Abstract
Various 3D imaging techniques are routinely used to examine biological materials, the results of which are usually a stack of grayscale images. In order to quantify structural aspects of the ...biological materials, however, they must first be extracted from the dataset in a process called segmentation. If the individual structures to be extracted are in contact or very close to each other, distance-based segmentation methods utilizing the Euclidean distance transform are commonly employed. Major disadvantages of the Euclidean distance transform, however, are its susceptibility to noise (very common in biological data), which often leads to incorrect segmentations (i.e., poor separation of objects of interest), and its limitation of being only effective for roundish objects. In the present work, we propose an alternative distance transform method, the random-walk distance transform, and demonstrate its effectiveness in high-throughput segmentation of three microCT datasets of biological tilings (i.e., structures composed of a large number of similar repeating units). In contrast to the Euclidean distance transform, the random-walk approach represents the global, rather than the local, geometric character of the objects to be segmented and, thus, is less susceptible to noise. In addition, it is directly applicable to structures with anisotropic shape characteristics. Using three case studies—tessellated cartilage from a stingray, the dermal endoskeleton of a starfish, and the prismatic layer of a bivalve mollusc shell—we provide a typical workflow for the segmentation of tiled structures, describe core image processing concepts that are underused in biological research, and show that for each study system, large amounts of biologically-relevant data can be rapidly segmented, visualized, and analyzed.
The mandibular apparatus of batoids (skates, electric rays, guitarfishes, stingrays, and sawfishes) is composed of a few skeletal elements to which the muscular bundles, responsible for all movements ...involved in the feeding mechanism, are inserted. The description of the different mandibular morphologies can help to understand the different feeding guilds in this group. In this study, we examined the cranio‐mandibular myology of adult Rostroraja velezi, Narcine entemedor, and Zapteryx exasperata, three species of rays that coexist in the Southern Gulf of California, Mexico. This study described the muscles on the ventral and the dorsal surfaces for each species, identified the origins and insertions of these muscles, as well as the general characteristics of muscle morphology. There were 17 and 18 muscle bundles attached to the feeding apparatus, including five on the dorsal surface. Only the levator rostri, which elevates the rostrum during feeding, showed considerable differences in shape and size among species. The muscles of the adductor complex showed the greatest differences in size among the three species. N. entemedor presented the exclusive muscle X in the lower mandibular area and the extreme reduction of the coracohyoideus in the pharyngeal area derived from the absence of the basihyal cartilage. The information generated in our study supports the morphological specialization of electric rays (N. entemedor) for an almost exclusive suction feeding strategy.
These species are nondurophagous rays and show a low variability in the number of mandibular muscles. The electric ray, N. entemedor, shows the greatest mandibular morphological variability, where the adductor complex is reduced and the muscles of the pharyngeal area are the largest, except for the coracohyoideus muscle, which is extremely reduced due to the absence of the basal cartilage. In addition, the presence of the depressor mandibularis muscle was described in all species.
The hydrodynamic performance of the locomotive near the water surface is impacted by its geometrical shape. For marine animals, their geometrical shape is naturally selective; thus, investigating ...gliding locomotion of marine animal under the water surface may be able to elucidate the influence of the geometrical shape. We investigate three marine animals with specific geometries: the killer whale is fusiform shaped; the manta ray is flat and broad-winged; and the swordfish is best streamlined. The numerical results are validated by the measured drag coefficients of the manta ray model in a towing tank. The friction drag of the three target models are very similar; the body shape affected form drag coefficient is order as swordfish < killer whale < manta ray; the induced wave breaking upon the body of the manta ray performs different to killer whale and swordfish. These bio-inspired observations provide a new and in-depth understanding of the shape effects on the hydrodynamic performances near the free surface.
Rays of the superorder Batoidea comprise the most diverse group of chondrichthyans in terms of valid species and morphological disparity. Up to the present little agreement is observed in studies ...based on morphological and molecular data focused on uncovering the interrelationships within Batoidea. Morphology-based phylogenies of batoids have not included characters related to the afferent branchial arteries, and little is known about the variation in this anatomical complex in rays. Herein, representatives of 32 genera from 19 families currently recognized of rays were examined as well as some shark taxa. Seven new characters are proposed and tested in two different analyses, one on their own and in the other they were added to the morphological data matrix of the most recent analysis of interrelationships within Batoidea. The arrangement of afferent branchial arteries differs mainly among orders and families of batoids. The absence of a common trunk from which the three posteriormost afferent arteries branch is interpreted as a synapomorphy for Myliobatiformes and the presence of a coronary cranial artery as an autapomorphy for Mobula hypostoma. A close spatial relationship between the second and third afferent arteries within the common branch from the ventral aorta is proposed as a synapomorphy for Rajiformes with a secondary modification in Sympterygia. Data about patterns in afferent branchial arteries in additional taxa such as Squaliformes and Chimaeriformes are needed to better understand the evolution of this character complex among chondrichthyans.
Batoids differ from other elasmobranch fishes in that they possess dorsoventrally flattened bodies with enlarged muscled pectoral fins. Most batoids also swim using either of two modes of locomotion: ...undulation or oscillation of the pectoral fins. In other elasmobranchs (e.g., sharks), the main locomotory muscle is located in the axial myotome; in contrast, the main locomotory muscle in batoids is found in the enlarged pectoral fins. The pectoral fin muscles of sharks have a simple structure, confined to the base of the fin; however, little to no data are available on the more complex musculature within the pectoral fins of batoids. Understanding the types of fibers and their arrangement within the pectoral fins may elucidate how batoid fishes are able to utilize such unique swimming modes. In the present study, histochemical methods including succinate dehydrogenase (SDH) and immunofluoresence were used to determine the different fiber types comprising these muscles in three batoid species: Atlantic stingray (Dasyatis sabina), ocellate river stingray (Potamotrygon motoro) and cownose ray (Rhinoptera bonasus). All three species had muscles comprised of two muscle fiber types (slow‐red and fast‐white). The undulatory species, D. sabina and P. motoro, had a larger proportion of fast‐white muscle fibers compared to the oscillatory species, R. bonasus. The muscle fiber sizes were similar between each species, though generally smaller compared to the axial musculature in other elasmobranch fishes. These results suggest that batoid locomotion can be distinguished using muscle fiber type proportions. Undulatory species are more benthic with fast‐white fibers allowing them to contract their muscles quickly, as a possible means of escape from potential predators. Oscillatory species are pelagic and are known to migrate long distances with muscles using slow‐red fibers to aid in sustained swimming.
Batoids differ from other species of fish in that they possess dorsoventrally flattened bodies with enlarged muscled pectoral fins. Unlike other species of elasmobranchs, the main locomotory muscle in batoids is found in the enlarged pectoral fins. The locomotory muscles of sharks have a simple structure that are confined to the base of the fin; however, little to no data are available on the more complex musculature within the pectoral fins of batoids. Using gross morphological, histochemical and immunohistochemical analyses, we demonstrate differences in muscle fiber measurements between multiple locations across the pectoral fins of three species of batoid fishes.
The rays of the order Myliobatiformes present several diagnostic characters, the most striking one being the presence of a serrated sting on the dorsal region of the tail. Although several ...morphological hypotheses have been proposed supporting the monophyly and interrelationships of its members, few characters of the appendicular skeleton were employed. In the present study, we analyzed comparatively the pelvic girdle morphology across all the groups of rays to investigate the distribution of the ischial process. To understand its significance, we tested this character of the pelvic girdle as a potential synapomorphy for the Myliobatiformes plus Zanobatus. Accordingly, the phylogenetic position of Zanobatus as a sister taxon to Myliobatiformes is reinforced and its pelvic girdle morphology reinterpreted in relation to previous morphological studies.
Ventral view of the pelvic girdle of Potamotrygon motoro exhibiting a highly developed ischial process (red arrowhead).
A new subfamily (Styracurinae, subfam. nov.) and genus (Styracura, gen. nov.) are erected for Trygon schmardae Werner, 1904 (type species) and Dasyatis pacificus Beebe & Tee-Van, 1941, species placed ...in Himantura Müller & Henle, 1837 since 1953 but which differ significantly from it and all dasyatid genera in many morphological features. Recent molecular phylogenetic hypotheses based on the entire protein-coding mitochondrial genome have recovered Styracura as the sister group of the Neotropical freshwater stingrays (Potamotrygonidae), agreeing with previous morphological and molecular phylogenies. The Styracurinae, subfam. nov., is therefore placed in the Potamotrygonidae to reflect the current phylogenetic view. Morphological characters of phylogenetic relevance of the dermal denticles, ventral lateral-line canals, hyoid arch, cranial musculature, and pectoral and pelvic girdles are discussed and compared to other stingrays, in particular to dasyatids and potamotrygonins (now ranked as a subfamily). Inferred derived characters of Styracura and potamotrygonins require homoplasy (they are absent from Paratrygon and Heliotrygon), and ventral lateral-line canal patterns and morphology of the scapular process and pelvic girdle generally reveal an affinity to different dasyatid genera, but one most likely based on plesiomorphies or independent evolution; Styracura is considered more closely related to potamotrygonins.
Most batoids have a unique swimming mode in which thrust is generated by either oscillating or undulating expanded pectoral fins that form a disc. Only one previous study of the freshwater stingray ...has quantified three-dimensional motions of the wing, and no comparable data are available for marine batoid species that may differ considerably in their mode of locomotion. Here, we investigate three-dimensional kinematics of the pectoral wing of the little skate,
, swimming steadily at two speeds 1 and 2 body lengths (BL) s
. We measured the motion of nine points in three dimensions during wing oscillation and determined that there are significant differences in movement amplitude among wing locations, as well as significant differences as speed increases in body angle, wing beat frequency and speed of the traveling wave on the wing. In addition, we analyzed differences in wing curvature with swimming speed. At 1 BL s
, the pectoral wing is convex in shape during the downstroke along the medio-lateral fin midline, but at 2 BL s
the pectoral fin at this location cups into the flow, indicating active curvature control and fin stiffening. Wing kinematics of the little skate differed considerably from previous work on the freshwater stingray, which does not show active cupping of the whole fin on the downstroke.
Durophagous predators consume hard‐shelled prey such as bivalves, gastropods, and large crustaceans, typically by crushing the mineralized exoskeleton. This is costly from the point of view of the ...bite forces involved, handling times, and the stresses inflicted on the predator's skeleton. It is not uncommon for durophagous taxa to display an ontogenetic shift from softer to harder prey items, implying that it is relatively difficult for smaller animals to consume shelled prey. Batoid fishes (rays, skates, sawfishes, and guitarfishes) have independently evolved durophagy multiple times, despite the challenges associated with crushing prey harder than their own cartilaginous skeleton. Potamotrygon leopoldi is a durophagous freshwater ray endemic to the Xingu River in Brazil, with a jaw morphology superficially similar to its distant durophagous marine relatives, eagle rays (e.g., Aetomylaeus, Aetobatus). We used second moment of area as a proxy for the ability to resist bending and analyzed the arrangement of the mineralized skeleton of the jaw of P. leopoldi over ontogeny using data from computed tomography (CT) scans. The jaws of P. leopoldi do not resist bending nearly as well as other durophagous elasmobranchs, and the jaws are stiffest nearest the joints rather than beneath the dentition. While second moment has similar material distribution over ontogeny, mineralization of the jaws under the teeth increases with age. Neonate rays have low jaw stiffness and poor mineralization, suggesting that P. leopoldi may not feed on hard‐shelled prey early in life. These differences in the shape, stiffness and mineralization of the jaws of P. leopoldi compared to its durophagous relatives show there are several solutions to the problem of crushing shelled prey with a compliant skeleton.
Changes to jaw stiffness over ontogeny suggest durophagous freshwater rays cannot consume shelled prey as juveniles. Contrary to other molluscivorous batoids, jaws are more robust and internally supported at the joints than under the teeth.
A large brain can offer several cognitive advantages. However, brain tissue has an especially high metabolic rate. Thus, evolving an enlarged brain requires either a decrease in other energetic ...requirements, or an increase in overall energy consumption. Previous studies have found conflicting evidence for these hypotheses, leaving the metabolic costs and constraints in the evolution of increased encephalization unclear. Mormyrid electric fishes have extreme encephalization comparable to that of primates. Here, we show that brain size varies widely among mormyrid species, and that there is little evidence for a trade-off with organ size, but instead a correlation between brain size and resting oxygen consumption rate. Additionally, we show that increased brain size correlates with decreased hypoxia tolerance. Our data thus provide a non-mammalian example of extreme encephalization that is accommodated by an increase in overall energy consumption. Previous studies have found energetic trade-offs with variation in brain size in taxa that have not experienced extreme encephalization comparable with that of primates and mormyrids. Therefore, we suggest that energetic trade-offs can only explain the evolution of moderate increases in brain size, and that the energetic requirements of extreme encephalization may necessitate increased overall energy investment.
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