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Studying population structure and gene flow patterns on temporal scales facilitates an evaluation of the consequences of demographic, physical, and environmental changes on the stability and persistence of populations. Here, we examine temporal genetic variation within and among Atlantic salmon (Salmo salar) rivers in Newfoundland and Labrador, Canada, using samples collected over a period of six decades (1951-2004). Our objective was to evaluate temporal changes in population connectivity associated with the closure of a commercial marine fishery. Despite demographic instability, we find that population structure remained temporally stable over more than 50 years. However, age structure can affect results when not taken into consideration, particularly in populations of large effective size where genetic drift is not strong. Where weak signals of genetic differentiation did not complicate analyses, contemporary migration was often asymmetric, yet low, suggesting patterns of intermittent gene flow. Nevertheless, we find some links between changes in population dynamics and contemporary gene flow. These findings may therefore imply that management decisions impacting the contemporary population dynamics of individual Atlantic salmon rivers can also affect the genetic stability of this species as a whole. Resume: L'etude de la structure demographique et des patrons de flux genique sur des echelles temporelles facilite l'evaluation des consequences des changements demographiques, physiques et environnementaux sur la stabilite et la persistance des populations. Nous examinons ici la variation genetique temporelle au sein des rivieres et entre les rivieres a saumons (Salmo salar) a Terre-Neuve et au Labrador, Canada, a l'aide d'echantillons preleves au cours de six decennies (1951-2004). Notre objectif est d'evaluer les changements temporels de connectivite des populations associes a la fermeture d'une peche commerciale marine. Malgre l'instabilite demographique, la structure de la population est demeuree stable dans le temps pendant plus de 50 ans. Cependant, si on ne tient pas compte de la structure en age, cela peut affecter les resultats particulierement dans les populations de forte taille effective dans lesquelles la derive genetique n'est pas elevee. Lorsque de faibles signaux de differenciation genetique ne compliquent pas les analyses, la migration contemporaine est souvent asymetrique, mais faible, ce qui laisse croire a des patrons de flux genique intermittents. Neanmoins, il existe des liens entre les changements dans la dynamique de population et le flux genique du moment. Ces resultats peuvent donc avoir comme consequence que les decisions de gestion qui affectent la dynamique de population a un moment donne dans les differentes rivieres a saumon atlantique peuvent aussi impacter la stabilite genetique de l'espece dans son ensemble. [Traduit par la Redaction], Introduction Population connectivity as conferred by gene flow has important implications for effective species conservation and management (Frankham et al. 2003). Hence, an understanding of the factors that regulate dispersal [...]

During the 1st millennium before the Common Era (BCE), nomadic tribes associated with the Iron Age Scythian culture spread over the Eurasian Steppe, covering a territory of more than 3,500 km in breadth. To understand the demographic processes behind the spread of the Scythian culture, we analysed genomic data from eight individuals and a mitochondrial dataset of 96 individuals originating in eastern and western parts of the Eurasian Steppe. Genomic inference reveals that Scythians in the east and the west of the steppe zone can best be described as a mixture of Yamnaya-related ancestry and an East Asian component. Demographic modelling suggests independent origins for eastern and western groups with ongoing gene-flow between them, plausibly explaining the striking uniformity of their material culture. We also find evidence that significant gene-flow from east to west Eurasia must have occurred early during the Iron Age.

We estimated local and metapopulation effective sizes ([Formula: see text] and meta-[Formula: see text]) for three coexisting salmonid species (Salmo salar, Salvelinus fontinalis, Salvelinus alpinus) inhabiting a freshwater system comprising seven interconnected lakes. First, we hypothesized that [Formula: see text] might be inversely related to within-species population divergence as reported in an earlier study (i.e., FST: S. salar> S. fontinalis> S. alpinus). Using the approximate Bayesian computation method implemented in ONeSAMP, we found significant differences in [Formula: see text] ([Formula: see text]) between species, consistent with a hierarchy of adult population sizes ([Formula: see text]). Using another method based on a measure of linkage disequilibrium (LDNE: [Formula: see text]), we found more finite [Formula: see text] values for S. salar than for the other two salmonids, in line with the results above that indicate that S. salar exhibits the lowest [Formula: see text] among the three species. Considering subpopulations as open to migration (i.e., removing putative immigrants) led to only marginal and non-significant changes in [Formula: see text], suggesting that migration may be at equilibrium between genetically similar sources. Second, we hypothesized that meta-[Formula: see text] might be significantly smaller than the sum of local [Formula: see text]s (null model) if gene flow is asymmetric, varies among subpopulations, and is driven by common landscape features such as waterfalls. One 'bottom-up' or numerical approach that explicitly incorporates variable and asymmetric migration rates showed this very pattern, while a number of analytical models provided meta-[Formula: see text] estimates that were not significantly different from the null model or from each other. Our study of three species inhabiting a shared environment highlights the importance and utility of differentiating species-specific and landscape effects, not only on dispersal but also in the demography of wild populations as assessed through local [Formula: see text]s and meta-[Formula: see text]s and their relevance in ecology, evolution and conservation.