The memory remains: application of historical DNA for scaling biodiversity loss.

Few species worldwide have attracted as much attention in relation to conservation and sustainable management as Pacific salmon. Most populations have suffered significant reductions, many have disappeared, and even entire evolutionary significant units (ESUs) are believed to have been lost. Until now, no 'smoking gun' in terms of direct genetic evidence of the loss of a salmon ESU has been produced. In this issue of Molecular Ecology, Iwamoto et al. (2012) use microsatellite analysis of historical scale samples of Columbia River sockeye salmon (Oncorhynchus nerka) from 1924 (Fig. 1) to ask the pertinent question: Do the historical samples contain salmon from extirpated populations or ESUs? They identified four genetic groups in the historical samples of which two were almost genetically identical to contemporary ESUs in the river, one showed genetic relationship with a third ESU, but one group was not related to any of the contemporary populations. In association with ecological data, the genetic results suggest that an early migrating Columbia River headwater sockeye salmon ESU has been extirpated. The study has significant importance for conservation and reestablishment of sockeye populations in the Columbia River, but also underpins the general significance of shifting baselines in conservation biology, and how to assess loss of genetic biodiversity. The results clearly illustrate the huge and versatile potential of using historical DNA in population and conservation genetics. Because of the extraordinarily plentiful historical samples and rapid advances in fish genomics, fishes are likely to spearhead future studies of temporal ecological and population genomics in non-model organisms. [Figure: see text].