No abstract

One of the key issues concerning the application of microsatellite DNA data in evolutionary studies is how the number of loci applied may influence the stability of genetic distances and corresponding phylograms. While computer simulations have suggested that over 30 microsatellites are required for accurate evolutionary inference, we show that a median of only six loci have been generally applied in studies of wild populations. Factors contributing to this contrast include: i) uncertainty regarding the potential benefits that can be gained from a realistic increase in the number of loci used; and ii) the lack of empirical studies assessing the influence of the number of microsatellites on the reliability of genetic distance estimation and phylogeny construction. In order to address these issues, we applied resampling techniques to microsatellite data in widely distributed populations of European grayling (Thymallus thymallus, Salmonidae). In agreement with expectations based on simulated data, we demonstrate empirically that the stability of commonly used genetic distances (DCE, DA and (deltamu)2) and the corresponding neighbor-joining phylograms is positively associated with the number of microsatellites utilized. For instance, increasing the number of loci from six to 17 resulted in a striking 75% increase in the proportion of DCE phylogram nodes supported by a bootstrap estimate of over 70%. Our results demonstrate that even moderately increasing the number of loci can be very beneficial--a finding extremely relevant for studies of natural populations for which optimally high microsatellite numbers are out of reach. Furthermore, the number of loci most commonly used to date may lead to erroneous inference of the evolutionary relationships between populations.

–  After release to the wild, captive reared salmon have shown lower foraging rates on natural prey and impaired ability to avoid natural predators and thus lower survival compared with wild‐born conspecifics. Here, we examine whether captive breeding influences learning of foraging on natural prey and how enriched rearing methods may improve foraging on natural prey by Atlantic salmon (Salmo salar) parr. We reared offspring of hatchery or wild salmon of the same population in either a standard or enriched environment at production‐scale densities. The enriched environment featured submerged overhead shelter, varying water current, depth and direction and consequently alterations in food dispersion. Parr reared in the enriched environment expressed higher feeding rates, and parr of wild origin started to forage earlier on natural prey. The enriched method promoted foraging of hatchery reared parr on natural prey and is easily applicable to commercial production of salmonids for reintroduction or stock enhancement purposes.

No abstract

Since food availability is known to affect both the precocious maturation and start of feeding migration in wild juvenile salmonids, we examined if a reduction in otherwise plentiful feeding in hatcheries could improve migration tendency and the subsequent survival of released Atlantic salmon (Salmo salar) smolts. A reduction in diet lipid content and feed ration (FR) the previous spring and in FR in the winter prior to release proved efficient; spring-diet treatment halved the proportion of mature males in the autumn prior to release, and a reduction in FR in the winter prior to release decreased latency before leaving the stocking site. In addition, a reduction in FR in winter affected the onset of migration, improved migration speed, and defined the direction of migration downstream in controlled experiments. However, diet manipulations neither affected the swimming endurance nor improved the generally poor tag recapture rates. We conclude that reduced FR at specific times could be used to reduce both precocious male maturity and improve the migration tendency of released salmon.