A diagnostic SNP marker to discriminate the European brook lamprey (Lampetra planeri), river lamprey (L. fluviatilis) and their hybrids

Abstract I. Background: The European river lamprey Lampetra fluviatilis and the brook lamprey L. planeri are two closely related species that are also considered as partially reproductively isolated ecotypes. At the larval stage, they cannot be morphologically distinguished. We aimed at developing a molecular tool to identify early life stages of L. fluviatilis and L. planeri.II. Methods and Results: We first identified Single Nucleotide Polymorphism (SNP) markers with distinct alleles between L. fluviatilis and L. planeri based on RADseq data from 186 individuals collected in France. Then, we developed a quantitative PCR protocol to genotype a species-specific SNP, which was tested on 287 samples including larvae and adults from both species and 17 sites from Western Europe. Results were consistent with morphological identification in all cases except for samples from the Rhône drainage and the Loch Lomond in Scotland.III. Conclusions: This marker allows the identification of larval stages of L. fluviatilis, L. planeri as well as hybrids. The two cases where the marker was not diagnostic might be explained by an isolated and distinct L. planeri lineage in the Rhône drainage, and high levels of admixture among L. fluviatilis, L. planeri and the lake-parasitic form in Loch Lomond.