Oum Kalthoum Ben Hassine

Fragmentation of sea bass populations in the western and eastern Mediterranean as revealed by microsatellite polymorphism

We studied the genetic structure at six microsatellite loci of the Mediterranean sea bass (Dicentrarchus labrax) on 19 samples collected from different localities in the western and eastern Mediterranean basins. Significant divergence was found between the two basins. The distance tree showed two separate clusters of populations which matched well with geography, with the noticeable exception of one Egyptian sample which grouped within the western clade, a fact attributable to the introduction of aquaculture broodstock. No heterogeneity was observed within the western basin (θ = 0.0014 and n.s.). However, a significant level of differentiation was found among samples of the eastern Mediterranean (θ = 0.026 and p 0.001). These results match with water currents but probably not with the dispersal abilities of this fish species. We thus hypothesize that selective forces are at play which limit long–range dispersal, a fact to be taken into account in the debate about speciation processes in the marine environment.

Geography and host specificity: Two forces behind the genetic structure of the freshwater fish parasite Ligula intestinalis (Cestoda: Diphyllobothriidae)

Parasite species with global distributions and complex life cycles offer a rare opportunity to study alternative mechanisms of speciation and evolution in a single model. Here, genealogy and genetic structure, with respect to geography and fish host preference, have been analyzed for Ligula intestinalis, a tapeworm affecting freshwater fish. The data analyzed consisted of 109 tapeworms sampled from 13 fish host species in 18 different localities on a macrogeographic scale. Two mitochondrial genes, cytochrome oxidase subunit I and cytochrome B, and the nuclear sequence of intergenic transcribed spacer 2 (ITS2) were used for the genetic reconstruction. Different evolutionary patterns were found at the local and at the global geographic scales. On a local scale, the flat genetic structure was mainly attributed to contiguous range expansion. Migrating birds are the most likely cause of the homogenisation of the whole population, preventing the creation of significant genetic barriers. By contrast, on a global scale, genetically distant and well-separated clusters are present in different geographic areas. Reproductive isolation was found even between clades living in sympatry and infecting the same definitive host, suggesting the existence of efficient biologically determined genetic barriers, and thus possibly separate species. Although the ITS2 sequences were found to display considerable intragenomic variability, their relationships were generally in good agreement with the topology derived from mitochondrial genes.

Comparative morphometric study of the invasive pearl oyster Pinctada radiata along the Tunisian coastline.

In order to study the relative growth of the pearl oyster Pinctada radiata in Tunisia, a total of 330 individuals of this species were collected from six sites along the Tunisian coastline. Quantitative measurements of collected oysters were conducted for shell height, shell length, shell width, hinge length, height and width of the nacreous part and wet weight. The size structure of the sampled populations was described and the relative growth between different morphometric characteristics was estimated as allometric growth lines for the six P. radiata samples. It appeared that the majority of examined samples were dominated by large individuals that exceed a shell height of 42 mm. The maximum size (100.5 mm), recorded in Bizerta lagoon, is bigger than that recorded elsewhere in particular in the Red Sea. Size distribution analysis also showed that the majority of P. radiata samples were dominated by two or more size groups. Differences of allometric regression were found between the examined samples for the tested relationships. Moreover, the Factorial Discriminant Analysis, coupled with Ascending Hierarchic Classification, classified the sub-populations according to geographic locations.

Spraguea lophii (Microsporidia) parasite of the teleost fish, Lophius piscatorius from Tunisian coasts: evidence for an extensive chromosome length polymorphism.

A microsporidian of the genus Spraguea was found parasitizing the nervous tissues of Lophius piscatorius collected from various localities in the Mediterranean coastal areas of Tunisia. The tissue localization, the infection focus aspect and sporal dimorphism are characteristics of Spraguea lophii species. Molecular data based on partial sequence of SSUrRNA encoding gene shows few nucleotide polymorphisms, compared to all described Spraguea isolates. Molecular karyotype obtained on pulsed field gel electrophoresis (1D-PFGE) shows a profile with 14 stained bands in the range of 230-880 kbp and a genome size estimated to 6.700 kbp. The rare cutter endonuclease MluI KARD 2-D-PFGE fingerprint shows an extensive chromosome length polymorphism, but the number of chromosome is unchanged and consists of 15 different molecules. The extensive chromosome length polymorphism is associated to a reduced number of genetic events.

Spatial and temporal variation of biochemical biomarkers in Gobius niger (Gobiidae) from a southern Mediterranean lagoon (Bizerta lagoon, Tunisia): Influence of biotic and abiotic factors.

This study aims at evaluating both the influence of natural and some anthropogenic pressures on spatio-temporal variations on biomarker responses in sedentary benthic fish Gobius niger. For this purpose, variability of biotransformation enzymes and oxidative stress parameters response were studied in six stations from Bizerta lagoon as well as a reference station located in Ghar El Melh lagoon. Biomarker responses were shown to vary according to both physico-chemical parameters and anthropogenic pressures, but no influence of sex was reported. Based on multivariate analyses, the responses of biomarkers, obtained after covariate analysis in order to weigh the effect of physico-chemical parameters, allowed us to discriminate all stations, with a good classification rate for those that are highly contaminated. Altogether, this study shows the usefulness of G. niger as a sentinel species and stresses the necessity of integrating natural variables for data interpretation.

Morphological variations of striped seabream, Lithognathus mormyrus , populations along the Tunisian coast

Morphological variations of Tunisian Lithognathus mormyrus populations were investigated using 41 morphometric measurements (27 truss elements and 14 traditional measurements) and eight meristic characters collected from ten marine and lagoon samples. Statistical analyses (e.g. discriminant function analysis (DFA)) performed separately to truss and traditional data revealed a significant degree of morphological dissimilarity of lagoon samples (Bizerta, Ghar El Melh and El Biban lagoons). For these three lagoon environments the overall assignment of individuals into their original sample (percentage classification success) by DFA was 94% for truss elements and 98% for traditional measurements. This morphological discrimination among lagoon samples, revealed with traditional measurements, seems to be associated only with the anterior part of the body (especially with the pre-orbit and snout length). However, for truss analyses, it was explained by both anterior and posterior parts (peduncle region). Statistical analyses for only marine samples showed partial overlapping with significant morphometric variation of the Chebba and Gabes samples mainly related to the anterior part of the body, for the first sample, but also to the posterior region, for the second one. These morphometric variations are often due to environmental conditions and mainly to the exploitation of different ecological niches that are particularly limited by the availability, type and size of prey. Thus, truss and traditional approaches are complementary and provide more accurate explanations of such a morphological discrimination. Meristic character analyses showed homogeneity of striped seabream samples, except for the Ghar El Melh lagoon sample which quietly differed from the others. This distinction was mainly explained by the number of soft anal rays.

Biomonitoring of the environmental contamination by organotins in the Gulf of Tunis: occurrence of imposex in Stramonita haemastoma (Linnaeus, 1767)

Imposex has been observed in several regions of the world to affect many species of prosobranch gastropods such as Stramonita haemastoma (Linnaeus, 1767). This irreversible sexual anomaly is caused mainly by the accumulation of organotin compounds in tissues. The present study aimed to confirm the existence of imposex and to determine the different levels of infection in individuals of Stramonita haemastoma collected from different stations along the rocky coastline of the Gulf of Tunis. To do this, 10 stations covering the entire rocky coastline of the gulf were sampled during March–May 2012. Rates of occurrence of imposex suggest that sexual modifications occur to different degrees in this species in all sampled stations of the gulf. The most contaminated sites were harbour areas (Sidi Bou Said and La Goulette). In addition, an inverse relationship between the distances from potential sources of pollution and the occurrence of this sexual anomaly was observed. It should be noted that toxic effects induced by marine xenobiotics could cause the loss of biodiversity and the disruption of this ecosystem stability.

Pathways of cryptic invasion in a fish parasite traced using coalescent analysis and epidemiological survey

Introduced species have the potential to outperform natives via the introduction of new parasites to which the native ecosystem is vulnerable. Cryptic diversity within an invasive species can obscure invasion patterns and confound proper management measures. The aim of this study is to use coalescent theory based methodology to trace recent routes of invasion in populations of Ligula intestinalis, a globally distributed fish parasite possessing both native and recently introduced populations in North Africa. Molecular analyses of mitochondrial DNA discerned a pronounced genetic divergence between introduced and native populations. Distribution of mitochondrial haplotypes demonstrated common origin of European populations with North African parasites sampled from introduced fish species in Tunisia. To test the suggested pathway of introduction, microsatellite data were examined in a model-based coalescent analysis using the software MIGRATE, where Europe to Tunisia direction of migration was favoured over alternative hypotheses of gene flow. Specificity of Tunisian populations to different host species was assessed in an epidemiologic survey confirming prevailing host-based division between introduced and native parasites in North Africa. This approach combining advanced analysis of molecular markers with host-specificity data allows revealing the evolution of host-parasite interactions following biological invasion and provides basis for devising future management measurements.

Liver histopathology and biochemical biomarkers in Gobius niger and Zosterisessor ophiocephalus from polluted and non-polluted Tunisian lagoons (Southern Mediterranean Sea)

The aim of this study was to appraise the response of a multi-marker approach in fish species, Gobius niger and Zosterisessor ophiocephalus, in a polluted lagoon (Bizerte lagoon: MB and ML sites) and in a reference site (Ghar-El-Melh lagoon entrance) by the analysis of physiological indexes, liver histopathology and some biochemical biomarkers. The results showed liver hypertrophy in fish collected from Bizerte lagoon as well as many non-specific lesions, unlike the reference site. All Bizerte lagoon sites had the same prevalence of histopathological lesions, but the mean intensity (MI) of parasites seemed to be more sensible as an indicator of pollution levels. Indeed, parasite MI was more important in MB site that has a higher pollution level. Also, biochemical biomarkers showed an induction in Bizerte lagoon sites with some differences within sites and species. The impact of the continuous release of pollution on the biomarkers response is discussed.

Seasonal rhythm of physiological indexes, liver protein level, and biotransformation biomarkers in Zosterisessor ophiocephalus and Gobius niger from a low contaminated lagoon (Ghar El Melh lagoon, Tunisia)

Abstract This study assessed seasonal variation of total liver proteins level (LPLs) and biotransformation biomarkers in two fish species, G. niger and Z. ophiocephalus, during a one year-survey in the low contaminated Ghar-El-Melh lagoon, Tunisia. Analyzed biomarkers were compared with physiological indexes such as the condition index, hepato-somatic index, and gonado-somatic index and environmental parameters. A significant annual rhythms of glutathione-S-transferase and ethoxyresorufin-O-deethylase activities were validated by cosinor. The highest peak (acrophase) of activities occurred in summer likely related to the elevated seawater temperature. Midline Estimating Statistic of Rhythm and amplitudes were higher in Z. ophiocephalus than in G. niger. The results showed, as well, an acrophase of (LPLs) in spring coinciding with reproductive period in Z. ophiocephalus and beginning of reproductive period in G. niger. This study established a baseline for the selected enzymatic activities in gobies, which required information for a correct interpretation of biomarker responses in environmental monitoring.