RESUMEN
Requiem sharks (genus Carcharhinus) have previously been reported to form large aggregations around marine infrastructures in the eastern Mediterranean Sea. While this behaviour may offer fitness advantages at the individual level, the implications of extended residency at human-altered habitats for population persistence have yet to be assessed. In this work, we investigated the phylogeographic and demographic composition of sharks near a coal-fired power and desalination station in Israel. Our aim was to infer habitat use and the mechanisms underlying the aggregation behaviour, and to highlight potential conservation impacts. We sampled, measured, and released 70 individuals between 2016 and 2022 to assess genetic variability within the cytochrome C oxidase I (COI) region and to analyse the aggregation's structure based on the sharks' size and sex distribution. In addition, we performed meristic counts on a reference specimen collected dead at another power station in Israel to supplement species identification using the abovementioned techniques. Our findings indicate size-based sex segregation of adult female dusky and male sandbar sharks (Carcharhinus obscurus and Carcharhinus plumbeus, respectively), with each species comprising two COI haplotypes. In the dusky shark, one haplotype corresponded to an Indo-Pacific lineage, and the other matched an Atlantic lineage. In the sandbar shark, we observed a haplotype previously sampled in the Mediterranean Sea, the Red Sea, the Northwest Indian Ocean, and South Africa, and another haplotype that was unique to our study site and genetically closer to the former than to sequences sampled in other ocean basins. This study provides the first indication of sympatric aggregation amongst phylogeographically distinct dusky and sandbar shark lineages, suggesting that human-altered habitats in the eastern Mediterranean Sea may influence the distribution of these species. Based on the observed segregation pattern, we conclude that the site does not function as a nursery, parturition, or mating area, and discuss other plausible explanations that warrant further research. Finally, we highlight important directions for future research and the implications of our findings for management and conservation.
Asunto(s)
Ecosistema , Complejo IV de Transporte de Electrones , Haplotipos , Tiburones , Tiburones/genética , Tiburones/clasificación , Mar Mediterráneo , Animales , Femenino , Masculino , Complejo IV de Transporte de Electrones/genética , Humanos , Israel , Variación Genética , Filogenia , FilogeografíaRESUMEN
The white shark (Carcharodon carcharias) (Linnaeus, 1758), an iconic apex predator occurring in all oceans,1,2 is classified as Vulnerable globally3-with global abundance having dropped to 63% of 1970s estimates,4-and as Critically Endangered in Europe.5 Identification of evolutionary significant units and their management are crucial for conservation,6 especially as the white shark is facing various but often region-specific anthropogenic threats.7,8,9,10,11 Assessing connectivity in a cosmopolitan marine species requires worldwide sampling and high-resolution genetic markers.12 Both are lacking for the white shark, with studies to date typified by numerous but geographically limited sampling, and analyses relying largely on relatively small numbers of nuclear microsatellites,13,14,15,16,17,18,19 which can be plagued by various genotyping artefacts and thus require cautious interpretation.20 Sequencing and computational advances are finally allowing genomes21,22,23 to be leveraged into population studies,24,25,26,27 with datasets comprising thousands of single-nucleotide polymorphisms (SNPs). Here, combining target gene capture (TGC)28 sequencing (89 individuals, 4,000 SNPs) and whole-genome re-sequencing (17 individuals, 391,000 SNPs) with worldwide sampling across most of the distributional range, we identify three genetically distinct allopatric lineages (North Atlantic, Indo-Pacific, and North Pacific). These diverged 100,000-200,000 years ago during the Penultimate Glaciation, when low sea levels, different ocean currents, and water temperatures produced significant biogeographic barriers. Our results show that without high-resolution genomic analyses of samples representative of a species' range,12 the true extent of diversity, presence of past and contemporary barriers to gene flow, subsequent speciation, and local evolutionary events will remain enigmatic.
Asunto(s)
Tiburones , Tiburones/genética , Tiburones/clasificación , Animales , Genoma , Polimorfismo de Nucleótido Simple , Filogenia , BlancoRESUMEN
Leptocharias smithii has been poorly explored in anatomical terms. This species bears a mosaic of morphological characters and is considered to represent an intermediate condition between other carcharhiniform clades. In the present paper, the anatomy of the appendicular skeleton of the species is thoroughly investigated and compared with other representatives of the order Carcharhiniformes. Leptocharias bears exclusive characteristics, such as the visible separation of the pro- and mesopterygia but it also has an aplesodic pectoral fin, a condition shared with carcharhiniforms placed at the base of the phylogenetic tree and at the same time a chevron-shaped coracoid bar, a condition characteristic of charcharhiniforms placed at the apex of the phylogenetic tree. Additionally, in an attempt to understand the evolution of its appendicular skeleton and of other carcharhiniforms, 20 characters of the paired fins and girdles are explored and discussed in light of two recent phylogenetic hypotheses. Most of these characters were not previously explored and support not only the monophyly of Carcharhiniformes, such as the mesopterygium overlapping the metapterygium in ventral view, but also the monophyly of the less inclusive clade Hemigaleidae + (Galeocerdonidae + (Carcharhinidae+Sphyrnidae)), such as the morphology and arrangement of the distal radials, which are pointed and spaced.
Asunto(s)
Filogenia , Tiburones , Animales , Tiburones/anatomía & histología , Tiburones/clasificación , Aletas de Animales/anatomía & histología , Masculino , Femenino , Evolución BiológicaRESUMEN
This paper describes the fishing profile and the temporal variation in the commercial landings of elasmobranchs in a global hotspot for their conservation and investigates the variables that influenced the landings. Census data on commercial catches were obtained between April 2008 and October 2010 from nine landing sites in Bragança (Pará, northern Brazil). Five vessel types, four fishing gears, and eight fishing techniques engaged with elasmobranch capture were identified. A total of 2,357 landings were recorded, with a total production of 354 t. The highest yields were recorded in 2009, with sharks being harvested mostly by small and medium-sized vessels, and batoids, by small vessels and canoes. Drifting nets and longlines played a prominent role in elasmobranch fisheries. The results show that the landings were influenced by days at sea, which is common in tropical fisheries. The elasmobranch data series is discontinuous as statistics are absent for most fishing sites albeit imperative for proper management, as well as relevant for decision-makers focusing on their conservation.
Asunto(s)
Conservación de los Recursos Naturales , Explotaciones Pesqueras , Tiburones , Animales , Tiburones/clasificación , Brasil , Elasmobranquios/clasificación , Estaciones del Año , Rajidae/clasificaciónRESUMEN
The fossil fish Ptychodus Agassiz, 1834, characterized by a highly distinctive grinding dentition and an estimated gigantic body size (up to around 10 m), has remained one of the most enigmatic extinct elasmobranchs (i.e. sharks, skates and rays) for nearly two centuries. This widespread Cretaceous taxon is common in Albian to Campanian deposits from almost all continents. However, specimens mostly consist of isolated teeth or more or less complete dentitions, whereas cranial and post-cranial skeletal elements are very rare. Here we describe newly discovered material from the early Late Cretaceous of Mexico, including complete articulated specimens with preserved body outline, which reveals crucial information on the anatomy and systematic position of Ptychodus. Our phylogenetic and ecomorphological analyses indicate that ptychodontids were high-speed (tachypelagic) durophagous lamniforms (mackerel sharks), which occupied a specialized predatory niche previously unknown in fossil and extant elasmobranchs. Our results support the view that lamniforms were ecomorphologically highly diverse and represented the dominant group of sharks in Cretaceous marine ecosystems. Ptychodus may have fed predominantly on nektonic hard-shelled prey items such as ammonites and sea turtles rather than on benthic invertebrates, and its extinction during the Campanian, well before the end-Cretaceous crisis, might have been related to competition with emerging blunt-toothed globidensine and prognathodontine mosasaurs.
Asunto(s)
Fósiles , Filogenia , Tiburones , Animales , Fósiles/anatomía & histología , México , Tiburones/anatomía & histología , Tiburones/clasificación , Tiburones/fisiología , Evolución Biológica , Diente/anatomía & histologíaRESUMEN
The lantern shark genus Etmopterus contains approximately 40 species of deep-sea bioluminescent cartilaginous fishes. They emit blue light mainly from the ventral body surface. The biological functions of this bioluminescence have been discussed based on the luminescence patterns, but the bioluminescence mechanism remains uncertain. In this study, we detected both coelenterazine and coelenterazine-dependent luciferase activity in the ventral photophore tissue of Etmopterus molleri. The results suggested that bioluminescence in lantern sharks is produced using coelenterazine as the substrate for the luciferin-luciferase reaction, as some luminous bony fishes.
Asunto(s)
Proteínas de Peces/metabolismo , Imidazoles/metabolismo , Luciferasas/metabolismo , Luminiscencia , Mediciones Luminiscentes/métodos , Pirazinas/metabolismo , Tiburones/metabolismo , Animales , Cromatografía Liquida/métodos , Proteínas de Peces/química , Concentración de Iones de Hidrógeno , Imidazoles/química , Luciferasas/química , Metanol/química , Pirazinas/química , Tiburones/clasificación , Piel/química , Especificidad de la Especie , Especificidad por Sustrato , Espectrometría de Masas en Tándem/métodosRESUMEN
Sharks and rays are at risk of extinction globally. This reflects low resilience to increasing fishing pressure, exacerbated by habitat loss, climate change, increasing value in a trade and inadequate information leading to limited conservation actions. Artisanal fisheries in the Bay of Bengal of Bangladesh contribute to the high levels of global fishing pressure on elasmobranchs. However, it is one of the most data-poor regions of the world, and the diversity, occurrence and conservation needs of elasmobranchs in this region have not been adequately assessed. This study evaluated elasmobranch diversity, species composition, catch and trade within the artisanal fisheries to address this critical knowledge gap. Findings show that elasmobranch diversity in Bangladesh has previously been underestimated. In this study, over 160000 individual elasmobranchs were recorded through landing site monitoring, comprising 88 species (30 sharks and 58 rays) within 20 families and 35 genera. Of these, 54 are globally threatened according to the IUCN Red List of Threatened Species, with ten species listed as Critically Endangered and 22 species listed as Endangered. Almost 98% juvenile catch (69-99% for different species) for large species sand a decline in numbers of large individuals were documented, indicating unsustainable fisheries. Several previously common species were rarely landed, indicating potential population declines. The catch pattern showed seasonality and, in some cases, gear specificity. Overall, Bangladesh was found to be a significant contributor to shark and ray catches and trade in the Bay of Bengal region. Effective monitoring was not observed at the landing sites or processing centres, despite 29 species of elasmobranchs being protected by law, many of which were frequently landed. On this basis, a series of recommendations were provided for improving the conservation status of the elasmobranchs in this region. These include the need for improved taxonomic research, enhanced monitoring of elasmobranch stocks, and the highest protection level for threatened taxa. Alongside political will, enhancing national capacity to manage and rebuild elasmobranch stocks, coordinated regional management measures are essential.
Asunto(s)
Conservación de los Recursos Naturales , Ecosistema , Especies en Peligro de Extinción/estadística & datos numéricos , Explotaciones Pesqueras/estadística & datos numéricos , Tiburones/fisiología , Rajidae/fisiología , Animales , Bangladesh , Cambio Climático , Océanos y Mares , Dinámica Poblacional , Tiburones/clasificación , Rajidae/clasificaciónRESUMEN
Shark fishing, driven by the fin trade, is the primary cause of global shark population declines. Here, we present a case study that exemplifies how industrial fisheries are likely depleting shark populations in the Eastern Tropical Pacific Ocean. In August 2017, the vessel Fu Yuan Yu Leng 999, of Chinese flag, was detained while crossing through the Galápagos Marine Reserve without authorization. This vessel contained 7639 sharks, representing one of the largest seizures recorded to date. Based on a sample of 929 individuals (12%), we found 12 shark species: 9 considered as Vulnerable or higher risk by the IUCN and 8 listed in CITES. Four species showed a higher proportion of immature than mature individuals, whereas size-distribution hints that at least some of the fishing ships associated with the operation may have been using purse-seine gear fishing equipment, which, for some species, goes against international conventions. Our data expose the magnitude of the threat that fishing industries and illegal trade represent to sharks in the Eastern Tropical Pacific Ocean.
Asunto(s)
Código de Barras del ADN Taxonómico/métodos , Tiburones/anatomía & histología , Tiburones/crecimiento & desarrollo , Animales , Tamaño Corporal , Conservación de los Recursos Naturales , Explotaciones Pesqueras , Océano Pacífico , Conducta Sexual Animal , Tiburones/clasificación , Tiburones/genéticaRESUMEN
Preexploitation shark baselines and the history of human impact on coral reef-associated shark communities in the Caribbean are tpoorly understood. We recovered shark dermal denticles from mid-Holocene (â¼7 ky ago) and modern reef sediments in Bocas del Toro, Caribbean Panama, to reconstruct an empirical shark baseline before major human impact and to quantify how much the modern shark community in the region had shifted from this historical reference point. We found that denticle accumulation rates, a proxy for shark abundance, declined by 71% since the mid-Holocene. All denticle morphotypes, which reflect shark community composition, experienced significant losses, but those morphotypes found on fast-swimming, pelagic sharks (e.g., families Carcharhinidae and Sphyrnidae) declined the most. An analysis of historical records suggested that the steepest decline in shark abundance occurred in the late 20th century, coinciding with the advent of a targeted shark fishery in Panama. Although the disproportionate loss of denticles characterizing pelagic sharks was consistent with overfishing, the large reduction in denticles characterizing demersal species with low commercial value (i.e., the nurse shark Ginglymostoma cirratum) indicated that other stressors could have exacerbated these declines. We demonstrate that the denticle record can reveal changes in shark communities over long ecological timescales, helping to contextualize contemporary abundances and inform shark management and ecology.
Asunto(s)
Escamas de Animales , Arrecifes de Coral , Fósiles , Tiburones/fisiología , Escamas de Animales/citología , Escamas de Animales/fisiología , Animales , Región del Caribe , Conservación de los Recursos Naturales , Sedimentos Geológicos/química , Actividades Humanas , Humanos , Panamá , Tiburones/clasificación , Factores de TiempoRESUMEN
Anecdotal reports from fishers in Southeast Queensland, Australia suggest that shark depredation is a significant issue, however little is known about which species are responsible for depredating catches. This research aimed to identify depredating species in Southeast Queensland line based fisheries, by undertaking a genetic analysis of depredated samples collected by commercial, charter and recreational fishers. The genetic analysis successfully identified ten depredating sharks, all from the genus Carcharhinus (19.2% success). The species identified using mitochondrial DNA included five C. leucas (bull sharks), two C. plumbeus (sandbar sharks), one C. amboinensis (pigeye shark), one C. brevipinna (spinner shark) and one unconfirmed C. plumbeus/C. altimus (bignose shark). While many species of Carcharhinus have been found to depredate catches in Australia, C. leucas has not been highlighted until this research as a potential problematic species. The optimised protocol allowed for the confident identification of shark species responsible for depredation in fisheries using frozen fish samples donated by fishers.
Asunto(s)
Tiburones , Animales , Conservación de los Recursos Naturales , ADN Mitocondrial , Explotaciones Pesqueras , Conducta Predatoria , Queensland , Tiburones/clasificación , Tiburones/genéticaRESUMEN
Chondrichthyes occupy a key position in the phylogeny of vertebrates. The complete sequence of the mitochondrial genome (mitogenome) of four species of sharks and five species of rays was obtained by whole genome sequencing (DNA-seq) in the Illumina HiSeq2500 platform. The arrangement and features of the genes in the assembled mitogenomes were identical to those found in vertebrates. Both Maximum Likelihood (ML) and Bayesian Inference (BI) analyses were used to reconstruct the phylogenetic relationships among 172 species (including 163 mitogenomes retrieved from GenBank) based on the concatenated dataset of 13 individual protein coding genes. Both ML and BI analyses did not support the "Hypnosqualea" hypothesis and confirmed the monophyly of sharks and rays. The broad notion in shark phylogeny, namely the division of sharks into Galeomorphii and Squalomorphii and the monophyly of the eight shark orders, was also supported. The phylogenetic placement of all nine species sequenced in this study produced high statistical support values. The present study expands our knowledge on the systematics, genetic differentiation, and conservation genetics of the species studied, and contributes to our understanding of the evolutionary history of Chondrichthyes.
Asunto(s)
Genoma Mitocondrial , Filogenia , Tiburones/genética , Rajidae/genética , Animales , Tiburones/clasificación , Rajidae/clasificaciónRESUMEN
The ecomorphological diversity of extinct elasmobranchs is incompletely known. Here, we describe Aquilolamna milarcae, a bizarre probable planktivorous shark from early Late Cretaceous open marine deposits in Mexico. Aquilolamna, tentatively assigned to Lamniformes, is characterized by hypertrophied, slender pectoral fins. This previously unknown body plan represents an unexpected evolutionary experimentation with underwater flight among sharks, more than 30 million years before the rise of manta and devil rays (Mobulidae), and shows that winglike pectoral fins have evolved independently in two distantly related clades of filter-feeding elasmobranchs. This newly described group of highly specialized long-winged sharks (Aquilolamnidae) displays an aquilopelagic-like ecomorphotype and may have occupied, in late Mesozoic seas, the ecological niche filled by mobulids and other batoids after the Cretaceous-Paleogene boundary.
Asunto(s)
Evolución Biológica , Fósiles , Tiburones/anatomía & histología , Tiburones/fisiología , Aletas de Animales/anatomía & histología , Animales , Ecosistema , Elasmobranquios/anatomía & histología , Elasmobranquios/fisiología , Conducta Alimentaria , México , Océanos y Mares , Paleodontología , Plancton , Tiburones/clasificación , Natación , Diente/anatomía & histologíaRESUMEN
Infiltration of the endothelial layer of the blood-brain barrier by leukocytes plays a critical role in health and disease. When passing through the endothelial layer during the diapedesis process lymphocytes can either follow a paracellular route or a transcellular one. There is a debate whether these two processes constitute one mechanism, or they form two evolutionary distinct migration pathways. We used artificial intelligence, phylogenetic analysis, HH search, ancestor sequence reconstruction to investigate further this intriguing question. We found that the two systems share several ancient components, such as RhoA protein that plays a critical role in controlling actin movement in both mechanisms. However, some of the key components differ between these two transmigration processes. CAV1 genes emerged during Trichoplax adhaerens, and it was only reported in transcellular process. Paracellular process is dependent on PECAM1. PECAM1 emerged from FASL5 during Zebrafish divergence. Lastly, both systems employ late divergent genes such as ICAM1 and VECAM1. Taken together, our results suggest that these two systems constitute two different mechanical sensing mechanisms of immune cell infiltrations of the brain, yet these two systems are connected. We postulate that the mechanical properties of the cellular polarity is the main driving force determining the migration pathway. Our analysis indicates that both systems coevolved with immune cells, evolving to a higher level of complexity in association with the evolution of the immune system.
Asunto(s)
Células Endoteliales/metabolismo , Leucocitos/metabolismo , Proteínas/genética , Migración Transcelular de la Célula/genética , Transcriptoma , Migración Transendotelial y Transepitelial/genética , Animales , Evolución Biológica , Barrera Hematoencefálica/citología , Barrera Hematoencefálica/metabolismo , Caenorhabditis elegans/clasificación , Caenorhabditis elegans/citología , Caenorhabditis elegans/genética , Caenorhabditis elegans/metabolismo , Pollos/clasificación , Pollos/genética , Pollos/metabolismo , Ciona intestinalis/clasificación , Ciona intestinalis/citología , Ciona intestinalis/genética , Ciona intestinalis/metabolismo , Drosophila melanogaster/clasificación , Drosophila melanogaster/citología , Drosophila melanogaster/genética , Drosophila melanogaster/metabolismo , Células Endoteliales/citología , Perfilación de la Expresión Génica , Regulación de la Expresión Génica , Ontología de Genes , Humanos , Leucocitos/citología , Ratones , Pan troglodytes/clasificación , Pan troglodytes/genética , Pan troglodytes/metabolismo , Petromyzon/clasificación , Petromyzon/genética , Petromyzon/metabolismo , Filogenia , Placozoa/clasificación , Placozoa/citología , Placozoa/genética , Placozoa/metabolismo , Proteínas/clasificación , Proteínas/metabolismo , Anémonas de Mar/clasificación , Anémonas de Mar/citología , Anémonas de Mar/genética , Anémonas de Mar/metabolismo , Tiburones/clasificación , Tiburones/genética , Tiburones/metabolismo , Pez Cebra/clasificación , Pez Cebra/genética , Pez Cebra/metabolismoRESUMEN
In southern Brazil, we investigated shark and ray capture records in an integral protection marine protection area (MPA) that allows fishing in that area. We found 10 shark and nine ray species, of which 88.5% and 66.2%, respectively, are endangered. Female adults and neonates of both sexes are abundant in the area, with records of stranding of large specimens, postcapture abortions and ovigerous capsules with fresh embryos on the beach. We suggest the application of continuous fisheries monitoring and an increase in guidelines on the capture of endangered species.
Asunto(s)
Biodiversidad , Especies en Peligro de Extinción/estadística & datos numéricos , Explotaciones Pesqueras/estadística & datos numéricos , Tiburones/fisiología , Rajidae/fisiología , Animales , Brasil , Conservación de los Recursos Naturales , Femenino , Masculino , Tiburones/clasificación , Rajidae/clasificaciónRESUMEN
An optimized alignment of related protein sequences helps to see their important shared features and to deduce their phylogenetic relationships. At low levels of sequence similarity, there are no suitable computer programs for making the best possible alignment. This review summarizes some guidelines for how in such instances, nevertheless, insightful alignments can be made. The method involves, basically, the understanding of molecular family features at both the protein and intron-exon level, and the collection of many related sequences so that gradual differences may be observed. The method is exemplified by identifying and aligning interleukin 2 (IL-2) and related sequences in Elasmobranchii (sharks/rays) and coelacanth, as other authors have expressed difficulty with their identification. From the point of general immunology, it is interesting that the unusual long "leader" sequence of IL-15, already known in other species, is even more impressively conserved in cartilaginous fish. Furthermore, sequence comparisons suggest that IL-2 in cartilaginous fish has lost its ability to bind an IL-2Rα/15Rα receptor chain, which would prohibit the existence of a mechanism for regulatory T cell regulation identical to mammals.
Asunto(s)
Interleucina-2/genética , Alineación de Secuencia/métodos , Tiburones/genética , Secuencia de Aminoácidos , Animales , Evolución Molecular , Interleucina-15/química , Interleucina-15/genética , Interleucina-15/metabolismo , Interleucina-2/química , Interleucina-2/metabolismo , Interleucinas/química , Interleucinas/metabolismo , Filogenia , Tiburones/clasificación , Tiburones/inmunología , Vertebrados/clasificación , Vertebrados/genética , Vertebrados/inmunologíaRESUMEN
The morphology of the articular region of the pectoral girdle and associated basals in Etmopteridae is revised in light of new evidence provided by taxa unavailable for previous studies. Such studies considered that etmopterids plesiomorphically had a single pectoral articular condyle, and only Etmopterus had two separate ones. Our reanalysis indicates that the possession of two separate condyles, one for the articulation of the propterygium and the second for the meso- and metapterygium, is the most widespread condition in this group. However, the presence of two separate articular condyles is not recovered as a synapomorphy for Etmopteridae. Previous studies also proposed that etmopterids lack a hook-like process on the anteroproximal margin of the anteriormost pectoral basal. We document that the hook-like process is plesiomorphically present in Etmopteridae, thus corroborating the hypothesis of closer relationships between this family and the other squaliforms that also share this process, namely Centrophoridae, Dalatiidae, Oxynotidae, and Somniosidae.
Asunto(s)
Huesos/anatomía & histología , Tiburones/anatomía & histología , Aletas de Animales/anatomía & histología , Animales , Filogenia , Tiburones/clasificaciónRESUMEN
Tessellated calcified cartilage (TCC) is a distinctive kind of biomineralized perichondral tissue found in many modern and extinct chondrichthyans (sharks, rays, chimaeroids and their extinct allies). Customarily, this feature has been treated somewhat superficially in phylogenetic analyses, often as a single "defining" character of a chondrichthyan clade. TCC is actually a complex hard tissue with numerous distinctive attributes, but its use as a character complex for phylogenetic analysis has not yet been optimized. This study attempts to improve this situation by presenting new terminology for certain aspects of tesseral architecture, including single-monolayered, multiple-monolayered, polylayered and voussoir tesserae; new histological data, including thin sections of TCC in several Palaeozoic taxa, and new proposals for ways in which various characters and states (many of which are defined here for the first time) could be applied in future phylogenetic analyses of chondrichthyan fishes. It can be concluded that many, but not all, of the unique attributes of modern TCC evolved by the Early Devonian (ca. 400 before present (bp)). The globular calcified cartilage reported in Silurian sinacanthids and the so-called subtessellated perichondral biomineralization (with irregular and ill-defined geometries of a layer or layers of calcified cartilage blocks) of certain extinct "acanthodians" (e.g., Climatius, Ischnacanthus, Cheiracanthus) could represent evolutionary precursors of TCC, which seems to characterize only part of the chondrichthyan total group. It is hypothesized that heavily biomineralized "layer-cake" TCC in certain Palaeozoic chondrichthyans perhaps served a dual physiological role, as a phosphate sink and in providing increased skeletal density in very large (>7 m) Devonian-Permian marine sharks such as ctenacanths and as an adaptation to calcium-deficient environments among Permo-Carboniferous non-marine sharks such as xenacanths. By contrast, the equivalent tissue in modern elasmobranchs probably serves only to reinforce regions of cartilage (mostly in the jaws) subjected to high loading. It is also noted that much of the variation observed in tesseral architecture (including localized remodelling), ultrastructure and histology in modern and extinct chondrichthyans is confined to the perichondrally facing cap zone (where Type-1 collagen matrix predominates in modern TCC), whereas the main body of the tessera (where Type-2 collagen matrix predominates) exhibits comparatively little evidence of remodelling and histological or structural variation.
Asunto(s)
Cartílago/ultraestructura , Fósiles , Tiburones/anatomía & histología , Tiburones/clasificación , Animales , Evolución Biológica , Maxilares/anatomía & histología , FilogeniaRESUMEN
Nitrogen stable isotopes ratios (δ15 N) were determined for selected tissues (muscle, liver, blood and yolk) of pregnant females and their embryos of a placental viviparous species, the Pacific sharpnose shark (Rhizoprionodon longurio), and a yolk-sac viviparous species, the speckled guitarfish (Pseudobatos glaucostigmus). The R. longurio embryo tissues were 15 N enriched compared to the same tissues in the pregnant female, using the difference in δ15 N (Δδ15 N) between embryo and adult. Mean Δδ15 N was 2.17 in muscle, 4.39 in liver and 0.80 in blood. For P. glaucostigmus, embryo liver tissue was significantly 15 N enriched in comparison with liver of the pregnant female (Δδ15 N mean = 1.22), whereas embryo muscle was 15 N depleted relative to the muscle of the pregnant female (Δδ15 N mean = -1.22). Both species presented a significant positive linear relationship between Δδ15 N and embryo total length (LT ). The results indicated that embryos have different Δδ15 N depending on their reproductive strategy, tissue type analysed and embryo LT .
Asunto(s)
Isótopos de Nitrógeno/metabolismo , Reproducción/fisiología , Tiburones/fisiología , Viviparidad de Animales no Mamíferos/fisiología , Animales , Femenino , Músculos/metabolismo , Isótopos de Nitrógeno/análisis , Tiburones/clasificaciónRESUMEN
Detailed information on shark and ray fisheries in the Andaman and Nicobar Islands, India are limited, including information on the diversity and biological characteristics of these species. We carried out fish landing surveys in South Andamans from January 2017 to May 2018, a comprehensive and cost-effective way to fill this data gap. We sampled 5,742 individuals representing 57 shark and ray species landed from six types of fishing gears. Of the 36 species of sharks and 21 species of rays landed, six species of sharks (Loxodon macrorhinus, Carcharhinus amblyrhynchos, Sphyrna lewini, C. albimarginatus, C. brevipinna, and Paragaleus randalli) comprised 83.35% of shark landings, while three species of rays (Pateobatis jenkinsii, Himantura leoparda and H. tutul) comprised 48.82% of ray landings, suggesting a species dominance in the catch or fishing region. We provide insights into the biology of species with extensions in maximum size for seven shark species. Additionally, we document an increase in the known ray diversity for the islands and for India with three previously unreported ray species. We found that amongst sharks, mature individuals of small-bodied species (63.48% males of total landings of species less than 1.5 m total length when mature) and immature individuals of larger species (84.79% males of total landings of species larger than 1.5 m total length when mature) were mostly landed; whereas for rays, mature individuals were predominantly landed (80.71% males of total landings) likely reflecting differences in habitat preferences along life-history stages across species and fishing gear. The largest size range in sharks was recorded in landings from pelagic longlines and gillnets. Further, the study emphasizes the overlap between critical habitats and fishing grounds, where immature sharks and gravid females were landed in large quantities which might be unsustainable in the long-term. Landings were female-biased in C. amblyrhynchos, S. lewini and P. jenkinsii, and male-biased in L. macrorhinus and H. leoparda, indicating either spatio-temporal or gear-specific sexual segregation in these species. Understanding seasonal and biological variability in the shark and ray landings over a longer study period across different fisheries will inform future conservation and fishery management measures for these species in the Andaman and Nicobar Islands.
Asunto(s)
Tiburones/clasificación , Tiburones/fisiología , Rajidae/clasificación , Rajidae/fisiología , Animales , Biodiversidad , Conservación de los Recursos Naturales , Especies en Peligro de Extinción , Femenino , Explotaciones Pesqueras , India , Masculino , Densidad de Población , Especificidad de la EspecieRESUMEN
Whereas the gill chambers of jawless vertebrates open directly into the environment, jawed vertebrates evolved skeletal appendages that drive oxygenated water unidirectionally over the gills. A major anatomical difference between the two jawed vertebrate lineages is the presence of a single large gill cover in bony fishes versus separate covers for each gill chamber in cartilaginous fishes. Here, we find that these divergent patterns correlate with the pharyngeal arch expression of Pou3f3 orthologs. We identify a deeply conserved Pou3f3 arch enhancer present in humans through sharks but undetectable in jawless fish. Minor differences between the bony and cartilaginous fish enhancers account for their restricted versus pan-arch expression patterns. In zebrafish, mutation of Pou3f3 or the conserved enhancer disrupts gill cover formation, whereas ectopic pan-arch Pou3f3b expression generates ectopic skeletal elements resembling the multimeric covers of cartilaginous fishes. Emergence of this Pou3f3 arch enhancer >430 Mya and subsequent modifications may thus have contributed to the acquisition and diversification of gill covers and respiratory strategies during gnathostome evolution.