1,721,082 research outputs found
Another piece of the evolutionary history of Atlantic skates (Chondrichthyes, Rajiformes ): integrating DNA barcoding approach and phylogenetic inferences
No full textConservation and long-term management plans of marine species need to be conceived upon a universally recognised key-feature: species identity. This important assignment resulted particularly arduous among skates (order Rajiformes), in which the phenotypic similarity between some taxa and the individual variability in others, entangled accurate species identification.
This study confirms the power of DNA barcoding for the discrimination between skate species across the Atlantic Ocean and for its use as effective tool to minimize the risk of species misidentification and to elucidate species boundaries. In this perspective, this work compiles and establish a new fully available and well-curated barcode library, the ELASMO-ATL project, which gathered biological and molecular information of 432 skate specimens and covered coastal waters of four FAO Major Fishing Areas (27, 34, 47, 41) of the Atlantic Ocean.
The evolutionary histories of 34 skate species were estimated with two concatenated mitochondrial markers (COI and NADH2) through Bayesian and species level phylogeny analyses. It was possible to discover a new evolutionary lineage within the genus Raja in the southern-most part of its distribution area and to enable deepening the relationship between South-African endemic species of Rajella. Once again, Western South African coasts and oceanographic fronts may play a fundamental role among skates’ speciation events in which the paleoclimatic and paleogeographic history joined to hydrography events could have contributed to the formation of refugial areas, characterised by geographical isolation. Subsequent contact zones in these areas between Senegal and Angola seems to constitute a continuum/cline of genetic change among some Raja species.
These data successfully resolved many taxonomic ambiguities and demonstrated a highly cohesive monophyletic clustering among the order laying the foundations for further inference of evolutionary patterns suitable for addressing management and conservation issue
First assessment of the genetic structure of deepwater blackmouth catshark (G. melastomus Rafinesque, 1810) in Atlantic and Mediterranean populations
No full textThe worldwide abundance of Galeus melastomus in the biological composition of fishery bycatch led to consider this species as a key-taxon for understanding the mysterious biology and ecology of sharks living in deep ecosystems. With the present work, we aim to unravel the population structure of the blackmouth catshark in the Mediterranean Sea and adjacent North-Eastern Atlantic with the use of nuclear molecular markers (simple sequence repeats, SSRs) and compare our results with recent findings based on mitochondrial DNA supporting total panmixia in the species. Given the absence of species-specific microsatellite markers we attempted the cross-amplification of a panel of 129 SSRs developed for Centroselachus crepidater, Galeorhinus galeus, Hexanchus griseus, Mustelus antarcticus, M. canis, M. henlei, M. mustelus, Negaprion brevirostris, Scyliorhinus canicula, Squalus acanthias and S. mitsukurii on blackmouth catsharks collected during scientific surveys undertaken in different years. The rationale of the chosen methodology was based on the calculation of genetic distances between NADH2 sequences (1044bp long) derived from 595 species of elasmobranchs. Our strategy focused on testing first SSRs markers developed on closely-related species. Then, we assessed highly polymorphic markers developed on non-closely-related species. After a pilot gradient amplification on few individuals from three different geographic macro-areas, we screened a total of 24 samples at the established conditions. To date, 16 microsatellite loci have been classified as potential candidates for the succesful cross-amplification on Atlantic and Mediterranean samples of G. melastomus. These candidate loci will be applied in the population genetic analysis delineated in the Atlantic Ocean (two sites) and in the Mediterranean Sea (five sites). Hopefully, the higher resolution power of the markers chosen for this study will be able to disclose any signal of genetic structure of the blackmouth catsharks and will contribute to improve the knowledge on deep-sharks
Acquacoltura di specie emergenti: Genotipizzazione e pedigree in Anguilla anguilla, primi risultati.
No full textAbstract - Anguilla anguilla (Linnaeus, 1758) is a critically endangered species, whose existence in the wild is highly threatened by human activities and is included in the IUCN Red List of threatened species as “Critically Endangered”. Restocking and captive breeding programs designed to preserve the residual genetic variability should represent the future for conservation of this species. In this perspective, the present study aims to increase the knowledge about the mechanisms at the basis of reproduction of the European eel in semi-natural conditions, through paternity assignment. Here we show the very first parental assignment results of a plenty successful reproductive event that occurred in 2016: four families of European eel founded by four female plus 11 males in different mixes and their progeny, for a total of 206 samples. Parental allocations revealed the presence of different percentage of success of males in fertilizing eggs, with two “super-males” at the top of the productivity, with the 19.9% and 18.8% of total larvae (males 128 and 129) and two “weak-males” at the end of the distribution of productivity curve (males 134 and 135). Since the artificial reproduction of European eel is a very challenging topic for world aquaculture, these first results may help in drawing future breeding plans aimed both to increase the productivity for human consumption and to develop restocking plans in order to try to reduce the speed of decreasing in worldwide stocks of European eels
Sexual behaviour and reproductive performance of the endangered European eel Anguilla anguilla (Linnaeus, 1758) based on direct observationsand paternity assignment in semi-natural conditions
Full text linkEuropean eel Anguilla anguilla is among the highly valued species for aquaculture. Since its peculiar biology, it is not yet possible to complete the whole life cycle in artificial conditions and its supply depends entirely on wild catches. In the last 50 years this species has suffered a population reduction of 99 % mainly due to overfishing. In a conservation perspective, it is of fundamental importance to improve the aquaculture production of European eel, to avoid the extinction of this species and preserve its residual genetic variability, allowing at the same time the fulfilling of costumers request without increasing its harvesting pressure. In this study we aimed to deepen the knowledge about the mechanisms at the basis of reproduction of the European eel in semi-natural conditions, through direct observation of spawning behaviour and through the paternity assignment using microsatellite markers. The systematic and prolonged observation of the reproductive behaviour of European eel and the contextual parentage analyses we carried out for the very first time in this species on 39 adults and 432 F1 randomly collected. We contributed to unravel the sexual behaviour of this species in the most common artificial reproduction conditions (polyandry), and define the precise courtship sequence until the release of gametes, and the male-male hierarchy in courtship. We characterized for the first time three main types of male: dominant (the first who starts the courtship, and the one with the majority of F1 assigned), subordinate (which starts the courtship only in a second time and with a minor percentage of F1 ascribed) and ineffective (which sometime appears totally disinterested to courtship and has few F1 or none). The evidences here produced represent an important attempt for developing good reproduction practices of the critically endangered European eel, providing a good starting point for its future aquaculture production
Step by step: the unprecedented evolutionary history of family Rajidae
No full textAmong skates, Rajidae represents one of the most enigmatic family of cartilaginous fish whose bio- ecological traits contributed to an extraordinary evolutionary success in terms of species richness and endemism. Past and present taxonomic conflicts and species misidentifications are linked to their extraordinary level of morphological stasis. In recent years, these issues have been overcome by wide- scale molecular taxonomy analyses, but also raised questions about their evolutionary history. Concerted actions as the ELASMOMED and ELASMOATL initiatives encouraged and improved large-scale sampling efforts in the Mediterranean and Eastern Atlantic Ocean over years, building unique voucher repositories of thousands of specimens and enabling the exploration of skates’ biogeography. Here, the maximum taxonomic (51 OTUs) and molecular (47 OTUs) diversity of tribes Rajini and Amblyrajini were measured using concatenated mitochondrial genes. We also estimated their evolutionary divergence using the molecular clock approach. Evidences produced so far showed that, despite the ancient origin of Rajidae (97 MYA), the Eastern Atlantic and Mediterranean faunas originated more recently, after the closure of connection between these areas and the Indo-Pacific Ocean (15 MYA). The endemic Mediterranean species originated with the recolonization of the Basin, after the Messinian salinity crisis (7-5 MYA). At least five independent vicariant events contributed from 7.4 to 3.15 MYA to the formation of allopatric or parapatric sister species, each distributed in the N-E Atlantic and S-E Atlantic respectively. On the whole, the Quaternary tectonic movement of continental masses, paleoclimatic events and present oceanographic discontinuities occurring along the western African continental shelf might explain this series of parallel and independent speciation events related to the maintenance of low or null levels of gene flow between closely related sibling and cryptic species
Molecular identification of endangered marine predators by barcoding ancient museum rostra of Mediterranean sawfish populations (Chondrichthyes, Pristidae)
No full textBackground: A growing concern in conserving threatened animals affected by human impact has been significant worldwide. Among marine animals, sawfishes (Chondrichthyes, Pristidae) are considered one of the most endangered families among
lasmobranchs, resulting in extinction in many coastal areas around the world, including the Mediterranean Sea. Here, sawfish
ccurred with two species, Pristis pristis and P. pectinata, until the second half of the last century and are now considered Critically
ndangered/Possibly Extinct. The historical occurrence of sawfish in the area is documented by bibliographic/ archival records and y numerous preserved historical rostra available in museum collections. In this study we attempted to genetically characterize the
istorical remains of sawfish from several European museums and to enable the investigation of their evolutionary and ecological relationships with global samples.
Results: A total of 80 rostra specimens, dated from 1700 to 1900 and catalogued as unknown origin or Mediterranean (11), were collected from 11 European museums and were properly prepared for ancient DNA genetic analysis. Taxonomic identification at the species level was obtained through PCR amplification of small fragments (150 bp) of two mitochondrial markers commonly used for species identification (i.e., the mitochondrial COII and the NADH 2). Sequence comparison with currently available ones from public repositories and phylogenetic tree analyses indicated that the historical specimens belonged to four species, P. pristis, P. zijsron, P. pectinata, and Anoxypristis cuspidate, with a high frequency of mismatches (69%) between molecular identification and species museum cataloguing, when present. These preliminary data also showed the presence of two sequence sub-clusters in the poorly barcoded species P. zijsron.
Significance: With the expansion of this initial analysis, we will contribute to increase the limited
olecular data of these critically endangered large predators and to exploit historical genetic data for reconstructing phylogenetic/phylogeographic extent of the possibly extinct population of Mediterranean sawfish
Historical ecology of the Mediterranean population of the Great White Shark, Carharodon Carcharias, from museum collection
No full textThe Great White Shark, Carcharodon carcharias, is Critically Endangered in the Mediterranean due to its low population density and the absence of
conventional aggregation sites, hampering data collection and reconstruction of the population behavioral ecology. Historical collections, being a repository of past biodiversity, can overcome these issues for a better understanding of fundamental processes such as paleo-ecological changes. In this perspective, this work deals with the historical ecology of the Mediterranean white shark population through a multi-element analysis of stable isotopes (carbon, nitrogen, zinc, and strontium) of 5 historical remains archived in Italian museums and private collections. Using individual vertebrae (N = 4), we provide information about the ontogenetic shifts and the trophic ecology by the estimate of the isotopic composition of carbon, nitrogen, and zinc from the vertebral collagen, and date back one fossil tooth using strontium isotope
composition. The main results show that: 1) isotopic values of nitrogen confirmed the white shark as a top predator, 2) the diet is based on dolphins and fishes, 3) the zinc analyses revealed a strong difference between the pre-birth and post-birth isotopic composition 4) the dating of the fossil tooth confirmed the Miocene-Pliocene presence in the Mediterranean. Overall, these multi-element isotope approaches have the potential to obtain important information on developmental physiology, ecology, and behavior of the poorly studied Mediterranean white shark, highlighting the fundamental role of historical remains for an overall knowledge of shark life-history, avoiding invasive sampling and analysis
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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