Genetic variation and population structure of the caramote prawn Penaeus kerathurus (Forskäl) from the eastern and western Mediterranean coasts in Tunisia

Ten populations of Penaeus kerathurus (Forskäl), a prawn of high commercial value, were sampled from the eastern and western Mediterranean coastal waters of Tunisia and screened electrophoretically for genetic variation at 13 allozyme loci. Four among the six polymorphic loci were out of Hardy–Weinberg equilibrium (H–WE) in at least one population. In the same way, the multilocus test showed deviation from H–WE in six populations. These populations showed heterozygote deficiency whereas the average heterozygosity for the four remaining ones is quite similar to the expected levels. Genetic variability was low. The number of alleles per locus ranged from 1.2 to 1.5 (average=1.3), and the observed heterozygosity varied between 0.010 and 0.048 (average=0.021). Significant population differentiation (F_ST=0.076, P<0.05) in the total data set reflected the differentiation of the two populations, which were at the margins of the range sampled, from all the others (Pairwise F_ST values ranged from 0.035 to 0.208). Although there was no significant differentiation among the other populations (pairwise F_ST values ranged from ?0.006 to 0.201, P>0.05). Our data suggest a population structure consistent with separation by Mediterranean Sea basins that might reflect different local biogeographical zones.