The denticle surface of thresher shark tails: Three-dimensional structure and comparison to other pelagic species

Shark skin denticles (scales) are diverse in morphology both among species and across the body of single individuals, although the function of this diversity is poorly understood. The extremely elongate and highly flexible tail of thresher sharks provides an opportunity to characterize gradients in denticle surface characteristics along the length of the tail and assess correlations between denticle morphology and tail kinematics. We measured denticle morphology on the caudal fin of three mature and two embryo common thresher sharks (Alopias vulpinus), and we compared thresher tail denticles to those of eleven other shark species. Using surface profilometry, we quantified 3D-denticle patterning and texture along the tail of threshers (27 regions in adults, and 16 regions in embryos). We report that tails of thresher embryos have a membrane that covers the denticles and reduces surface roughness. In mature thresher tails, surfaces have an average roughness of 5.6 μm which is smoother than some other pelagic shark species, but similar in roughness to blacktip, porbeagle, and bonnethead shark tails. There is no gradient down the tail in roughness for the middle or trailing edge regions and hence no correlation with kinematic amplitude or inferred magnitude of flow separation along the tail during locomotion. Along the length of the tail there is a leading-to-trailing-edge gradient with larger leading edge denticles that lack ridges (average roughness = 9.6 μm), and smaller trailing edge denticles with 5 ridges (average roughness = 5.7 μm). Thresher shark tails have many missing denticles visible as gaps in the surface, and we present evidence that these denticles are being replaced by new denticles that emerge from the skin below.     

An Application of the Shark Skin Denticle Geometry for Windbreak Fence Design and Fabrication

Windbreak fences in open and urban areas can be used to effectively reduce the wind velocity.In this paper we examine how the geometrical shape of the windbreak fence can optimally mitigate wind velocity.We propose an approach for windbreak fence design based on a bionic parametric model of the shark skin denticle geometry,which improves the reduction of the wind velocity around and behind the windbreak fences.The generative model was used to estimate improvements by variations in the parameters of the fence panel's geometrical shape,inspired by shark skin denticles.The results of the Computational Fluid Dynamics (CFD) analysis indicates that the fence surface inspired by shark skin performs much better than both flat and corrugated surfaces.Taking into account the complex geometry of the surface inspired by shark skin denticles,we propose a fabrication process using an expanded polystyrene foam (EPS) material,created using an industrial robot ann with a hot-wire tool.Creating EPS moulds for the shark skin denticle panels allows for a richer variety material to be used in the final design,leading both to higher efficiency and a more attractive design.     

Diversity of dermal denticle structure in sharks: Skin surface roughness and three‐dimensional morphology

Shark skin is covered with numerous placoid scales or dermal denticles. While previous research has used scanning electron microscopy and histology to demonstrate that denticles vary both around the body of a shark and among species, no previous study has quantified three‐dimensional (3D) denticle structure and surface roughness to provide a quantitative analysis of skin surface texture. We quantified differences in denticle shape and size on the skin of three individual smooth dogfish sharks (Mustelus canis) using micro‐CT scanning, gel‐based surface profilometry, and histology. On each smooth dogfish, we imaged between 8 and 20 distinct areas on the body and fins, and obtained further comparative skin surface data from leopard, Atlantic sharpnose, shortfin mako, spiny dogfish, gulper, angel, and white sharks. We generated 3D images of individual denticles and measured denticle volume, surface area, and crown angle from the micro‐CT scans. Surface profilometry was used to quantify metrology variables such as roughness, skew, kurtosis, and the height and spacing of surface features. These measurements confirmed that denticles on different body areas of smooth dogfish varied widely in size, shape, and spacing. Denticles near the snout are smooth, paver‐like, and large relative to denticles on the body. Body denticles on smooth dogfish generally have between one and three distinct ridges, a diamond‐like surface shape, and a dorsoventral gradient in spacing and roughness. Ridges were spaced on average 56 µm apart, and had a mean height of 6.5 µm, comparable to denticles from shortfin mako sharks, and with narrower spacing and lower heights than other species measured. We observed considerable variation in denticle structure among regions on the pectoral, dorsal, and caudal fins, including a leading‐to‐trailing edge gradient in roughness for each region. Surface roughness in smooth dogfish varied around the body from 3 to 42 microns.     

Teeth outside the mouth: The evolution and development of shark denticles

Vertebrate skin appendages are incredibly diverse. This diversity, which includes structures such as scales, feathers, and hair, likely evolved from a shared anatomical placode, suggesting broad conservation of the early development of these organs. Some of the earliest known skin appendages are dentine and enamel-rich tooth-like structures, collectively known as odontodes. These appendages evolved over 450 million years ago. Elasmobranchs (sharks, skates, and rays) have retained these ancient skin appendages in the form of both dermal denticles (scales) and oral teeth. Despite our knowledge of denticle function in adult sharks, our understanding of their development and morphogenesis is less advanced. Even though denticles in sharks appear structurally similar to oral teeth, there has been limited data directly comparing the molecular development of these distinct elements. Here, we chart the development of denticles in the embryonic small-spotted catshark (Scyliorhinus canicula) and characterize the expression of conserved genes known to mediate dental development. We find that shark denticle development shares a vast gene expression signature with developing teeth. However, denticles have restricted regenerative potential, as they lack a sox2+ stem cell niche associated with the maintenance of a dental lamina, an essential requirement for continuous tooth replacement. We compare developing denticles to other skin appendages, including both sensory skin appendages and avian feathers. This reveals that denticles are not only tooth-like in structure, but that they also share an ancient developmental gene set that is likely common to all epidermal appendages.     

Biological characterization of the skin of shortfin mako shark Isurus oxyrinchus and preliminary study of the hydrodynamic behaviour through computational fluid dynamics

This study characterized the morphology, density and orientation of the dermal denticles along the body of a shortfin mako shark Isurus oxyrinchus and identified the hydrodynamic parameters of its body through a computational fluid‐dynamics model. The study showed a great variability in the morphology, size, shape, orientation and density of dermal denticles along the body of I. oxyrinchus. There was a significant higher density in dorsal and ventral areas of the body and their highest angular deviations were found in the lower part of the mouth and in the areas between the pre‐caudal pit and the second dorsal and pelvic fins. A detailed three‐dimensional geometry from a scanned body of a shark was carried out to evaluate the hydrodynamic properties such as drag coefficient, lift coefficient and superficial (skin) friction coefficient of the skin together with flow velocity field, according to different roughness coefficients simulating the effect of the dermal denticles. This preliminary approach contributed to detailed information of the denticle interactions. As the height of the denticles was increased, flow velocity and the effect of lift decreased whereas drag increased. The highest peaks of skin friction coefficient were observed around the pectoral fins.     

The influence of natural surface microtopographies on fouling

Multiple antifouling strategies of marine organisms may consist of combinations of physical, chemical and mechanical mechanisms. In this study, the role of surface microtopography (< 500 microns) of different marine organisms, such as Cancer pagurus, Mytilus edulis, Ophiura texturata and the eggcase of Scyliorhinus canicula, has been investigated as a possible component of their defence systems. High resolution resin replicates of these natural surface structures were exposed to natural fouling in field experiments. Abundances of recruits were determined and compared to those on untextured, but otherwise identical, control surfaces to quantify the influence of the different microtopographies on fouling rates. Antifouling effects of microtopographies varied with type of microtopography and coloniser species. The surface microtopography of C. pagurus significantly rejected macrofoulers. The surface structures of the eggcase and O. texturata had repellent effects on microfoulers. Barnacle settlement was temporarily reduced on surface microtopographies of M. edulis and the eggcase. These results emphasise the promising nontoxic antifouling properties of microtextured surfaces.     

Marine microbial natural products in antifouling coatings

Ecological problems associated with current antifouling technologies have increased interest in the natural strategies that marine organisms use to keep their surfaces clean and free from fouling. Bacteria isolated from living surfaces in the marine environment have been shown to produce chemicals that are potential antifoulants. Active compounds from the cells and culture supernatant of two bacterial strains, FS‐55 and NudMB50–11, isolated from surface of the seaweed, Fucus serratus, and the nudibranch, Archidoris pseudoargus, respectively, were extracted using solid phase extraction. The extracts were combined with acrylic base paint resin and assayed for antifouling activity by measuring their ability to inhibit the growth of fouling bacteria. These formulations were found to be active against fouling bacteria isolated from marine surfaces. The formulation of antifouling paints that incorporate marine microbial natural products is reported here for the first time. This is a significant advance towards the production of an environmentally friendly antifouling paint that utilises a sustainable supply of natural biodegradable compounds.     

Biomimetic characterisation of key surface parameters for the development of fouling resistant materials

Material science provides a direct route to developing a new generation of non-toxic, surface effect-based antifouling technologies with applications ranging from biomedical science to marine transport. The surface topography of materials directly affects fouling resistance and fouling removal, the two key mechanisms for antifouling technologies. However, the field is hindered by the lack of quantified surface characteristics to guide the development of new antifouling materials. Using a biomimetic approach, key surface parameters are defined and quantified and correlated with fouling resistance and fouling removal from the shells of marine molluscs. Laser scanning confocal microscopy was used to acquire images for quantitative surface characterisation using three-dimensional surface parameters, and field assays correlated these with fouling resistance and fouling release. Principle component analysis produced a major component (explaining 54% of total variation between shell surfaces) that correlated with fouling resistance. The five surface parameters positively correlated to increased fouling resistance were, in order of importance, low fractal dimension, high skewness of both the roughness and waviness profiles, higher values of isotropy and lower values of mean surface roughness. The second component (accounting for 20% of variation between shells) positively correlated to fouling release, for which higher values of mean waviness almost exclusively dictated this relationship. This study provides quantified surface parameters to guide the development of new materials with surface properties that confer fouling resistance and release.     

Biomimetic characterisation of key surface parameters for the development of fouling resistant materials

Material science provides a direct route to developing a new generation of non-toxic, surface effect-based antifouling technologies with applications ranging from biomedical science to marine transport. The surface topography of materials directly affects fouling resistance and fouling removal, the two key mechanisms for antifouling technologies. However, the field is hindered by the lack of quantified surface characteristics to guide the development of new antifouling materials. Using a biomimetic approach, key surface parameters are defined and quantified and correlated with fouling resistance and fouling removal from the shells of marine molluscs. Laser scanning confocal microscopy was used to acquire images for quantitative surface characterisation using three-dimensional surface parameters, and field assays correlated these with fouling resistance and fouling release. Principle component analysis produced a major component (explaining 54% of total variation between shell surfaces) that correlated with fouling resistance. The five surface parameters positively correlated to increased fouling resistance were, in order of importance, low fractal dimension, high skewness of both the roughness and waviness profiles, higher values of isotropy and lower values of mean surface roughness. The second component (accounting for 20% of variation between shells) positively correlated to fouling release, for which higher values of mean waviness almost exclusively dictated this relationship. This study provides quantified surface parameters to guide the development of new materials with surface properties that confer fouling resistance and release.     

The Influence of Natural Surface Microtopographies on Fouling

Multiple antifouling strategies of marine organisms may consist of combinations of physical, chemical and mechanical mechanisms. In this study, the role of surface microtopography (?<?500?μm) of different marine organisms, such as Cancer pagurus, Mytilus edulis, Ophiura texturata and the eggcase of Scyliorhinus canicula, has been investigated as a possible component of their defence systems. High resolution resin replicates of these natural surface structures were exposed to natural fouling in field experiments. Abundances of recruits were determined and compared to those on untextured, but otherwise identical, control surfaces to quantify the influence of the different microtopographies on fouling rates. Antifouling effects of microtopographies varied with type of microtopography and coloniser species. The surface microtopography of C. pagurus significantly rejected macrofoulers. The surface structures of the eggcase and O. texturata had repellent effects on microfoulers. Barnacle settlement was temporarily reduced on surface microtopographies of M. edulis and the eggcase. These results emphasise the promising non-toxic antifouling properties of microtextured surfaces.     

化学生态学在海洋污损生物防除中的应用

在海洋环境中,许多海洋生物都能产生对环境无危害的、具有防污活性的次生代谢产物以保护自身的洁净,利于自身的生存.用化学生态学的方法从海洋生物中提取天然防除物质成为近年来解决海洋污损生物问题的新思路,其目标是寻找高效无毒的防污材料取代原有的对海洋环境有严重危害的化学合成防污材料.虽然目前对提取生物的次生代谢产物的防污机理还所知甚少,但不少从海洋生物中获得的天然产物已显示出良好的防污活性.要解决污损生物防污问题,还需对天然产物的作用机制、生态学效应、天然产物与涂料的结合、控制和释放及野外实验进行更加深入的研究与探讨.     

Anomalies in the expression of abdominal denticle belts of partial larvae produced by fragmentation of theDrosophila melanogaster egg

Summary Abnormal denticle belt patterns can occasionally be observed in abdominal belts of partial larvae obtained from egg fragments. The abdominal belts have the following features in common: 1) The number of denticles of an abdominal denticle belt may increase, depending on the space occupied by a distinct segment or the whole body region. The arrangement of the denticles in such enlarged belts is less regular than in normal belts. 2) Enlarged denticle belts are also found in the terminal segment of a fragment, or in the segment next to it when the larval pattern is interrupted by fragmentation. The denticle belt in the adjacent segment(s) may then be supressed. 3) All denticles in a belt (or part of a belt) are orientated posteriorly if the distance to the posteriorly adjacent belt (or part of a belt) is larger than normal, or if this denticle belt is suppressed. Conditions anterior to a segment do not seem to exert any influence on denticle orientation.     

Phylogenetic relationship and antifouling activity of bacterial epiphytes from the marine alga Ulva lactuca

It is widely accepted that bacterial epiphytes can inhibit the colonization of surfaces by common fouling organisms. However, little information is available regarding the diversity and properties of these antifouling bacteria. This study assessed the antifouling traits of five epiphytes of the common green alga, Ulva lactuca . All isolates were capable of preventing the settlement of invertebrate larvae and germination of algal spores. Three of the isolates also inhibited the growth of a variety of bacteria and fungi. Their phylogenetic positions were determined by 16S ribosomal subunit DNA sequencing. All isolates showed a close affiliation with the genus Pseudoalteromonas and, in particular, with the species P. tunicata . Strains of this bacterial species also display a variety of antifouling activities, suggesting that antifouling ability may be an important trait for members of this genus to be highly successful colonizers of animate surfaces and for such species to protect their host against fouling.     

Origin and evolution of gnathostome dentitions: a question of teeth and pharyngeal denticles in placoderms

The fossil group Placodermi is the most phylogenetically basal of the clade of jawed vertebrates but lacks a marginal dentition comparable to that of the dentate Chondrichthyes, Acanthodii and Osteichthyes (crown-group Gnathostomata). The teeth of crown-group gnathostomes are part of an ordered dentition replaced from, and patterned by, a dental lamina, exemplified by the elasmobranch model. A dentition recognised by these criteria has been previously judged absent in placoderms, based on structural evidence such as absence of tooth whorls and typical vertebrate dentine. However, evidence for regulated tooth addition in a precise spatiotemporal order can be observed in placoderms, but significantly, only within the group Arthrodira. In these fossils, as in other jawed vertebrates with statodont, non-replacing dentitions, new teeth are added at the ends of rows below the bite, but in line with biting edges of the dentition. The pattern is different on each gnathal bone and probably arises from single odontogenic primordia on each, but tooth rows are arranged in a distinctive placoderm pattern. New teeth are made of regular dentine comparable to that of crown-gnathostomes, formed from a pulp cavity. This differs from semidentine previously described for placoderm gnathalia, a type present in the external dermal tubercles. The Arthrodira is a derived taxon within the Placodermi, hence origin of teeth in placoderms occurs late in the phylogeny and teeth are convergently derived, relative to those of other jawed vertebrates. More basal placoderm taxa adopted other strategies for providing biting surfaces and these vary substantially, but include addition of denticles to the growing gnathal plates, at the margins of pre-existing denticle patches. These alternative strategies and apparent absence of regular dentine have led to previous interpretations that teeth were entirely absent from the placoderm dentition. A consensus view emerged that a dentition, as developed within a dental lamina, is a synapomorphy characterising the clade of crown-group gnathostomes. Recent comparisons between sets of denticle whorls in the pharyngeal region of the jawless fish Loganellia scotica (Thelodonti) and those in sharks suggest homology of these denticle sets on gill arches. Although the placoderm pharyngeal region appears to lack denticles (placoderm gill arches are poorly known), the posterior wall of the pharyngeal cavity, formed by a bony flange termed the postbranchial lamina, is covered in rows of patterned denticle arrays. These arrays differ significantly, both in morphology and arrangement, from those of the denticles located externally on the head and trunkshield plates. Denticles in these arrays are homologous to denticles associated with the gill arches in other crown-gnathostomes, with pattern similarities for order and position of pharyngeal denticles. From their location in the pharynx these are inferred to be under the influence of a cell lineage from endoderm, rather than ectoderm. Tooth sets and tooth whorls in crown-group gnathostomes are suggested to derive from the pharyngeal denticle whorls, at least in sharks, with the patterning mechanisms co-opted to the oral cavity. A comparable co-option is suggested for the Placodermi.     

Sexual Dimorphisms in the Dermal Denticles of the Lesser-Spotted Catshark,Scyliorhinus canicula (Linnaeus, 1758)

The dermal layers of several elasmobranch species have been shown to be sexually dimorphic. Generally, when this occurs the females have thicker dermal layers compared to those of males. This sexual dimorphism has been suggested to occur as a response to male biting during mating. Although male biting as a copulatory behaviour in Scyliorhinus canicula has been widely speculated to occur, only relatively recently has this behaviour been observed. Male S. canicula use their mouths to bite the female’s pectoral and caudal fins as part of their pre-copulatory behaviour and to grasp females during copulation. Previous work has shown that female S. canicula have a thicker epidermis compared to that of males. The structure of the dermal denticles in females may also differ from that of males in order to protect against male biting or to provide a greater degree of friction in order to allow the male more purchase. This study reveals that the length, width and density of the dermal denticles of mature male and female S. canicula are sexually dimorphic across the integument in areas where males have been observed to bite and wrap themselves around females (pectoral fin, area posterior to the pectoral fin, caudal fin, and pelvic girdle). No significant differences in the dermal denticle dimensions were found in other body areas examined (head, dorsal skin and caudal peduncle). Sexually dimorphic dermal denticles in mature S. canicula could be a response to male biting/wrapping as part of the copulatory process.     

Cell shape and epithelial patterning in the Drosophila embryonic epidermis

The development of denticle rows on the ventral Drosophila embryo is a valuable system for studying the genetic control of epithelial patterning. During late embryogenesis, the apical surfaces of denticle-producing cells acquire a distinctive rectangular morphology with long anteroposterior boundaries, along which the denticles form, and short ventrolateral boundaries that stain strongly for adherens junction proteins. We observe that ventrolateral denticle cell boundaries are also convoluted, suggesting that the strong adherens staining results, at least in part, from the additional membrane in these regions. Embryos mutant for the Planar Cell Polarity (PCP) Effector gene multiple wing hairs (mwh), or expressing dominant negative form of the small GTPase Rac1, have cells present between the normal denticle cell rows. These 'Interloper Cells' do not have convoluted ventrolateral boundaries with strong adherens protein staining, but have normal denticle placement, suggesting that adherens protein localization is not critical for denticle cell PCP. Based on these and other observations, we propose that denticle cell morphology arises from an epithelial stretch without junction remodeling. A crude mechanical model suggests that this mechanism can generate both the straight anteroposterior boundaries and the compacted ventrolateral boundaries typical of denticle cells. We discuss the significance of cell adhesion for denticle cell morphogenesis, especially given the established role for Rac1 in cell adhesion.     

Vertebrate dentitions at the origin of jaws: when and how pattern evolved

New evidence shows that teeth evolved with a greater degree of independence from jaws than previously considered. Pharyngeal denticles occur in jawless fish and also in early gnathostomes and precede jaw teeth in phylogeny. Many of these denticles form joined polarized sets on each branchial arch; these resemble whorl-shaped tooth sets on the jaws of stem and crown gnathostomes and are proposed as homologous units. Therefore, the source of patterning of these pharyngeal denticle and tooth sets is conserved from jawless conditions. It is proposed that developmental regulatory systems, responsible for all such tooth patterns on the jaws, are co-opted from the pharyngeal region and not from the skin as classically understood. This strongly implicates embryonic endoderm as opposed to ectoderm in the genetic control of dentition patterning. New interpretations of ontogenetic data on patterning dentitions of extant sharks are proposed, together with those of osteichthyan fish. Two entirely fossil groups, placoderms and acanthodians, at the base of gnathostome phylogeny are reassessed on the basis of a new model. It is concluded that within stem group and crown group gnathostomes several different strategies, unique to each taxon, were adopted to produce different developmental models of dentition patterning from pharyngeal denticles. One shared developmental pattern is that of initiation from primordial tooth sites, independently in each dentate zone of the jaws. The new model is proposed as a framework for data on evolutionary developmental genetics.     

天然产物防除海洋污损生物的研究进展

天然防污剂是当前海洋污损生物防除的研究热点,本文综述了天然防污剂的种类和来源,以及天然防污剂的防除机理,并着重叙述了天然防污涂料配制时应关注的问题。     

Scanning electron microscopy of the lip denticiles of Ascaris suum adults of known ages.

Purebred Hampshire pigs, farrowed and maintained under conditions precluding extraneous helminth infection, were exposed to a single dose of 10,000 Ascaris suum infective eggs. The pigs were killed at intervals of 28, 41, 55, 86, 115, 145, 175, and 206 days after infection. At necropsy, no gross lesions were found in the lungs or livers of infected pigs. The worms were recovered from the small intestine, identified, counted, and fixed. The heads were excised, critical point dried, mounted en face, and examined by scanning electron microscopy. Worms 28 to 115 days old had unworn denticles that were triangular when viewed laterally but blunt when viewed tangentially. Wearing of the denticles was observed first with 145-day-old worms; wearing increased with age both in numbers of denticles affected and in degree of wear so that by 206 days after inoculation, almost all denticles in the center of the lip were worn. Worn denticles appear truncated when viewed from any angle. The denticles outside the central area were not affected by wear. The size of the denticles varies not only between specimens of the same age, but also on each specimen. However, average denticle size is directly related to the size and, accordingly, to the age of the worm. External to each denticle is a corresponding depression that we have called the denticular groove. One 28-day-old specimen had some extra denticles aligned irregularly along the lip; this irregularity gave the appearance of a double row. The denticles of the two subventral lips are similar to those of the dorsal and are equally affected by wear. There was no detectable difference in denticles of male and female worms. Since wear can now be specifically correlated with age, we conclude that the denticles are functional and become worn through use. Consequently, adult A. suum may be an even more injurious pathogen than heretofore supposed.     

Observations on the mechanisms of attachment of some marine fouling blue-green algae

Using scanning electron microscopy (SEM), differential interference contrast microscopy (DICM) and cytochemical staining techniques, preliminary observations have been made on the mechanisms of attachment of some common, marine, benthic fouling blue-green algae ("cyanobacteria") isolated into culture from various toxic and non-toxic surfaces in Langstone Harbour, south coast of England. Blue-green algae investigated included species of Calothrix, Dermocarpa, Plectonema, Phormidium and Xenococcus. The blue-green algae are rapid colonisers and can make an important contribution to the pioneering communities on both toxic and non-toxic surfaces. A characteristic feature of the colonization process is the production of variable quantities of extracellular polymeric substances (EPS) which appear to function as adhesives. Cytochemical staining revealed the EPS to be an acidic polysaccharide and, therefore, chemically similar to the EPS produced by sessile diatoms. It is suggested that the EPS additionally assists in cell motility, acts as an antidesiccant and may influence the fouling process by combining with antifouling paint toxins and modifying the surface energy of substrata.