Development of zebrafish (Danio rerio) pectoral fin musculature

During posthatching development the fins of fishes undergo striking changes in both structure and function. In this article we examine the development of the pectoral fins from larval through adult life history stages in the zebrafish (Danio rerio), describing in detail their pectoral muscle morphology. We explore the development of muscle structure as a way to interpret the fins' role in locomotion. Genetic approaches in the zebrafish model are providing new tools for examining fin development and we take advantage of transgenic lines in which fluorescent protein is expressed in specific tissues to perform detailed three-dimensional, in vivo fin imaging. The fin musculature of larval zebrafish is organized into two thin sheets of fibers, an abductor and adductor, one on each side of an endoskeletal disk. Through the juvenile stage the number of muscle fibers increases and muscle sheets cleave into distinct muscle subdivisions as fibers orient to the developing fin skeleton. By the end of the juvenile period the pectoral girdle and fin muscles have reoriented to take on the adult organization. We find that this change in morphology is associated with a switch of fin function from activity during axial locomotion in larvae to use in swim initiation and maneuvering in adults. The examination of pectoral fins of the zebrafish highlights the yet to be explored diversity of fin structure and function in subadult developmental stages. J. Morphol. (c) 2005 Wiley-Liss, Inc.     

Sipunculid‐like ocellar tubes in a polychaete,Fauveliopsis cf. adriatica (Annelida,Fauveliopsidae): implications for eye evolution

Abstract. A retractable head region somewhat resembling the introvert of sipunculans is a characteristic feature of members of the annelid taxon Fauveliopsidae. The morphology of fauvelopsids is not well known, and additional data might help to resolve their relationships with other annelids and sipunculans. Ultrastructural investigations of the anterior end of adults of Fauveliopsis cf. adriatica revealed peculiar brain and sensory structures. From the neuropil of the brain, two pairs of lobes mainly composed of neuronal somata extend posteriorly into the peristomium and the following segment. The nuchal organs are embedded in the median pair of lobes, as are additional photoreceptor‐like sensory structures, the ocellar tubes, which are found at the bases of epidermal follicles that extend deeply into the brain. The retractor muscles of the prostomium are attached to the apices of these follicles, which are lined by tendon and supportive cells. The lumen of each follicle is completely filled with cuticular material that forms a rod. Monociliary sensory cells are present all along the length of each follicle; their cilia extend into the cuticle, and are oriented parallel to the longitudinal axis of the tube. Basally, each follicle forms an ovoid extension that is devoid of cuticular material and densely filled with numerous sensory processes—microvilli and cilia—of bipolar sensory cells. The terminal end of the 40‐μm‐deep follicle is formed by two conspicuous cells that contain numerous densely packed vesicles that resemble pigment granules. The ocellar tubes of fauveliopsids are strikingly similar to the ocular tubes of sipunculids. These similarities may reflect common ancestry or may represent convergent evolution; both alternatives are partially supported by previous morphological and molecular studies.     

Getting to the root of fireworms' stinging chaetae—chaetal arrangement and ultrastructure of Eurythoe complanata (Pallas, 1766) (Amphinomida)

Amphinomid species are since long known to cause urtication upon contact with the human skin. Since it has been reported that amphinomid chaetae are hollow, it has repeatedly been suggested that poison is injected upon epidermal contact. To test predictions for the structural correlate of such a stinging device we studied the structure and formation of chaetae in the fireworm Eurythoe complanata (Amphinomida). Neither the structure of the chaetae nor their formation and their position within the parapodium provide evidence for their function as hollow needles to inject poison. The chaetae even turned out to be not hollow, but containing calcareous depositions. The latter most likely cause artificial ruptures of delicate chitin lamellae in the inner of the chaeta when treated with acidic fixatives. Inorganic calcium compounds harden the chaetae and make them brittle so that they break easily. Additional information on the structure of the chaetal sac, the site of formation and the acicula do not contradict the position of the Amphinomida within Annelida as revealed by phylogenomic studies.     

Sexual differences in locomotor performance in Tropidurus catalanensis lizards (Squamata: Tropiduridae) – body shape,size and limb musculature explain variation between males and females

Sexual dimorphism (SD) is the evolutionary outcome of selection acting differently on males and females. Several studies describe sexual differences in body size, although other morphological traits might be allometric between sexes and imply functional consequences. Here we test whether morphological differences between sexes in size and shape in the lizard Tropidurus catalanensis explain variation in performance of four locomotor traits. Our results show that males are larger than females and also exhibit longer limbs, longer muscles and larger muscle cross‐sectional areas, while females have longer trunks and more sharped anterior claws; males outperform females in all locomotor performances measured. Sexual differences in sprinting and climbing is related with body size, and climbing performance is also explained by limb lengths, by differences in lengths and cross‐sectional areas of specific muscles, and by interlimb distances. Between‐sex differences in exertion are also related to SD, despite associations with sharper posterior claws that are independent of sex. Grasping performance, however, is associated with some muscle and morphological parameters that are not sexually dimorphic. Together our results suggest that morphology might be under sexual selection in T. catalanensis, given that better locomotor performance likely favours male lizards in typical activities of this polygenic species, such as territory defence and female acquisition. Moreover, the longer trunks that characterize females may confer more space to accommodate eggs. On the other hand, territory defence by males probably increases their exposure to predators, resulting in a synergistic effect of sexual and natural selection in the evolution of SD in T. catalanensis.     

Anterior regeneration in the polychaete Marenzelleria viridis (Annelida: Spionidae)

The objective of this study was to examine the regeneration capacity of the spionid polychaete Marenzelleria viridis from Long Island, New York. In the field, ~7% of the worms exhibited regeneration of the anterior end. In the laboratory, worms were ablated at the 10th–50th chaetiger and their regeneration documented. Anterior morphogenesis was similar to that previously reported for spionids, with wound healing, blastema formation, differentiation of segments, and formation of feeding and sensory structures (mouth, palps, nuchal organs) occurring within 14 d. Unlike in some spionids, the segments do not appear to all form simultaneously from the blastema; rather, external differentiation of segments was observed from posterior to anterior on the regenerate. The number of segments replaced was equal to the number ablated for up to 10 segments. A maximum of 17 segments were replaced when 20–30 chaetigers were ablated, and the number replaced decreased to 14 when 40–50 chaetigers were ablated. Survival and normal growth of the worms decreased with more chaetigers ablated; a significantly higher number of worms died or grew abnormally with ≥30 chaetigers ablated, compared to worms with ≤20 chaetigers ablated. Members of M. viridis could be valuable model organisms in the study of the cellular mechanisms involved in regeneration, and further research on regeneration in the field should be completed.     

Push and bite: trade‐offs between burrowing and biting in a burrowing skink (Acontias percivali)

Trade‐offs are thought to be important in constraining evolutionary divergence, as they may limit phenotypic diversification. Limbless animals that burrow head‐first have been suggested to be evolutionarily constrained in the development of a large head size and sexual head shape dimorphism because of potential trade‐offs associated with burrowing. Here we use an acontiine skink (Acontias percivali) to test for the existence of trade‐offs between traits thought to be important in burrowing (speed and force). As head size dimorphism has been shown to be limited in acontiine lizards, thus suggesting constraints on head size and shape, we additionally explore the potential for trade‐offs between burrowing and biting. Our data show that A. percivali uses a burrowing style different from those previously described for caecilians and amphisbaenians, which relies on the use of extensive lateral and dorsoventral head movements. Our data also show that animals use their entire bodies to generate force, as peak force was determined by total length only. Additionally, both bite force and the time needed to burrow into the substrate were principally determined by relative head width, suggesting a trade‐off between biting and burrow speed. Performance data were indeed suggestive of a correlation between bite force and the time needed to burrow, but additional data are needed to confirm this pattern. In summary, our data suggests that trade‐offs may exist, and may have been of crucial importance in shaping the evolution of head shape in A. percivali, and burrowing lizards more generally. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 102 , 91–99.     

Lateral organs in sedentary polychaetes (Annelida) – Ultrastructure and phylogenetic significance of an insufficiently known sense organ

Lateral organs are sense organs visible as densely ciliated pits or papillae between the noto‐ and the neuropodia in certain taxa of sedentary polychaetes. Ultrastructural studies in about 10 species of the following taxa Maldanidae, Opheliidae, Orbiniidae, Paraonidae, Magelonidae, Spionidae, Poecilochaetidae and Terebellidae have been designed to evaluate whether these organs are homologous among polychaetes. In spite of great external diversity, the investigations revealed an overall ultrastructural similarity. Differences between species investigated mainly concern the size of the organs as well as the number and arrangement of cells. The organs comprise supportive cells and uniciliated penetrative sensory cells. Their dendrites are closely arranged and thus their cilia may resemble multiciliated cells. There are two types of sensory cells: one type possesses no or mainly thin microvilli of which usually only a few reach the cuticular surface, and in the other type the cilium is consistently surrounded by 10 strong microvilli, which form a pore‐like opening in the cuticle. Further differences occur in the structure of the rootlet system. Basally, a retractor muscle attaches to the organ. The systematic significance of these organs within Annelida is discussed with respect to the conflicting phylogenetic hypotheses explaining the relationships of annelid taxa.     

Unveiling biases in soft‐tissue phosphatization: extensive preservation of musculature in the Cretaceous (Cenomanian) polychaete Rollinschaeta myoplena (Annelida: Amphinomidae)

The process of soft‐tissue phosphatization (the replication of labile tissues by calcium phosphate) is responsible for many instances of high‐resolution soft tissue preservation, often revealing anatomical insights into the animals that so preserved. However, while much work has gone into exploring key issues such as biases and micro‐controls, phosphatization remains poorly understood as a taphonomic process. Here, using camera lucida, plain‐light microscopy and SEM imagery, we address this issue by describing the taphonomy and fidelity of the musculature of Rollinschaeta myoplena Parry et al., a phosphatized annelid from the Cretaceous Konservat‐Lagerstätten of Hakel and Hjoula, Lebanon, with an unprecedented quantity of three‐dimensional soft‐tissue preservation. Analysis highlights two strong, previously recognized biases affecting the process of phosphatization: (1) a taxonomic bias restricted to R. myoplena that triggers unusually extensive phosphatization; and (2) a tissue bias whereby longitudinal and parapodial musculature show markedly higher fidelity in comparison to the musculature of the intestine and body wall circular muscles. Potential explanations for these biases include internal phosphate‐enrichment by relative muscle density, the relative rate of decay and the physiology of musculature. Incongruence between experimental decay series for polychaetes and the prevalence of labile tissue preservation over recalcitrant tissues in R. myoplena exposes the limits of decay experiments for understanding exceptional preservation.     

Development and embryonic pattern of body wall musculature in the crassiclitellate Eisenia andrei (Annelida,Clitellata)

During early development of Eisenia andrei (Crassiclitellata), a loose arrangement of primary circular and longitudinal muscles encloses the whole embryo. Circular muscles differentiate in an anterior–posterior progression creating a segmental pattern. Primary circular muscles emerge at the segmental borders while later in development the central part of each segment is filled with circular strands. Longitudinal muscles develop in an anterio‐posterior manner as well, but by continuous lengthening. Muscle growth is not restricted by segmental boundaries. The development begins with one pair of prominent longitudinal muscles differentiating ventrally along the right and the left germ band. These first muscles provide a guiding structure for the parallel organization of the afterwards differentiating longitudinal musculature. Additional primary longitudinal muscles emerge and form, together with the initial circular muscles, the primary muscle grid of the embryo. During the following development, secondary longitudinal muscle strands develop and integrate themselves into the primary grid. Meanwhile the primary circular muscles split into thin strands in a ventral to dorsal progression. Thus, a fine structured mesh of circular and longitudinal muscles is generated. Compared to other “Oligochaeta”, embryonic muscle patterns in E. andrei are adapted to the development of a lecithotrophic embryo. Nevertheless, two general characteristics of annelid muscle development become evident. The first is the segmental development of the circular muscles from a set of initial muscles situated at the segment borders. Second, there is a continuous development of primary longitudinal muscles starting at the anterior pole. At least one pair of main primary longitudinal strands is characteristic in Annelida. The space between all primary strands is filled with secondary longitudinal strands during further development. J. Morphol. 2009. © 2009 Wiley‐Liss, Inc.     

Adaptive features of protoceratopoids (Ornithischia: Neoceratopsia)

The analysis of some morphological characteristics of protoceratopoid skeletons, the extent of mobility of the vertebral column, and the probable adaptive significance of these features suggest that Bagaceratops had a mostly aquatic mode of life, Protoceratops was semiaquatic, Udanoceratops was facultatively aquatic, and Leptoceratops was predominantly terrestrial. Protoceratopoids were quadrupeds, with the prevalence of hind limbs, probably using slow or rapid trotlike gait. An asymmetrical locomotion was most likely impossible. On dry land, Bagaceratops and Protoceratops moved slowly. Udanoceratops and Leptoceratops approximately equally used rapid and slow locomotor modes, although the second could run for a longer time than the first.     

The trackmaker of Apatopus (Late Triassic, North America): implications for the evolution of archosaur stance and gait

Abstract:  For some decades, a major focus of research has been on how locomotor modes changed in some archosaurian reptiles from a more or less 'sprawling' to an 'erect' posture, whether there were discrete intermediate stages, and how many times 'erect' posture evolved. The classic paradigm for the evolution of stance and gait in archosaurs, a three-stage transition from sprawling to 'semi-erect' to erect posture, has been replaced by a subtler understanding of a continuum of changing limb joint angles. We suggest a further separation of terminology related to stance vs. gait so as not to entail different processes: 'sprawling' and 'erect' should refer to continua of stance; 'rotatory' and 'parasagittal' are more appropriate ends of a continuum that describes the motions of gait. We show that the Triassic trackway Apatopus best fits the anatomy and proportions of phytosaurs, based on a new reconstruction of their foot skeleton; it is less likely to have been made by another pseudosuchian or non-archosaurian archosauromorph. Moreover, the trackmaker was performing the high walk. A phytosaurian trackmaker would imply that the common ancestor of pseudosuchians, and therefore archosaurs could approximate the high walk (depending on phylogeny), and if so, erect stance and parasagittal gait did not evolve independently in pseudosuchians and ornithosuchians, although the kinematic mechanisms differed in the two groups. It remains to be seen how far outside Archosauria, if at all, more or less erect posture and parasagittal gait may have evolved.     

Pelvic and hindlimb musculature of Tyrannosaurus rex (Dinosauria: Theropoda)

In this article, we develop a new reconstruction of the pelvic and hindlimb muscles of the large theropod dinosaur Tyrannosaurus rex. Our new reconstruction relies primarily on direct examination of both extant and fossil turtles, lepidosaurs, and archosaurs. These observations are placed into a phylogenetic context and data from extant taxa are used to constrain inferences concerning the soft-tissue structures in T. rex. Using this extant phylogenetic bracket, we are able to offer well-supported inferences concerning most of the hindlimb musculature in this taxon. We also refrain from making any inferences for certain muscles where the resulting optimizations are ambiguous. This reconstruction differs from several previous attempts and we evaluate these discrepancies. In addition to providing a new and more detailed understanding of the hindlimb morphology of T. rex--the largest known terrestrial biped--this reconstruction also helps to clarify the sequence of character-state change along the line to extant birds.     

我国3种姬蛙Microhyla骨骼系统的比较研究(Amphibian:Microhylidae)

对分布于我国的3种姬蛙:饰纹姬蛙Microhyla ornata、粗皮姬蛙M. butleri和小弧斑姬蛙M. heymonsi的骨骼系统进行了比较研究.研究发现这3种蛙的第8椎体皆为双凹型,属参差型椎体;左、右上喙软骨在中线处愈合,属典型的固胸型肩带;3种姬蛙的前喙骨、锁骨以及前胸骨都不同程度地退化甚至缺失;后胸骨保留较为完整,并且3种姬蛙的后胸骨有较为明显的差异.对姬蛙科中相关的成员进行了简单比较.     

Evolutionary patterns of shape and functional diversification in the skull and jaw musculature of triggerfishes (Teleostei: Balistidae)

The robust skull and highly subdivided adductor mandibulae muscles of triggerfishes provide an excellent system within which to analyze the evolutionary processes underlying phenotypic diversification. We surveyed the anatomical diversity of balistid jaws using Procrustes‐based geometric morphometric analyses and a phylomorphospace approach to quantifying morphological transformation through evolution. We hypothesized that metrics of interspecific cranial shape would reveal patterns of phylogenetic diversification that are congruent with functional and ecological transformation. Morphological landmarks outlining skull and adductor mandibulae muscle shape were collected from 27 triggerfish species. Procrustes‐transformed skull shape configurations revealed significant phylogenetic and size‐influenced structure. Phylomorphospace plots of cranial shape diversity reveal groupings of shape between different species of triggerfish that are mostly consistent with phylogenetic relatedness. Repeated instances of convergence upon similar cranial shape by genetically disparate taxa are likely due to the functional demands of shared specialized dietary habits. This study shows that the diversification of triggerfish skulls occurs via modifications of cranial silhouette and the positioning of subdivided jaw adductor muscles. Using the morphometric data collected here as input to a biomechanical model of triggerfish jaw function, we find that subdivided jaw adductors, in conjunction with a unique cranial skeleton, have direct biomechanical consequences that are not always congruent with phylomorphospace patterns in the triggerfish lineage. The integration of geometric morphometrics with biomechanical modeling in a phylogenetic context provides novel insight into the evolutionary patterns and ecological role of muscle subdivisions in triggerfishes. J. Morphol. 277:737–752, 2016. © 2016 Wiley Periodicals, Inc.     

Morphological specializations in heterocongrinae (Anguilliformes: Congridae) related to burrowing and feeding

The remarkable lifestyle of heterocongrines has drawn the attention of many authors in the past, though no or little attention has been paid to the morphology of the tail and the head of these species. In order to examine the true nature of possible morphological specializations of the head and tail and their relation to their tail-first burrowing habit and/or feeding mode, a detailed myological and osteological study of Heteroconger hassi and Heteroconger longissimus was performed. The osteological similarities of the cranial skeleton between H. hassi and H. longissimus are striking. Most of the cranial muscles show no variation in presence, insertion or origin between these two species except for the adductor mandibulae complex, the adductor hyomandibulae and the intermandibularis. The adductor mandibulae complex is small, compared to that of other anguilliform species, and is probably related to their suction-dominated feeding mode and a diet, comprising mainly small, soft prey items. Heterocongrinae have undergone several morphological specializations in the tail for their tail-first burrowing lifestyle. The skeleton and musculature of the tail of H. hassi and H. longissimus are similar. In both species the caudal skeleton is highly reduced and fortified, forming a firm, pointed burrowing tool. Intrinsic caudal musculature is reduced and some muscles (interradials, supracarinalis) are even absent.     

An integrative phylogenetic and extrapolatory approach to the reconstruction of dromaeosaur (Theropoda: Eumaniraptora) shoulder musculature

Dromaeosauridae is the sister taxon of the Avialae; thus, an investigation of dromaeosaur shoulder girdle musculature and forelimb function provides substantial information regarding changes in the size and performance of the theropod shoulder girdle musculature leading to avian powered flight. Twenty-two shoulder girdle muscles were reconstructed for the dromaeosaurid shoulder apparatus, based on phylogenetic inference, which involves the comparison of lepidosaurian, crocodilian and avian musculature, and extrapolatory inference, which involves a secondary comparison with functional analogues of theropods. In addition to these comparative methodologies, osteological correlates of shoulder musculature preserved in eumaniraptorans are identified, and comparisons with those of extant archosaurs allow these muscles to be definitively inferred in dromaeosaurids. This muscle reconstruction provides a foundation for subsequent investigation of differences in muscular attachment and function, based on scapulocoracoid morphology, across the theropod lineage leading to birds.  © 2006 The Linnean Society of London, Zoological Journal of the Linnean Society , 2006, 146 , 301–344.     

Pelvic limb musculature in the emu Dromaius novaehollandiae (Aves: Struthioniformes: Dromaiidae): Adaptations to high-speed running

Emus provide an excellent opportunity for studying sustained high-speed running by a bird. Their pelvic limb musculature is described in detail and morphological features characteristic of a cursorial lifestyle are identified. Several anatomical features of the pelvic limb reflect the emus' ability for sustained running at high speeds: (1) emus have a reduced number of toes and associated muscles, (2) emus are unique among birds in having a M. gastrocnemius, the most powerful muscle in the shank, that has four muscle bellies, not the usual three, and (3) contribution to total body mass of the pelvic limb muscles of emus is similar to that of the flight muscles of flying birds, whereas the pelvic limb muscles of flying birds constitute a much smaller proportion of total body mass. Generally, the pelvic limb musculature of emus resembles that of other ratites with the notable exception of M. gastrocnemius. The presence and arrangement of four muscle bellies may increase the effectiveness of M. gastrocnemius and other muscles during cursorial locomotion by moving the limb in a cranio-caudal rather than a latero-medial plane. J. Morphol. 238:23–37, 1998. © 1998 Wiley-Liss, Inc.     

A reappraisal of the phylogeny of Mylodontidae (Mammalia,Xenarthra) and the divergence of mylodontine and lestodontine sloths

The phylogeny of mylodontid sloths has recently been the subject of multiple studies. Contrasting hypotheses have been proposed, especially for the relationships among late Miocene–Pleistocene mylodontines and lestodontines. In this paper, a new and detailed phylogenetic analysis is conducted, after adding new characters and taxa previously unexplored from a phylogenetic point of view. New features derived from postcranial skeletal anatomy are added to previous studies based on craniodental evidence. In this way, the current reappraisal represents the first exhaustive phylogenetic study on the Mylodontidae that incorporates features coded for the entire skeleton. When available, multiple specimens of each bony element are observed for each operational taxonomic unit, in order to take into account intraspecific variation. The taxonomic sample of this study considers Mylodontinae at the specific level. However, many other Mylodontidae are considered, and their phylogenetic relationships tested. The taxonomic sample of this study is enriched with new taxa from central and northern South America, with the aim of compensating for the knowledge bias in favour of austral mylodontids, which have historically been more extensively studied than those from tropical latitudes. Special emphasis is given to the phylogenetic relationships of Mylodontinae, and particularly to the mylodontine and lestodontine sloths, that are recovered in the present study as monophyletic clades, and together form a larger monophyletic group. According to the present results, the Mylodontini–Lestodontini split occurred at the middle–late Miocene transition, giving rise to independent adaptive radiations across South and North America.