Said Khaled - Academia.edu (original) (raw)

Papers by Said Khaled

Biologia, Aug 1, 2010

Surveys of allozyme polymorphisms in the carpet shell clam Ruditapes decussatus have revealed sha... more Surveys of allozyme polymorphisms in the carpet shell clam Ruditapes decussatus have revealed sharp genetic differentiation of populations. Analysis of population structure in this species has now been extended to include nuclear and mitochondrial genes. A partial sequence of a mitochondrial COI gene and of the internal transcribed spacer region (ITS-1) were used to study haplotype distribution, the pattern of gene flow, and population genetic structure of R. decussatus. The samples were collected from twelve populations from the eastern and western Mediterranean coasts of Tunisia, one from Concarneau and one from Thau. A total of twenty and twenty-one haplotypes were detected in the examined COI and ITS1 regions respectively. The study revealed higher levels of genetic diversity for ITS1 compared to COI. The analysis of haplotype frequency distribution and molecular variation indicated that the majority of the genetic variation was distributed within populations (93% and 86% for COI and ITS1 respectively). No significant differentiation was found among eastern and western groups on either side of the Siculo-Tunisian strait. However, distinct and significant clinal changes in haplotypes frequencies between eastern and western samples were found at the most frequent COI haplotype and at three out of five major ITS1 haplotypes. These results suggest the relative importance of historical processes and contemporary hydrodynamic features on the observed patterns of genetic structure.

Pakistan Journal of Zoology, 2012

Genetic variation among 39 samples from 16 populations of the North African green frog Pelophylax... more Genetic variation among 39 samples from 16 populations of the North African green frog Pelophylax saharicus from Tunisia was investigated, using 513 bp partial sequences of the mitochondrial gene cytochrome b. P. saharicus exhibits little genetic differentiation, with overall nucleotide diversity Pi = 0.002 and haplotype diversity Hd = 0.7. The intraspecific pairwise divergence was low (mean 0.2 %). The results from AMOVA analyses indicate that there is no evidence of genetic structuring related to the three studied groups (north, center, and south Tunisia). As shown by the mismatch distributions, significantly negative values of Fu's Fs and Tajima's D statistics, this reduced genetic variability may be due to a recent population expansion from a smaller founder population.

Marine Biology Research, 2020

This investigation aims at assessing patterns of spatial genetic structure of the teleost fish Sa... more This investigation aims at assessing patterns of spatial genetic structure of the teleost fish Sardina pilchardus across the Siculo-Tunisian Strait (a well-known discontinuous biogeographic area) and delineating putative genetic stocks within the species. For this purpose, a total of 180 specimens, collected from 11 locations stretching across the western and eastern Mediterranean coasts of Tunisia, were analysed genetically by means of 18 nuclear allozyme loci. The outcome of this study revealed strong genetic differentiation among populations, with the marked genetic distinctiveness of the central Tunisian population at Mahdia. Despite the delineation of seven well-defined genetic groups, no significant correlation was found between genetic and geographic distances. Besides, the recorded population subdivision did not align with biogeographic boundaries, suggesting the presence of chaotic genetic patchiness. Recent genetic bottlenecks were evidenced in S. pilchardus populations. Patchy migration patterns were recorded among the examined pairs of sardine populations. Among the recorded 16 polymorphic loci, GPI-2 and SOD appeared to be subject to natural selection. Patterns of population genetic differentiation and structuring were not found to be driven by outlier loci that appeared to be under selection. Furthermore, the detected neutral GPI-1 locus was found to be responsible for most of the genetic variation among identified genetic clusters. Hence, natural selection cannot cause the detected genetic heterogeneity among sardine samples. Different explanations to the origin of chaotic genetic patterns, observed within S. pilchardus, were discussed.

Zoology, 2020

Chameleons display high karyological diversity in chromosome number (from 2n = 20 to 62), morphol... more Chameleons display high karyological diversity in chromosome number (from 2n = 20 to 62), morphology, heterochromatin distribution and location of specific chromosomal markers, making them unique study models in evolutionary cytogenetics. However, most available cytogenetic data are limited to the description of the chromosome number and morphology. Concerning sex chromosomes, our knowledge is limited to ZZ/ZW and Z1Z1Z2Z2/Z1Z2W systems in the genus Furcifer and the isolation of sex-linked, male-specific, sequences in Chamaeleo calyptratus, but the putative XY chromosomes have still to be identified in Chamaeleo and the conservation of male heterogamety in the genus needs confirmation from other species. In this study we performed a molecular and a cytogenetic analysis on C. chamaeleon, using standard, banding methods and molecular cytogenetics to provide a throughout karyological characterization of the species and to identify and locate the putative XY chromosomes. We confirm that the chromosome formula of the species is 2n = 24, with 12 metacentric macrochromosomes, 12 microchromosomes and NORs on the second chromosome pair. Heterochromatin was detected as weak C-bands on centromeric regions, differently from what was previously reported for C. calyptratus. Fluorescence in situ hybridization (FISH) showed the occurrence of interspersed telomeric signals on most macrochromosomes, suggesting that ancient chromosome fusions may have led to a reduction of the chromosome number. Using a combination of molecular and FISH analyses, we proved that male specific Restriction site-Associated DNA sequences (RADseq) isolated in C. calyptratus are conserved in C. chamaeleon and located the putative XY chromosomes on the second chromosome pair. We also identified different transposable elements in the focal taxa, which are highly interspersed on most chromosome pairs.

Systematics and Biodiversity, 2016

We examined morphological and genetic variation within and among populations of the spider Argiop... more We examined morphological and genetic variation within and among populations of the spider Argiope trifasciata (Forsskål, 1775) in Tunisia. One hundred and twenty-five spiders were collected from 13 localities spread over three climatic subdivisions. Analyses of sequence variation in a 631bp segment of the mitochondrial cytochrome oxidase c subunit I (cox1) gene revealed low nucleotide diversity but high genetic diversity within populations (Hd = 0.729). A noticeable genetic differentiation was found in all populations. However, no genetic differentiation was observed within climatic subdivisions. Sixteen haplotypes were identified. Connectivity between populations, except for the Gabes population, was relatively high, which could be explained by the high dispersal ability of these spiders by passive aerial movement through the wind (ballooning). Our results indicate that gene flow between Gabes and the remaining regions was limited. In corroboration with the genetic data, morphological analyses did not show differentiation among populations or according to climatic subdivisions. Demographic stability of A. trifasciata populations mediated by gene flow was observed. Moreover, a homogeneous phenotypic trend was observed within A. trifasciata populations across Tunisia. This finding could be explained by the high conservation of external morphological characters within the spider lineages, which are therefore not affected by environmental factors.

Marine Biology Research, 2016

We investigate the influence of previously postulated biogeographic barriers in the Mediterranean... more We investigate the influence of previously postulated biogeographic barriers in the Mediterranean Sea on the population genetic structure of a highly dispersive and continuously distributed coastal species. In particular, we examine nuclear and mitochondrial genetic variation in the marbled crab, Pachygrapsus marmoratus, across part of the African Mediterranean coast in order to assess the influence of the Siculo-Tunisian Strait on its population genetic structure. Four polymorphic microsatellite loci were genotyped for 110 individuals, collected from eight locations covering parts of the Algerian, Tunisian and Libyan coasts. In addition, mtDNA corresponding to the Cox1 gene was sequenced for 80 samples. The corresponding results show contrasting patterns of genetic differentiation. While mtDNA results revealed a homogeneous haplotype composition in our study area, microsatellite data depicted genetic differentiation among populations, but not associated with any geographic barrier. This pattern, already recorded for this species from different geographic regions, may hint at the involvement of a complex series of abiotic and biotic factors in determining genetic structure. Demographic history reconstruction, inferred from mtDNA data, supports demographic and spatial expansion for the North African metapopulation dating back to the Mid-Pleistocene and following an historical bottleneck. Comparison of these African mitochondrial sequences with new sequences from a Turkish population and previously published sequences revealed a weak but significant separation of Atlantic and Mediterranean populations across the Gibraltar Strait, which was not recorded in previous studies of this grapsid species.

Mediterranean Marine Science, 2013

Spatial distribution and ecology of the larvae of three tuna species (Thunnus thynnus, Auxis roch... more Spatial distribution and ecology of the larvae of three tuna species (Thunnus thynnus, Auxis rochei and Euthynnus alletteratus) were studied during an ichthyoplankton survey carried out in the Gulf of Gabes (Tunisia) in June and July 2009. A total of 80 stations, distributed on a regular sampling grid, were sampled. The main objectives of this survey were to provide information on tuna larvae distribution in the Gulf of Gabes in relation to the environmental parameters. Regarding small tunas, larvae of A. rochei (bullet tuna) showed the more widespread distribution, being found at both inshore and offshore stations. E. alletteratus (Atlantic black skipjack) larvae were mainly found at the inshore stations covering the wide continental shelf of this region. On the other hand, larvae of the large migratory tuna T. Thynnus (Atlantic bluefin tuna), were mainly recorded at offshore stations, suggesting that spawning possibly takes place mainly near the shelf break. Regarding the biologic...

Ecology and Evolution, 2022

Despite the strategic localization of Tunisia in the Mediterranean Sea, no phylogeographic study ... more Despite the strategic localization of Tunisia in the Mediterranean Sea, no phylogeographic study on sponges has been investigated along its shores. The demosponge Chondrosia reniformis, descript only morphologically along Tunisian coasts, was chosen to estimate the influence of natural oceanographic and biogeographic barriers on its genetic differentiation and its Phylogeography. The cytochrome oxidase subunit I (COI) gene was amplified and analyzed for 70 Mediterranean Chondrosia reniformis, collected from eight localities in Tunisia. Polymorphism results revealed high values of haplotype diversity (Hd) and very low nucleotide diversity (π). Thus, these results suggest that our sponge populations of C. reniformis may have undergone a bottleneck followed by rapid demographic expansion. This suggestion is strongly confirmed by the results of neutrality tests and “mismatch distribution.” The important number of haplotypes between localities and the high genetic differentiation (Fst ra...

Autoimmunity, 2013

Graves' disease (GD) is a complex genetic autoimmune thyroid diseases (AITD). TSHR is considered ... more Graves' disease (GD) is a complex genetic autoimmune thyroid diseases (AITD). TSHR is considered as candidate gene in GD. IL1RN gene shown to be related to the pathogenesis of a number of autoimmune diseases. These finding prompted us to investigate the association of TSHR and IL1RN genes polymorphism with the risk and the prognosis of GD in Tunisia. A total of 249 healthy controls and 68 GD patients were genotyped for TSHR D727E and IL1RN VNTR polymorphism. No significant difference was found for D727E polymorphism between GD patients and healthy controls. For IL1RN VNTR , we found an association between GD and IL1RN A1A2 genotype. TSHR polymorphism was associated with GD susceptibility in patients older than 40 years. We found for the first time an association of IL1RN VNTR polymorphism with the production of anti-thyroglobulin and anti-thyroid peroxidase antibody at the onset of disease. These preliminary results suggest that TSHR polymorphism may be a risk factor for late onset of GD, and that IL1RN VNTR polymorphism may be associated with GD susceptibility and may represent prognostic factor for predicting the severity of GD.

Data in Brief, 2020

The data presented in this paper stand as supplementary information of the associated article "Ka... more The data presented in this paper stand as supplementary information of the associated article "Karyological characterization of the common chameleon (Chamaeleo chamaeleon) provides insights on the evolution and diversification of sex chromosomes in Chamaeleonidae" [1]. This work provides (i) raw experimental data on the karyology of the common chameleon Chamaeleo chamaeleon and (ii) the results of bioinformatic analysis on sex-specific and repeated DNA sequences found in the same species. The karyological information here presented includes traditional staining method (Giemsa staining) and sequential C-banding + fluorochromes performed on Tunisian samples of the species. The sequence data include the alignments of the isolated DNA sequences with homologous sequences found in squamate Short Read Archives (SRAs) and the results of searches in public nucleic acid databases.

Biological Journal of the Linnean Society, 2004

We examined the population structure and phylogeny of Buthus occitanus (Amoreux, 1789), Androcton... more We examined the population structure and phylogeny of Buthus occitanus (Amoreux, 1789), Androctonus amoreuxi (Audouin & Savigny 1812) and Androctonus australis (Linnaeus, 1758) in Tunisia, using horizontal starch gel and polyacrylamide gel electrophoresis to resolve allozymes at 18 loci. Populations of B. occitanus and A. amoreuxi showed little genetic variation, whereas A. australis populations showed moderate genetic variation. Moreover, despite the restricted dispersal abilities of these species, the allozyme analysis indicated very low levels of intraspecific population differentiation. The Island model of population differentiation best fitted the intraspecific variation, both for mainland populations and for the slightly more differentiated populations from two Mediterranean islands. No diagnostic, fixed alleles were observed between the species of Androctonus , which concurs with the results of nuclear ribosomal DNA analysis. Two subspecies of A. australis , A. a. garzonii Goyffon & Lamy, 1973 and A. a. hector Vachon, 1948, were not resolved by a phylogenetic analysis of the allozyme data. The most likely reasons for the slight population differentiation are either low mutation rates or recent range extensions promoted by human activities. The possibility of indirect gene flow between Androctonus species should also be explored.

Biological Journal of the Linnean Society, 1999

Two chromosomal races of house mice are present in Tunisia, one represented by mice carrying the ... more Two chromosomal races of house mice are present in Tunisia, one represented by mice carrying the 40-acrocentric standard karyotype and the other by a Robertsonian race (2n= 22) homozygous for nine centric fusions (Rb). A comparative summary on allozyme divergence, geographical distribution and level of reproductive isolation in the Tunisian and European Rb races is presented, to which new data on mitochondria1 DNA and morphological divergence are added. The Tunisian 22Rb race revealed unique features not matched by the European chromosomal races, such as a decrease in allozymic variability, a higher level of genetic and morphological differentiation and a mosaic geographical distribution. The mtDNA analysis argued in favour of a local origin of the chromosomal divergence suggesting that the higher level of differentiation between the Tunisian races resulted from the older age of the 22Rb race and/or from a severe bottleneck. The decrease in fertility of chromosomal hybrids between the Tunisian races was compatible with the limited genetic introgression between them. Furthermore, data on the restricted distribution of hybrid populations suggested that premating reproductive barriers may be evolving. The Tunisian 22Rb race is thus an appropriate model to investigate a chromosomally-mediated speciation event.

Biochemical Genetics, 2011

This study reports on the polymorphism of 15 allozyme loci in Ruditapes decussatus clams collecte... more This study reports on the polymorphism of 15 allozyme loci in Ruditapes decussatus clams collected from 11 locations along the Tunisian coasts. We concentrated our sampling effort around the Siculo-Tunisian region to verify if any population structuring exists in this region and to identify the factors that have shaped this structure. Measurements of genetic diversity were quantified both within and between populations, and the geographic variability of gene frequencies was analyzed. Our study shows that the Siculo-Tunisian Strait is an important genetic boundary between eastern and western regions, which agrees with findings for a variety of other species. We suggest that vicariance is a predominant factor shaping the current distribution of genetic diversity of R. decussatus, and the mixing of divergent gene pools from the eastern and western regions still seems to be limited by some physical and/or biological factors.

Biochemical Genetics, 2012

Page 1. NOTE Very Low Mitochondrial Diversity and Genetic Homogeneity in the Starfish Echinaster ... more Page 1. NOTE Very Low Mitochondrial Diversity and Genetic Homogeneity in the Starfish Echinaster sepositus Along the Tunisian Coast Noureddine Chatti Rym Zitari-Chatti Mohamed Habib Attia Yosra Ben Khadra Khaled Said ...

Biochemical Genetics, 2013

Regeneration in echinoderms has proved to be more amenable to study in the laboratory than the mo... more Regeneration in echinoderms has proved to be more amenable to study in the laboratory than the more classical vertebrate models, since the smaller genome size and the absence of multiple orthologs for different genes in echinoderms simplify the analysis of gene function during regeneration. In order to understand the role of homeobox-containing genes during arm regeneration in echinoderms, we isolated the complement of genes belonging to the Hox class that are expressed during this process in two major echinoderm groups: asteroids (Echinaster sepositus and Asterias rubens) and ophiuroids (Amphiura filiformis), both of which show an extraordinary capacity for regeneration. By exploiting the sequence conservation of the homeobox, putative orthologs of several Hox genes belonging to the anterior, medial, and posterior groups were isolated. We also report the isolation of a few Hox-like genes expressed in the same systems.

Archives of Environmental Contamination and Toxicology, 2010

Cadmium (Cd), one of the most widely distributed heavy metals, is highly toxic to humans and anim... more Cadmium (Cd), one of the most widely distributed heavy metals, is highly toxic to humans and animals. It is well known that zinc (Zn) and selenium (Se) administration reduce the Cd-induced toxicity and that metallothioneins can have a protective effect to mitigate Cd toxicity in biological systems. In this study we report the expression analysis of the two metallothioneines gene classes MT-1 and MT-2 as well as the total metalloprotein content in the liver of rats exposed to Cd (200 ppm), Cd ? Zn (200 ppm ? 500 ppm), Cd ? Se (200 ppm ? 0.1 ppm) or Cd ? Zn ? Se (200 ppm ? 500 ppm ? 0.1 ppm) in their drinking water for 35 days. Metals accumulation was quantified in rat liver. Cd decreased significantly the hepatic concentrations of Se and increased those of Zn. The treatment of Cd-exposed rats with Se alone or combined with Zn reversed the Cd-induced depletion of Se concentrations in the liver. However, Zn or Zn ? Se administration significantly increased the liver Cd uptake and had no effect on the Cd-induced increase in hepatic concentrations of Zn. The molecular assay showed a decreasing trend of MT-1 relative gene expression levels in animals supplemented with Zn (6.87-fold), Se (3.58-fold), and their combination (1.69-fold) when compared to Cdtreated animals (16.22-fold). Upregulation of the MT-2 expression were recorded in all conditions, although fold induction levels were less pronounced than MT-1 expressions. Our data suggest that the well-established protective effect of Zn and Se against Cd-induced toxicity passes through non-MT gene expression mechanisms, being more dependent on the oxidative stress status of the cell. Cadmium (Cd) is a widespread environmental pollutant, characterized by its toxicity in various organisms (Gunnarsson et al. 2003). Because this element is often released simultaneously in the environment from a number of natural and man-made sources, adverse health effects caused by exposure to Cd have provoked a significant public health concern (Liu 2003). Indeed, Cd is associated with numerous adverse toxic effects, including prostate and lung cancer in humans and damage to numerous organs in animals (Magos 1991). Due to a very long biological half-life, Cd exposure is often associated with significant accumulation in soft tissues (Friberg et al. 1986). Metallothioneins (MT) are low-molecular-weight proteins (6-7 kDa), rich in cysteine which confers them with a high capacity to bind heavy metal ions [zinc (Zn), Cd, copper (Cu), silver (Ag), mercury (Hg), etc.] in biological systems (Dondero et al. 2005; Sadhu and Gedamu 1988). There are at least four mammalian major MT isoforms. The MT-1 and MT-2 isoforms are most widely expressed, whereas MT-3 is largely brain-specific and MT-4 is located mainly in stratified squamous epithelia (Cherian et al. 2003; Quaife et al. 1994). The induction of MT synthesis represents a sensitive biomarker of heavy metal exposure (Dunn et al. 1987; Viarengo et al. 1997). Several studies M. Banni (&)

Aquaculture Research, 2008

The Mugilidae family is an important ¢sh group representing a major source for ¢sheries and aquac... more The Mugilidae family is an important ¢sh group representing a major source for ¢sheries and aquaculture. In the south Mediterranean bank, no data are available on this fauna, except for some morphological studies on Tunisian samples. In this study, 16 allozymic loci were used to investigate the phylogenetic relationships within Tunisian mugilids. The results obtained from Hergla lagoon samples highlight ¢ve operational taxonomic unit corresponding to the well-known species (Liza aurata, Liza ramada, Liza saliens, Chelon labrosus, Mugil cephalus). Several loci appeared to be diagnostic of these species, but in contrast to Greek mugilid samples, we did not ¢nd any diagnostic locus ¢xed di¡erently for the ¢ve species. These results can help aquaculture units to identify accurately the mullet species they subsequently use for stocking aquaculture ponds and inland waters. However, species identity represents very important information, as each species has a di¡erent growth rate and salinity tolerance. On the other hand, when compared with North Mediterranean Mugilidae analysed until now, Tunisian samples show a genetic di¡erentiation that could be related to di¡erent physicochemical conditions between the North and South banks, similar to those recorded in the eastern and western two Mediterranean basins separated by the Siculo-Tunisian strait. In addition, this study con¢rms the morphological taxonomy, except for the subdivision of the Liza genus into two sub-genera. The phylogenetic tree is in agreement with that on Languedoc Mugilidae samples (France), indicating that the subdivision of the Liza genus into two sub-genera appears to be without any genetic base.

Annales Zoologici, 2010

The water frog Pelophylax saharicus is the most widespread anuran in North Africa and thus subjec... more The water frog Pelophylax saharicus is the most widespread anuran in North Africa and thus subjected to widely differing environmental conditions in different parts of its distribution range. In this paper we examined genetic structure of species 15 populations across ...

Annales Zoologici, 2013

ABSTRACT