Morphological and genetic variations of Diplodus vulgaris along the Tunisian coasts
In order to characterize populations of Diplodus vulgaris (Geoffroy St.-Hilaire, 1817) along the Tunisian coasts and to test the prospective role of geographical barrier of the Siculo-Tunisian Strait, we performed a study of morphological and genetic variability of samples collected in six sites distributed on each side of the Strait. Two types of morphological descriptors, 25 truss elements and six complementary conventional linear measurements, and genetic markers (allozymes of four enzyme systems) were used. Multivariate analyses revealed morphological variations among the prospected localities. El Biban sample differs by the suborbital part of the head and the eye diameter, while those of Ghar El Melh and Mahdia diverge mainly by the length and height of the head. Compared to all remaining samples, El Biban specimens showed a large head. The study of genetic polymorphism showed the absence of any genetic structuring among Diplodus vulgaris and the presence of an homogeneous (global FST = 0.004) panmictic unit (f = 0.046 NS). Thus, the Siculo-Tunisian Strait does not seem to act as a barrier between the populations, at least at the scale of the Tunisian coast. The morphological diversity observed seems to reflect the environmental heterogeneity and is not structured by the Siculo-Tunisian Strait (phenotypic plasticity).