomic regions showing this pattern are unlikely to control spawning time but may be involved in adaptation to ecological factor(s) shared among these populations.

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