1,721,241 research outputs found
Lo studio del tonno rosso a partire dalla collezione Sella
No full textIl tonno rosso Thunnus thynnus (Atlantic Bluefin tuna) è una specie che ha attirato l’interesse delle civiltà del Mediterraneo sin dalla loro nascita. Accanto ad un interesse di tipo economico si è da sempre posto un parallelo interesse scientifico e culturale. Oggi questa specie rappresenta per la comunità civile e scientifica una attualissima sfida-simbolo su cui tentare di riconciliare con successo pesca e conservazione. Da un lato i dati scientifici ottenuti dalla pesca indicano una situazione di forte rischio di sopravvivenza degli stock e declino delle popolazioni. Dall’altro la pesca del tonno rosso è rilevante e prioritaria per la socioeconomia dei paesi del Mediterraneo e dell’Atlantico centro settentrionale. Ai fini di ottenere una conoscenza scientifica sempre più approfondita della complessa ecologia di questo grande predatore e migratore, all’approccio investigativo di tipo monodisciplinare basato sulle analisi dei dati pesca si stanno affiancando ricerche interdisciplinari condotte con approcci indipendenti dai dati di pesca. Il preziosissimo lavoro di raccolta dati di pesca e campioni delle popolazioni di tonno rosso del Mediterraneo svolto dal Massimo Sella nei primi decenni del secolo scorso ha prodotto una collezione di circa 7000 reperti scheletrici (colonne vertebrali, pinne caudali e crani), la quale per consistenza e natura appare unica per la specie, per la datazione storica e per la consistenza. La buona qualità di conservazione dei reperti scheletrici e la loro consistenza numerica per differenti aree geografiche di pesca rappresenta un materiale di enorme potenzialità per lo studio dei cambiamenti che queste popolazioni hanno subito in rapporto ai cambiamenti ambientali, incluso la differente pressione antropica sugli stock da pesca. Un esempio di sfruttamento scientifico di questa potenzialità è venuta dall’utilizzo del DNA antico e dallo studio comparativo delle caratteristiche genetiche delle popolazioni storiche e contemporanee al fine di evidenziare segnali di erosione e strutturazione genetica svolta da ricercatori delle Università di Bologna, Ferrara e Padova con il supporto finanziario di due PRIN (2005: TUNING, TUNa’s changING; 2008: BFTbySNP). Tuttavia questa enorme potenzialità di fruibilità da parte dei ricercatori è fortemente limitata dall’assenza di una musealizzazione scientifica adeguata della collezione e dalla mancanza di risorse per realizzarla
Genomic analysis of population structure of yellowfin tuna (Thunnus albacares) at the global scale
No full textMetabarcoding analysis of European hake diet in the Mediterranean Sea.
No full textEuropean hake (EH), Merluccius merluccius, is a demersal fish distributed from the North Sea and Atlantic to the Levantine Sea in the Mediterranean. EH is an important predator of deep Mediterranean upper shelf slope communities and it is currently characterised by growth overexploitation. EH adults feed mainly on fish and squids whereas the young (<16 cm) feed on crustaceans. All current EH diet studies relied on the morphological identification of prey remains in stomach content, however this method is labour intensive and it precludes the identification of strongly digested food. The development of High-Throughput Sequencing (HTS) approaches provide more accurate methods for dietary studies revealing many consumed species simultaneously (DNA metabarcoding). The aim of this study is to use a HTS approach based on COI amplification, contextually to classic microscopic morphological identification, to analyse EH stomach content and to evaluate the efficiency of the molecular method. HTS sequencing has been carried out on the amplicons obtained by PCR amplification (Leray et al. 2013) of stomach remains and all the Miseq Illumina paired-end reads have been analysed by using bioinformatic tools (Boyer et al. 2015) for taxonomic assignment. The selected sequences clustered in OCTUs (Operational Clustered Taxonomic Units) and taxonomically assigned, will be used in diversity analyses to compute distance matrices among samples, to compare taxa summaries from different samples, to create networks and perform PCA and PcoA analysis. Classic microscopic morphological analyses on stomach content remains have been carried out contextually to compare the results of the two methods. The molecular approach has proven a promising method to study marine fish dietary habits. All the data will be summarized to reconstruct EH trophic dynamics in the Mediterranean Sea
First microsatellite loci of red mullet (Mullus barbatus) and their application to genetic structure analysis in transboundaries Adriatic shared stock
No full textIn order to study the genetic structure of the Adriatic shared stock of red mullet (Mullus barbatus), we developed a set of dinucleotide microsatellite markers. A dinucleotide-enriched genomic library was obtained, and 6 polymorphic dinucleotide loci were successfully optimized. The markers showed high expected heterozygosity (from 0.68 to 0.92) and allele number (from 12 to 33); thus they appear to be suitable for detecting genetic differences in the population of red mullet. Four Adriatic samples were subsequently analyzed for microsatellite variation, and the results showed subtle but statistically significant genetic differentiation, indicating that the Adriatic red mullet may group into local, genetically isolated populations. No correlation between geographic distance and genetic differentiation was observed. In addition, the evidence of recent bottlenecks in the Adriatic samples indicates that the observed population subdivision might reflect random local allelic variations, generated by reproductive success, survival rates, or fishing pressure
Genetics of local adaptation of Atlantic Bluefin Tuna from the Mediterranean Sea.
No full textThe Atlantic Bluefin tuna (ABFT, Thunnus thynnus), one of the largest top-predator fish inhabiting the pelagic ecosystems of the North Atlantic Ocean and Mediterranean Sea, has been extensively overexploited in recent decades. However, in the Mediterranean Sea, the mixing rates between the eastern, central and western basins have not yet been resolved. Both electronic tagging, otolith and genetic markers cannot still depict a clear scenario of tuna movements and structuring, essential requirement for a proper management of ABFT fisheries. Here we used Expressed Sequence Tag-linked (EST-linked) microsatellites to explore the patterns of adaptive evolution of T. thynnus population and of its population dynamics in the Mediterranean Sea. For this purpose 16 EST-linked microsatellites were genotyped in 177 tuna individuals from the Mediterranean and several methods were used to explore population genetic structuring and estimate/detect signals of local adaptation. Bayesian clustering results indicated the presence of a single cluster, corroborated also by the Correspondence Analysis and pairwise FSTs. Similarly the two methods, used for the detection of FST outliers, did not reveal any pattern suggesting the presence of selective pressure. Our results advise that the low level of polymorphism detected in EST-SSR loci used in this study could be ascribed to the presence of relatively conserved regions flanking these microsatellites. These genomic regions are probably not involved in physiological responses to local adaptation and we were able to rule out action of divergent or balancing selection on EST-SSR polymorphism
Yet another non-indigenous fish from Maltese waters, central Mediterranean: a first record of Lagocephalus guentheri Miranda Ribeiro, 1915 (Tetraodontiformes, Tetraodontidae)
No full textThe first occurrence of Lagocephalus guentheri in Maltese waters is validated through morphological and molecular analysis of a specimen collected in 2023. This non-indigenous tetraodontid entered into the Mediterranean from the Red Sea via the Suez Canal and has established itself in the Levantine basin. The finding represents a first indication of L. guentheri westward expansion toward the MaltaSicily Channel within the central sector of the Mediterranean Sea
DNA metabarcoding suggests dietary niche partitioning in the Adriatic European hake
Full text linkThe Northern Adriatic Sea (FAO Geographical Sub-Area 17) is one of the most productive fishing areas of the Mediterranean Sea and it includes a broad diversity of habitats. In the Northern Adriatic basin, the Pomo Pit (200–273 m of depth) is one of the most important areas of aggregation for some demersal stocks shared in the Adriatic Sea and it is an important spawning/nursery area of the European hake (Merluccius merluccius). Through a metabarcoding approach we investigated the feeding habits of European hake, both inside and outside the Pomo Pit, and their temporal variability comparing samples collected in 2016 and 2014. Our analyses proved the presence of an ontogenetic shift from a diet based mainly on crustaceans in juveniles to a more piscivorous feeding behaviour in adult hakes and suggested the presence of a specific niche partitioning and food preferences between hakes living inside and outside the Pomo Pit. The main differences among adult hakes refer to the presence of molluscs in the stomachs of hakes collected within the Pomo Pit and the presence of high depth prey species (i.e., Micromesistius poutassou). Metabarcoding revealed the relevant ecological role played by the Pomo Pit in M. merluccius feeding behaviour and ontogenetic development, promoting a careful ecosystem-based management of fisheries in this area through focused conservation measures
UNVEILING THE ENIGMATIC NATURAL HISTORY OF MEDITERRANEAN COMMON DOLPHIN (DELPHINUS DELPHIS, LINNAEUS 1758): INSIGHTS FOR CONSERVATION CHALLENGES
No full textThe common dolphin (Delphinus delphis, Linnaeeus, 1785) is one of the most enigmatic species in the Mediterranean Sea. Once widely prevalent, it faced a significant decline across most of the basin by the late 1960s. The precise reasons and mechanisms behind this decline remain largely unknown or poorly understood. However, a range of potential causes has been identified, encompassing deliberate culling, accidental deaths in fishing gear, reduced prey availability, and habitat degradation. Present estimates derived from surveys and monitoring campaigns suggest either a complete absence or a near disappearance of common dolphins from areas historically known to harbor substantial populations. The International Union for Conservation of Nature has designated the Inner Mediterranean subpopulation of common dolphin as “Endangered”.
We reconstructed the little-known natural history of this species using osteological museum finds from the last two centuries. The multidisciplinary approach consisting of genetic analysis on ancient DNA, geometric morphometry on skulls, and collagen stable isotope analysis, has enabled a better understanding of the ecology of the historical Mediterranean common dolphin population.
The main findings of the research include: i) Incorrect taxonomic attributions in museum collections and historical literature represent a bias in the identification of Mediterranean dolphin species and in the knowledge of their demographic and ecological history over the past decades and centuries; ii) the molecular/morphometrical integrated approach permitted the successful species-specific identification of museum specimens and to highlight misidentifications and potential interspecific hybridization events between the rare Delphinus delphis and other more common species in the basin, such as Stenella coeruleoalba and Tursiops truncatus; iii) Results from stable isotope analysis (δ13C and δ15N) show different ecological and/or trophic patterns of Mediterranean common dolphin over time, indicating a possible shift in the ecological niche across the past centuries
Complementing morphological classification of Anguilliform leptocephali with DNA barcoding
Full text linkDNA barcoding is a molecular tool that enables rapid and accurate identification of biological species by sequencing a short, standardized region of the mitochondrial gene cytochrome c oxidase I ( COI) as internal species tag. The aim of the present study was to use DNA barcoding in addition to classical taxonomy in order to obtain a more reliable species-identification of leptocephali, the characteristic larval forms of the superorder Elopomorpha, often difficult to identify and to match with their adult stage. Based on the examination of external morphology, meristics, and pigmentation, 2785 leptocephalus larvae collected in the Adriatic Sea between 2010 and 2012, were ascribed to 7 morphotypes, belonging to Anguilliform order (Ariosoma balearicum, Conger conger, Gnathophis mystax, Nettastoma melanurum, Dalophis imberbis, Chlopsis bicolor, Facciolella sp.) and 69 specimens were sequenced for a 655 bp region of the mitochondrial cytochrome oxidase subunit I gene (COI) to confirm the previous morphological analysis.
The highly consistent results obtained revealed a good performance of COI barcoding as a diagnostic method for the identification of these larvae, but the limited number of leptocephali species annotated in the reference databases for barcode (Barcode of Life Data Systems and GenBank) allowed to validate only partially the morphological analysis. Moreover two species, Gnathophis mystax and Facciolella sp., showed unexpected outcomes. The data obtained in this work represent the first results of a wider project aimed at the creation of a new barcode database for the assessment of leptocephali diversity in the Mediterranean Sea (Barcoding of the Adriatic Leptocephali [BAL]), contributing to the knowledge of these unusual larvae and of their adult forms
Species diversity and morphological stasis in skates (order Rajiformes): The challenge of skin transcriptome profiling in non-model species
No full textApproximately twenty years have passed since the beginning of concentrated investigations into the evolutionary history and ecology of skates. The evidence generated thus far suggests that skates have experienced multiple and parallel adaptive radiations at a regional scale, starting in the upper Cretaceous, which contributed to the delineation of strong phylo-geographical and population structuring. Despite the high species diversity characterising the Order Rajiformes, a strikingly stable gross morphology has been maintained on the evolutionary level. The combined use of morphometric analyses and genotyping by various panels of molecular markers on a large number of samples of widely distributed and endemic geographic populations provided efficient tools for stock identification and management. Nonetheless, the adaptive value of some phenotypic traits as, for instance, particular ornaments of the dorsal part of the body, remains poorly understood. Here, we applied transcriptome profiling of skin pictorial motifs (eyespots and dots on a uniformly coloured matrix) on recently diverged species with sibling and sister phylogenetic relationships (Raja clavata, R. straeleni and R. asterias respectively) and on species that are easily recognized by specific patterning traits and show strong monophyly (the Mediterranean R. miraletus and the South African R. ocellifera). The on-going differential expression analysis at skin transcriptome level will help to understand mechanisms of divergence, hybridisation signals and could be considered one of the tiles allowing to evaluate whether the same or alternative traits have been used in parallel adaptations to similar environments
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