Lacustrine spatial distribution of landlocked Atlantic salmon populations assessed across generations by multilocus individual assignment and mixed-stock analyses

The objective of this study was to assess the spatiotemporal distribution o f four landlocked Atlantic salmon (Salmo salar) populations during their sy mpatric feeding phase in lake St-Jean (Quebec, Canada). A total of 1100 fis h captured over a period of 25 years was genotyped at six microsatellite lo ci in order to assess the temporal stability of the relative proportion of each population in different lake sectors using both individual-based assig nment and mixed-stock analysis. Estimates of relative proportions obtained from both methods were highly correlated. A nonrandom spatial distribution of populations was observed for each period and, despite the fact that the overall proportion of each population varied over time, the pattern of diff erential distribution remained generally stable over time. Furthermore, the re were indications that the extent of horizontal spatial overlap among pop ulations was negatively correlated with that of their genetic differentiati on at both microsatellites and a major histocompatibility complex locus, an d independent of the geographical distance between the rivers of origin. We discuss the hypothesis that the temporal stability of spatial distribution , the lack of an association between spatial partitioning and geographical distance between rivers of origin, and the apparent negative correlation be tween spatial overlap and genetic differentiation, reflect the outcome of s elective pressures driving behavioural differences for spatial niche partit ioning among populations.