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Development and sexual dimorphism of the sonic system in three deep-sea neobythitine fishes and comparisons between upper mid and lower continental slope
No full textBased on morphology, NB Marshall identified cusk-eels (family Ophidiidae) as one of the chief sound-producing groups on the continental slope. Due to food scarcity, we hypothesized that sonic systems will be reduced at great depths despite their potential importance in sexual reproduction. We examined this hypothesis in the cusk-eel subfamily Neobythitinae by comparing sonic morphology in Atlantic species from the upper-mid (Dicrolene intronigra) and deeper continental slope (Porogadus miles and Bathyonus pectoralis) with three Taiwanese species previously described from the upper slope (Hoplobrotula armatus, Neobythites longipes and N. unimaculatus). In all six species, medial muscles are heavier in males than in females. Dicrolene has four pairs of sonic muscles similar to the shallow Pacific species, suggesting neobythitine sonic anatomy is conservative and sufficient food exists to maintain a well-developed system at depths exceeding 1 km. The sonic system in Porogadus and Bathyonus was reduced to a single pair of ventral medial muscles that connects to a smaller and thinner swimbladder via a long tendon. Small muscle fiber diameters, a likely indicator of rapid contraction, were present in males of five of the species. However, in Bathyonus, the deepest species (pale coloration, reduced eye size, shorter sonic muscles and longer tendons), muscle fibers were larger suggesting an adaptation to facilitate rapid bladder movement for sound production while using slower contractions and less metabolic energy. The six species separate into three groups in length-weight regressions: the three upper slope species have the greatest weights per unit length, Dicrolene is lower, and the two deep species are further reduced consistent with the hypothesis that food limitation affects sonic anatomy at great depths
The effects of salinity on growth and survival of mangrove seedlings changes with age
Get PDFSix wide-ranging mangrove species, Rhizophora apiculata, R. mucronata, Avicennia marina, A. officinalis, Bruguiera gymnorrhiza, and B. sexangula, were selected to study the growth and survival of seedlings under three contrasting salinity treatments over a 30-week period: low (3-5psu), moderate (15-17psu) and high (33-36psu). Seedlings grown under high salinity exhibited significantly lower performance (p<0.05) in survival rates, cumulative shoot height, mean growth rates, mean total leaf area, and mean dry weight, compared to those under low and moderate salinity regimes. The low salinity treatment provided the best conditions for initial establishment and growth of the seedlings of all species until 15-20 weeks of age. However, the same seedlings showed better performance under moderate salinity after 15-20 weeks of age (shift in optimal salinity), implying that adaptation to salt and physiological needs of mangrove seedlings varies with age. These results have practical implications of use in raising up mangrove nurse species for planting since it indicates that seedlings should get low salinity water until four to five months of age and then moderately saline water, in order to achieve maximum growth and survival
Evolution and estimated age of the C5 Lukala carbonate-evaporite ramp complex in the Lower Congo region (Democratic Republic of Congo): New perspectives in Central Africa
Get PDFNew detailed lithological, sedimentological, chemostratigraphic data were obtained from exploration drilling samples on the C5 carbonate-dominated formation of the Neoproterozoic Lukala Subgroup (former Schisto-Calcaire Subgroup) from the West Congo Belt (WCB) in the Democratic Republic of Congo. This formation records the last post-Marinoan sea-level events that occurred in the whole basin, followed by the development of the Araçuaï-West Congo Orogen between 630 and 560 Ma. The C5 Formation consists of back-reef lagoonal and peritidal/sabkha cycles of ∼2.0 m in thickness, that record a short-time marine regression, rapidly flooded by a marine transgression with deposition of organic-rich argillaceous carbonates or shales under dysoxia and anoxia conditions. These dysoxic/anoxic waters were rapidly followed by a regional-scale marine transgression, favouring mixing with well-oxygenated waters, and the development of benthic Tonian to Cambro-Ordovician Obruchevella parva-type ‘seagrasses’ in the nearshore zones of the lagoons. New δ13C and 87Sr/86Sr isotopic data in the C5 Formation of the Lukala Subgroup are used in the frame of a correlation with the Sete Lagoas Formation in Brazil. Relatively comparable negative to positive δ13C excursions point to marine flooding of the whole basin and allow extension of the debatable Late Ediacaran age of the uppermost Sete Lagoas and C5 formations. Sr isotope “blind dating” failed due to low Sr concentration related to a dolomitization event close 540 Ma. Several tentative datings of the C5 Formation converge to a Late Ediacaran age ranging between 575 and 540 Ma. As the overlying Mpioka folded Subgroup, the C5 series suffered the Pan African deformation, dated at 566 ± 42 Ma. Unlike the previously generally accepted interpretation, our data suggests that the Mpioka Subgroup was deposited in the Early Cambrian
Identifying marine biodiversity by DNA barcoding and DNA chips
Get PDFSpecies identification is a key problem throughout the life cycle of marine invertebrates and fishes: from eggs and larvae to adults in ecological research, but also more applied in fisheries research and control, as well as processed seafood products in consumer protection. The application of molecular genetic tools is a powerful method to assign specimens that cannot be identified by morphological character to certain species and also has the potential to be automated, allowing identifying species with highest precision and in large sample sizes. In DNA barcoding a fragment of the mitochondrial cytochrome oxidase subunit I (COI) gene is sequenced and compared with a reference database in order to identify the species. DNA microarrays use a different approach: the DNA of the specimen to be identified is not sequenced, but applied to a DNA chip and hybridises to species-specific probes, which is detected. This has the potential for a high-throughput technology that can analyse even mixed samples, such as plankton hauls or environmental DNA
Monitoring van kustbroedvogels in de SBZ-V ‘Kustbroedvogels te Zeebrugge-Heist’en de westelijke voorhaven van Zeebrugge tijdens het broedseizoen 2017
Get PDFThis report describes the fluctuations in the numbers of breeding pairs in the Special Protected Area under the Bird Directive ‘Kustbroedvogels te Zeebrugge‐Heist’ and in the adjacent western port of Zeebrugge during the period 1985‐2017. Until recently, this was by far the most important breeding site for coastal breeders in Belgium and of high importance for the European tern populations as a whole. The conservation targets that were set in 2004 (being 22 ha of suitable nesting habitat without significant impact by land predators) for terns breeding in the Special Protected Area were never met since.The populations of the 3 tern species (Sandwich, Common and Little Tern) and of Black‐headed Gulls breeding in the Special Protected Area have strongly declined after 2008 and the reproductive output was extremely poor. The decline is due to the presence of land predators, initially cats and rats, and from 2009 onwards also fox. The maximum number of breeding pairs amounted to 4,067, 3,052 and 425 for Sandwich, Common and Little Tern, respectively, but in 2016 these species no longer bred in the SPA. In 2017 fox was no longer present and the area again hosted 576 pairs of Common Tern, 21 pairs of Lesser Black‐backed Gull, 1 pair of Mediterranean Gull, 2 pairs of Kentish Plover , 12 pairs of Ringed Plover and 16 pairs of Oystercatcher. The SPA also attracted 114 pairs of Lesser Black‐backed and 44 pairs of Herring Gulls that were actively chased away in the nearby western part of the Zeebrugge port. Some of them developed into specialised predators of Common Tern leading to a reproductive output of only 0.1 fledged chick per pair.Also in the non‐protected western part of the Zeebrugge port, breeding numbers are in strong decline due to fox disturbance and predation, and loss of breeding grounds and deterioration of the habitat. Crested Lark, Northern Wheatear, Mediterranean Gull and Yellow‐legged Gull used to breed in small numbers, but these species were no longer present in 2016. This area used to host large numbers of Herring Gulls (max 2,433 pairs in 2010) and Lesser Black‐backed Gulls (max 4,760 pairs in 2011), but both species strongly decreased in numbers as fox frequented the breeding site after 2013. In 2017, 516 pairs of Herring Gull and 1.326 pairs of Lesser Black‐backed Gull bred in Zeebrugge, the majority (65.9%) on fox‐free rooftops. After 2013 the numbers of Herring and Lesser Black‐backed Gull have increased elsewhere in Flanders and especially along the coast the number of breeding sites is rapidly growing. This suggests that part of the Zeebrugge colony has moved to both new and existing breeding sites. Indeed, recoveries of colour‐ringed individuals revealed that there is a strong connection between Zeebrugge and other breeding sites along the Flemish coast. Other ringed gulls originating from Zeebrugge moved to existing colonies in the north of France, the south of the Netherlands and the south‐east of the UK
How different sterols contribute to saponin tolerant plasma membranes in sea cucumbers
Get PDFSea cucumbers produce saponins as a chemical defense mechanism, however their cells can tolerate the cytotoxic nature of these chemicals. To elucidate the molecular mechanisms behind this tolerance a suite of complementary biophysical tools was used, firstly using liposomes for in vitro techniques then using in silico approaches for a molecular-level insight. The holothuroid saponin Frondoside A, caused significantly less permeabilization in liposomes containing a Δ7 holothuroid sterol than those containing cholesterol and resulted in endothermic interactions versus exothermic interactions with cholesterol containing liposomes. Lipid phases simulations revealed that Frondoside A has an agglomerating effect on cholesterol domains, however, induced small irregular Δ7 sterol clusters. Our results suggest that the structural peculiarities of holothuroid sterols provide sea cucumbers with a mechanism to mitigate the sterol-agglomerating effect of saponins, and therefore to protect their cells from the cytotoxicity of the saponins they produce
Early Palaeozoic ocean anoxia and global warming driven by the evolution of shallow burrowing
Get PDFThe evolution of burrowing animals forms a defining event in the history of the Earth. It has been hypothesised that the expansion of seafloor burrowing during the Palaeozoic altered the biogeochemistry of the oceans and atmosphere. However, whilst potential impacts of bioturbation on the individual phosphorus, oxygen and sulphur cycles have been considered, combined effects have not been investigated, leading to major uncertainty over the timing and magnitude of the Earth system response to the evolution of bioturbation. Here we integrate the evolution of bioturbation into the COPSE model of global biogeochemical cycling, and compare quantitative model predictions to multiple geochemical proxies. Our results suggest that the advent of shallow burrowing in the early Cambrian contributed to a global low-oxygen state, which prevailed for ~100 million years. This impact of bioturbation on global biogeochemistry likely affected animal evolution through expanded ocean anoxia, high atmospheric CO2 levels and global warming
