Adrian Bird

comprised populations that differ genetically in their response to the environment at spatial scales of around 600–800 km, undetected by microsatellite DNA variations. They caught cod from four populations within the Atlantic and looked at larval growth in the laboratory. Among all four populations, growth increased with food supply and temperature but the influence of changes in food and temperature on survival differed between warmand cold-water populations, the researchers found. The results imply that Atlantic cod do not respond as a whole to similar changes in the environment in a similar manner. Increased water temperature, for example, is predicted to have a positive influence on the larval survival of warm-water populations. But the interactive effect of temperature and food had different effects on survival amongst the different populations. The team found that, at lower temperatures, survival of the cod from warmer waters increased with food supply, whereas growth of cold-water-derived cod was unaffected by increased food. The authors believe their data reveal “significant genetic differences among populations of Atlantic cod at a spatial scale at which disjunctions in gene flow were not detectable using traditional population genetics markers.” The collapse of many of the world’s fisheries underscores a pressing need to study the adaptive variation in commercially exploited marine species with the aim of establishing recovery strategies at biological meaningful and genetically relevant spatial scales, the researchers write. “In this regard this work underscores the merit in undertaking experiments in conjunction with studies of population structure based solely on allelic variability, particularly for genes thought to be under natural selection.” From the results of this research, restocking fisheries may require a very particular type of fish. Q & A