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Preview: Journal of Morphology

Journal of Morphology

Wiley Online Library : Journal of Morphology

Published: 2017-10-01T00:00:00-05:00


Developmental mechanisms of longitudinal stripes in the Japanese four-lined snake


The developmental mechanisms of color patterns formation and its evolution remain unclear in reptilian sauropsids. We, therefore, studied the pigment cell mechanisms of stripe pattern formation during embryonic development of the snake Elaphe quadrivirgata. We identified 10 post-ovipositional embryonic developmental stages based on external morphological characteristics. Examination for the temporal changes in differentiation, distribution, and density of pigment cells during embryonic development revealed that melanophores first appeared in myotome and body cavity but not in skin surface at Stage 5. Epidermal melanophores were first recognized at Stage 7, and dermal melanophores and iridophores appeared in Stage 9. Stripe pattern first appeared to establish at Stage 8 as a spatial density gradient of epidermal melanophores between the regions of future dark brown longitudinal stripes and light colored background. Our study, thus, provides a comprehensive pigment-cell-based understanding of stripe pattern formation during embryonic development. We briefly discuss the importance of the gene expression studies by considering the biologically relevant theoretical models with standard developmental staging for understanding reptilian color pattern evolution. We described 10 post-ovipositional embryonic developmental stages of Elaphe quadrivirgata embryos. We examined temporal changes in the differentiation, distribution, and density of pigment cells during embryonic development.

Ultrastructure of spermatozoa of spider crabs, family Mithracidae (Crustacea, Decapoda, Brachyura): Integrative analyses based on morphological and molecular data


Recent studies based on morphological and molecular data provide a new perspective concerning taxonomic aspects of the brachyuran family Mithracidae. These studies proposed a series of nominal changes and indicated that the family is actually represented by a different number and representatives of genera than previously thought. Here, we provide a comparative description of the ultrastructure of spermatozoa and spermatophores of some species of Mithracidae in a phylogenetic context. The ultrastructure of the spermatozoa and spermatophore was observed by scanning and transmission electron microscopy. The most informative morphological characters analysed were thickness of the operculum, shape of the perforatorial chamber and shape and thickness of the inner acrosomal zone. As a framework, we used a topology based on a phylogenetic analysis using mitochondrial data obtained here and from previous studies. Our results indicate that closely related species share a series of morphological characteristics of the spermatozoa. A thick operculum, for example, is a feature observed in species of the genera Amphithrax, Teleophrys, and Omalacantha in contrast to the slender operculum observed in Mithraculus and Mithrax. Amphithrax and Teleophrys have a rhomboid perforatorial chamber, while Mithraculus, Mithrax, and Omalacantha show a wider, deltoid morphology. Furthermore, our results are in agreement with recently proposed taxonomic changes including the separation of the genera Mithrax (previously Damithrax), Amphithrax (previously Mithrax) and Mithraculus, and the synonymy of Mithrax caribbaeus with Mithrax hispidus. Overall, the spermiotaxonomy of these species of Mithracidae represent a novel set of data that corroborates the most recent taxonomic revision of the family and can be used in future taxonomic and phylogenetic studies within this family. The key characters found to the spermatozoa ultrastructure are the operculum, perforatorial chamber, and inner acrosomal zone. All these structures allowed the separation of the species in different genera and corroborate the molecular phylogeny.

Who wins in the weaning process? Juvenile feeding morphology of two freshwater mussel species


The global decline of freshwater mussels can be partially attributed to their complex life cycle. Their survival from glochidium to adulthood is like a long obstacle race, with juvenile mortality as a key critical point. Mass mortality shortly after entering into a juvenile state has been reported in both wild and captive populations, thus weakening the effective bivalve population. A similar phenomenon occurs during metamorphosis in natural and hatchery populations of juvenile marine bivalves. Based on a morphological analysis using scanning electron microscopy of newly formed juveniles of the freshwater species Margaritifera margaritifera (L.) (Margaritiferidae) and Unio mancus Lamarck (Unionidae), we show that a second metamorphosis, consisting of drastic morphological changes, occurs that leads to suspension feeding in place of deposit feeding by the ciliated foot. We hypothesize that suspension feeding in these two species improves due to a gradual development of several morphological features including the contact between cilia of the inner gill posterior filaments, the inner gill reflection, the appearance of the ctenidial ventral groove and the formation of the pedal palps. Regardless of the presence of available food, a suspension feeding mode replaces deposit feeding, and juveniles unable to successfully transition morphologically or adapt to the feeding changes likely perish. The decline of freshwater mussels (Unionoida) is attributed to their complex life cycle and mass mortality of juveniles has been reported. We show that a second metamorphosis occurs and juveniles unable to successfully transition perish.

Gross brain morphology of the armoured catfish Rineloricaria heteroptera, Isbrücker and Nijssen (1976), (Siluriformes: Loricariidae: Loricariinae): A descriptive and quantitative approach


The gross morphology of the brain of Rineloricaria heteroptera and its relation to the sensory/behavioural ecology of the species is described and discussed. The sexual and ontogenetic intraspecific variation in the whole brain length and mass, as well as within/between the eight different brain subdivisions volumes, is also examined and discussed. Negative allometry for the whole brain length/mass and relative growth of the telencephalon and optic tecta was observed. Positive allometry was observed for the relative growth of the olfactory bulbs and medulla oblongata. Univariate and multivariate statistical analyses did not reveal significant differences in the brain subdivision growth rates among sexes and/or developmental stages, except for the optic tectum and some portions of the medulla oblongata, with juveniles and males showing more developed optic tecta and medullary subdivisions, respectively. The growth rates for each brain subdivision were relatively constant, and the slopes of the growth equations were almost parallel, except for those of the olfactory bulbs and medulla oblongata subdivisions, suggesting some degree of tachyauxesis of subdivisions against the entire brain. The corpus cerebelli was the more voluminous brain subdivision in most specimens (principally adults), followed by the optic tectum (the more voluminous subdivision in juveniles), hypothalamus, and telencephalon, in that order. Differences in the number of lamellae and relative size of the olfactory organ were also detected among developmental stages, which were more numerous and larger in adults. Based on these results, it is possible to infer an ontogenetic shift in the habitat/resource use and behaviour of R. heteroptera. Vision, primarily routed through the optic tectum, could be fundamental in early stages, whereas in adults, olfaction and taste, primarily routed through the olfactory bulbs and medulla oblongata, play more important roles. Generalized brain of Rineloricaria heteroptera (Siluriformes: Loricariidae: Loricariinae); (a) dorsal, (b) lateral (left side), and (c) ventral views, showing major brain structures/subdivisions. Scale bar = 2 mm.

Expression of caveolin-1 in the interfollicular but not the follicle-associated epithelial cells in the bursa of fabricius of chickens


The surface epithelium of the bursa of Fabricius consists of interfollicular (IFE) and follicle-associated epithelium (FAE). The IFE comprises (i) cylindrical-shaped secretory cells (SC) and (ii) cuboidal basal cells (BCs). The FAE provides histological and two-way functional connections between the bursal lumen and medulla of the follicle. We used a carbon solution and anti-caveolin-1 (Cav-1) to study the endocytic activity of FAE. Carbon particles entered the intercellular space of FAE, but the carbon particles were not internalized by the FAE cells. Cav-1 was not detectable in the FAE cells or the medulla of the bursal follicle. The absence of Cav-1 indicates that no caveolin-mediated endocytosis occurs in the FAE cells, B cells, bursal secretory dendritic cells (BSDC), or reticular epithelial cells. Surprisingly, a significant number of Cav-1 positive cells can be found among the SC, which are designated SC II. Cav-1 negative cell are called SC I, and they produce mucin for lubricating the bursal lumen and duct. Occasionally, BCs also express Cav-1, which suggests that BC is a precursor of a SC. Transmission electron microscopy confirmed the existence of type I and II SC. The SC II are highly polarized and have an extensive trans-Golgi network that is rich in different granules and vesicles. Western blot analysis of bursa lysates revealed a 21–23 kDa compound (caveolin) and Filipin fluorescence histochemistry provided evidence for intracellular cholesterol. High amount of cholesterol in the feces shows the cholesterol efflux from SC II. The presence of Cav-1 and cholesterol in SC II indicates, that the bursa is a complex organ in addition to possessing immunological function contributes to the cholesterol homeostasis in the chickens. The bursa of Fabricius comprises two units: (i) the FAE plus the follicle is a primary lymphoid organ, committed to B cell differentiation and (ii) the IFE. Type I SC produce mucus and type II SC express Cav-1 and contribute to cholesterol homeostasis.

Ovarian structure and oogenesis of the extremophile viviparous teleost Poecilia mexicana (Poeciliidae) from an active sulfur spring cave in Southern Mexico


The structure of the ovary and oogenesis of Poecilia mexicana from an active sulfur spring cave is documented. Poecilia mexicana is the only poeciliid adapted to a subterranean environment with high hydrogen sulfide levels and extreme hypoxic conditions. Twenty females were captured throughout one year at Cueva del Azufre, located in the State of Tabasco in Southern Mexico. Ovaries were processed with histological techniques. P. mexicana has a single, ovoid ovary with ovigerous lamella that project to the ovarian lumen. The ovarian wall presents abundant loose connective tissue, numerous melanomacrophage centers and large blood vessels, possibly associated with hypoxic conditions. The germinal epithelium bordering the ovarian lumen contains somatic and germ cells forming cell nests projecting into the stroma. P. mexicana stores sperm in ovarian folds associated with follicles at different developmental phases. Oogenesis in P. mexicana consisted of the following stages: (i) oogonial proliferation, (ii) chromatin nucleolus, (iii) primary growth, subdivided into: (a) one nucleolus, (b) multiple nucleoli, (c) droplet oils-cortical alveoli steps; (iv) secondary growth, subdivided in: (a) early secondary growth, (b) late secondary growth, and (c) full grown. Follicular atresia was present in all stages of follicular development; it was characterized by oocyte degeneration, where follicle cells hypertrophy and differentiate in phagocytes. The ovary and oogenesis are similar to these seen in other poeciliids, but we found frequent atretic follicles, melanomacrophage centers, reduced fecundity and increased of offspring size. Poecilia mexicana is adapted to high hydrogen sulfide and hypoxic conditions. As in viviparous teleosts, the ovary is the site not only for oogenesis but also for gestation. The ovary and oogenesis are similar to these seen in other poeciliids, but occur frequent atretic follicles, melanomacrophage centers, reduced fecundity, and increased of offspring size.

Structure of supporting elements in the dorsal fin of percid fishes


The dorsal fin is one of the most varied swimming structures in Acanthomorpha, the spiny-finned fishes. This fin can be present as a single contiguous structure supported by bony spines and soft lepidotrichia, or it may be divided into an anterior, spiny dorsal fin and a posterior, soft dorsal fin. The freshwater fish family Percidae exhibits especially great variation in dorsal fin spacing, including fishes with separated fins of varying gap length and fishes with contiguous fins. We hypothesized that fishes with separated dorsal fins, especially those with large gaps between fins, would have stiffened fin elements at the leading edge of the soft dorsal fin to resist hydrodynamic loading during locomotion. For 10 percid species, we measured the spacing between dorsal fins and calculated the second moment of area of selected spines and lepidotrichia from museum specimens. There was no significant relationship between the spacing between dorsal fins and the second moment of area of the leading edge of the soft dorsal fin. In fishes the dorsal fin can be a single contiguous structure (red) or it may be separated (blue) into an anterior, spiny dorsal fin and a posterior, soft dorsal fin. We hypothesized that fishes with separated dorsal fins would have stiffened fin elements at the leading edge of the soft dorsal fin in order to resist hydrodynamic loading during swimming. Our micro-CT-data showed no significant difference in cross-sectional shape or size between the leading edge of the soft dorsal fin in fishes with separated fins and the equivalent fin element in fishes with contiguous fins.

Burrowing with a kinetic snout in a snake (Elapidae: Aspidelaps scutatus)


Of the few elongate, fossorial vertebrates that have been examined for their burrowing mechanics, all were found to use an akinetic, reinforced skull to push into the soil, powered mostly by trunk muscles. Reinforced skulls were considered essential for head-first burrowing. In contrast, I found that the skull of the fossorial shield-nosed cobra (Aspidelaps scutatus) is not reinforced and retains the kinetic potential typical of many non-fossorial snakes. Aspidelaps scutatus burrows using a greatly enlarged rostral scale that is attached to a kinetic snout that is independently mobile with respect to the rest of the skull. Two mechanisms of burrowing are used: (1) anteriorly directed head thrusts from a loosely bent body that is anchored against the walls of the tunnel by friction, and (2) side-to-side shovelling using the head and rostral scale. The premaxilla, to which the rostral scale is attached, lacks any direct muscle attachments. Rostral scale movements are powered by, first, retractions of the palato-pterygoid bar, mediated by a ligament that connects the anterior end of the palatine to the transverse process of the premaxilla and, second, by contraction of a previously undescribed muscle slip of the m. retractor pterygoidei that inserts on the skin at the edge of the rostral scale. In derived snakes, palatomaxillary movements are highly conserved and power prey capture and transport behaviors. Aspidelaps scutatus has co-opted those mechanisms for the unrelated function of burrowing without compromising the original feeding functions, showing the potential for evolution of functional innovations in highly conserved systems. The shield-nosed snake (Aspidelaps scutatus) co-opts structures usually used for feeding to perform a new burrowing function. A new muscle is described. Burrowing occurs without a reinforced skull, which has previously been considered necessary.

Three-dimensional reconstruction of the pharyngeal gland cells in the predatory nematode Pristionchus pacificus


Pristionchus pacificus is a model system in evolutionary biology and for comparison to Caenorhabditis elegans. As a necromenic nematode often found in association with scarab beetles, P. pacificus exhibits omnivorous feeding that is characterized by a mouth-form dimorphism, an example of phenotypic plasticity. Eurystomatous animals have a dorsal and a sub-ventral tooth enabling predatory feeding on other nematodes whereas stenostomatous animals have only a dorsal tooth and are microbivorous. Both mouth forms of P. pacificus, like all members of the Diplogastridae family, lack the grinder in the terminal bulb of the pharynx resulting in a fundamentally different organization of several pharynx-associated structures. Here, we describe the three-dimensional reconstruction of the pharyngeal gland cells in P. pacificus based on serial transmission electron microscopical analysis of 2527 sections of 50 nm thickness. In comparison to C. elegans, P. pacificus lacks two gland cells (g2) usually associated with grinder function, whereas the three gland cells of g1 (g1D, g1VL, and g1VR) are very prominent. The largest expansion is seen for g1D, which has an anterior process that opens into the buccal cavity through a canal in the dorsal tooth. We provide the morphological description and fine structural analysis of the P. pacificus gland cells, the behavior of the pharynx and preliminary insight into exocytosis of gland cell vesicles in P. pacificus. Three-dimensional reconstruction of the pharyngeal gland cells in the predatory nematode Pristionchus pacificus. In comparison to Caenorhabditis elegans, P. pacificus has only three gland cells, all of which show massive expansions of their cell bodies. The dorsal gland cell has a long anterior process that opens through the dorsal tooth into the buccal cavity, whereas the two ventral glands open into the posterior metacorpus.

Comparative ultrastructure of coxal glands in unfed larvae of Leptotrombidium orientale (Schluger, 1948) (Trombiculidae) and Hydryphantes ruber (de Geer, 1778) (Hydryphantidae)


Coxal glands of unfed larvae Leptotrombidium orientale (Schluger, 1948) (Trombiculidae), a terrestrial mite parasitizing vertebrates, and Hydryphantes ruber (de Geer, 1778) (Hydryphantidae), a water mite parasitizing insects were studied using transmission electron microscopy. In both species, the coxal glands are represented by a paired tubular organ extending on the sides of the brain from the mouthparts to the frontal midgut wall and are formed of the cells arranged around the central lumen. As in other Parasitengona, the coxal glands are devoid of a proximal sacculus. The excretory duct, joining with ducts of the prosomal salivary glands constitutes the common podocephalic duct, opening into the subcheliceral space. The coxal glands of L. orientale are composed of a distal tubule with a basal labyrinth, an intermediate segment without labyrinth, and a proximal tubule bearing tight microvilli on the apical cell surface and coiled around the intermediate segment. The coxal glands of H. ruber mainly consist of the uniformly organized proximal tubule with apical microvilli of the cells lacking the basal labyrinth. This tubule shows several loops running backward and forward in a vertical plane on the side of the brain. In contrast to L. orientale, larvae of H. ruber reveal a terminal cuticular sac/bladder for accumulation of secreted fluids. Organization of the coxal glands depends on the ecological conditions of mites. Larvae of terrestrial L. orientale possess distal tubule functioning in re-absorption of ions and water. Conversely, water mite larvae H. ruber need to evacuate of the water excess, so the filtrating proximal tubule is prominent. The upper figure, named L. orientale, demonstrates the proximal portion of a coxal gland in larva of L. orientale composed of the proximal tubule with a microvillous brush border on the apical cell surface coiled around the intermediate segment devoid both of the brush border and of the basal infolds/labyrinth. Longitudinal sagittal section in low magnification. The lower figure, named H. ruber, shows the proximal tubule of a coxal gland in larva of H. ruber in transverse section with middle magnification. Note that the tubule is totally devoid of the basal infolds/labyrinth, whereas the microvillous brush border is well developed.

Distinct histomorphology for growth arrest and digitate outgrowth in cultivated Haliclona sp. (Porifera: Demospongiae)


The use of sponges in biotechnological processes is limited by the supply problem, and sponge biomass production is becoming a current topic of research. The distinction between characteristics for growth and growth arrest is also important for environmental monitoring. In this study, we analyze the morphology of the digitate outgrowths from the sponge Haliclona sp. The sponge Haliclona sp. was successfully cultivated for 14 months in a closed system. The morphological characterization of growth arrest was performed after submitting explants to starvation-stress for approximately 2 weeks, to correlate morphology with growth and growth arrest. The digitate outgrowth showed three distinct regions: mature (MR), transition (TR) and immature (IR). Our data suggest a growth developmental program, with collagen fascicles guiding axial growth in IR, followed by progressive development of choanocyte chambers and large aquiferous systems at the more mature proximal region (choanosome). The intercalation of choanocyte chambers and small aquiferous systems inside collagen fascicles previously originated at the IR region can be responsible for thickening expansion and conversion of the collagen fascicles into columnar choanosome in MR. The growth arrest after starvation-stress assay showed morphological changes in the IR corroborating collagen in the extreme tip of the digitate outgrowth as an important role in guiding of axial growth of Haliclona sp. The identification of distinct morphologies for growth and growth arrest suggest a growth developmental program, and these data could be useful for further investigations addressing sponge biomass gain and environmental monitoring. Haliclona sp. axial extension is a result of collagen fascicles pushing forward the tip pinachoderm of immature region. Lateral expansion is a result of choanosome presence in transitory and mature region. The growth arrested morphology supports it.

An examination of surface epithelium structures of the embryo across the genus Poeciliopsis (Poeciliidae)


In viviparous, teleost fish, with postfertilization maternal nutrient provisioning, embryonic structures that facilitate maternal-fetal nutrient transfer are predicted to be present. For the family Poeciliidae, only a handful of morphological studies have explored these embryonic specializations. Here, we present a comparative morphological study in the viviparous poeciliid genus, Poeciliopsis. Using microscopy techniques, we examine the embryonic surface epidermis of Poeciliopsis species that vary in their level of postfertilization maternal nutrient provisioning and placentation across two phylogenetic clades and three independent evolutionary origins of placentation. We focus on surface features of the embryo that may facilitate maternal-fetal nutrient transfer. Specifically, we studied cell apical-surface morphology associated with the superficial epithelium that covers the body and sac (yolk and pericardial) of embryos at different developmental stages. Scanning electron microscopy revealed common surface epithelial cells across species, including pavement cells with apical-surface microridges or microvilli and presumed ionocytes and/or mucus-secreting cells. For three species, in the mid-stage embryos, the surface of the body and sac were covered in microvillus epithelium. The remaining species did not display microvillus epithelium at any of the stages examined. Instead, their epithelium of the body and sac were composed of cells with apical-surface microridges. For all species, in the late stage embryos, the surface of the body proper was composed of apical-surface microridges in a “fingerprint-like arrangement.” Despite the differences in the surface epithelium of embryos across Poeciliopsis species and embryonic developmental stages, this variation was not associated with the level of postfertilization maternal nutrient provisioning. We discuss these results in light of previous morphological studies of matrotrophic, teleost fish, phylogenetic relationships of Poeciliopsis species, and our earlier comparative microscopy work on the maternal tissue of the Poeciliopsis placenta. Across Poeciliopsis species examined in this study, the epithelial surface features of the embryo, such as the microvillus epithelium shown here, appear to be associated with phylogenetic relationship not level of postfertilization maternal nutrient provisioning.

Allometry and morphometrics of clypeal membrane size and shape in Nicrophorus (Coleoptera: Silphidae)


Contests between same-sex opponents over resources necessary for reproduction, as well interactions used to discern mate quality, often involve exaggerated traits wherein large individuals have disproportionately larger traits. This positive allometric scaling of weapons or signals facilitates communication during social interactions by accentuating body size differences between individuals. Typically, males carry these exaggerated traits, as males must compete over limited female gametes. However, in Nicrophorus beetles both males and females engage in physical contests over the vertebrate carcasses they need to provision and raise offspring. Male and female Nicrophorus beetles have extended clypeal membranes directly above their mandibles, which could serve as signals. We investigated the scaling relationships between clypeal membrane size and shape and body size for five species of North American burying beetle to determine whether clypeal membranes contain exaggerated body size information. We found that clypeal membranes for both sexes of all species scaled positively with body size (slope > 1). Three of the five species also displayed sexual dimorphism in aspects of clypeal membrane size and shape allometry despite lack of dimorphism in body size. In two dimorphic species, small male clypeal membranes were statistically indistinguishable from the female form. We conclude that colored clypeal membranes in Nicrophorus beetles do contain exaggerated body size information. Observed patterns of dimorphism suggest that males sometimes experience stronger selection on marking size and shape, which might be explained by life history differences among species. Nicrophorus clypeal membranes exaggerate body size, sometimes more noticeably in males.

The vocal sac of Hylodidae (Amphibia, Anura): Phylogenetic and functional implications of a unique morphology


Anuran vocal sacs are elastic chambers that recycle exhaled air during vocalizations and are present in males of most species of frogs. Most knowledge of the diversity of vocal sacs relates to external morphology; detailed information on internal anatomy is available for few groups of frogs. Frogs of the family Hylodidae, which is endemic to the Atlantic Forest of Brazil and adjacent Argentina and Paraguay, have three patterns of vocal sac morphology—that is, single, subgular; paired, lateral; and absent. The submandibular musculature and structure of the vocal sac mucosa (the internal wall of the vocal sac) of exemplar species of this family and relatives were studied. In contrast to previous accounts, we found that all species of Crossodactylus and Hylodes possess paired, lateral vocal sacs, with the internal mucosa of each sac being separate from the contralateral one. Unlike all other frogs for which data are available, the mucosa of the vocal sacs in these genera is not supported externally by the mm. intermandibularis and interhyoideus. Rather, the vocal sac mucosa projects through the musculature and is free in the submandibular lymphatic sac. The presence of paired, lateral vocal sacs, the internal separation of the sac mucosae, and their projection through the m. interhyoideus are synapomorphies of the family. Furthermore, the specific configuration of the m. interhyoideus allows asymmetric inflation of paired vocal sacs, a feature only reported in species of these diurnal, stream-dwelling frogs. Unlike all other anurans, the vocal sac wall of hylodids projects through submandibular musculature. We report three synapomorphies for Hylodidae and a mechanism for unilateral inflation of paired vocal sacs, only observed in these frogs.

Identification of a new mineralized tissue in the notochord of reared Siberian sturgeon (Acipenser baerii)


In a study aiming to improve knowledge on the mineralization of the axial skeleton in reared Siberian sturgeon (Acipenser baerii Brandt, 1869), we discovered a new mineralized tissue within the notochord. To our knowledge, such a structure has never been reported in any vertebrate species with the exception of the pathological mineralization of the notochord remains in degenerative intervertebral disks of mammals. Here, we describe this enigmatic tissue using X-ray microtomography, histological analyses and solid state NMR-spectroscopy. We also performed a 1-year monitoring of the mineral content (MC) of the notochord in relation with seasonal variations of temperature. In all specimens studied from 2-year-old juveniles onwards, this mineralized structure was found within a particular region of the notochord called funiculus. This feature first appears in the abdominal region then extends posteriorly with ageing, while the notochord MC also increases. The mineral phase is mainly composed of amorphous calcium phosphate, a small amount of which changes into hydroxyapatite with ageing. The putative role of this structure is discussed as either a store of minerals available for the phosphocalcic metabolism, or a mechanical support in a species with a poorly mineralized axial skeleton. A pathological feature putatively related to rearing conditions is also discussed. A mineralized structure, composed of amorphous calcium phosphates and never reported in vertebrates, was found in the notochord of Acipenser baerii from 2 years onwards. We describe this enigmatic tissue using CT-scan, histological analyses and solid state NMR spectroscopy

The colonic groove of the plains viscacha (Lagostomus maximus): Histochemical evidence of an abrupt change in the glycosylation pattern of goblet cells


The ascending colon of most rodent species shows a longitudinal colonic groove that works as a retrograde transport pathway for a mixture of bacteria and mucus toward the cecum. We describe the morphology and glycosylation pattern of the colonic groove of Lagostomus maximus to analyze the role of mucins in this anatomical feature. We also studied the distribution pattern of the interstitial cells of Cajal (ICC) to evaluate their regulatory influence on gut motility. The groove originated near the cecocolic junction and extended along the mesenteric side of the ascending colon, limited at both ends by nonpapillated ridges. These ridges divided the lumen of the ascending colon into two compartments: a narrow channel and a large channel, called the groove lumen and the main lumen, respectively. The histochemical analysis showed differences in the glycosylation pattern of the goblet cells inside and outside the groove. Unlike the mucosa lining the main lumen of the colon, the groove was rich in goblet cells that secrete sulfomucins. The PA/Bh/KOH/PAS technique evidenced an abrupt change in the histochemical profile of goblet cells, which presented a negative reaction in the groove and a strongly positive one in the rest of the colonic mucosa. The anti-c-kit immunohistochemical analysis showed different ICC subpopulations in the ascending colon of L. maximus. Of all types identified, the ICC-SM were the only cells located solely within the colonic groove. The groove was formed by two nonpapillated ridges (R). These ridges divided the lumen of the ascending colon into two compartments: the groove lumen (G) and the large main lumen (MLu). The histochemical analysis revealed significant differences among goblet cells in and out of the colonic groove, being this the first time an abrupt change in the glycosylation pattern of the intestinal tract of L. maximus is described (see dotted lines).

Dimorphic ejaculates and sperm release strategies associated with alternative mating behaviors in the squid


Sperm competition is a powerful postcopulatory selective force influencing male adaptations associated with increasing fertilization success, and it is usually related to the evolution of different strategies of ejaculate expenditure between individuals. Ejaculates may also be influenced by additional selective pressures associated with sperm competition, such as timing between insemination and fertilization, female reproductive tract morphology, and fertilization environment. Also, males that adopt alternative mating tactics may face distinct sperm competition pressures, which may lead to the evolution of intraspecific diversity in ejaculates. In loliginid squids, males with alternative reproductive tactics (sneakers and consorts) differ not only in mating behavior, but also transfer spermatophores into two distinct sites within the female. Here, we compared structure and functioning of spermatophores between sneakers and consorts in the squid Doryteuthis plei applying microscopy techniques and in vitro experiments. Sneakers and consorts exhibit differences in spermatophore structure that lead to distinct spermatophoric reactions and spermatangium morphologies. Moreover, in sneakers, sperm release lasts longer and their sperm show an aggregative behavior not detected in consorts. Slow sperm release may be a strategy to guarantee longer sperm provision, given the wide interval between sneaker mating and egg release. For consorts, in turn, intense and quick sperm discharge may be advantageous, as timing between mating and egg-laying is relatively short. Within the complex squid mating system, factors such as (i) different fertilization sites and (ii) interval between mating and egg release may also influence sperm competition, and ultimately shape the evolution of divergent ejaculates between dimorphic males. Different selective pressures over males with alternative mating tactics may lead to intraspecific diversity in ejaculates, for example, sneakers sperm aggregation, possibly related to avoiding dilution and slowing spermatozoa release until fertilization.

Trunk elongation and ontogenetic changes in the axial skeleton of Triturus newts


Body elongation in vertebrates can be achieved by lengthening of the vertebrae or by an increase in their number. In salamanders, longer bodies are mostly associated with greater numbers of vertebrae in the trunk or tail region. However, studies on the relative contribution of the length of single vertebra to body elongation are lacking. In this study, we focus on evolutionary and ontogenetic changes in differentiation of the trunk vertebrae and the relative contribution of individual vertebrae to trunk lengthening in Triturus newts, a monophyletic group of salamanders that shows remarkable disparity in body shape. We compared juveniles and adults of the most elongated T. dobrogicus, which has 17 trunk vertebrae, with juveniles and adults of two closely related species (T. ivanbureschi and T. anatolicus belonging to the T. karelinii species complex) representing a stout and robust morphotype with thirteen trunk vertebrae. We show that trunk vertebrae are uniform in size at the juvenile stage of both analyzed morphotypes. In adults, the trunk vertebrae of the elongated T. dobrogicus are largely uniform, while in those of T. anatolicus, the first two vertebrae differ from the remaining trunk vertebrae. There was no difference in the relative contribution of individual vertebrae to body lengthening between species or stages. We conclude that body elongation in Triturus newts is achieved by increasing the number of vertebrae but not their length. Evolutionary changes in body elongation in Triturus newts are achieved by increasing the number of vertebrae but not their length. Ontogenetic changes of vertebrae in axial skeleton are proportional in T. dobrogicus, but disproportional in T. karelinii morphotype.

Embryonic development of Eucorydia yasumatsui Asahina, with special reference to external morphology (Insecta: Blattodea, Corydiidae)


As the first step in the comparative embryological study of Blattodea, with the aim of reconstructing the groundplan and phylogeny of Dictyoptera and Polyneoptera, the embryonic development of a corydiid was examined and described in detail using Eucorydia yasumatsui. Ten to fifteen micropyles are localized on the ventral side of the egg, and aggregated symbiont bacterial “mycetomes” are found in the egg. The embryo is formed by the fusion of paired blastodermal regions, with higher cellular density on the ventral side of the egg. This type of embryo formation, regarded as one of the embryological autapomorphies of Polyneoptera, was first demonstrated for “Blattaria” in the present study. The embryo undergoes embryogenesis of the short germ band type, and elongates to its full length on the ventral side of the egg. The embryo undergoes katatrepsis and dorsal closure, and then finally, it acquires its definitive form, keeping its original position on the ventral side of the egg, with its anteroposterior axis never reversed throughout development. The information obtained was compared with that of previous studies on other insects. “Micropyles grouped on the ventral side of the egg” is thought to be a part of the groundplan of Dictyoptera, and “possession of bacteria in the form of mycetomes” to be an apomorphic groundplan of Blattodea. Corydiid embryos were revealed to perform blastokinesis of the “non-reversion type (N)”, as reported in blaberoid cockroaches other than Corydiidae (“Ectobiidae,” Blaberidae, etc.) and in Mantodea; the embryos of blattoid cockroaches (Blattidae and Cryptocercidae) and Isoptera undergo blastokinesis of the “reversion type (R),” in which the anteroposterior axis of the embryo is reversed during blastokinesis. Dictyopteran blastokinesis types can be summarized as “Mantodea (N) + Blattodea [= Blaberoidea (N) + Blattoidea (R) + Isoptera (R)]”. Two types of blastokinesis are found in Dictyoptera: one is the “reversion type” (top) in blattoidean cockroaches and termites, and another the “non-reversion type” (below) in blaberoidean cockroaches and mantises.

Interspecific variation in the tetradactyl manus of modern tapirs (Perissodactyla: Tapirus) exposed using geometric morphometrics


The distal forelimb (autopodium) of quadrupedal mammals is a key morphological unit involved in locomotion, body support, and interaction with the substrate. The manus of the tapir (Perissodactyla: Tapirus) is unique within modern perissodactyls, as it retains the plesiomorphic tetradactyl (four-toed) condition also exhibited by basal equids and rhinoceroses. Tapirs are known to exhibit anatomical mesaxonic symmetry in the manus, although interspecific differences and biomechanical mesaxony have yet to be rigorously tested. Here, we investigate variation in the manus morphology of four modern tapir species (Tapirus indicus, Tapirus bairdii, Tapirus pinchaque, and Tapirus terrestris) using a geometric morphometric approach. Autopodial bones were laser scanned to capture surface shape and morphology was quantified using 3D-landmark analysis. Landmarks were aligned using Generalised Procrustes Analysis, with discriminant function and partial least square analyses performed on aligned coordinate data to identify features that significantly separate tapir species. Overall, our results support the previously held hypothesis that T. indicus is morphologically separate from neotropical tapirs; however, previous conclusions regarding function from morphological differences are shown to require reassessment. We find evidence indicating that T. bairdii exhibits reduced reliance on the lateral fifth digit compared to other tapirs. Morphometric assessment of the metacarpophalangeal joint and the morphology of the distal facets of the lunate lend evidence toward high loading on the lateral digits of both the large T. indicus (large body mass) and the small, long limbed T. pinchaque (ground impact). Our results support other recent studies on T. pinchaque, suggesting subtle but important adaptations to a compliant but inclined habitat. In conclusion, we demonstrate further evidence that the modern tapir forelimb is a variable locomotor unit with a range of interspecific features tailored to habitual and biomechanical needs of each species. A simplified phylogeny demonstrating gross differences in the manus morphology of modern tapirs. Bones with lighter colours (higher specificity %) represent higher levels of morphological difference between species, darker colours represent bones that are misclassified more frequently. Each tapir species is represented by a silhouette diagram demonstrating generalised appearance.

The morphology of the male reproductive system, spermatogenesis and the spermatozoon of Daphnia magna (Crustacea: Branchiopoda)


This study analyses the histological and cellular morphology of the testis and sperm development in the male Daphnia magna Straus 1820. Due to the rarity of males and predominately parthenogenetic lifecycle of Daphnia, there has been limited detailed information on males in contrast to the well-studied female. Using light and electron microscopy approaches, we describe the morphology of the testis during the progression from an immature to mature testis. The testis has an encasing muscular mesh sheath outside the basal lamina, beneath which is a thin somatic epithelial cell layer. Internal to the epithelium are the spermatogonial stem cells and subsequent syncytial clusters of the germ cells as they progress through spermatogenesis; spermatozoa occupy the entire testis in sexually mature D. magna. We describe the structure of developing and mature spermatozoa; mature spermatozoa are non-flagellated, ovoid in shape with plasmalemma filapodia and are encased in an extracellular capsule. Testis structure of Daphnia magna, showing muscles in red, labeled with Phalloiden, and developing nuclei in blue, labeled with Hoechst.

Formation and function of the “Xestoleberis-spot” in Xestoleberis hanaii (Crustacea: Ostracoda)


The crescent sculpture of the so-called “Xestoleberis-spot” develops inside the calcified valve of the family Xestoleberididae. Electron microscopic observations on both, intermoult and postmoult stages of Xestoleberis species reveal that the “Xestoleberis-spot” system consists of three elements; two calcified chambers, a vesicle of electron-dense material and an uncalcified procuticle. The formation and function of the “Xestoleberis-spot” system are discussed. In conclusion, the “Xestoleberis-spot” system functions as the muscle attachment site for several antennal muscles, and provides the material for chitinous fibers in the exocuticle of outer lamella. The unique cuticular structures of the family Xestoleberididae are due to the “Xestoleberis-spot” system. EM observations on both, intermoult and postmoult stages of Xestoleberis species reveal that the “Xestoleberis-spot” system consists of three elements; two calcified chambers, a vesicle of electron-dense material and an uncalcified procuticle.

Intra- and Intersexual swim bladder dimorphisms in the plainfin midshipman fish (Porichthys notatus): Implications of swim bladder proximity to the inner ear for sound pressure detection


The plainfin midshipman fish, Porichthys notatus, is a nocturnal marine teleost that uses social acoustic signals for communication during the breeding season. Nesting type I males produce multiharmonic advertisement calls by contracting their swim bladder sonic muscles to attract females for courtship and spawning while subsequently attracting cuckholding type II males. Here, we report intra- and intersexual dimorphisms of the swim bladder in a vocal teleost fish and detail the swim bladder dimorphisms in the three sexual phenotypes (females, type I and II males) of plainfin midshipman fish. Micro-computerized tomography revealed that females and type II males have prominent, horn-like rostral swim bladder extensions that project toward the inner ear end organs (saccule, lagena, and utricle). The rostral swim bladder extensions were longer, and the distance between these swim bladder extensions and each inner-ear end organ type was significantly shorter in both females and type II males compared to that in type I males. Our results revealed that the normalized swim bladder length of females and type II males was longer than that in type I males while there was no difference in normalized swim bladder width among the three sexual phenotypes. We predict that these intrasexual and intersexual differences in swim bladder morphology among midshipman sexual phenotypes will afford greater sound pressure sensitivity and higher frequency detection in females and type II males and facilitate the detection and localization of conspecifics in shallow water environments, like those in which midshipman breed and nest. Plainfin midshipman females and type II males (an alternative male sexual phenotype) have prominent, horn-like rostral swim bladder extensions which are lacking in nesting type I males, that increase the proximity to the auditory end organs.

In Memoriam: Dr. Frederick W. Harrison (1938–2016)


Ear ossicle morphology of the Jurassic euharamiyidan Arboroharamiya and evolution of mammalian middle ear


The middle ear bones of Mesozoic mammals are rarely preserved as fossils and the morphology of these ossicles in the earliest mammals remains poorly known. Here, we report the stapes and incus of the euharamiyidan Arboroharamiya from the lower Upper Jurassic (∼160 Ma) of northern China, which represent the earliest known mammalian middle ear ossicles. Both bones are miniscule in relation to those in non-mammalian cynodonts. The skull length/stapedial footplate diameter ratio is estimated as 51.74 and the stapes length as the percentage of the skull length is 4%; both numbers fall into the stapes size ranges of mammals. The stapes is “rod-like” and has a large stapedial foramen. It is unique among mammaliaforms in having a distinct posterior process that is interpreted as for insertion of the stapedius muscle and homologized to the ossified proximal (stapedial) end of the interhyal, on which the stapedius muscle attached. The incus differs from the quadrate of non-mammalian cynodonts such as morganucodontids in having small size and a slim short process. Along with lack of the postdentary trough and Meckelian groove on the medial surface of the dentary, the ossicles suggest development of the definitive mammalian middle ear (DMME) in Arboroharamiya. Among various higher-level phylogenetic hypotheses of mammals, the one we preferred places “haramiyidans” within Mammalia. Given this phylogeny, development of the DMME took place once in the allotherian clade containing euharamiyidans and multituberculates, probably independent to those of monotremes and therians. Thus, the DMME has evolved at least three times independently in mammals. Alternative hypothesis that placed “haramiyidans” outside of Mammalia would require independent acquisition of the DMME in multituberculates and euharamiyidans as well as parallel evolution of numerous derived similarities in the dentition, occlusion pattern, mandibles, cranium, and postcranium between the two groups and between “haramiyidans” and other mammals. J. Morphol., 2016. © 2016 Wiley Periodicals, Inc.

Bony labyrinth morphology in early neopterygian fishes (Actinopterygii: Neopterygii)


Endocasts of the osseous labyrinth have the potential to yield information about both phylogenetic relationships and ecology. Although bony labyrinth morphology is well documented in many groups of fossil vertebrates, little is known for early Neopterygii, the major fish radiation containing living teleosts, gars and the bowfin. Here, we reconstruct endocasts of the bony labyrinth and associated structures for a sample of Mesozoic neopterygian fishes using high-resolution computed tomography. Our sample includes taxa unambiguously assigned to either the teleost (Dorsetichthys, “Pholidophorus,” Elopoides) and holostean (“Aspidorynchus,” “Caturus,” Heterolepidotus) total-groups, as well as examples of less certain phylogenetic position (an unnamed parasemionotid and Dapedium). Our models provide a test of anatomical interpretations for forms where bony labyrinths were reconstructed based on destructive tomography (“Caturus”) or inspection of the lateral wall of the cranial chamber (Dorsetichthys), and deliver the first detailed insights on inner ear morphology in the remaining taxa. With respect to relationships, traits apparent in the bony labyrinth and associated structures broadly support past phylogenetic hypotheses concerning taxa agreed to have reasonably secure systematic placements. Inner ear morphology supports placement of Dapedium with holosteans rather than teleosts, while preserved structure in the unnamed parasemionotid is generalized to the degree that it provides no evidence of close affinity with either of the crown neopterygian lineages. This study provides proof-of-concept for the systematic utility of the inner ear in neopterygians that, in combination with similar findings for earlier-diverging actinopterygian lineages, points to the substantial potential of this anatomical system for addressing the longstanding questions in the relationships of fossil ray-finned fishes to one another and living groups. J. Morphol., 2016. © 2016 Wiley Periodicals, Inc.

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Patterns of morphological integration between parietal and temporal areas in the human skull


Modern humans have evolved bulging parietal areas and large, projecting temporal lobes. Both changes, largely due to a longitudinal expansion of these cranial and cerebral elements, were hypothesized to be the result of brain evolution and cognitive variations. Nonetheless, the independence of these two morphological characters has not been evaluated. Because of structural and functional integration among cranial elements, changes in the position of the temporal poles can be a secondary consequence of parietal bulging and reorientation of the head axis. In this study, we use geometric morphometrics to test the correlation between parietal shape and the morphology of the endocranial base in a sample of adult modern humans. Our results suggest that parietal proportions show no correlation with the relative position of the temporal poles within the spatial organization of the endocranial base. The vault and endocranial base are likely to be involved in distinct morphogenetic processes, with scarce or no integration between these two districts. Therefore, the current evidence rejects the hypothesis of reciprocal morphological influences between parietal and temporal morphology, suggesting that evolutionary spatial changes in these two areas may have been independent. However, parietal bulging exerts a visible effect on the rotation of the cranial base, influencing head position and orientation. This change can have had a major relevance in the reorganization of the head functional axis. The curvature and form of the parietal bone does not influence the position of the temporal poles in the human skull The size and shape of the parietal bone influences the orientation on the head

The lungs of Polypterus senegalus and Erpetoichthys calabaricus: Insights into the structure and functional distribution of the pulmonary epithelial cells


The present article is a comparative, structural study of the lung of Polypterus senegalus and Erpetoichthys calabaricus, two species representative of the two genera that constitute the Polypteriformes. The lung of the two species is an asymmetric, bi-lobed organ that arises from a slit-like opening in the ventral side of the pharynx. The wall is organized into layers, being thicker in P. senegalus. The inner epithelium contains ciliated and non-ciliated bands. The latter constitute the respiratory surface and are wider in E. calabaricus. The air-blood barrier is thin and uniform in P. senegalus and thicker and irregular in E. calabaricus. In the two species, the ciliated areas contain ciliated cells, mucous cells and cells with lamellar bodies. Additionally, P. senegalus contains polymorphous granular cells (PGCs) and neuroendocrine cells (NECs) while E. calabaricus lacks PGCs but shows granular leukocytes and a different type of NEC. Interestingly, ciliated cells and secretory cells show a dual morphology in E. calabaricus indicating the presence of cellular subtypes and suggesting more complex secretory activity. Also in E. calabaricus, cilia show a novel doublet-membrane interaction that may control the displacement of the microtubule doublets. The subepithelium is a connective layer that appears thicker in P. senegalus and contains, in the two species, fibroblasts and granulocytes. The outer layer contains bundles of richly innervated striated muscle. This layer is likely involved in the control of lung motion. In the two species, smooth muscle cells constitute a limiting layer between the subepithelium and the striated muscle compartment. The role of this layer is unclear. E. calabaricus. Detail of ciliated band. Ciliated cells (arrow) show prominent ciliary tufts and contain secretory bodies. Goblet cells (G) show secretory bodies and may contain lamellar bodies. Pneumocytes type 2 (double arrow) contain lamellar bodies, may also contain secretory bodies, and are restricted to the ciliated bands. The subepithelium is a thin layer, appears limited by collagen and contains fibroblasts (F) and granulocytes. External to this area is a thin layer of smooth muscle and a thick striated muscle layer with myelinated and non-myelinated nerve fibers. Scale bar, 5 microns.

Correlates between calcaneal morphology and locomotion in extant and extinct carnivorous mammals


Locomotor mode is an important component of an animal's ecology, relating to both habitat and substrate choice (e.g., arboreal versus terrestrial) and in the case of carnivores, to mode of predation (e.g., ambush versus pursuit). Here, we examine how the morphology of the calcaneum, the ‘heel bone’ in the tarsus, correlates with locomotion in extant carnivores. Other studies have confirmed the correlation of calcaneal morphology with locomotion behaviour and habitat. The robust nature of the calcaneum means that it is frequently preserved in the fossil record. Here, we employ linear measurements and 2D-geometric morphometrics on a sample of calcanea from eighty-seven extant carnivorans and demonstrate a signal of correlation between calcaneal morphology and locomotor mode that overrides phylogeny. We used this correlation to determine the locomotor mode, and hence aspects of the palaeobiology of, 47 extinct carnivorous mammal taxa, including both Carnivora and Creodonta. We found ursids (bears), clustered together, separate from the other carnivorans. Our results support greater locomotor diversity for nimravids (the extinct ‘false sabertooths’, usually considered to be more arboreal), than previously expected. However, there are limitations to interpretation of extinct taxa because their robust morphology is not fully captured in the range of modern carnivoran morphology. We employ linear measurements and 2D geometric morphometrics to examine how the morphology of the calcaneum, the ‘heel bone’, correlates with locomotion in extant carnivores. We use these correlations to determine the locomotor mode, and hence aspects of the probable palaeobiology, of 47 extinct taxa including members of Carnivora and Creodonta.

Pretarsal structures in Leiodidae and Agyrtidae (Coleoptera, Staphylinoidea)


We analysed pretarsal characters of 87 species of Leiodidae (including 10 cholevines and representatives of all tribes and ca. 60% of the genera of non-cholevines), five species of Agyrtidae, and nine representatives of outgroup taxa (Hydraenidae, Staphylinidae, Hydrophilidae, and Histeridae) using scanning electron microscopy. We focused our observations on the architecture of the empodium (including the sclerites and associated setae), the shape and composition of the medial projection of the distal margin of the terminal tarsomere, and the armature of the claws, which were considered a promising source of information for delimiting supraspecific taxa in our previous study. We identified several diagnostic features and recognize potential synapomorphies at the tribal, subtribal and generic levels. The internal systematic arrangement and/or even the monophyletic status of most of the subfamilies of Leiodidae (Camiarinae, Catopocerinae, Leiodinae, and Platypsyllinae) are challenged. We identified potential synapomorphies for Camiarinae (Camiarini and Agyrtodini) and Leiodinae. The non-monophyly of Cholevinae is possible because part of the tribe (Anemadini, Eucatopini, and Oritocatopini) shares potentially apomorphic features with Leiodinae (e.g., a triangular medial projection with a diagonal row of conical spines), whereas another part (Leptodirini and Ptomaphagini) shares a potentially apomorphic feature with Coloninae and Platypsyllinae (a typical medial projection with two distinct triangular projections). Comparative morphology of the empodium and medial projection of distal margin of the apical tarsomere and armature of tarsal claws in leiodids and related taxa indicate a wealth of new diagnostic features and potential synapomorphies for family-groups.

Morphology of the tongue of Vermilingua (Xenarthra: Pilosa) and evolutionary considerations


The tongue of anteaters (Xenarthra, Pilosa, Vermilingua) is a highly specialized for myrmecophagy. Here, we describe the topography and histology of the tongue, and compare it to that of other xenarthrans and other myrmecophagous eutherian mammals. The tongue of Vermilingua is long and slender, with an apical protuberance, which differs between Myrmecophagidae and Cyclopes didactylus. In the former, the rostral region is conical, and in the latter, it is dorsoventrally compressed, as observed in sloths. The tongue of Vermilingua has filiform and circumvallate papillae on the surface; foliate and fungiform papillae are absent. The filiform papillae of Myrmecophaga tridactyla are simple all over the tongue, differing from Tamandua tetradactyla and Cyclopes didactylus, which present composed filiform papillae in the rostral and middle regions. Histologically, the tongue has a peculiar organization of muscular and neurovascular tissues, differing from the usual mammalian pattern. However, the tongue structure is less divergent in Cyclopes. The presence of two circumvallate papillae is common to the three major clades of Xenarthra (Cingulata, Folivora and Vermilingua). In each group, the tongue may reflect functional features related to myrmecophagous (anteaters and some armadillos), omnivorous (remaining armadillos) and folivorous (sloths) feeding habits. The similarities between the tongues of Vermiligua and other non-xenarthran eutherian myrmecophagous mammals are somewhat general and, under close inspection, superficial, being an example of different lineages achieving the same morphofunctional adaptations through distinct evolutionary pathways. The peculiar tongue of anteaters was investigated with gross anatomical observations, scanning electron microscopy and histological techniques. The morphology observed in the tongues of anteaters reflects the adaptive specialization of the organ for myrmecophagy. Comparing it with that of other xenarthrans, it is possible to infer some aspects about the evolution of the organ in the group. Picture of Tamandua tetradactyla by Karina Molina.

How common are cranial sesamoids among squamates?


Sesamoids are elements that originate as intratendinous structures due to genetic and epigenetic factors. These elements have been reported frequently in vertebrates, although cranial sesamoids have been recorded almost exclusively in non-tetrapod Osteichthyes. The only tetrapod cranial sesamoids reported until now have been the transiliens cartilage (of crocodiles and turtles), and another one located in the quadrate-mandibular joint of birds. Here, we examined seven squamate species using histological sections, dissections of preserved specimens, dry skeletons, cleared and stained specimens, computed tomographies (CT), and report the presence of other cranial sesamoids. One is attached to the cephalic condyle of the quadrate, embedded in the bodenaponeurosis and jaw adductor muscles of Ophiodes intermedius (Anguidae). The other sesamoid is found at the base of the basicranium of several squamates, capping the sphenoccipital tubercle, on the lateral side of the basioccipital–basisphenoid suture. This bone has previously been reported as “element X.” We reinterpret it as a basicranial sesamoid, as it is associated with tendons of the cranio-cervical muscles. This bone seems to have the function of resisting tension-compression forces generated by the muscle during flexion the head. This element was previously known in several squamates, and we confirmed its presence in three additional squamate families: Gymnophthalmidae, Gekkonidae, and Pygopodidae. The evidence suggests that cranial sesamoids are a widespread character in squamates, and it is possible that this feature has been present since the origin of the group. The presence of sesamoids on the skeleton of squamate lizards have been described almost exclusively from the appendicular skeleton. In this article, we report two ossicles in the skull of squamates that fulfill the definition of sesamoid elements: one associated with the quadrate bone, and the other with the braincase, previously described as the element X. The latter bone is widespread among squamates, being present in members of major squamate clades with the exception of snakes. Graphic abstract figure indicates the presence of element X among squamate clades (red branches), illustrated here by three groups where this element was unknown, Gekkota (1. Chondrodactylus angulifer, 2. Paradelma orientalis) and Gymophthalmidae (3. Calyptommatus leiolepis).

Shape analysis of the jaws between two minnow species over ontogeny


This study compares sand shiner (Notropis stramineus) and silverjaw (Ericymba buccata) minnows, in terms of the morphological shape changes of the upper, lower, and pharyngeal jaws over ontogeny. These two species of minnows initially feed on midge larvae and undergo an ontogenic prey shift. The traditional morphometrics measured—total length, snout-to-vent length, eye diameter, premaxilla length, lower jaw length, gape—were regressed onto total length to test for allometry. Digital pictures were processed with tpsDig and further analyzed with MorphoJ utilizing a regular geometric morphometrics procedure using principle component analyses. We examined gut contents for 16 fish of each species. For the silverjaw minnows, we found all jaw variables to exhibit positive allometric growth with increasing total length, while most of the jaw variables for the sand shiner exhibited negative allometric growth with increasing total length. This correlates with an ontogenic prey shift for both species. Sand shiner minnows have been found to be more omnivorous, feeding on algae later in life, while silverjaw minnows undergo a prey shift to larger invertebrates. These species lack oral dentition causing an increased reliance on the pharyngeal apparatus. Principle component analyses revealed elongation of pharyngeal jaw elements in the silverjaw minnows and a relative shortening and bulking of pharyngeal jaws in the sand shiner minnows. The ontogenic dietary shifts observed in these two species provide possible explanation for the morphological changes over ontogeny in jaw elements, which are likely enabling these species to occupy the same habitat with little niche overlap. Pharyngeal jaws of two minnow species.

Structure and ultrastructure of eyes and brains of Thalia democratica (Thaliacea, Tunicata, Chordata)


Salps are marine planktonic chordates that possess an obligatory alternation of reproductive modes in subsequent generations. Within tunicates, salps represent a derived life cycle and are of interest in considerations of the evolutionary origin of complex anatomical structures and life history strategies. In the present study, the eyes and brains of both the sexual, aggregate blastozooid and the asexual, solitary oozooid stage of Thalia democratica (Forskål, ) were digitally reconstructed in detail based on serial sectioning for light and transmission electron microscopy. The blastozooid stage of T. democratica possesses three pigment cup eyes, situated in the anterior ventral part of the brain. The eyes are arranged in a way that the optical axes of each eye point toward different directions. Each eye is an inverse eye that consists of two different cell types: pigment cells (pigc) and rhabdomeric photoreceptor cells (prcs). The oozooid stage of T. democratica is equipped with a single horseshoe-shaped eye, positioned in the anterior dorsal part of the brain. The opening of the horseshoe-shaped eye points anteriorly. Similar to the eyes of the blastozooid, the eye of the oozooid consists of pigment cells and rhabdomeric photoreceptor cells. The rhabdomeric photoreceptor cells possess apical microvilli that form a densely packed presumably photosensitive receptor part adjacent to the concave side of the pigc. We suggest correspondences of the individual eyes in the blastozooid stage to respective parts of the single horseshoe-shaped eye in the oozooid stage and hypothesize that the differences in visual structures and brain anatomies evolved as a result of the aggregate life style of the blastozooid as opposed to the solitary life style of the oozooid. Salps are unusual marine plankton with alternating generations. Sexual stages possess three eyes, asexual stages a single horseshoe-shaped eye. Eyes consist of pigment cells and rhabdomeric photoreceptor cells. We suggest that differences evolved as a result of life styles of the two stages.

Ovarian nests in cultured females of the Siberian sturgeon Acipenser baerii (Chondrostei, Acipenseriformes)


Ovaries of Acipenser baerii are of an alimentary type and probably are meroistic. They contain ovarian nests, individual follicles, inner germinal ovarian epithelium, and fat tissue. Nests comprise cystoblasts, germline cysts, numerous early previtellogenic oocytes, and somatic cells. Cysts are composed of cystocytes, which are connected by intercellular bridges and are in the pachytene stage of the first meiotic prophase. They contain bivalents, finely granular, medium electron dense material, and nucleoli in the nucleoplasm. Many cystocytes degenerate. Oocytes differ in size and structure. Most oocytes are in the pachytene and early diplotene stages and are referred to as the PACH oocytes. Oocytes in more advanced diplotene stage are referred to as the DIP oocytes. Nuclei in the PACH oocytes contain bivalents and irregularly shaped accumulation of DNA (DNA-body), most probably corresponding to the rDNA-body. The DNA-body is composed of loose, fine granular material, and comprises multiple nucleoli. At peripheries, it is fragmented into blocks that remain in contact with the inner nuclear membrane. In the ooplasm, there is the rough endoplasmic reticulum, Golgi complexes, free ribosomes, complexes of mitochondria with cement, fine fibrillar material containing granules, and lipid droplets. The organelles and material of nuclear origin form a distinct accumulation (a granular ooplasm) in the vicinity of the nucleus. Some of the PACH oocytes are surrounded by flat somatic cells. There are lampbrush chromosomes and multiple nucleoli present (early diplotene stage) in the nucleoplasm. These PACH oocytes and neighboring somatic cells have initiated the formation of ovarian follicles. The remaining PACH oocytes transform to the DIP oocytes. The DIP oocytes contain lampbrush chromosomes and a DNA-body is absent in nuclei. Multiple nucleoli are numerous in the nucleoplasm and granular ooplasm is present at the vegetal region of the oocyte. Germline cysts are composed of cystocytes (Cyst). The PACH oocytes are in the pachytene and early diplotene stages of first prophase, the DIP oocytes are in the diplotene stage. Somatic cells (SC) and degenerating cystocytes (asterisks) are present.

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