Showing papers in "Journal of Morphology in 2018"

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

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

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

Abstract: 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. 279:441-457, 2018. © 2016 Wiley Periodicals, Inc.

Allometric scaling of morphology and engulfment capacity in rorqual whales.

Abstract: Body length is one of the most important factors that influence organismal function and ecological niche. Although larger animals tend to have a suite of physiological advantages, such as lower mass-specific metabolic rates and lower costs of transport, they may also experience significant limitations to unsteady locomotor performance or maneuverability because of the relative scaling of control surface areas and body mass. Rorqual whales are the largest of all animals and thus represent a unique study system for understanding how animals function at the extreme of body mass. Rorquals are characterized by an engulfment-filtration foraging strategy facilitated by a complex set of morphological adaptations. We studied the scaling of key morphological structures related to locomotion and feeding in six rorqual species in a comparative framework. Our analyses show that most rorqual species exhibit positive allometry of both the control surfaces and body length, but the large scaling differences between these parameters suggest that larger rorquals will predictably suffer from decreased maneuverability and unsteady locomotor performance. However, we found that the dimensions of the engulfment apparatus also exhibit positive allometry, and thus engulfment capacity was relatively greater in larger rorquals. We posit that the allometric growth in the engulfment apparatus may be an adaptation that ameliorates the detrimental effects of large size on maneuverability. Our analyses also reveal significant differences in the scaling of mass-specific engulfment capacity among rorqual species that may reflect the evolution of unique foraging behaviors and the exploitation of divergent ecological niches.

Tarsal attachment devices of the southern green stink bug Nezara viridula (Heteroptera: Pentatomidae).

Abstract: Based on analyses with cryo-scanning and transmission electron microscopy, the present study reports on the morphology and ultrastructure of the attachment structures of the green stinkbug Nezara viridula L. (Heteroptera: Pentatomidae), a cosmopolitan pest of different crops in most areas of the world. In addition, the presence and distribution of large proportions of the elastic protein resilin in these structures was revealed by confocal laser scanning microscopy. The attachment structures of each leg comprise two sclerotised claws, a pair of smooth flexible pulvilli and a hairy adhesive pad located at the ventral side of the basitarsus. No sexual dimorphism is evident. Contact areas of resting individuals on a smooth surface show that N. viridula creates contact to the substrate with the ventral surface of (a) the distal portions of the pulvilli, (b) the setae of the hairy adhesive pad, (c) the two paraempodia representing mechanosensory setae, and (d) the tips of the claws. Each pulvillus is a sac-like structure formed by complex cuticular layers that vary in their structure and resilin content. The dorsal side consists of sclerotised chitinous material, while the ventral cuticle consists mainly of resilin and shows a very thin epicuticle and a thick exocuticle. The setae of the hairy adhesive pad are pointed and socketed. They exhibit a pronounced longitudinal gradient in the material composition, with large proportions of resilin being present in the setal tips. In most of these setae, especially in those of the distal-most part of the pad, also a transverse gradient in the material composition is visible.

Evolution of facial innervation in anomodont therapsids (Synapsida): Insights from X‐ray computerized microtomography

Abstract: Anomodontia was the most successful herbivorous clade of the mammalian stem lineage (non-mammalian synapsids) during the late Permian and Early Triassic. Among anomodonts, Dicynodontia stands apart because of the presence of an osseous beak that shows evidence of the insertion of a cornified sheath, the ramphotheca. In this study, fourteen anomodont specimens were microCT-scanned and their trigeminal canals reconstructed digitally to understand the origin and evolution of trigeminal nerve innervation of the ramphotheca. We show that the pattern of innervation of the anomodont "beak" is more similar to that in chelonians (the nasopalatine branch is enlarged and innervates the premaxillary part of the ramphotheca) than in birds (where the nasopalatine and maxillary branches play minor roles). The nasopalatine branch is noticeably enlarged in the beak-less basal anomodont Patranomodon, suggesting that this could be an anomodont or chainosaur synapomorphy. Our analyses suggest that the presence or absence of tusks and postcanine teeth are often accompanied by corresponding variations of the rami innervating the caniniform process and the alveolar region, respectively. The degree of ossification of the canal for the nasal ramus of the ophthalmic branch also appears to correlate with the presence of a nasal boss. The nasopalatine canal is absent from the premaxilla in the Bidentalia as they uniquely show a large plexus formed by the internal nasal branch of the maxillary canal instead. The elongated shape of this plexus in Lystrosaurus supports the hypothesis that the rostrum evolved as an elongation of the subnarial region of the snout. Finally, the atrophied and variable aspect of the trigeminal canals in Myosaurus supports the hypothesis that this genus had a reduced upper ramphotheca.

Size and shape correlation of birds' pelvis and egg: Impact of developmental mode, habitat, and phylogeny.

Abstract: While eggs shapes and sizes have been subject of many studies, we still know little about factors affecting these characteristics of birds' eggs. We revealed that shapes of pelvis and egg correlated less than their respective sizes. Egg measurements (length or diameter) scaled with negative allometry against pelvis size, that is, eggs become relatively larger with decreasing pelvis size. Studied birds with altricial developmental mode had on average the smallest pelvic dimensions and the largest relative size of eggs. However, this is due to the effect of small pelvis size (and body as a whole) of most altricials. At the similar size of the pelvis, birds with altricial developmental mode had a smaller relative size of eggs than their precocial counterparts. Correlation between the shape of egg and pelvis is affected by habitat. Narrow pelvis with an elongated postacetabular region correlated with elongated eggs in diving waterfowl. In raptorial birds, the relatively wide pelvis with the shortened postacetabular region correlated with the nearly rounded shape of eggs.

Cranial shape variation in jacarean caimanines (Crocodylia, Alligatoroidea) and its implications in the taxonomic status of extinct species: The case of Melanosuchus fisheri

Abstract: Melanosuchus niger (Crocodylia, Alligatoroidea) is one of the six living caimanine species widely distributed throughout the Amazon River basin today. Although there is only one extant species of Melanosuchus, fossil material assigned to this genus, represented by M. fisheri, has been reported from the late Miocene in South America. However, the validity of this taxon has been questioned and a recent investigation indicates that the referred specimen of M. fisheri (MCZ 4336) actually belongs to Globidentosuchus brachyrostris, while those diagnostic characters present in the holotype (MCNC 243) fall into the spectrum of intraspecific variation of M. niger. Here, we compare the skull shape of the holotype of M. fisheri with the ontogenetic series of the four jacarean species (M. niger, Caiman yacare, Caiman crocodilus, and Caiman latirostris) using 2D-geometric morphometric analyses in two different views. The analyses indicate that MCNC 243 falls into the morphospace of M. niger and C. latirostris. Despite strong shape similarities between juveniles of C. latirostris and MCNC 243, further anatomical comparisons reveal notable differences between them. In contrast, no concrete anatomical differences can be found between MCNC 243 and M. niger, although shape analyses indicate that MCNC 243 is relatively robust for its size. Thus, this study is able to confirm that the genus Melanosuchus was present in the late Miocene, but it still remains unclear if MCNC 243 should be treated as a junior synonym or probably a sister species of M. niger. Its Miocene age favors the second option, but as the shape analyses were also not able to extract any diagnostic characters, it should be retained as Melanosuchus cf. niger.

Links between the discovery of primates and anatomical comparisons with humans, the chain of being, our place in nature, and racism.

Abstract: I focus on the crucial links between the discovery of nonhuman primates by Westerners, discussions on our place in nature, the chain of being, racism, and the history of primate comparative anatomy and of so-called "anatomical human racial studies." Strikingly, for more than a millennium humans knew more about the internal anatomy of a single monkey species than about that of their own bodies. This is because Galen used monkeys to infer human anatomy, in line with the human-animal continuity implied by the Greek notion of scala naturae. With the rise of Christianity, nonhuman primates were increasingly seen in a negative way. A more positive view emerged in the 14th century when nonhuman primates were directly studied/seen by Europeans, culminating in Tyson's 1699 work showing that chimps share more gross anatomical similarities with humans than with monkeys. However, the discomfort caused by this human-chimp similarity then led to a new idea of animal-human discontinuity, now related not to anatomy but to "civilization": between Europeans vs. non-Europeans + other primates. Moreover, Linnaeus' Systema Naturae and the emergence of "anatomical racial studies" influenced by Camper's craniology then led to even more extreme ideas, such as the notion that Europeans were both mentally and morphologically "ideal." Unfortunately the biased and often incorrect "results" of such studies, combined with ideas based on Darwin's "struggle for survival", became crucial in propaganda that lead to the rise of eugenics in the end of the 19th/first half of 20th centuries and that culminated in Nazism. Since the 1950s there has been an emphasis on the continuity/unity between all human groups and other primates, in great part influenced by what happened during World War 2. Reviews such as this one are, therefore, particularly necessary to illuminate and guard against attitudes against "the Other" and racist ideologies that are re-emerging in modern political discourse across the globe.

Cephalic muscle development in the Australian lungfish, Neoceratodus forsteri.

Abstract: Lungfishes are the extant sister group of tetrapods. As such, they are important for the study of evolutionary processes involved in the water to land transition of vertebrates. The evolution of a true neck, that is, the complete separation of the pectoral girdle from the cranium, is one of the most intriguing morphological transitions known among vertebrates. Other salient changes involve new adaptations for terrestrial feeding, which involves both the cranium and its associated musculature. Historically, the cranium has been extensively investigated, but the development of the cranial muscles much less so. Here, we present a detailed study of cephalic muscle development in the Australian lungfish, Neoceratodus forsteri, which is considered to be the sister taxon to all other extant lungfishes. Neoceratodus shows several developmental patterns previously described in other taxa; the tendency of muscles to develop from anterior to posterior, from their region of origin toward insertion, and from lateral to ventral/medial (outside-in), at least in the branchial arches. The m.protractor pectoralis appears to develop as an extension of the most posterior m.levatores arcuum branchialium, supporting the hypothesis that the m.cucullaris and its derivatives (protractor pectoralis, levatores arcuum branchialium) are branchial muscles. We present a new hypothesis regarding the homology of the ventral branchial arch muscles (subarcualis recti and obliqui, transversi ventrales) in lungfishes and amphibians. Moreover, the morphology and development of the cephalic muscles confirms that extant lungfishes are neotenic and have been strongly influenced via paedomorphosis during their evolutionary history.

Are there general laws for digit evolution in squamates? The loss and re-evolution of digits in a clade of fossorial lizards (Brachymeles, Scincinae).

Abstract: Evolutionary simplification of autopodial structures is a major theme in studies of body-form evolution. Previous studies on amniotes have supported Morse's law, that is, that the first digit reduced is Digit I, followed by Digit V. Furthermore, the question of reversibility for evolutionary digit loss and its implications for "Dollo's law" remains controversial. Here, we provide an analysis of limb and digit evolution for the skink genus Brachymeles. Employing phylogenetic, morphological, osteological, and myological data, we (a) test the hypothesis that digits have re-evolved, (b) describe patterns of morphological evolution, and (c) investigate whether patterns of digit loss are generalizable across taxa. We found strong statistical support for digit, but not limb re-evolution. The feet of pentadactyl species of Brachymeles are very similar to those of outgroup species, while the hands of these lineages are modified (2-3-3-3-2) and a have a reduced set of intrinsic hand muscles. Digit number variation suggests a more labile Digit V than Digit I, contrary to Morse's law. The observed pattern of digit variation is different from that of other scincid lizards (Lerista, Hemiergis, Carlia). Our results present the first evidence of clade-specific modes of digit reduction.

A potential link between lateral semicircular canal orientation, head posture, and dietary habits in extant rhinos (Perissodactyla, Rhinocerotidae).

Abstract: Extant rhinoceroses share the characteristic nasal horn, although the number and size of horns varies among the five species. Although all species are herbivores, their dietary preferences, occipital shapes, and common head postures vary. Traditionally, to predict the “usual” head posture (the most used head posture of animals during normal unstressed activities, i.e., standing) of rhinos, the occipital shape was used. While a backward inclined occiput implies a downward hanging head (often found in grazers), a forward inclined occiput is related to the horizontal head posture in browsing rhinos. In this study, the lateral semicircular canal (LSC) of the bony labyrinth was virtually reconstructed from µCT-images in order to investigate a possible link between LSC orientation and head posture in extant rhinoceroses. The usual head posture was formerly reconstructed for several non-rhinoceros taxa with the assumption that the LSC of the inner ear is held horizontal (parallel to the ground) during normal activity of the living animal. The current analysis of the LSC orientation resulted in a downward inclined usual head posture for the grazing white rhinoceros and a nearly horizontal head posture in the browsing Javan rhinoceros. The other three browsing or mixed feeding species show subhorizontal (closer to horizontal than a downgrade inclination) head postures. The results show that anatomical and behavioral aspects, like occipital shape, presence and size of horns/tusk-like lower incisors, as well as feeding and feeding height preferences influence the usual head posture. Because quantitative behavioral data are lacking for the usual head postures of the extant rhinos, the here described relationship between the LSC orientation and the resulting head posture linked to feeding preferences gives new insights. The results show, that the inner ear provides additional information to interpret usual head postures linked to feeding preferences that can easily be adapted to fossil rhinoceroses.

Size, shape, and sex-dependent variation in force production by crayfish chelae.

Abstract: The ability to generate large closing forces is important for many animals. Several studies have demonstrated that bite or pinching force capacity is usually related to the linear dimensions of the closing apparatus. However, relatively few studies have applied geometric morphometrics to examine the effects of size-independent shape on force production, particularly in studies of crustacean pinching force. In this study, we utilized traditional and geometric morphometric techniques to compare the pinching force of Procambarus clarkii crayfish to their chela morphology. We found that males possessed larger chelae and pinched harder than females, but that their chela shape and size were weak predictors of strength. Female pinching force was significantly affected by both chela size and shape, with shape variation along the short axis of the claw contributing most to pinching force. We discuss our results in the context of reliable signaling of strength by males and females, and the different selective forces acting on chela shape in the two sexes.

The evolution of underwater flight: The redistribution of pectoral fin rays, in manta rays and their relatives (Myliobatidae).

Abstract: Batoids are a diverse clade of flat cartilaginous fishes that occur primarily in benthic marine habitats. The skates and rays typically use their flexible pectoral fins for feeding and propulsion via undulatory swimming. However, two groups of rays have adopted a pelagic or bentho-pelagic lifestyle and utilize oscillatory swimming-the Myliobatidae and Gymnuridae. The myliobatids have evolved cephalic lobes, anteriorly extended appendages that are optimized for feeding, while their pectoral fins exhibit several modifications that likely arose in association with functional optimization of pelagic cruising via oscillatory flight. Here, we examine variation in fin ray distribution and ontogenetic timing of fin ray development in batoid pectoral fins in an evolutionary context using the following methods: radiography, computed tomography, dissections, and cleared and stained specimens. We propose an index for characterizing variation in the distribution of pectoral fin rays. While undulatory swimmers exhibit symmetry or slight anterior bias, we found a posterior shift in the distribution of fin rays that arose in two distinct lineages in association with oscillatory swimming. Undulatory and oscillatory swimmers occupy nonoverlapping morphospace with respect to fin ray distribution illustrating significant remodeling of pectoral fins in oscillatory swimmers. Further, we describe a derived skeletal feature in anterior pectoral fins of the Myliobatidae that is likely associated with optimization of oscillatory swimming. By examining the distribution of fin rays with clearly defined articulation points, we were able to infer evolutionary trends and body plan remodeling associated with invasion of the pelagic environment. Finally, we found that the number and distribution of fin rays is set early in development in the little skate, round stingray, and cownose ray, suggesting that fin ray counts from specimens after birth or hatching are representative of adults and therefore comparable among species.

Ecological lifestyles and the scaling of shark gill surface area.

Abstract: Fish gill surface area varies across species and with respect to ecological lifestyles. The majority of previous studies only qualitatively describe gill surface area in relation to ecology and focus primarily on teleosts. Here, we quantitatively examined the relationship of gill surface area with respect to specific ecological lifestyle traits in elasmobranchs, which offer an independent evaluation of observed patterns in teleosts. As gill surface area increases ontogenetically with body mass, examination of how gill surface area varies with ecological lifestyle traits must be assessed in the context of its allometry (scaling). Thus, we examined how the relationship of gill surface area and body mass across 11 shark species from the literature and one species for which we made measurements, the Gray Smoothhound Mustelus californicus, varied with three ecological lifestyle traits: activity level, habitat, and maximum body size. Relative gill surface area (gill surface area at a specified body mass; here we used 5,000g, termed the 'standardized intercept') ranged from 4,724.98 to 35,694.39 cm2 (mean and standard error: 17,796.65 ± 2,948.61 cm2 ) and varied across species and the ecological lifestyle traits examined. Specifically, larger-bodied, active, oceanic species had greater relative gill surface area than smaller-bodied, less active, coastal species. In contrast, the rate at which gill surface area scaled with body mass (slope) was generally consistent across species (0.85 ± 0.02) and did not differ statistically with activity level, habitat, or maximum body size. Our results suggest that ecology may influence relative gill surface area, rather than the rate at which gill surface area scales with body mass. Future comparisons of gill surface area and ecological lifestyle traits using the quantitative techniques applied in this study can provide further insight into patterns dictating the relationship between gill surface area, metabolism, and ecological lifestyle traits.

Change of lecithotrophic to matrotrophic nutrition during gestation in the viviparous teleost Xenotoca eiseni (Goodeidae).

Abstract: Teleosts possess unique features of the female reproductive system compared with the rest of vertebrates, features that define the characteristics of their viviparity. Viviparity involves new maternal-embryonic relationships detailing the most diverse structures during gestation that include embryonic nutrition. In order to analyze the morphological features of the complex nutrition in viviparous teleosts during intraovarian gestation, this study utilizes the goodeid Xenotoca eiseni as a model. Ovarian gestation in X. eiseni, as in all goodeids, is intraluminal; the early embryo moves from the follicle to the ovarian lumen where gestation continues. The scarce yolk in the oocytes implies that the initial lecithotrophy is replaced by matrotrophy, with nutrients provided via maternal tissues. The nutrients are absorbed by the embryo mainly by trophotaenia, extensions of the embryonic intestine into the ovarian lumen. This histological study analyses the structures involved in these two types of nutrition and when they occur during gestation in X. eiseni. The morphology displayed in this study demonstrated the extended simultaneity of lecithotrophy and matrotrophy during gestation with the progressive reduction of lecithotrophy and increase of matrotrophy. Similarly, it describes the development of complex embryonic structures for metabolic exchange with the maternal tissues associated with matrotrophy; specifically the branchial placenta and mainly the trophotaenia.

Do chitons have a brain? New evidence for diversity and complexity in the polyplacophoran central nervous system.

Abstract: Molluscs demonstrate astonishing morphological diversity, and the relationships among clades have been debated for more than a century. Molluscan nervous systems range from simple 'ladder-like' cords to the complex brains of cephalopods. Chitons (Polyplacophora) are assumed to retain many molluscan plesiomorphies, lacking neural condensation and ganglionic structure, and therefore a brain. We reconstructed three-dimensional anatomical models of the nervous system in eight species of chitons in an attempt to clarify chiton neuroarchitecture and its variability. We combined new data with digitised historic slide material originally used by malacologist Johannes Thiele (1860-1935). Reconstructions of whole nervous systems in Acanthochitona fascicularis, Callochiton septemvalvis, Chiton olivaceus, Hemiarthrum setulosum, Lepidochitona cinerea, Lepidopleurus cajetanus and Leptochiton asellus, and the anterior nervous system of Schizoplax brandtii, demonstrated consistent and substantial anterior neural concentration in the circumoesophageal nerve ring. This is further organised into three concentric tracts, corresponding to the lateral, ventral and cerebral nerve cords. These represent homologues to the three main pairs of ganglia in other molluscs. Their relative size, shape and organisation are highly variable among the examined taxa, but consistent with previous studies of select species, and we formulated a set of neuroanatomical characters for chitons. These support anatomical transitions at the ordinal and subordinal levels; the identification of robust homologies in neural architecture will be central to future comparisons across Mollusca and, more broadly, Lophotrochozoa. Contrary to almost all previous descriptions, the size and structure of the chiton anterior nerve ring unambiguously qualify it as a true brain with cordal substructure.

Making a master filterer: Ontogeny of specialized filtering plates in silver carp (Hypophthalmichthys molitrix)

Abstract: Filter feeding fishes possess several morphological adaptations necessary to capture and concentrate small particulate matter from the water column. Filter feeding teleosts typically employ elongated and tightly packed gill rakers with secondary bony or epithelial modifications that increase filtering efficiency. The gill rakers of Hypophthalmichthys molitrix, silver carp, are anatomically distinct from and more complex than the filtering apparatus of other teleostean fishes. The silver carp filtering apparatus is composed of biserial, fused filtering plates used to capture particles ranging in size from 4 to 80 μm. Early in ontogeny, at 15-25 mm standard length (SL), silver carp gill rakers are reminiscent of other more stereotypical teleostean rakers, characterized by individual lanceolate rakers that are tightly packed along the entirety of the branchial arches. At 30 mm SL, secondary epithelial projections and concomitant dermal ossification begin to stitch together individual gill rakers. During later juvenile stages, dermal bone further modifies the individual gill rakers and creates a bony scaffold that supports the now fully fused and porous epithelium. By adulthood, the stitching of bone and complete fusion of the overlying epithelium creates rigid filtering plates with morphologically distinct faces. The inner face of the plates is organized into a net-like matrix while the outer face has a sponge-like appearance comprised of differently sized pores. Here, we present morphological data from an ontogenetic series of the filtering apparatus within silver carp. These data inform hypotheses regarding both how these gill raker plates may have evolved from a more basal condition, as well as how this novel architecture allows this species to feed on exceedingly small phytoplankton, particles that represent a greater filtering challenge to the typical anatomy of the gill rakers of fishes.

Sequence and timing of early cranial skeletal development in Xenopus laevis.

Abstract: Xenopus laevis is widely used as a model organism in biological research Morphological descriptions of the larval cartilaginous skeleton are more than half a century old and comprehensive studies of early cartilage differentiation and development are missing A proper understanding of early cranial skeletal development in X laevis requires a detailed description that can function as a baseline for experimental studies This basis makes it possible to evaluate skeletal defects produced by experiments on gene interactions, such as gain- or loss-of function experiments In this study, we provide a detailed description of the pattern and timing of early cartilage differentiation and development in the larval head of X laevis Methods used include antibody staining, confocal laser scanning microscopy and 3D-reconstruction Results were than compared to earlier studies based on classical histological approaches and clearing-and-staining The first cartilage to chondrify is, in contrast to other vertebrates investigated so far, the ceratohyal The components of the branchial basket chondrify in anterior-to-posterior direction as reported for other amphibians Chondrification of different cartilages begins at different stages and the majority of cartilages are fully developed at Ziermann and Olsson stage 17 Our baseline data on the pattern and timing of early cartilaginous development in X laevis is useful for evaluation of experiments which alter head skeletal development as well as for identifying heterochronic shifts in head development in other amphibians

Morphological changes of the optic lobe from late embryonic to adult stages in oval squids Sepioteuthis lessoniana.

Abstract: The optic lobe is the largest brain area within the central nervous system of cephalopods and it plays important roles in the processing of visual information, the regulation of body patterning, and locomotive behavior. The oval squid Sepioteuthis lessoniana has relatively large optic lobes that are responsible for visual communication via dynamic body patterning. It has been observed that the visual behaviors of oval squids change as the animals mature, yet little is known about how the structure of the optic lobes changes during development. The aim of the present study was to characterize the ontogenetic changes in neural organization of the optic lobes of S. lessoniana from late embryonic stage to adulthood. Magnetic resonance imaging and micro-CT scans were acquired to reconstruct the 3D-structure of the optic lobes and examine the external morphology at different developmental stages. In addition, optic lobe slices with nuclear staining were used to reveal changes in the internal morphology throughout development. As oval squids mature, the proportion of the brain making up the optic lobes increases continuously, and the optic lobes appear to have a prominent dent on the ventrolateral side. Inside the optic lobe, the cortex and the medulla expand steadily from the late embryonic stage to adulthood, but the cell islands in the tangential zone of the optic lobe decrease continuously in parallel. Interestingly, the size of the nuclei of cells within the medulla of the optic lobe increases throughout development. These findings suggest that the optic lobe undergoes continuous external morphological change and internal neural reorganization throughout the oval squid's development. These morphological changes in the optic lobe are likely to be responsible for changes in the visuomotor behavior of oval squids from hatching to adulthood.

Comparative morphology of male genitalic structures in the minute litter bugs Dipsocoromorpha (Insecta: Hemiptera: Heteroptera)

Abstract: Insect male genitalia show an evolutionarily variable morphology that has proven to be valuable for both, species identifications and phylogenetic analyses at higher taxonomic levels Accurate usage of genitalic characters in taxonomic descriptions and phylogenetic analyses depends on consistency of terminology and validity of homology hypotheses Both areas are underdeveloped in many insect groups We here document the morphology and advance homology hypotheses of male genitalic features for the hemipteran infraorder Dipsocoromorpha, the minute litter bugs Genitalic structures and the pregenital abdomen in Dipsocoromorpha are strikingly modified and diverse compared to other Heteroptera In addition to variation in the shape of phallic structures (parameres and aedeagus), minute litter bug genitalia vary in the direction and degree of asymmetry and feature a plethora of processes derived from various abdominal segments with significant variation at low taxonomic levels Here, male genitalic structures for an extensive taxonomic sample (32 genera and 71 specimens) are documented using scanning electron and confocal microscopy, and a universal terminology for genitalic structures across minute litter bugs is established that will facilitate species discovery and evolutionary research We conclude by proposing primary homology hypotheses across the infraorder that now can be tested in a phylogenetic framework

Neuroanatomy of Hyalinella punctata: Common patterns and new characters in phylactolaemate bryozoans

Abstract: Studies on the bryozoan adult nervous system employing immunocytochemical techniques and confocal laser scanning microscopy are scarce. To gain a better view into the structure and evolution of the nervous system of the Phylactolaemata, the earliest extant branch and sister taxon to the remaining Bryozoa, this work aims to characterize the nervous system of Hyalinella punctata with immunocytochemical techniques and confocal laser scanning microscopy. The cerebral ganglion is located between the anus and the pharynx and contains a lumen. Two ganglionic horns and a circum-oral nerve ring emanate from the cerebral ganglion. The pharynx is innervated by a diffuse neural plexus with two prominent neurite bundles. The caecum is innervated by longitudinal neurite bundles and a peripheral plexus. The intestine is characterized by longitudinal and circular neurite bundles, mostly near the anus. Novel putative sensory cells were found in the foregut and intestine. The tentacle sheath is innervated by a diffuse neural plexus, which emanates from several neurite bundles from the cerebral ganglion, but also parts of the pharyngeal plexus. There are six tentacle neurite bundles of intertentacular origin. The retractor muscles are innervated by two thin neurite bundles. Several characters are described herein for the first time in Phylactolaemata: Longitudinal neurite bundles and a peripheral plexus of the caecum, putative sensory structures of the gut, retractor muscle innervation, specific duplicature band neurite bundles. The tentacle innervation differs from previous descriptions of phylactolaemates regarding the origin of the three abfrontal neurite bundles. In general, most organ systems are innervated by a diffuse plexus in phylactolaemates as opposed to gymnolaemates. In contrast to the Gymnolaemata, representatives of Phylactolaemata show a higher number of tentacle nerves. Although the plesiomorphic condition for zooidal features among bryozoans remains unclear, having a diffuse nerve plexus may represent an ancestral feature for freshwater bryozoans.

Evolution of hindlimb bone dimensions and muscle masses in house mice selectively bred for high voluntary wheel‐running behavior

Abstract: We have used selective breeding with house mice to study coadaptation of morphology and physiology with the evolution of high daily levels of voluntary exercise. Here, we compared hindlimb bones and muscle masses from the 11th generation of four replicate High Runner (HR) lines of house mice bred for high levels of voluntary wheel running with four non-selected control (C) lines. Mass, length, diameter, and depth of the femur, tibia-fibula, and metatarsal bones, as well as masses of gastrocnemius and quadriceps muscles, were compared by analysis of covariance with body mass or body length as the covariate. Mice from HR lines had relatively wider distal femora and deeper proximal tibiae, suggesting larger knee surface areas, and larger femoral heads. Sex differences in bone dimensions were also evident, with males having thicker and shorter hindlimb bones when compared with females. Several interactions between sex, linetype, and/or body mass were observed, and analyses split by sex revealed several cases of sex-specific responses to selection. A subset of the HR mice in two of the four HR lines expressed the mini-muscle phenotype, characterized mainly by an ∼50% reduction in hindlimb muscle mass, caused by a Mendelian recessive mutation, and known to have been under positive selection in the HR lines. Mini-muscle individuals had elongated distal elements, lighter and thinner hindlimb bones, altered 3rd trochanter muscle insertion positions, and thicker tibia-fibula distal widths. Finally, several differences in levels of directional or fluctuating asymmetry in bone dimensions were observed between HR and C, mini- and normal-muscled mice, and the sexes. This study demonstrates that skeletal dimensions and muscle masses can evolve rapidly in response to directional selection on locomotor behavior.

Morphology and evolution of bioluminescent organs in the glowbellies (Percomorpha: Acropomatidae) with comments on the taxonomy and phylogeny of Acropomatiformes.

Abstract: Bioluminescent organs have evolved many times within teleost fishes and exhibit a wide range of complexity and anatomical derivation. Although some bioluminescent organs have been studied in detail, the morphology of the bacterial light organs in glowbellies (Acropoma) is largely unknown. This study describes the anatomy of the bioluminescent organs in Haneda's Glowbelly (Acropoma hanedai) and the Glowbelly (Acropoma japonicum) and places the evolution of this light-producing system in the context of a new phylogeny of glowbellies and their relatives. Gross and histological examination of the bioluminescent organs indicate that they are derived from perianal ectodermal tissue, likely originating from the developmental proctodeum, contrary to at least one prior suggestion that the bioluminescent organ in Acropoma is of endodermal intestinal derivation. Additionally, anterior bioluminescent organ development in both species is associated with lateral spreading of the bacteria-containing arms of the bioluminescent organ from an initial median structure. In the context of a 16-gene molecular phylogeny, the bioluminescent organ in Acropoma is shown to have evolved within the Acropomatidae in the ancestor of Acropoma. Further, ancestral-states reconstruction demonstrates that the bioluminescent organs in Acropoma evolved independently from the light organs in related howellid and epigonid taxa which have esophageal or intestinally derived bioluminescent organs. Across the acropomatiforms, our reconstructions indicate that bioluminescent organs evolved independently four or five times. Based on the inferred phylogeny of the order where Acropoma and Doederleinia were separated from other traditional acropomatids, the familial taxonomy of the Acropomatidae was modified such that the previously described Malakichthyidae and Synagropidae were recognized. We also morphologically diagnose and describe the family Lateolabracidae.

Origin and transformation of the in-flight wing-coupling structure in Psocodea (Insecta: Paraneoptera).

Abstract: Many four-winged insects have mechanisms that unite the forewings and hindwings in a single plane. Such an in-flight wing coupling apparatus may improve flight performance in four-winged insects, but its structure is variable among different insect groups. The wings of bark lice (Insecta: Psocodea: "Psocoptera") also have an in-flight wing coupling apparatus, but to date, its morphology has not been studied in detail. In this study, we examined the wing-coupling structure in representative species of the three suborders of bark lice (Trogiomorpha, Troctomorpha, and Psocomorpha) and inferred its origin and transformation. We conclude that the main component of the psocodean wing coupling apparatus evolved once in the common ancestor via modification of cuticular structures at the apex of the forewing CuP vein. Morphological differences in components of the coupling structures are phylogenetically informative at the intraorder level and include an autapomorphy that characterizes Troctomorpha and a synapomorphy that supports a sister relationship between Troctomorpha and Psocomorpha.

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

Abstract: 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. 279:426-440, 2018. © 2016 Wiley Periodicals, Inc.

Copulatory mechanism and functional morphology of genitalia and anal horn of the scorpionfly Cerapanorpa dubia (Mecoptera: Panorpidae).

Abstract: The scorpionfly genus Cerapanorpa is characterized by the male possessing a single finger-like anal horn on the posterior portion of tergite VI. However, the functional morphology of this anal horn and the genitalia have not been studied to date. Herein, we investigated the functional morphology of the genitalia and the nongenital structures of the scorpionfly Cerapanorpa dubia by observing the mating process and dissecting the freeze-fixated pairs in copula to reveal the copulatory mechanism. The male C. dubia provides a solid salivary mass to the female as a nuptial gift prior to copulation. When the female starts to feed on the gift, the male uses his notal organ and complex genital structures to control the closest wing and genitalia of the female to establish a V-shaped mating position. In the maintenance phase of copulation, the male uses his anal horn in cooperation with the basally-constricted abdominal segment VII to clamp female abdominal segment VIII. The male hypovalves grasp female cerci, and move up and down rhythmically. The paired parameres clasp both sides of female tergite IX. The basal processes on male gonostyli grip the pleural membranes of the female genital chamber. In the sperm transfer phase, the male aedeagus directly couples with the female medigynium to transmit sperm by connecting his phallotreme to the female's copulatory pore. The evolution of the male complex grasping structures in Panorpidae is also briefly discussed.

Ultrastructural variation and adaptive evolution of the ovipositor in the endemic Hawaiian Drosophilidae.

Abstract: Ecological diversification of the endemic Hawaiian Drosophilidae has been accompanied by striking divergence in egg morphology, and ovarian structure and function. To determine how these flies successfully oviposit in a variety of breeding substrates, we used Scanning Electron Microscopy to examine the ultrastructure of the ovipositor of a sample of 65 Drosophila species and five Scaptomyza species of this hyperdiverse monophyletic group. The Drosophila species analyzed included representatives of the fungus-breeding haleakalae group, the leaf-breeding antopocerus and modified tarsus groups, the modified mouthparts species group, the nudidrosophila, and the picture wing clade; the latter sample of 41 species from four species groups included stem- and bark-breeders, as well as tree sap flux-breeders. Ovipositor length was found to vary more than 12-fold among Hawaiian drosophilids, with the longest ovipositors observed in the bark-breeding species and the shortest among the Scaptomyza and fungus-breeders. More noteworthy is the striking variation in overall shape and proportions of the ovipositor, in the shape of the apical region, and in the pattern of sensory structures or ovisensilla. Ultrastructural observations of the pair of long subapical sensilla on the ventral side identify these, for the first time, as taste bristles. Ovipositor form correlates strongly with the oviposition substrate used by the species, being of a distinctive shape and size in each case. We infer that the observed morphological divergence in the ovipositor is adaptive and the product of natural selection for successful reproduction in alternate microhabitats. The array of ovipositor forms that have evolved among the Hawaiian Drosophila species represent a series of ecomorphs that along with other divergent traits of the female reproductive system, have contributed to the successful adaptive radiation of this remarkable fauna.

Macroscopic and microscopic analyses in flexor tendons of the tarsometatarso-phalangeal joint of ostrich (Struthio camelus) foot with energy storage and shock absorption.

Abstract: Flexor tendons function as energy storage and shock absorption structures in the tarsometatarso-phalangeal joint (TMTPJ) of ostrich feet during high-speed and heavy-load locomotion. In this study, mechanisms underlying the energy storage and shock absorption of three flexor tendons of the third toe were studied using histology and scanning electron microscopy (SEM). Macroscopic and microscopic structures of the flexor tendons in different positions of TMTPJ were analyzed. Histological slices showed collagen fiber bundles of all flexor tendons in the middle TMTPJ were arranged in a linear-type, but in the proximal and distal TMTPJ, a wavy-type arrangement was found in the tendon of the M. flexor digitorum longus and tendon of the M. flexor perforans et perforatus digiti III, while no regular-type was found in the tendon of the M. flexor perforatus digiti III. SEM showed that the collagen fiber bundles of flexor tendons were arranged in a hierarchically staggered way (horizontally linear-type and vertically linear-type). Linear-type and wavy-type both existed in the proximal TMTPJ for the collagen fiber bundles of the tendon of the M. flexor perforatus digiti III, but only the linear-type was found in the distal TMTPJ. A number of fibrils were distributed among the collagen fiber bundles, which were likely effective in connection, force transmission and other functions. The morphology and arrangement of collagen fiber bundles were closely related to the tendon functions. We present interpretations of the biological functions in different positions and types of the tendons in the TMTPJ of the ostrich feet.

Functional morphology and paleoecology of Pilosa (Xenarthra, Mammalia) based on a two-dimensional geometric Morphometrics study of the Humerus.

Abstract: The relationship between humerus shape and the modes of exploring substrate among extinct and extant Pilosa (especially anteaters and ground sloths) were investigated here. We used geometric morphometrics and discriminant analyses to relate morphological patterns and their possible ecological categories. Our results suggest that plesiomorphic taxa such as Nothrotheriidae, most Megalonychidae and basal Megatheriidae tend to have more slender humerus, associated to generalist habitus (climbing, swimming and digging activities), and while Mylodontidae developed specialized digging habitus. Additionally, we inferred ground sloths which inhabited the Brazilian territory during the Quaternary likely occupied at least four different niches. Mammals display morphofunctional adaptations on the limbs which are reflected on their modes of substrate exploration. Herein, we analyzed the humerus morphology of ground sloths and anteaters. Our results suggest that most of the Pleistocene Mylodonts were fossorial taxa, while most of the Santacrucian sloths plus extant anteaters were semiarboreal or semiaquatic taxa. The Pleistocene Megatheriidae should be ambulatory.

Constitutive cardiomyocyte proliferation in the leopard gecko (Eublepharis macularius).

Abstract: Although the contractile function of the heart is universally conserved, the organ itself varies in structure across species. This variation includes the number of ventricular chambers (one, two, or an incompletely divided chamber), the structure of the myocardial wall (compact or trabeculated), and the proliferative capacity of the resident cardiomyocytes. Whereas zebrafish are capable of comparatively high rates of constitutive cardiomyocyte proliferation, humans and rodents are not. However, for most species, the capacity to generate new cardiomyocytes under homeostatic conditions remains unclear. Here, we investigate cardiomyocyte proliferation in the lizard Eublepharis macularius, the leopard gecko. As for other lizards, the leopard gecko heart has a partially septated ventricular lumen with a trabeculated myocardial wall. To test our hypothesis that leopard gecko cardiomyocytes routinely proliferate, we performed 5-bromo-2'-deoxyuridine incorporation and immunostained for the mitotic marker phosphorylated histone H3 (pHH3) and the DNA synthesis phase (S phase) marker proliferating cell nuclear antigen (PCNA). Using double immunofluorescence, we co-localized pHH3 or PCNA with the cardiomyocyte marker myosin heavy chain (MHC). We found that ~0.5% of cardiomyocytes were mitotically active (pHH3+/MHC+), while ~10% were in S phase (PCNA+/MHC+). We also determined that cell cycling by gecko cardiomyocytes is not impacted by caudal autotomy (tail loss), a dramatic form of self-amputation. Finally, we show that populations of cardiac cells are slow cycling. Overall, our findings provide predictive evidence that geckos may be capable of spontaneous cardiac self-repair and regeneration following a direct injury.