Lessepsian invasion without bottleneck:: example of two rabbitfish species (Siganus rivulatus and Siganus luridus)

Since the opening of the Suez Canal in the 19th century, a growing number of teleosts species have become permanently established in the eastern Mediterranean. As environmental parameters in the Mediterranean are very different from those in the Red Sea, there is an opportunity to evaluate the gene flow associated with the acclimatisation of these species to their new environment. Initial colonisation may have been restricted to individuals with marginal genotypes compared to populations of the Red Sea, eventually better adapted to the Mediterranean environment. Alternatively, colonisation may have occurred without major genetic differentiation, due to a large flux of immigrants and a continuous gene flow from the populations of origin. Using different molecular genetic techniques (mitochondrial DNA, Exon-Primed Intron-Crossing PCR amplification (EPIC) and Inter-Simple Sequence Repeats (ISSRs), patterns of genetic differentiation on both sides of the Suez isthmus were tested on two Lessepsian rabbitfish species (Siganus rivulatus and Siganus luridus). The absence of genetic differentiation between Mediterranean and Red Sea populations in both species showed that a great number of migrants participated to the colonisation of the Mediterranean, excluding any bottleneck event. This colonisation success suggests large eco-physiological plasticity in S. rivulatits and S. luridus that allowed them to thrive in the new environment. (C) 2003 Elsevier Science B.V. All rights reserved.