• FST;
  • phylogeography;
  • proteins – scorpions;
  • subspecies;
  • West Mediterranean

I assess here the importance of the Strait of Gibraltar as a barrier to gene flow for populations of the scorpion Buthus occitanus. This polytypic buthid scorpion occurs in Europe and in North Africa where it is morphologically more diverse. The phylogenetic relationship between B. occitanus populations across the Strait of Gibraltar is investigated by nuclear allozymes analysis (15 loci scored). Phylogenetic analysis based on estimated gene frequency data results in a tree topology that divides the populations into three clades, i.e. a European, an Atlas (= Morocco samples) and a Tell-Atlas clade (= Tunisian samples). The Tell-Atlas clade grouped with the European clade with a rather high bootstrap support of 70%. Within these clades low levels of genetic variability are observed. Calibrating a molecular clock under the assumption that the European populations are autochthonous and have been isolated from the North African for at least 5.33 Myr reveals a divergence rate of 0.060 genetic distance (D) per Myr estimated between European and Moroccan samples and 0.036D Myr−1 between European and Tunisian samples, respectively. © 2004 The Linnean Society of London, Biological Journal of the Linnean Society, 2004, 81, 519–534.