Plastic pollution is increasing dramatically worldwide, causing adverse effects on a wide variety of marine organisms at all trophic levels. As predators, sharks play a key role in marine ecosystems ...and they could especially be threatened by the ingestion of microplastics. This study contributes to expand the existing data on the MPs ingestion by a Mediterranean elasmobranch species, Scyliorhinus canicula, adding new information on the potential impact that this class of contaminants can have on the metabolism of this ecologically relevant species. The present research is aimed: i) to assess if the ingestion of MPs in S. canicula is related to sex, size and depth of catch; ii) to evaluate the effect of MPs on fish body condition; iii) to evaluate if the ingested MPs influence the amino acid and fatty acid composition of eye and liver.
A total of 61 specimens of S. canicula were analysed. Forty-nine individuals (80.3 %) had ingested plastic items. Totally, 147 plastic elements were found, mainly belonging to small MPs (49 %), and large MPs (46 %), mostly represented by fibers (84 %). The predominant colour was black. No differences were found between sex and size. A difference in the number of items/specimens related to the deep, highest between 50 and 100 m (4.4), while the lowest between 101 and 500 m (2.1) was found. The condition factor (Kn) value was equal to 1.00 highlighting the wellness of the fish. Arginine (20.1 %), Glutamate (17.4), Phenylalanine (15.7 %), Proline (15.6 %) and were the most abundant amino acids in the eyes of S. canicula. The relative fatty acid composition of the livers was dominated by fatty acids SA (30.2 %) (SFA), CA (29.9 %) (SFA) and OA (22.4 %) (MUFA). This paper reports a study on the relationship between amino acids and fatty acids composition and ingested MPs, highlighting that no significant effects were found.
Display omitted
•MPs were found in Scyliorhinus canicula specimens from the South of Sicily.•The most of them were black fibers.•No relationship between amino acids and fatty acids levels and ingested MPs were found.
Ladybird homeobox (Lbx) transcription factors have crucial functions in muscle and nervous system development in many animals. Amniotes have two Lbx genes, but only Lbx1 is expressed in spinal cord. ...In contrast, teleosts have three lbx genes and we show here that zebrafish lbx1a, lbx1b, and lbx2 are expressed by distinct spinal cell types, and that lbx1a is expressed in dI4, dI5, and dI6 interneurons, as in amniotes. Our data examining lbx expression in Scyliorhinus canicula and Xenopus tropicalis suggest that the spinal interneuron expression of zebrafish lbx1a is ancestral, whereas lbx1b has acquired a new expression pattern in spinal cord progenitor cells. lbx2 spinal expression was probably acquired in the ray‐finned lineage, as this gene is not expressed in the spinal cords of either amniotes or S. canicula. We also show that the spinal function of zebrafish lbx1a is conserved with mouse Lbx1. In zebrafish lbx1a mutants, there is a reduction in the number of inhibitory spinal interneurons and an increase in the number of excitatory spinal interneurons, similar to mouse Lbx1 mutants. Interestingly, the number of inhibitory spinal interneurons is also reduced in lbx1b mutants, although in this case the number of excitatory interneurons is not increased. lbx1a;lbx1b double mutants have a similar spinal interneuron phenotype to lbx1a single mutants. Taken together these data suggest that lbx1b and lbx1a may be required in succession for correct specification of dI4 and dI6 spinal interneurons, although only lbx1a is required for suppression of excitatory fates in these cells.
Research Highlights
lbx1 spinal expression and function is conserved in vertebrates. In contrast, zebrafish lbx1b and lbx2 have novel spinal expression patterns that probably evolved in the ray‐finned vertebrate lineage (lbx2) or teleosts (lbx1b).
Plastics are widely diffused in the oceans and their ingestion by marine organisms is raising concern for potentially adverse effects. The risk of harmful interactions with marine plastic pollution ...depends on the biology of the species as well as the distribution and abundance of the different plastic types.
The aim of this study was to assess the occurrence of plastic ingestion by the small-spotted catshark (Scyliorhinus canicula), one of the most abundant elasmobranchs in the Mediterranean Sea. The expression levels of genes indicative of total immune system function were analyzed to gather preliminary data for further investigation of any potential correlations between plastic presence and immune activation.
One hundred catsharks were collected during the Spring 2018 in two geographic locations in the southern region of the central Mediterranean Sea: 1) near Mazara del Vallo, SW Sicily and 2) near Lampedusa island, Italy's southernmost. Standard measurements were recorded for each specimen and its organs and sex was determined. The gastrointestinal tract (GIT) was preserved for plastic detection and identification. Where present, plastics (macro- and micro-) were characterized in terms of size, shape and polymer typology through microscopy and μ-Raman spectroscopy. Spleen from a subset of thirty samples was preserved for RNA extraction, then used to quantify by real time PCR the transcripts of T cell receptor beta (TCRB), T cell receptor delta (TCRD) and IgM genes.
The results indicated that ingestion of plastic is widespread, with microplastics (MP, from 1 μm to <1 mm) abundantly present in nearly all samples and macroplasticplastic (MaP, > 1 cm) in approximately 18% of the specimens collected. A significant increase in the expression of TCRB, TCRD and IgM was observed in the spleen of MaP + specimens from Mazara del Vallo waters, in parallel with 67% increase in liver weight.
While the presence of MP alone is not enough to induce a strong activation of the immunity, some type of plastics falling into the MaP category may be more toxic than others and crucial in the activation of the immune response.
The results of this study represent a first evidence that plastic pollution represents an emerging threat to S. canicula, the Mediterranean food web and human consumers.
•We describe microplastics and macroplastics in small spotted sharks, Scyliorhinus canicula.•We used samples from two geographic locations in the southern region of the central Mediterranean Sea.•We characterized the plastics in the shark’s gastrointestinal tract (GIT) using microscopy and μ-Raman spectroscopy.•We analyzed morphometric data in correlation of geographical location and plastic load.•We measured the expression of immune-related genes for potential correlation to location and plastic detection.
Pulse fishing may pose a promising alternative for diminishing the ecosystem effects of beam trawling. However, concerns about the impact on both target and non-target species still remain, amongst ...others the possible damage to the electro-receptor organs, the Ampullae of Lorenzini, of elasmobranchs. The current study aimed to examine the role of pulsed direct current (PDC) used in pulse trawls on the electro-detection ability of the small-spotted catshark, Scyliorhinus canicula. The electroresponse of the sharks to an artificially created prey-simulating electrical field was tested before and after exposure to the pulsed electrical field used to catch flatfish and shrimp. No statistically significant differences were noted between control and exposed animals, both in terms of the number of sharks exhibiting an electroresponse prior to and following exposure as well as regarding the timing between onset of searching behaviour and biting at the prey simulating dipole. These results indicate that, under the laboratory circumstances as adopted in this study, the small-spotted catshark are still able to detect the bioelectrical field of a prey following exposure to PDC used in pulse trawls. However, to fully grasp the impact of PDC on elasmobranchs, further studies are imperative, including examining the effect on reproduction and young life stages, the longer-term and indirect influences and experiments under field conditions.
•Catsharks were exposed to electrical field used to catch brown shrimp or flatfish.•Prey detection of sharks was tested using a prey simulating bio-electrical field.•Sharks were still able to detect a prey bio-electrical field following exposure.•No impact on bite response to prey simulator•No difference in timing of bite response to prey simulator
The present study, based on microsatellite markers, describes a population genetic analysis of the small-spotted catshark Scyliorhinus canicula (Linnaeus, 1758), representing one of the most abundant ...and commonly caught cartilaginous fishes in the Mediterranean Sea and adjacent areas. The analyses were performed to unravel the genetic features (variability, connectivity, sex-biased dispersal) of their relative geographic populations, both at the small (around the coast of Sardinia, Western Mediterranean Sea) and at a larger spatial scale (pan-Mediterranean level and between the Atlantic Ocean and the Mediterranean Sea). Individual clustering, multivariate and variance analyses rejected the hypothesis of genetic homogeneity, with significant genetic differences mainly within the Mediterranean between the Western and Eastern basins, as well as between the Mediterranean and the NE Atlantic Ocean. In detail, our results seem to confirm that the Strait of Gibraltar could not represent a complete barrier to the exchange of individuals of small-spotted catshark between the Atlantic Ocean and the Mediterranean Sea. In the latter area, a complex genetic structuring for S. canicula was found. Apart from differences among the Western, Eastern and Adriatic sites, within the Western basin the small-spotted catsharks around Sardinian waters are strongly differentiated from all others (both from the eastern Tyrrhenian Sea and southernmost part of the Algerian basin) and are demographically stable. Several possible mechanisms, both biological and abiotic (e.g., migratory behavior, waterfronts, and oceanographic discontinuities), are discussed here to explain their peculiar characteristics. Overall, the genetic data presented, both at the local and regional level, could represent a baseline information, useful for the temporal monitoring of populations, and to assess the effects of present or future fishing/management/conservation measures.
The parasitic fauna of the small-spotted catshark, Scyliorhinus canicula in the north-eastern Aegean Sea was investigated. Twenty-one out of the 52 (prevalence 40.4%) specimens collected were found ...infected with parasites; an arthropod and two nematode genera. Seven specimens (prevalence 13.5%) were infected by a Neoalbionella sp. copepod. Ten and 14 specimens were infected by the nematodes Proleptus obtusus (prevalence 19.2%) and Anisakis sp. (prevalence 26.9%), respectively. Female S. canicula specimens were significantly more heavily infected during autumn and when the whole sampling period is considered. Nematode infection was significantly related to season, becoming progressively heavier from spring to autumn. No correlation was found between TL of specimens and number of parasites for males or females, irrespective of gender. The present study provided a first record of Neoalbionella sp., P. obtusus and Anisakis sp. infections of S. canicula in the north-eastern Mediterranean. The lower prevalence of Proleptus obtusus and the higher prevalence of Anisakis sp. infection recorded in this study may be due to prey availability and parasite populations in this locality.
Despite the growing interest in human-made noise effects on marine wildlife, few studies have investigated the potential role of underwater noise on elasmobranch species. In this study, twelve ...specimens of small-spotted catshark (
) were exposed to biological and anthropogenic sounds in order to assess their behavioural changes in response to prey acoustic stimuli and to different amplitude levels of shipping noise. The sharks, individually held in aquariums, were exposed to four experimental acoustic conditions characterized by different spectral (Hz) components and amplitude (dB re 1 µPa) levels. The swimming behaviour and spatial distribution of sharks were observed. The results highlighted significant differences in swimming time and in the spatial use of the aquarium among the experimental conditions. When the amplitude levels of biological sources were higher than those of anthropogenic sources, the sharks' swimming behaviour was concentrated in the bottom sections of the aquarium; when the amplitude levels of anthropogenic sources were higher than biological ones, the specimens increased the time spent swimming. Moreover, their spatial distribution highlighted a tendency to occupy the least noisy sections of the aquarium. In conclusion, this study highlighted that anthropogenic noise is able to affect behaviour of catshark specimens and the impact depends on acoustic amplitude levels.
Since 2014 elasmobranch egg cases that are washed up on the Dutch North Sea beaches can be registered by beachcombers using the Great Eggcase Hunt database. For this study, individuals often ...registering multiple egg cases were asked to send these to the authors for a predation study. After disposing of heavily damaged (over 50% gone) egg cases, a total of 736 egg cases of six different elasmobranch species (
Raja microocellata, Raja brachyura, Raja montagui, Raja undulata, Raja clavata, Scyliorhinus canicula
) were examined. All egg cases were scored for number of predation marks, the condition of the egg case and status of the hatching slit. The shape of the predation marks was classified into five types: parabolic, circular, elongated, scratched and irregular shaped and it was noted whether or not the boreholes were complete. Predation rate across species was 14.4%. Results show no discernible difference in proportion of egg cases with any kind of predation mark between species, which is beneficial for future analysis and conservation strategies, as the same approach can be used for all species. The presence of multiple incomplete predation marks on 38% of predated egg cases shows evidence of site selection by the predator. This site selection, as well as borehole shape and diameter found points to gastropods and octopus as potential predators.
Within-species sexual segregation is a widespread phenomenon among vertebrates, but its causes remain a topic of much debate. Female avoidance of male coercive mating attempts has the potential to ...influence the social structure of animal populations, yet it has been largely overlooked as a driver of sexual separation. Indeed, its potential role in long-term structuring of natural populations has not been studied. Here we use a comparative approach to examine the suitability of multiple hypotheses forwarded to account for sexual segregation (i.e., activity budget, predation risk, thermal niche-fecundity, and social factors) as drivers underlying sex-specific habitat use in a monomorphic model vertebrate, the small-spotted catshark,
Scyliorhinus canicula
. Using this hypothesis-driven approach, we show that year-round sexual habitat segregation in
S. canicula
can be accounted for directly by female avoidance of male sexual harassment. Long-term electronic tracking reveals that sperm-storing female catsharks form daytime refuging aggregations in shallow-water caves (∼3.2 m water depth) and undertake nocturnal foraging excursions into deeper water (∼25 m) on most nights. In contrast, males occupy deeper, cooler habitat (∼18 m) by day and exploit a range of depths nocturnally (1-23 m). Males frequent the locations of shallow-water female refuges, apparently intercepting females for mating when they emerge from, and return to, refuges on foraging excursions. Females partly compensate for higher metabolic costs incurred when refuging in warmer habitat by remaining inactive; however, egg production rates decline in the warmest months, but refuging behavior is not abandoned. Thermal choice experiments confirm that individual females are willing to "pay" in energy terms to avoid aggressive males and unsolicited male mating attempts. Long-term evasion of sexual harassment influences both the social structure and fecundity of the study population, with females trading off potential injury and unsolicited matings with longer-term fitness. This identifies sexual harassment as a persistent cost to females that can mediate vertebrate population dynamics.
PDF
