Despite the importance of Lessepsian invasion by migrant fish species from the Red Sea into the Mediterranean Sea via the Suez Canal, determinants of invasive success have been poorly investigated. In this study, we reconstructed the spatio-temporal dynamics of all Lessepsian fish species in the Mediterranean Sea and analysed the relationship between ecological variables and dispersal rate. We created a database on species occurrences based on historical data (1869 to 2005) and estimated the dispersal rate of each species. Overall, 30% of the Lessepsian species succeeded in colonizing the Mediterranean Sea. On average, the 43 Lessepsian species not included in the category 'absence of dispersal' disperse at a rate of 221 ± 5.4 km yr -1 (SE) on the northern side and 70 km yr -1 (SE = 3 km yr -1
The relationship between heterozygosity and age, as well as growth-related traits, was explored in the common pandora Pagellus erythrinus, a sparid fish subjected to commercial exploitation in the Mediterranean Sea. Allozyme electrophoresis was used to quantify the levels of heterozygosity of 238 adult fish from 3 to 7 yr old, aged by means of otoliths and captured in the Gabes Gulf, located along the south-eastern coast of Tunisia. Analyses were conducted by using individual single-locus and multi-locus heterozygosity and 4 growth-related parameters -standard length, total body weight, otolith length and otolith weight -as well as 2 measures of condition (condition factor and relative condition factor). For the 4 growth-related parameters and 2 condition parameters analyzed at 8 polymorphic loci, heterozygotes had higher average values than homozygotes in 36 out of 48 comparisons. However, since these 6 biometric parameters are highly correlated, this proportion should not be considered globally as strong evidence of a hetero zygosity−fitness correlation (HFC). Interpreting these data on a per parameter basis, only otolith weight appeared significantly and positively correlated with multi-locus heterozygosity. Thus, although there was evidence for HFC, it appeared relatively weak for the growth para meters analyzed and may have arisen by chance. The results we obtained relative to survival are more convincing. Although cohorts did not appear genetically differentiated and the whole sample did not display any internal structure after a Bayesian analysis with the STRUCTURE software, multi-locus individual heterozygosity was significantly and positively correlated with fish age. This suggests better survival of heterozygotes and establishes the presence of a heterozygosity− fitness correlation in the Tunisian population of the common pandora.
The taxonomy of oysters has been traditionally based on characteristics of the shell. More recently, the analysis of protein and DNA polymorphism has provided a means to overcome difficulties in distinguishing the different species of oysters based solely on shell morphology. In order to identify oysters of the Tunisian northeast coast, we sequenced a 16S rRNA mitochondrial fragment from 68 oysters sampled from the Bizert Lagoon and the Gulf of Hammamet in northern Tunisia. Comparison of oyster 16S rRNA sequences available in GenBank showed the presence of both Ostreola stentina and Crassostrea gigas in our samples, which could not be detected on the basis of shell morphology only. These data confirmed that C. gigas, a non-native species, is now naturalised in the Bizert Lagoon. Furthermore, significant levels of genetic divergence among the 16S rRNA haplotypes from O. stentina populations have been observed. Specifically, the haplotypes found in the Bizert Lagoon are closer to those previously detected from Morocco and Portugal, whereas those in the Gulf of Hammamet are closer to the haplotypes from the south of Tunisia, with a divergence ranging from 2.1% to 2.7% between the northern and eastern Tunisian haplotypes. The possible impact of the Siculo-Tunisian Strait on the phylogeography of O. stentina is discussed.
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