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  • Shikano, Takahito; Järvinen, Antero; Marjamaki, Paula; Kahilainen, Kimmo K.; Merilä, Juha (2015)
    Variation in presumably neutral genetic markers can inform us about evolvability, historical effective population sizes and phylogeographic history of contemporary populations. We studied genetic variability in 15 microsatellite loci in six native landlocked Arctic charr (Salvelinus alpinus) populations in northern Fennoscandia, where this species is considered near threatened. We discovered that all populations were genetically highly (mean F-ST approximate to 0.26) differentiated and isolated from each other. Evidence was found for historical, but not for recent population size bottlenecks. Estimates of contemporary effective population size (N-e) ranged from seven to 228 and were significantly correlated with those of historical N-e but not with lake size. A census size (N-C) was estimated to be approximately 300 individuals in a pond (0.14 ha), which exhibited the smallest N-e (i.e. N-e/N-C = 0.02). Genetic variability in this pond and a connected lake is severely reduced, and both genetic and empirical estimates of migration rates indicate a lack of gene flow between them. Hence, albeit currently thriving, some northern Fennoscandian populations appear to be vulnerable to further loss of genetic variability and are likely to have limited capacity to adapt if selection pressures change.
  • Teacher, Amber G. F.; Shikano, Takahito; Karjalainen, Marika E.; Merila, Juha (2011)
  • Wang, Cui; Shikano, Takahito; Persat, Henri; Merila, Juha (2017)
    Pleistocene glaciations have strongly affected the biogeography of many species residing in periglacial and previously glaciated regions. Smoothtail nine-spined sticklebacks (Pungitius laevis) have three highly divergent mitochondrial lineages in France, one of which shares the same mitochondrial cluster with a congener P. pungitius. To understand if interspecific introgression has happened between the two species, we carried out phylogeographic and population genetic analyses using mitochondrial and nuclear gene sequences. Our results indicated asymmetric mitochondrial introgression from P. pungitius to P. laevis and genetic admixture of these species in one of the P. laevis lineages, suggesting historical hybridization. Deep intraspecific mitochondrial divergence within P. laevis in central and southern France mostly coinciding with major drainages suggests that these areas were important glacial refugia for the species explaining the observed intraspecific divergence. The historical hybridization between P. laevis and P. pungitius likely occurred in a refugium at central France, and the newly formed P. laevis lineage spread northward during postglacial recolonization. The study adds to the long list of species showing complete mitogenome capture owing to historical hybridizations, and highlights the reticulate nature of population differentiation in taxa subject to postglacial range-expansions.
  • Castel, Guillaume; Chevenet, Francois; Razzauti, Maria; Murri, Severine; Marianneau, Philippe; Cosson, Jean-Francois; Tordo, Noel; Plyusnin, Alexander (2019)
    Puumala virus is an RNA virus hosted by the bank vole (Myodes glareolus) and is today present in most European countries. Whilst it is generally accepted that hantaviruses have been tightly co-evolving with their hosts, Puumala virus (PUUV) evolutionary history is still controversial and so far has not been studied at the whole European level. This study attempts to reconstruct the phylogeographical spread of modern PUUV throughout Europe during the last postglacial period in the light of an upgraded dataset of complete PUUV small (S) segment sequences and by using most recent computational approaches. Taking advantage of the knowledge on the past migrations of its host, we identified at least three potential independent dispersal routes of PUUV during postglacial recolonization of Europe by the bank vole. From the Alpe-Adrian region (Balkan, Austria, and Hungary) to Western European countries (Germany, France, Belgium, and Netherland), and South Scandinavia. From the vicinity of Carpathian Mountains to the Baltic countries and to Poland, Russia, and Finland. The dissemination towards Denmark and North Scandinavia is more hypothetical and probably involved several independent streams from south and north Fennoscandia.