RESEARCH ARTICLE Genetic structure of a vulnerable species, the freshwater blenny (Salaria fluviatilis)

endemic fish to the tributaries of the Mediterranean and Black seas, is considered endangered in five of the nine Mediterranean-European countries. Substantial effort has recently been made to improve our understanding of its biology (i.e., habitat modelling, morphology, behaviour), but developing a conservation program for a species is less effective without a thorough knowledge of its genetic heterogeneity. The goal of this study was to assess the existence and boundaries of freshwater blenny genetic clusters in the occidental basin of the Mediterranean Sea. Our results suggest a genetic structure at two levels. The first is a range-wide product of two different glacial ref-uges, potentially the Iberian Peninsula (South of Spain; the origin of the ‘‘western’ ’ group) and Corsica (the ‘‘eastern’’ group). Subsequent northward migration likely took place along the Mediterranean coasts from these two glacial refuges to the southern part of mainland France, where a second contact zone potentially occurred. The second level is a fine-scale genetic structure corresponding to eight genetic groups—four to the west from the ‘‘western’ ’ ref-uge and four to the east from the ‘‘eastern’ ’ refuge. Fur-thermore, we demonstrate that population differentiation between the western and eastern groups had occurred far enough in the past that new mutations and not solely drift effects were detectable. These results provide a foundation on which to design future conservation efforts of the freshwater blenny in the occidental basin of the Mediter-ranean Sea