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Free keywords:
admixture; anadromous fish; conservation; evolutionarily significant unit; gill raker; introgression; stocking
Abstract:
Natural hybridization plays a key role in the process of speciation. However,
anthropogenic (human induced) hybridization of historically isolated taxa raises
conservation issues. Due to weak barriers to gene flow and the presence of endangered
taxa, the whitefish species complex is an excellent study system to investigate
the consequences of hybridization in conservation. We focused on three
naturally reproductively isolated whitefish taxa in Germany: the endangered,
anadromous North Sea houting (NSH) and Baltic houting (BH), which were
reintroduced after local extinction, and the commercially stocked European
whitefish (EW). To evaluate the genetic integrity of each taxon, source and reintroduced
populations of NSH and BH, and EW populations were characterized
based on two mitochondrial and 17 microsatellite loci. Additionally, we investigated
gill raker counts as an adaptive phenotypic trait. Even though clear genetic
and phenotypic differentiation confirmed the houtings as separate evolutionarily
significant units, admixture analyses revealed an extensive hybrid zone. Hybridizations
were introgressive, positively correlated with genetic diversity, and were
reflected in the gill raker counts. The BH distribution range showed higher heterogeneity
and stronger admixture than the NSH range. Erroneous stocking with
non-native genotypes best explained these patterns, which pose challenges for the
conservation of the endangered NSH and BH.
