Journal of Morphology最新文献

Rotifers possess complex morphologies despite their microscopic size and simple appearance. Part of this complexity is hidden in the structure of their organs, which may be cellular or syncytial. Surprisingly, organs that are cellular in one taxon can be syncytial in another. Pedal glands are widespread across Rotifera and function in substrate attachment and/or egg brooding. These glands are normally absent in Asplanchna, which lack feet and toes that function as outlets for pedal glandular secretions in other rotifers. Here, we describe the ultrastructure of a pedal gland that is singular and syncytial in Asplanchna aff. herricki, but is normally paired and cellular in all other rotifers. Asplanchna aff. herricki has a single large pedal gland that is active and secretory; it has a bipartite, binucleate, syncytial body and a cytosol filled with rough endoplasmic reticulum, Golgi, and several types of secretory vesicles. The most abundant vesicle type is large and contains a spherical electron-dense secretion that appears to be produced through homotypic fusion of condensing vesicles produced by the Golgi. The vesicles appear to undergo a phase transition from condensed to decondensed along their pathway toward the gland lumen. Decondensation changes the contents to a mucin-like matrix that is eventually exocytosed in a “kiss-and-run” fashion with the plasma membrane of the gland lumen. Exocytosed mucus enters the gland lumen and exits through an epithelial duct that is an extension of the syncytial integument. This results in mucus that extends from the rotifer as a long string as the animal swims through the water. The function of this mucus is unknown, but we speculate it may function in temporary attachment, prey capture, or floatation.

The mechanosensory lateral line (LL) system of salmonid fishes has been the focus of comparative morphological studies and behavioral and physiological analyses of flow sensing capabilities, but its morphology and development have not been studied in detail in any one species. Here, we describe the post-embryonic development of the cranial LL system in Brook Trout, Salvelinus fontinalis, using vital fluorescent staining (4-Di-2-ASP), scanning electron microscopy, µCT, and clearing and staining to visualize neuromasts and the process of cranial LL canal morphogenesis. We examined the relationship between the timing of LL development, the prolonged life history of salmonids, and potential ecological implications. The LL system is composed of seven canals containing canal neuromasts (CNs) and four lines of superficial neuromasts (SNs) on the skin. CNs and SNs increase in number and size during the alevin (larval) stage. CN number stabilizes as canal morphogenesis commences, but SN number increases well into the parr (juvenile) stage. CNs become larger and more elongated than SNs, but the relative area occupied by sensory hair cells decreases during ontogeny in both types of neuromasts. Neuromast-centered canal morphogenesis starts in alevins (yolk sac larvae), as they swim up into the water column from their gravel nests (~4 months post-fertilization), after which yolk sac absorption is completed and exogenous feeding begins. Canal morphogenesis proceeds asynchronously within and among canal series and is not complete until ~8 months post-fertilization (the parr stage). Three characters in the LL system and associated dermal bones were used to identify their homologs in other actinopterygians and to consider the evolution of LL canal reduction, thus demonstrating the value of salmonids for the study of LL evolution. The prolonged life history of Brook Trout and the onset of canal morphogenesis at swim-up are predicted to have implications for neuromast function at these critical behavioral and ecological transitions.

Siphons are tubular organs formed by fusion and posterior extension of the marginal mantle folds. They are supposed to have performed key roles in the evolution of bivalves by enabling these animals to occupy several ecological niches. However, anatomical details of these organs are scarce for one of the most diverse lineages of tropical bivalves, the superfamily Tellinoidea. We investigated the siphonal morphology of 15 species, sampling five tellinoidean families, by integrating scanning electron microscopy, confocal microscopy, and histology. The siphons revealed variations in length, pigmentation, tentacles, papillae, and number of nerve cords. Due to the presence of sensorial structures, such as papillae and tentacles, we reclassify the siphons of Tellinoidea from type A to A+. Additional anatomical patterns were identified at family and genus levels. For example, the incurrent siphon shorter than the excurrent and 24 tentacles are putative synapomorphies of Donacidae. We also highlight shared siphonal traits between Donacidae and Solecurtidae as well as between Semelidae and Tellinidae. In addition, our data support the idea of Psammobiidae as a paraphyletic lineage. Overall, we provide an extensive comparative data set on siphonal traits with significant relevance for bivalve taxonomy, functional anatomy, and evolutionary investigations.

Anatomy compromises the precision and accuracy of measurements made of the body length and head size of live snakes. Body measures (snout-vent length, SVL) incorporate many synovial intervertebral joints, each allowing flexion and limited extension and compression. Radiographs of the trunk in 14 phylogenetically diverse species in resting and stretched conditions combined with dissections and histological analysis of intervertebral joints show that the synovial nature of these joints underlies the variance in SVL measures. Similarly, the ubiquity and variety of viscoelastic tissues connecting mobile snout and jaw elements of alethinophidian snakes underlie variances in length and width measures of the head. For the overall size of the head and jaw apparatus, the part that can be most easily and relatively precisely measured for many snakes is the mandible because it has only one mobile joint. As to accuracy, the anatomy of intervertebral and cranial joints supports the hypothesis that in living snakes, the head and trunk have no exact size.

Biological variation in the mammalian skull is the product of a series of factors including changes in gene expression, developmental timing, and environmental pressures. When considering the diversity of extant mammalian crania, it is important to understand these mechanisms that contribute to cranial growth and in turn, how differences in cranial morphology have been attained. Various researchers, including Dr. Sue Herring, have proposed a variety of mechanisms to explain the process of cranial growth. This work has set the foundation on which modern analysis of craniofacial morphology happens today. This study focused on the analysis of modularity in three mammalian taxa, all of which exhibit facial reduction. Specifically, we examined facial reduction as a morphological phenomenon through the use of two-module and six-module modularity hypotheses. We recorded three-dimensional coordinate data for 55 cranial landmarks that allowed us to analyze differences in cranial shape in these three taxa (primates n = 88, bats n = 64, dogs n = 81). When assessing modularity within the two-module modularity hypothesis specifically, dogs exhibited the lowest levels of modularity, while bats and primates both showed a slightly more modular covariance structure. We further assessed modularity in the same sample using the Goswami six-module model, where again dogs exhibited a low degree of modularity, with bats and primates being more moderate. We then broke the sample into subsets by analyzing each morphotype separately. We hypothesized that the modularity would be more pronounced in the brachycephalic morphotype. Surprisingly, we found that in brachycephalic dogs, normocephalic dogs, brachycephalic primates, and normocephalic primates, there was a moderate degree of modularity. Brachycephalic bats had a low degree of modularity, while normocephalic bats were the most modular group observed in this study. Based on these results, it is evident that facial reduction is a complex and multifaceted phenomenon with unique morphological changes observed in each of the three taxa studied.

This study aimed to assess the impact of occlusal loading on secondary tooth eruption and to determine the extent to which altering the occlusal loading influences the magnitude of secondary eruption through an experimental rat model. The present sample consisted of 48 male Wistar rats. At the onset of the experiment, 24 rats were 4 weeks old (young rats) and 24 rats were 26 weeks old (adult). Within each age group, the rats were further divided into two equal subgroups (12 rats each), receiving either a soft- or hard-food diet for the 3-month duration of the experiment. The primary outcome was the tooth position changes relative to stable references in the coronal plane by evaluating the distance between the mandibular first molars and the inferior alveolar canal. Microcomputed tomography scans were taken from all rats at three standardized intervals over the 3-month study period. Descriptive statistics were calculated by age and diet over time, and the evolution of the outcomes were plotted by age and diet over time. Longitudinal data analysis via generalized estimating equations was performed to examine the effect of age, diet and time on the primary outcomes. Secondary tooth eruption was observed in all age groups (young and adult) regardless of diet consistency (soft or hard food). In young rats, the secondary eruption was greater in the animals fed a soft diet than those fed a hard diet. In adult rats, minimal difference in secondary tooth eruption were found between different diet consistencies. Occlusal loading influences secondary tooth eruption in teeth with an established occlusal contact. The quantity of eruption in growing rats is higher when occlusal loading is less, providing a certain amount of secondary tooth eruption occurs. This difference, however, is not evident in adult rats, at least during the given 3-month time frame.

Using immunocytochemistry, serotonergic nerve elements were documented in the nervous system of the planarian Girardia tigrina. Serotonin-immunopositive components were observed in the brain, ventral, dorsal and longitudinal nerve cords, transverse nerve commissures connecting the nerve cords, and in the nerve plexus. Whole-mount preparations of G. tigrina were analyzed by fluorescent and confocal laser scanning microscopy. An essential quantitative morphometric measurement of serotonin-immunopositive structures was conducted in three body regions (anterior, middle, and posterior) of the planarian. The number of serotonin neurons was maximal in the head region. The ventral nerve cords gradually decreased in thickness from anterior to posterior body ends. Physiological action of exogenously applied serotonin was studied in G. tigrina for the first time. It was found that serotonin (0.1 and 1 µmol L⁻¹) accelerated eye regeneration. The transcriptome sequencing performed for the first time for the planarian G. tigrina revealed the transcripts of the tryptophan hydroxylase (trph), amino acid decarboxylase (aadc) and serotonin transporter (sert) genes. The data obtained indicate the presence of the components of serotonin pathway in G. tigrina. The identified transcripts can take part in serotonin turnover and participate in the realization of biological effects of serotonin in planarians, associated with eyes regeneration and differentiation.

The Ophidiidae is a group of more than 300 species of fishes characterized by elongated, snake-like bodies and continuous dorsal, anal, and caudal fins. While describing a new species in the genus Monomitopus, we discovered a bilaterally paired fenestra on the dorsomedial surface of the neurocranium. We surveyed the distribution of this fenestra across species of Monomitopus and previously hypothesized allies in the genera Dannevigia, Dicrolene, Homostolus, Neobythites, and Selachophidium, finding variation in its presence and size. We also found a prominent bilaterally paired lateral fenestra and a posterior expansion of the exoccipital in the neurocrania of M. americanus and S. guentheri, with soft tissue connecting the back of the neurocranium to the first epineural and pectoral girdle in S. guentheri. In this study, we describe the distribution of and variation in these features. We integrate morphological characters and DNA data to generate a phylogeny of Monomitopus and allies to understand their relationships and trace the evolutionary history of these novel features. Our results call the monophyly of Monomitopus into question. The presence of the lateral neurocranial fenestra and posterior expansion of the exoccipital support the reclassification of M. americanus as a species of Selachophidium.

Although the knowledge of the skeletal morphology of bees has progressed enormously, a corresponding advance has not happened for the muscular system. Most of the knowledge about bee musculature was generated over 50 years ago, well before the digital revolution for anatomical imaging, including the application of microcomputed tomography. This technique, in particular, has made it possible to dissect small insects digitally, document anatomy efficiently and in detail, and visualize these data three dimensionally. In this study, we document the skeletomuscular system of a cuckoo bee, Thyreus albomaculatus and, with that, we provide a 3D atlas of bee skeletomuscular anatomy. The results obtained for Thyreus are compared with representatives of two other bee families (Andrenidae and Halictidae), to evaluate the generality of our morphological conclusions. Besides documenting 199 specific muscles in terms of origin, insertion, and structure, we update the interpretation of complex homologies in the maxillolabial complex of bee mouthparts. We also clarify the complicated 3D structure of the cephalic endoskeleton, identifying the tentorial, hypostomal, and postgenal structures and their connecting regions. We describe the anatomy of the medial elevator muscles of the head, precisely identifying their origins and insertions as well as their homologs in other groups of Hymenoptera. We reject the hypothesis that the synapomorphic propodeal triangle of Apoidea is homologous with the metapostnotum, and instead recognize that this is a modification of the third phragma. We recognize two previously undocumented metasomal muscle groups in bees, clarifying the serial skeletomusculature of the metasoma and revealing shortcomings of Snodgrass' “internal–external” terminological system for the abdomen. Finally, we elucidate the muscular structure of the sting apparatus, resolving previously unclear interpretations. The work conducted herein not only provides new insights into bee morphology but also represents a source for future phenomic research on Hymenoptera.

Accurate identification of waterfowl bones in archaeological and fossil assemblages has potential to unlock new methods of past environmental reconstruction, as species have differing habitat preferences and migration patterns. Therefore, identifying the presence of avian species with different ecological niches is key to determining past environments and ultimately how prehistoric people responded to climatic and environmental realignments. However, the identification of osteological remains of waterbirds such as ducks to species level is notoriously challenging. We address this by presenting a new two-dimensional geometric morphometric protocol on wing elements from over 20 duck species and test the utility of these shape data for correct species identification. This is an ideal starting point to expand utilization of these types of approaches in avifaunal research and test applicability to an extremely difficult taxonomic group.