Sequence variability at the mitochondrial ND1, ND6, cyt b and D-loop segments in tench (Tinca tinca L.)

The authors’ previous PCR-RFLP studies on ND1, ND6, cyt b and D-loop segments of mtDNA in tench revealed the existence of 9 composite haplotypes, named H1-H9. As cyt b is the only mtDNA segment whose variability has been widely studied in tench, the same four segments were sequenced in 29 individuals from 17 populations covering all 9 haplotypes, with the aim of providing additional data on tench mtDNA variation. Ninety-six polymorphic sites were identified and all the differences were single nucleotide substitutions, except for six indels found in the D-loop. The observed polymorphisms gave origin to five different ND1 sequences, seven ND6 sequences, six cyt b sequences and 17 D-loop sequences. The comparison with data in GenBank revealed that all the five ND1 sequences were not yet reported, as well as one for cyt b and sixteen for D-loop; concerning ND6, the data were the first contribution on the variability of this segment. The combination of the haplotypes at the single segments determined 20 composite haplotypes: seven (H1a-H1g) had been classified as H1 and six (H2a-H2f) as H2 with the PCR-RFLP analysis, while for the other haplotypes previously identified (H3-H9) no additional variability was found. The analysis of phylogenetic trees showed that each segment was informative enough to clearly identify the two highly divergent haplogroups already reported in tench, but only the D-loop gave a good resolution of the tree branching, thanks to its high variability. The Median-Joining network, constructed using the composite haplotypes, indicated H1a as the founder node for haplogroup A and the haplotypes H2a-H2f as ancestral with respect to H7-H9. The new data on the variability of mtDNA can contribute to a better understanding of the between and within population diversity in tench.