Although selachian fossil remains have been studied for nearly three centuries, little is known about their evolutionary history. Recent studies have suggested different timings of early ...diversification events in the Late Triassic, Jurassic, and Early Cretaceous. However, Late Cretaceous selachian diversity has remained little explored despite numerous and diversified selachian assemblages known from this time interval. Sampling standardization, origination/extinction rates, and raw ordinal diversity were examined based on taxonomic occurrences in three data sets representing distinct geographical areas (Anglo-Paris Basin, northwestern Europe, and Western Interior Seaway) spanning the Cenomanian-Campanian interval. This examination allowed the identification of regional diversity events, previously reported for some invertebrate groups, but presented for the first time for a marine vertebrate group. The local mid-Cenomanian diversity drop (Anglo-Paris Basin) is interpreted as a possible consequence of changes in bottom seawater conditions related to the rapid mid-Cenomanian transgression. The Cenomanian/Turonian faunal turnover is likely to be due to various sampling biases (Anglo-Paris Basin and northwestern Europe), but a genuine extinction in the Western Interior Seaway cannot be excluded. The Santonian diversity peak synchronous with a marked global increase in seawater temperatures contrasts with the rapid temperature decrease linked with low diversity in the early Campanian.
Age-structured demographic models were constructed based on empirical estimates of longevity and maturity for five deepwater Bering Sea skates to investigate how observed differences in life history ...parameters affect population growth rates. Monte Carlo simulations were used to incorporate parameter uncertainty. Estimated population growth rates ranged from 1.045 to 1.129 yr-1 and were lower than those reported for other Alaskan skates and most chondrichthyans. Population growth rates of these and other high-latitude skates increased with relative reproductive lifespan, but displayed no significant relationship with body size or depth distribution, suggesting that assemblage shifts may be difficult to predict for data-poor taxa. Elasticity analyses indicated that juvenile and adult survival had greater per-unit effects on population growth rates than did egg-case survival or fecundity. Population growth rate was affected more by uncertainty in age at maturity than maximum age. The results of this study indicate that if skates are deemed to be a management concern, gear modifications or depth-specific effort controls may be effective.
Abstract The objective of this study was to describe the histology and histochemistry of the integument covering the back and stinger of the freshwater stingray Potamotrygon rex, endemic to the ...Middle Upper Tocantins River. The species has a dark back and yellowish circular spots that extend to the tail, which has one to two stings located in the median portion of the tail. Through histological study it was observed that the epithelia of the back and stinger are composed of non-keratinized stratified pavement epithelial tissue, and are organized in three layers: basal, intermediate and superficial. The differences between the tissues are related to the cell types that compose them. The back is organized with epithelial cells, mucus cells, granulocyte cells and chromatophores. The mucus cells are distributed in different layers along the animal's back, influencing the thickness of the tissue. The tissue that covers the stinger is composed of epithelial cells, chromatophores and specialized cells in protein synthesis. In the histochemistry, the stinger epithelial cells were stained with Bromophenol Blue, especially those of the intermediate layer, which were called specialized cells. In the back the epithelial cells were stained with Bromophenol Blue, Alcian Blue and PAS, and the mucous cells with PAS. In both tissues the presence of protein reserves was detected, areas so called because they are stained strongly with Bromophenol Blue. The results show that the stinger presents activity directed to the production of proteins, and that the back is organized to produce different components, which constitute the cuticle that covers the animal's body.
Resumo O objetivo deste estudo foi descrever a histologia e histoquímica do tegumento que reveste o dorso e o ferrão da arraia de água doce Potamotrygon rex, endêmica do Médio Alto Tocantins. A espécie possui o dorso escuro e manchas circulares amareladas que se estendem até a cauda, que possui de um a dois ferrões localizados na porção mediana da cauda. Através do estudo histológico observou-se que os epitélios do dorso e do ferrão são compostos por tecido epitelial pavimentoso estratificado não queratinizado, e estão organizados em três camadas: basal, intermediária e superficial. As diferenças entre os tecidos estão relacionadas aos tipos de células que os compõem. O dorso é organizado com células epiteliais, células mucosas, células de granulócitos e cromatóforos. As células mucosas estão distribuídas em diferentes camadas ao longo do dorso do animal, influenciando na espessura do tecido. O tecido que reveste o ferrão é composto por células epiteliais, cromatóforos e células proteicas. Na histoquímica, as células epiteliais do ferrão foram coradas com Azul de Bromofenol, principalmente as da camada intermediária, que foram denominadas células proteicas. No dorso as células epiteliais foram coradas com Azul de Bromofenol, Azul Alcian e PAS, e as células mucosas com PAS. Em ambos os tecidos também foi detectada a presença de reservatórios de proteínas, áreas assim denominadas por estarem fortemente coradas com Azul de Bromofenol. Os resultados mostram que o ferrão apresenta atividade direcionada à produção de proteínas, e que o dorso se organiza para produzir diferentes componentes que constituem a cutícula que reveste o corpo do animal.
Special Issue Carlson, John K; Goldman, Kenneth J
2007, 2006, Letnik:
25
eBook
Over the last few years there have been advances in the quantitative study of age and growth of chondrichthyan fishes. Novel approaches to ageing of various chondrichthyan fishes continue to arise. ...This volume is a collection of papers on several of these topics that include new hard parts (e.g. caudal thorns) for assessments of age, new techniques for validation (e.g. bomb radiocarbon) and reexaminations of previous age and growth models. This volume also contains papers on the importance of assessing the precision and accuracy of statistical formulas, analyses, and models that are used in age and growth studies. There is currently a great deal of research being conducted, some of which is truly 'pushing the envelope,' in attempts to assess the life history parameters of numerous chondrichthyan fishes.
The structure of marine communities is affected by both fishing and climate variability. The Argentinean-Uruguayan Common Fishing Zone (AUCFZ) comprising the Rio de la Plata and its oceanic front (SW ...Atlantic, 34degrees 30' to 39degrees 30' S) has a high environmental variability. Intensive trawling activity results in the bycatch of many chondrichthyan species. Using generalized linear mixed models, we analyzed the effects of commercial fishing effort, sea surface thermal anomalies (SSTA) and depth on the spatiotemporal dynamics of chondrichthyan species richness and total number of individuals in 3 zones of the AUCFZ between 1984 and 2009. Species richness increased with fishing effort in warmer years in the northern zone but displayed the opposite trend in the river and southern zones. While the total number of individuals decreased in the coldest years and at greater depths in the northern zone, these 2 variables had opposite effects in the southern zone. Depth had a stronger effect on both chondrichthyan species richness and the total number of individuals than the other 2 explanatory variables. While SSTA and depth had statistically significant effects on species richness and the total number of individuals, commercial fishing effort was significantly related only with species richness. The spatial variability of both response variables was greater than their temporal variation during the study period. These findings contribute to a greater understanding of the spatio-temporal dynamics of demersal chondrichthyans in the AUCFZ and are of relevance to the longterm sustainable management of chondrichthyans in this area and elsewhere.
The immune system is composed of two subsystems-the innate immune system and the adaptive immune system. The innate immune system is the first to respond to pathogens and does not retain memory of ...previous responses. Innate immune responses are evolutionarily older than adaptive responses and elements of innate immunity can be found in all multicellular organisms. If a pathogen persists, the adaptive immune system will engage the pathogen with specificity and memory. Several components of the adaptive system including immunoglobulins (Igs), T cell receptors (TCR), and major histocompatibility complex (MHC), are assumed to have arisen in the first jawed vertebrates-the Gnathostomata. This review will discuss and compare components of both the innate and adaptive immune systems in Gnathostomes, particularly in Chondrichthyes (cartilaginous fish) and in Osteichthyes bony fish: the Actinopterygii (ray-finned fish) and the Sarcopterygii (lobe-finned fish). While many elements of both the innate and adaptive immune systems are conserved within these species and with higher level vertebrates, some elements have marked differences. Components of the innate immune system covered here include physical barriers, such as the skin and gastrointestinal tract, cellular components, such as pattern recognition receptors and immune cells including macrophages and neutrophils, and humoral components, such as the complement system. Components of the adaptive system covered include the fundamental cells and molecules of adaptive immunity: B lymphocytes (B cells), T lymphocytes (T cells), immunoglobulins (Igs), and major histocompatibility complex (MHC). Comparative studies in fish such as those discussed here are essential for developing a comprehensive understanding of the evolution of the immune system.
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