Recent developments in molecular biology and genomics along with novel statistical methods and conceptual advances in population genetics and evolutionary biology have greatly increased the applicability of molecular markers for assisting in the preservation of wild populations. So far, mitochondrial DNA and, particularly, microsatellite DNA are the most commonly applied markers, but Single Nucleotide Polymorphisms (SNPs) and novel methods for massively parallel sequencing are likely to revolutionize the field. This presentation provides examples of the application of molecular markers in conservation biology of fishes.
The first example concerned the critically endangered North Sea houting (Coregonus oxyrhynchus), of which only one indigenous population remains. Samples from 1980 to the present have been subject to microsatellite DNA analysis, and effective population size (a measure of the number of individuals that successfully pass their genes on to the next generation) has been estimated. The effective population size was shown to be high (ca. 500) and the population is not immediately in danger of inbreeding and loss of evolutionary potential, although the fact that it is the only remaining indigenous population obviously raises significant conservation concerns.
The second example concerned genetic interactions between stocked hatchery strain brown trout (Salmo trutta) and wild brown trout populations. Analysis of DNA from old scale samples (1910s-1950s) pre-dating major stocking activities has enabled estimation of the proportions of hatchery strain trout and indigenous trout in contemporary populations. In the majority of cases the stocked hatchery strain trout have made a surprisingly small genetic contribution, but in some cases strong introgression has occurred. It has been concluded that stocking wild populations with hatchery strain trout does not contribute to population rehabilitation and if there is an effect it is likely to be negative. Consequently, stocking with hatchery strain trout has been discontinued in Denmark.
The third example concerned a study of local adaptation in brown trout populations. Four populations, derived from rivers with different thermal regimes during incubation of eggs, were reared in a common garden set-up. Differences among populations in length of alevins at hatching and at first feeding were observed, and this could be ascribed to adaptation to different thermal regimes in the environments experienced by the different populations.
The fourth example concerned the European eel (Anguilla anguilla), which has experienced recent drastic population declines. The species is known to spawn in the Sargasso Sea, but there is considerable controversy as to whether the species is panmictic or consists of several genetically distinct populations. During the Danish Galathea 3 Expedition ca. 300 larvae of European and the closely related American eel (A. rostrata) were collected in the Sargasso Sea. These samples are currently subject to analysis using microsatellite DNA markers, and some preliminary results were presented.