Lack of reproductive isolation between the Western and Eastern phylogroups of the tench

Abstract

The Eurasian range of the tench distribution is subdivided into deeply divergent Western and Eastern phylogroups evidenced by nuclear and mitochondrial DNA sequence markers. A broad zone of overlap exists in central and western Europe, suggesting post-glacial contact with limited hybridisation. We conducted a population genetic test of this indication that the two phylogroups may represent distinct species. We analysed variation at introns of nuclear genes, microsatellites, allozymes and mitochondrial DNA in populations from two postglacial lakes within the contact zone in Germany. The test is based on the expectation that in the presence of strong barriers to reproduction, a hybrid population will show genome-wide associations among alleles and genotypes from each phylogroup even after hundreds of generations of interbreeding. In contrast to this expectation, no consistent significant deviations from linkage and Hardy-Weinberg equilibria were found. Samples from both lakes did show significant disequilibria but they were limited to individual loci and were not concordant between populations, and were not robust to the method used. The single consistent association can be attributed to physical linkage between two microsatellite loci. Thus, results of our study support the hypothesis of free interbreeding between the two phylogroups of tench. Therefore, although the phylogroups may be considered as separate phylogenetic species, the present data suggest that they are a single species under the biological species concept.

Genetic variability in tench (Tinca tincaL.) as revealed by PCR-RFLP analysis of mitochondrial DNA

“…On the other hand, mtDNA markers were shown to be an excellent tool for revealing the between-population variability. The identification of 2 mtDNA haplogroups in the present study, along with the recent discovery of 2 major growth hormone gene classes in tench (Kocour and Kohlmann, 2011) further support the results of Lajbner et al (2007 who investigated the molecular phylogeography of tench by the analysis of the cyt b locus and some nuclear markers. They showed that the species is subdivided into deeply divergent Western and Eastern phylogroups which are not, however, distinct species (Lajbner et al, 2010).…”

“…The identification of 2 mtDNA haplogroups in the present study, along with the recent discovery of 2 major growth hormone gene classes in tench (Kocour and Kohlmann, 2011) further support the results of Lajbner et al (2007 who investigated the molecular phylogeography of tench by the analysis of the cyt b locus and some nuclear markers. They showed that the species is subdivided into deeply divergent Western and Eastern phylogroups which are not, however, distinct species (Lajbner et al, 2010). Also in other freshwater species, including the chub (Leuciscus cephalus) (Durand et al, 1999), perch (Perca fluviatilis) (Nesbø et al, 1999) and barbel (Barbus barbus) (Kotlik and Berrebi, 2001), genetic lines related to the geographical location were observed which could indicate an evolutionary history common to different freshwater species.…”

“…Also in other freshwater species, including the chub (Leuciscus cephalus) (Durand et al, 1999), perch (Perca fluviatilis) (Nesbø et al, 1999) and barbel (Barbus barbus) (Kotlik and Berrebi, 2001), genetic lines related to the geographical location were observed which could indicate an evolutionary history common to different freshwater species. On the basis of the haplogroup composition, composite haplotype distribution and population location, it can be inferred that the haplogroup A observed in the present study corresponds to the Western phylogroup reported by Lajbner et al (2007 while the haplogroup B corresponds to the Eastern phylogroup.…”

“…Also, the complete mitochondrial DNA (mtDNA) sequence has only recently been made available (Saitoh et al, 2006). The subsequent analysis of the mitochondrial cyt b gene, together with 3 nuclear genes, has helped clarify the molecular phylogeography of the tench with the discovery of 2 geographical clades (Eastern and Western), possibly developed in response to recurrent isolation in glacial refugia during the Pleistocene (Lajbner et al, 2007). Within the Eastern phylogroup, the analysis of cyt b also allowed the identification of populations distinct from the major Eastern clade in the Anzalee lagoon of the Caspian Sea in Iran and in the Iskar River of the Danube River drainage in Bulgaria .…”

Tinca Gobba Dorata del Pianalto di Poirino: genetic characterization by microsatellite markers

“…In absence of information on the genomic location of the considered loci, the linkage disequilibrium was tested and all the markers were found to be independent; so, the significant linkage disequilibrium between MTT-2 and MTT-6 loci, observed by Lajbner et al (2009) using various methods, including the one adopted in the present study, was not confirmed. Moreover, none of the deviations from the Hardy-Weinberg equilibrium, estimated for each locus -population pair, were significant, thereby suggesting that the 7 microsatellites were neutral markers.…”