“…In North America the species is spread along the West Coast (Prevosti et al, 1987;1989). This phenomenon of colonization has been studied at different genetic levels: the chromosomal polymorphism (Prevosti et al, 1985;1988;, the allozyme polymorphism (Prevosti et al, 1983;Balanyà et al, 1994), the lethal genes (Mestres et al, 1990;Solé et al, 2000), the polygenes for quantitative traits (Pegueroles et al, 1995;1999;Huey et al, 2000), the mtDNA (Latorre et al, 1986;Rozas et al, 1990), the genomic DNA variation (Rozas and Aguadé, 1991) and the effect of inbreeding (Pegueroles et al, 1996).…”