Effect of the introgression of Atlantic brown trout, Salmo trutta, into Adriatic trout, Salmo farioides in a stream at the drainage area of the Adriatic Sea basin of Montenegro

Abstract

Background. The diversity of wild trout stocks in Montenegro is compromised by insufficiently controlled stocking. Adriatic and Mediterranean areas show a high degree of endemism of the salmonid species, with numerous native Salmo taxa described. The invasive effect of brown trout, Salmo trutta Linnaeus, 1758, of the Atlantic haplogroup on the endemic Adriatic trout, Salmo farioides Karaman, 1938, in the drainage area of the Adriatic Sea basin is lower compared to the effect inflicted by S. trutta has on Salmo labrax Pallas, 1814 of the Danubian haplogroup. The presently reported study was intended to describe the genetic structure of the population of Adriatic trout, Salmo farioides, from the Mrtvica River, a right tributary of the Morača River, Montenegro, in order to get an insight into the spread of non-native strains and their introgression into the native Adriatic trout gene pool. Material and methods. Trout specimens sampled from the lower section of the Mrtvica River from 2004 to 2007, and from its upper section in the spring of 2014, were analysed for their mtDNA haplotypes. Nuclear DNA markers (microsatellites, LDH-C1* gene) were also included in genetic analyses since mtDNA is inherited only maternally. After statistical analyses, relations between individuals from the upper and lower Mrtvica River were reconstructed. Results. Using both LDH-C1* and seven microsatellite loci with several alleles exclusive to S. trutta, an introgression was detected only in the upper reaches of the Mrtvica River, where only stream-dwelling trout form occurs. In the lower reaches no introgression was detected at all, as revealed by the absence of both the Atlantic mitochondrial haplotype and microsatellite alleles exclusive to S. trutta. Conclusion. The allelic frequency at seven microsatellite loci of Salmo spp. from the two river sections revealed very different population structure, as a consequence of a low rate of gene flow between them. In addition to the physical barrier that prevents Salmo sp. from the lower Mrtvica River to migrate to the upper river section, it seems that the opportunity to mate with the large pool of conspecifics, including lake-dwelling S. farioides (i.e., Salmo cf. dentex), prevents Salmo trutta from surviving at the lower reach and spread to the rest of the Morača River and Lake Skadar systems.

Alternative Life-History in Native Trout (Salmo spp.) Suppresses the Invasive Effect of Alien Trout Strains Introduced Into Streams in the Western Part of the Balkans

“…From each fish, an anal fin clip was taken and stored in microtubes filled with 96% ethanol. Fin clips were collected from 10 individuals from the Svetinja River, from 11 caught in the Krušnica River, from 11 individuals caught in the lower reach, and 12 from the upper reach of the Mrtvica River, where the size of samples was limited most likely by extensive poaching occurring there (Škraba Jurlina et al, 2018). As for the Danube River tributaries in the Iron Gate Gorge area, fin clips were collected from each of a very small number of individuals due to their small size and the scarcity of water and brown trout in those streams (Tošić et al, 2016), [e.g., two samples from the Brnjica River, 18 from the KoŽica River, six from the Mala Boljetinska River, 12 from the Zlatica River, 11 from the north fork of the Rečka River, 10 from the Vratna River, and seven from the Zamna River (Figure 1, localities 7, 4, 5, 6, 3, 2, and 1, respectively) ( Supplementary Table)].…”

“…All were amplified in four duplex reactions. The last microsatellite locus, SsoSL438, was excluded from the analysis of specimens from the Mrtvica River, while the remaining seven loci were combined in one single and three duplex reactions, with the forward primer labeled with a fluorescent dye (FAM or NED) (Škraba Jurlina et al, 2018). Fragment analysis was performed using GeneScan 500 LIZ Size Standard (Applied Biosystems, USA) on an ABI-3130 Genetic Analyzer (Applied Biosystems, USA).…”

“…Statistical analysis was performed on the microsatellite data to determine the differences in genetic structure between populations whose members revealed an alternative life history by partial migration and populations consisting exclusively of resident, stream-dwelling brown trout. Genetic structure from microsatellite data was determined as reported in Škraba Jurlina et al (2018). Factorial correspondence analysis (FCA) was carried out using the program GENETIX 4.05 (Belkhir et al, 2004).…”

“…In the upper course of the Mrtvica River, where Adriatic trout is the native brown trout taxon bearing the Adcs11 haplotype (#AY836340; Cortey et al, 2004), three of 12 (25%) fish were of the A17 haplotype (#HQ848368; Kohout et al, 2012), and all of 11 fish from the lower course were native Adriatic trout (Škraba Jurlina et al, 2018).…”

“…presented here was recently supplemented with a prominent insight into their diversity, assessed using molecular markers, both mitochondrial, [e.g., cytochrome b and control region (CR), i.e., the D-loop (Bernatchez et al, 1992;Bernatchez, 2001), and nuclear, e.g., LDH-C * and several microsatellite loci (Hamilton et al, 1989;Richard and Thorpe, 2001)]. The basic mapping of indigenous populations of nominal trout taxa accomplished using CR as a marker in the Adriatic Sea Basin assigned them to the Adriatic (AD), marmoratus (MA), and Danubian (DA) mtDNA lineages (Marić et al, 2006;Mrdak, 2011;Mrdak et al, 2012;Simonović et al, 2017b;Škraba Jurlina et al, 2018); those native to the Black Sea Basin belonged to the DA lineage (Marić et al, 2006;Mrdak, 2011;Tošić et al, 2014Tošić et al, , 2016Simonović et al, 2017b;Škraba et al, 2017), whereas in the Aegean Sea Basin, they belonged to the AD lineage (Marić et al, 2006(Marić et al, , 2017LoBrutto et al, 2010).…”