Alpine headwater streams as reservoirs of remnant populations of the Danubian clade of brown trout

Abstract

1. The watercourses of Austria are mainly part of the Danube drainage system. Nonetheless, only few brown trout (Salmo trutta) populations of the Danubian phylogenetic lineage have been found in this region, not being introgressed by hatchery-reared fish of the allochthonous Atlantic lineage. The present study was aimed at identifying further waterbodies that might harbour the non-admixed gene pool of the Danubian clade trout. 2. In a first step, the complete mitochondrial DNA control region of 447 specimens from 20 sampling sites was sequenced to screen for the presence of specific haplotypes. In a second step, 332 individuals from 15 populations were analysed at 10 microsatellite DNA loci. 3. Although sampling concentrated on remote Alpine headwater streams, introgression of hatchery strains was more common than expected from existing stocking records. For seven populations, however, no evidence of recent hatchery trout introgression was found and it is suggested that they might represent the indigenous gene pool. 4. Populations showing no evidence of hatchery introgression displayed lower levels of intrapopulation variability and higher degrees of differentiation compared to purported admixed populations. 5. Our study demonstrates the necessity of combining different molecular markers to reveal the impact of introgression into wild populations, since at some sampling sites admixture would have remained undetected if only a single molecular technique was applied. 6. The identification and characterisation of non-introgressed populations provides important information for setting conservation priorities and preventing further loss of genetic integrity of a unique element of the native fish fauna.

Anthropogenic and habitat correlates of hybridization between hatchery and wild brook trout

“…These findings may have implications for conservation efforts seeking to identify nonintrogressed individuals or populations or to control undesirable anthropogenic hybridization (e.g., Meraner et al 2008; Baric et al 2010), as well as for risk assessment analyses of projects that may potentially result in unintentional hybridization (e.g., Hutchings and Fraser 2008). For this reason, we recommend that steps be taken to formally test some of the predictions that this study has proposed, as have other such recent studies Marie et al 2012;Yau and Taylor 2013).…”

“…First, they may shed light on which indigenous populations or species are more at risk of hybridizing. Second, they may provide an efficient and a cost-effective means of identifying indigenous populations that have resisted admixture following stocking using readily available data, an increasingly common situation for restoration and biodiversity conservation (see Meraner et al 2008; Baric et al 2010).…”

Phylogeography, genetic structure, and conservation of the endangered Caspian brown trout, Salmo trutta caspius (Kessler, 1877), from Iran

“…This has resulted in population homogenization and a reduction of the genetic diversity (Almodovar et al, 2006) leading to the loss of local adaptations . Genetic introgression of hatchery strains into wild brown trout populations has been extensively documented for Atlantic (Ruzzante et al, 2001), Mediterranean (Sanz et al, 2009), Marmoratus (Fumagalli et al, 2002), and Danubian lineages (Baric et al, 2010).…”

“…Intensive fishing in combination with habitat destruction as well as chemical and biological pollution has led to the decline of local populations. For many decades, stocking with hatchery-reared strains was regarded as the main way to counterbalance these negative effects (Baric et al, 2010). In spite of the complex pattern of genetic differentiation both at macro-and microgeographical levels in the species, stocking of European basins have been mostly carried out with uniform commercial stocks of North-European origin.…”

Genetic variation in brown trout Salmo truttaacross the Danube, Rhine, and Elbe headwaters: a failure of the phylogeographic paradigm?

“…Map of all 97 sites sampled in this study as well as the 17 populations sampled in [30] and their corresponding drainages. The purple dotted lines correspond to the maximum extension of glacial ice at the height of the Würm glaciation [31].…”