Showing papers in "Journal of Morphology in 1999"

Craniofacial sutures: morphology, growth, and in vivo masticatory strains.

Abstract: The growth and morphology of craniofacial sutures are thought to reflect their functional environment. However, little is known about in vivo sutural mechanics. The present study investigates the strains experienced by the internasal, nasofrontal, and anterior interfrontal sutures during masticatory activity in 4-6-month-old miniature swine (Sus scrofa). Measurements of the bony/fibrous arrangements and growth rates of these sutures were then examined in the context of their mechanical environment. Large tensile strains were measured in the interfrontal suture (1,036 microepsilon +/- 400 SD), whereas the posterior internasal suture was under moderate compression (-440 microepsilon +/- 238) and the nasofrontal suture experienced large compression (-1,583 microepsilon +/- 506). Sutural interdigitation was associated with compressive strain. The collagen fibers of the internasal and interfrontal sutures were clearly arranged to resist compression and tension, respectively, whereas those of the nasofrontal suture could not be readily characterized as either compression or tension resisting. The average linear rate of growth over a 1-week period at the nasofrontal suture (133.8 micrometer, +/- 50.9 S.D) was significantly greater than that of both the internasal and interfrontal sutures (39.2 micrometer +/- 11.4 and 65. 5 micrometer +/- 14.0, respectively). Histological observations suggest that the nasofrontal suture contains chondroid tissue, which may explain the unexpected combination of high compressive loading and rapid growth in this suture.

Scaling of the limb long bones to body mass in terrestrial mammals

Abstract: Long-bone scaling has been analyzed in a large number of terrestrial mammals for which body masses were known. Earlier proposals that geometric or elastic similarity are suitable as explanations for long-bone scaling across a large size range are not supported. Differential scaling is present, and large mammals on average scale with lower regression slopes than small mammals. Large mammals tend to reduce bending stress during locomotion by having shorter limb bones than predicted rather than by having very thick diaphyses, as is usually assumed. The choice of regression model used to describe data samples in analyses of scaling becomes increasingly important as correlation coefficients decrease, and theoretical models supported by one analysis may not be supported when applying another statistical model to the same data. Differences in limb posture and locomotor performance have profound influence on the amount of stress set up in the appendicular bones during rigorous physical activity and make it unlikely that scaling of long bones across a large size range of terrestrial mammals can be satisfactorily explained by any one power function. J. Morphol. 239:167–190, 1999. © 1999 Wiley-Liss, Inc.

Guineafowl hind limb function. I: Cineradiographic analysis and speed effects.

Abstract: Avian striding bipedalism was studied in the helmeted guineafowl, Numidameleagris. High-speed cineradiographs, light films, and videos were used to record hind limb movements across a wide range of speeds. In particular, direct visualization of the skeleton in X-ray images allowed changes in pelvic and femoral position to be quantified with great accuracy for the first time. With the exception of limb protraction angle, all stride parameters are speed-dependent. During the stance phase, guineafowl primarily employ knee flexion at very low speeds. At higher speeds, the magnitudes of hip and knee extension in the second half of stance progressively increase. Pelvic rotations are relatively small, but birds gradually pitch further forward with speed. An aerial phase is not present at speeds less than 2.0 m/sec, but discontinuities in the relationship of some parameters to speed indicate a gait transition near 0.9 m/sec. Birds are considered to be flying theropod dinosaurs, making characterization of bipedalism in living birds essential to understanding the evolution of theropod locomotion. Data from guineafowl, including the kinematic effects of speed, are informative about several aspects of locomotion in extinct theropods. However, many details of avian bipedalism evolved only within a subset of Theropoda, and are therefore not directly applicable to all members of the clade. J. Morphol. 240:115–125, 1999. © 1999 Wiley-Liss, Inc.

Guineafowl hind limb function. II: Electromyographic analysis and motor pattern evolution

Abstract: The neuromuscular control of the hind limb of helmeted guineafowl (Numida meleagris) locomoting on a treadmill at 1.0 m/sec was analyzed using simultaneous electromyography (EMG) and cineradiography. Activity from 16 heads representing 14 hip and knee muscles was recorded and correlated with limb movement and myological data to help discern muscle function. The first half of the stance phase is characterized by activity in many hip extensors, which counteract a flexor moment of the ground reaction force to yield hip stability. Simultaneously, medial rotators of the femur mediate pelvic roll and coactive antagonists about the knee control knee flexion of ca. 60°. Later in stance, hip extensors pull the hip through an arc of ca. 25°; knee extension occurs in some strides. N. meleagris hind limb motor patterns were compared to those of their homologs in representative lizards and crocodilians. Using a cladogram of living saurians, motor patterns were reconstructed in hypothetical ancestors. Although data are limited, lizards appear to have very conservative muscle activity similar to that of the ancestral saurian. The extant crocodilian Alligator mississippiensis resembles the reconstructed ancestor of Archosauria in at least 9 of 11 hind limb motor patterns. In contrast, N. meleagris differs from this same ancestor in at least four muscles. Most novelties in extant saurian motor patterns arose on the line to living birds. J. Morphol. 240:127-142, 1999. © 1999 Wiley-Liss, Inc.

Morphology of the pupal heart, adult heart, and associated tissues in the fruit fly, Drosophila melanogaster.

Abstract: The early pupal heart of the fruit fly Drosophila melanogaster has recently been the subject of intense physiological and molecular work, yet it has not been well described, nor has it been compared with the heart of the adult fly. In the work reported here, the hearts of adults and early pupae of D. melanogaster were studied by scanning and transmission electron microscopy and by light microscopy. The hearts of adults and early pupae both consist of a tube of circular striated muscle one cell in thickness. The alary muscles, which suspend the heart, are more delicate in the adult compared to the early pupa. The pericardial cells in both early pupae and adults are connected to the heart by connective tissue radiating from the alary muscles or dorsal diaphragm. We confirm that four major changes occur in the heart during metamorphosis: 1) a conical chamber is formed de novo in the first and second abdominal segments; 2) the adult heart curves to conform to the contour of the abdomen; 3) a layer of longitudinal striated muscle appears on the ventral surface of the heart; 4) a fourth pair of ostia is added to the three already present in the early pupa; and note additionally that 5) the ostia appear as simple openings in the heart of the early pupa but are valve-like in the adult. J. Morphol. 240:225–235, 1999. © 1999 Wiley-Liss, Inc.

Functional and historical determinants of shape in the scapula of Xenarthran mammals: Evolution of a complex morphological structure

Abstract: The mammalian scapula is a complex morphological structure, composed of two ossification plates that fuse into a single structure. Most studies on morphological differentiation in the scapula have considered it to be a simple, spatially integrated structure, primarily influenced by the important locomotor function presented by this element. We used recently developed geometric morphometric techniques to test and quantify functional and phylogenetic influences on scapular shape variation in fossil and extant xenarthran mammals. The order Xenarthra is well represented in the fossil record and presents a stable phylogenetic hypothesis for its genealogical history. In addition, its species present a large variety of locomotor habits. Our results show that approximately half of the shape variation in the scapula is due to phylogenetic heritage. This is contrary to the view that the scapula is influenced only by functional demands. There are large-scale shape transformations that provide biomechanical adaptation for the several habits (arboreality, terrestriality, and digging), and small scale-shape transformations (mostly related to the coracoid process) that are not influenced by function. A nonlinear relationship between morphometric and phylogenetic distances indicates the presence of a complex mixture of evolutionary processes acting on shape differentiation of the scapula.

Ultrastructure of the reproductive system of the black swamp snake (Seminatrix pygaea): Part I. Evidence for oviducal sperm storage.

Abstract: Oviducal sperm storage in the viviparous (lecithotrophic) colu- brid snake Seminatrix pygaea was studied by light and electron microscopy. Out of 17 adult snakes examined from May-October, sperm were found in the oviducts of only two specimens. In a preovulatory female sacrificed 14 May, sperm were found in the oviducal lumen and sperm storage tubules (SSTs) of the posterior infundibulum. In a nonvitellogenic female sacrificed 9 June, sperm were found in the lumen and glands of the posterior uterus and anterior vagina, indicating a recent mating. The glands in the posterior infundibulum and vagina were simple or compound tubular, whereas glands in the uterus always were simple tubular. The epithelium of the sperm storage glands was not modified from that lining the rest of the oviduct. The cuboidal or columnar epithelium consisted of alternating ciliated and secre- tory areas. The secretory product released into the lumen by a merocrine process contained mucoprotein. Lipid droplets also were numerous in the epithelium. Portions of sperm sometimes were embedded in the apical cyto- plasm or in secretory material. A carrier matrix containing a mucoid sub- stance, desquamated epithelium, lipids, membranous structures, and possi- bly phagocytes was found around sperm in the posterior uterus. J. Morphol. Sperm storage tubules (SSTs) probably occur in the oviducts of all female snakes (Fox and Dessauer, '62; Devine, '84), and sperm storage in the female oviduct also has been reported in the other extant reptile groups, except Rhynocephalia (for reviews see Howarth, '74; Saint-Girons, '75, '82; Fox, '77; Devine, '84; Gist and Jones, '87; Birk- head and Moller, '93; Blackburn, '98). The reptilian oviduct basically consists of an an- terior infundibulum, into which eggs are ovulated from the ovary; a middle uterus where eggs are held until oviposition or em- bryos develop until parturition; and a poste- rior vagina that opens into the cloaca (Gist and Jones, '87; Blackburn, '98). In addition, turtles and crocodilians have a ''tubal'' re- gion between the infundibulum and uterus where albumen-secreting glands, absent in snakes and lizards, are found. The site of sperm storage in the oviduct of crocodilians is unknown (Davenport, '95), but in turtles SSTs occur in the tubal region (Gist and Jones, '87). In lizards and snakes, SSTs oc- cur at the junction of the infundibulum and uterus, and sperm also may be stored in furrows or glands in the vaginal mucosa (Fox, '56; Cuellar, '66; Halpert et al., '82). Detailed anatomical studies on the histol- ogy and cytology of the sperm storage re- gions of the oviduct in reptiles are few. In snakes, studies at the light microscopy level exist (chronologically) for Thamnophis sirta- lis (Rahn, '40; Fox, '56; Hoffman and Wim- satt, '72; Halpert et al., '82), Crotalus viridis

Experimental alteration of limb posture in the chicken (Gallus gallus) and its bearing on the use of birds as analogs for dinosaur locomotion.

Abstract: Extant birds represent the only diverse living bipeds, and can be informative for investigations into the life-history parameters of their extinct dinosaurian relatives. However, morphological changes that occurred during early avian evolution, including the unique adoption of a nearly horizontal femoral orientation associated with a shift in center of mass (CM), suggest that caution is warranted in the use of birds as analogs for nonavian dinosaur locomotion. In this study, we fitted a group of white leghorn chickens (Gallus gallus) with a weight suspended posterior to the hip in order to examine the effects on loading and morphology. This caused a CM shift that necessitated a change in femoral posture (by 35 degrees towards the horizontal, P < 0.001), and resulted in reorientation of the ground reaction force (GRF) vector relative to the femur (from 41 degrees to 82 degrees, P < 0.001). Despite similar strain magnitudes, an overall increase in torsion relative to bending (from 1.70 to 1.95 times bending, P < 0.001) was observed, which was weakly associated with a tendency for increased femoral cross-sectional dimensions (P = 0.1). We suggest that a relative increase in torsion is consistent with a change in femoral posture towards the horizontal, since this change increases the degree to which the bone axis and the GRF vector produce mediolateral long-axis rotation of the bone. These results support the hypothesis that a postural change during early avian evolution could underlie the allometric differences seen between bird and nonavian dinosaur femora by requiring more robust femoral dimensions in birds due to an increase in torsion.

Osteology and skeletal development of Pyxicephalus adspersus (Anura: Ranidae: Raninae).

Abstract: Despite the abundance and diversity of neobatrachians, relatively few descriptions exist of their ontogenesis and skeletal development. Herein, the adult and larval skeleton and the ontogenesis of the skeleton of the African frog, Pyxicephalus adspersus (Ranidae: Raninae), are described on the basis of cleared and double-stained, dry, and alcohol-preserved specimens. In P. adspersus, the first elements that ossify are the neural arches of the pre- and postsacral vertebrae (Gosner Stage 35), followed by the parasphenoid, frontoparietals, and exoccipitals (beginning at Stage 36). Major modifications of the chondrocranium begin at approximately Stage 40. The skull of the adult P. adspersus is exostosed and hyperossified, with many of the dermal bones of the cranium fused and highly ornamented. The osteology of the adult P. adspersus is compared to the skeletal morphologies of Conraua alleni (Raninae), which represents an African ranine for which osteological descriptions exist, and Ceratophrys cornuta (Leptodactylidae), which represents a hyperossified anuran with convergent morphology and behavior. The larval morphology and development of P. adspersus is compared to those of Rana pipiens and R. temporaria, which have been described in relative detail. The sequence of ossification of elements is compared with those of R. pipiens and R. temporaria. This study includes a discussion of the morphology of the elements forming the orbit, as well as a survey of the distribution of several characters related to dentary tusks of other Asian and African ranids. J. Morphol. 240:49-75, 1999. © 1999 Wiley-Liss, Inc.

Development and evolution of melanophore patterns in fishes of the genus Danio (Teleostei: Cyprinidae)

Abstract: Pigmentation patterns in vertebrates have become an important model for those interested in mechanisms of pattern determination. I present detailed information on the development of melanophore patterns in the zebrafish, Danio rerio, five close relatives of that species, and an outgroup. The comparison of the ontogeny of melanophore patterns in this group is an important first step towards understanding the developmental basis of the interspecific variation. Pigment patterns in this group range from no distinct patterning at all to stripes of differing numbers and widths to reticulated stripes. Species examined form identical larval patterns and follow a common sequence of events from which different elements are eliminated or altered to produce the variety of patterns seen in the group. As flexion is completed, melanophores move from larval positions onto the flanks of the fish. In D. rerio, D. rerio 'leo,' D. kerri, and D. malabaricus, xanthophores become established on the body of the fish as the melanophores move; erythrophores become established on the flanks of D. albolineatus and D. sp. cf. aequipinnatus. An increase in melanophore number, begun at this time, continues at a higher rate in D. rerio, D. kerri, D. sp. cf. aequipinnatus and Tanichthys albonubes than in the other three species. This results in a greater number of melanophores on adults in those species with a higher rate of melanophore increase. No distinct pattern forms, except on the caudal peduncle, in D. albolineatus. In all other Danio species, melanophore stripes form first below then above the horizontal myoseptum. Additional stripes are added first below then above these initial two stripes. D. kerri develops fewer, wider melanophore stripes than D. rerio. After initial stripe formation, D. malabaricus and D. sp. cf. aequipinnatus both developed vertical pattern elements and reticulations in the melanophore pattern. Differences in patterns between species are similar in several cases to described mutants of the zebrafish, suggesting that some aspects of interspecific pigmentation pattern variation may be under relatively simple genetic control. Copyright 1999 Wiley-Liss, Inc.

Anatomy of the feeding apparatus of the nurse shark, Ginglymostoma cirratum.

Abstract: The anatomy of the feeding apparatus of the nurse shark, Ginglymostoma cirratum, was investigated by gross dissection and computer axial tomography. The labial cartilages, jaws, jaw suspension, muscles, and ligaments of the head are described. Palatoquadrate cartilages articulate with the chondrocranium caudally by short, laterally projecting hyomandibu- lae and rostrally by ethmoorbital articulations. Short orbital processes of the palatoquadrates are joined to the ethmoid region of the chondrocranium by short, thin ethmopalatine ligaments. In addition, various ligaments, muscles, and the integument contribute to the suspension of the jaws. When the mouth is closed and the palatoquadrate retracted, the palatine process of the palato- quadrate is braced against the ventral surface of the nasal capsule and the ascending process of the palatoquadrate is in contact with the rostrodorsal end of the suborbital shelf. When the mandible is depressed and the palato- quadrate protrudes slightly rostroventrally, the palatoquadrate moves away from the chondrocranium. A dual articulation of the quadratomandibular joint restricts lateral movement between the mandible and the palatoquad- rate. The vertically oriented preorbitalis muscle spans the gape and is hypothesized to contribute to the generation of powerful crushing forces for its hard prey. The attachment of the preorbitalis to the prominent labial carti- lages is also hypothesized to assist in the retraction of the labial cartilages during jaw closure. Separate levator palatoquadrati and spiracularis muscles, which are longitudinally oriented and attach the chondrocranium to the palatoquadrate, are hypothesized to assist in the retraction of the palatoquad- rate during the recovery phase of feeding kinematics. Morphological special- izations for suction feeding that contribute to large subambient suction pressures include hypertrophied coracohyoideus and coracobranchiales muscles to depress the hyoid and branchial arches, a small oral aperture with well-developed labial cartilages that occlude the gape laterally, and small teeth. J. Morphol. 241:33-60, 1999. r 1999 Wiley-Liss, Inc.

Description of the chondrocranium and osteogenesis of the Chacoan burrowing frog, Chacophrys pierotti (Anura: Leptodactylidae).

Abstract: The larval chondrocranium of the large-headed leptodactylid frog, Chacophrys pierotti (Ceratophryinae), is described in detail. Descriptions include the ontogeny of the chondrocranium and osteogenesis of the cranial skeleton. The chondrocranium of C. pierotti is profoundly different from the chondrocrania previously described for the other genera of the Ceratophryinae (Ceratophrys and Lepidobatrachus). The chondrocranium of Chacophrys is longer than wide and not particularly robust or laterally expanded; that of Ceratophrys is very robust, whereas the chondrocranium of Lepidobatrachus is widely expanded laterally. These differences are particularly apparent in the elements associated with the jaw (i.e., suprarostral, infrarostral, Meckel's cartilage, palatoquadrate, cornua trabeculae), which are robust in Ceratophrys and thin and elongate in Lepidobatrachus. Unlike Ceratophrys and Lepidobatrachus, which possess highly specialized carnivorous larva, the chondrocranium of Chacophrys more closely resembles the typical microphagous herbivore morphology characteristic of other leptodactylid frogs for which the chondrocrania are known. These data suggest that Chacophrys is the basal taxon within the monophyletic Ceratophryinae. The ontogeny of the chondrocranium of Chacophrys, as well as the cranial ossification sequence, do not differ greatly from those described for Ceratophrys. Detailed descriptions of the ontogeny of the chondrocranium and the bony skeleton are needed for additional taxa within the Ceratophryinae (especially Lepidobatrachus). Such descriptive ontogenetic studies promise new insight into the phylogeny and morphological evolution of this remarkable group of large-headed frogs.

Comparative study on the cranial morphology of Gymnallabes typus (Siluriformes: Clariidae) and their less anguilliform relatives, Clariallabes melas and Clarias gariepinus.

Abstract: We compare the cranial morphology of four fish species with an increasing anguilliformism in the following order: Clarias gariepinus, Clariallabes melas, Gymnallabes typus, and Channallabes apus. The main anatomical-morphological disparities are the stepwise reduction of the skull roof along with the relative enlargement of the external jaw muscles, which occurred in each of them. Gymnallabes typus and C. apus lack a bony protection to cover the jaw muscles. The neurocranial bones of C. gariepinus, however, form a closed, broad roof, whereas the width of the neurocranium in C. melas is intermediate. Several features of the clariid heads, such as the size of the mouth and the bands of small teeth, may be regarded as adaptations for manipulating large food particles, which are even more pronounced in anguilliform clariids. The jaw musculature of G. typus is hypertrophied and attached on a higher coronoid process of the lower jaw, causing a larger adductive force. The hyomandibula interdigitates more strongly with the neurocranium and its dentition with longer teeth is posteriorly extended, closer to the lower jaw articulation. The anguilliform clariids also have their cranial muscles modified to enable a wider gape. The adductor mandibulae and the levator operculi extend more posteriorly, and the anterior attachment site of the protractor hyoidei dorsalis shifts toward the sagittal plane of the head. A phylogenetic analysis of the Clariidae, which is in progress, could check the validity of Boulenger's hypothesis that predecessors of the primitive fishes, such as Heterobranchus and most Clarias, would have evolved into progressively anguilliform clariids. J. Morphol. 240:169-194, 1999. © 1999 Wiley-Liss, Inc.

Historical and biomechanical analysis of integration and dissociation in molluscan feeding, with special emphasis on the true limpets (Patellogastropoda: Gastropoda).

Abstract: Modifications of the molluscan feeding apparatus have long been recognized as a crucial feature in molluscan diversification, related to the important process of gathering energy from the environment. An ecologically and evolutionarily significant dichotomy in molluscan feeding kinematics is whether radular teeth flex laterally (flexoglossate) or do not (stereoglossate). In this study, we use a combination of phylogenetic inference and biomechanical modeling to understand the transformational and causal basis for flexure or lack thereof. We also determine whether structural subsystems making up the feeding system are structurally, functionally, and evolutionarily integrated or dissociated. Regarding evolutionary dissociation, statistical analysis of state changes revealed by the phylogenetic analysis shows that radular and cartilage subsystems evolved independently. Regarding kinematics, the phylogenetic analysis shows that flexure arose at the base of the Mollusca and lack of flexure is a derived condition in one gastropod clade, the Patellogastropoda. Significantly, radular morphology shows no change at the node where kinematics become stereoglossate. However, acquisition of stereoglossy in the Patellogastropoda is correlated with the structural dissociation of the subradular membrane and underlying cartilages. Correlation is not causality, so we present a biomechanical model explaining the structural conditions necessary for the plesiomorphic kinematic state (flexoglossy). Our model suggests that plesiomorphically the radular teeth must flex laterally as they pass over the bending plane as a result of the mechanical restrictions in the flexible but inelastic subradular membrane and close association between subradular membrane and cartilages. Relating this model to the specific character states of the clades, we conclude that lack of flexure in patellogastropods is caused by the dissociation of the subradular membrane and cartilage supports.

Testing an inference of function from structure: snake vertebrae do the twist.

Abstract: The zygapophyses and zygosphene-zygantrum articulations of snake vertebrae are hypothesized to restrict or eliminate vertebral torsion. This hypothesis is apparently based solely on the inference of function from structure, despite the limitations of such inferences, as well as contradictory observations and measurements. In this study, I observed and measured axial torsion in gopher snakes, Pituophis melanoleucus. To examine the structural basis of axial torsion, I measured the vertebral articulation angles along the body and the insertion angles of five epaxial muscles. To examine torsion in a natural behavior, I digitized video images and measured the degree of appar- ent axial torsion during terrestrial lateral undulation. Finally, I measured the mechanical capacity of the vertebral joints for actual torsion over intervals of 10 vertebrae in fresh, skinned segments of the trunk. Vertebral articulation angles vary up to 30° and are associated with variation in torsional capacity along the trunk. The freely crawling P. melanoleucus twisted up to 2.19° per vertebra, which produced substantial overall torsion when added over several vertebrae. The vertebral joints are mechanically capable of torsion up to 2.89° per joint. Therefore, despite the mechanical restriction imposed by the com- plex articulations, vertebral torsion occurs in snakes and appears to be functionally important in several natural behaviors. Even in cases in which mechanical function appears to be narrowly constrained by morphology, specific functions should not be inferred solely from structural analyses. J. Morphol. 241:217-225, 1999. r 1999 Wiley-Liss, Inc.

Development of dermal denticles in skates (Chondrichthyes, Batoidea): patterning and cellular differentiation.

Abstract: Patterning, cellular differentiation, and developmental se- quences of dermal denticles (denticles) are described for the skate Leucoraja erinacea. Development of denticles proceeds caudo-rostrally in the tail and trunk. Once three rows of denticles form in the tail and trunk, denticles begin to appear in the region of the pelvic girdle, medio-caudal to the eyes and on the pectoral fins. Although timing of cellular differentiation of denticles differs among different locations of the body, cellular development of a denticle is identical in all locations. Thickening of the epidermis as a denticle lamina marks initiation of development. A single lamina for each denticle forms, and a small group of mesenchymal cells aggregates underneath it. The lamina then invaginates caudo-rostrally to form the inner- and outer-denticle epithe- lia (IDE and ODE, respectively). Before nuclei of IDE cells are polarized, enameloid matrix appears between the basement membrane of the IDE and the apical surface of the pre-odontoblasts. Pre-dentin is then laid down along with collagenous materials. Von Kossa stain visualizes initial mineralization of dentin, but not enameloid. During the growth of a denticle, dense fibrous connective tissue of the dermis forms the deep dermal tissue over the dorsal musculature. Attachment fibers and tendons anchor denticles and dorsal musculature, respectively, on deep dermal tissue. Basal tissue of the denticles develops as the denticle crown grows. If the basal tissue is bone of attachment, then the cells along the basal tissue would be osteoblasts. However, these cells could not be distinguished from odontoblasts using immunolocalization of type I pro-collagen (Col I), alkaline phosphatase (APase), and neural cell adhesion molecule (N-CAM). Well-developed dentin, (not pre-dentin), the enameloid matrix (probably when it begins to mineralize), and deep dermal tissue are Verhoeff stain-positive, suggesting that these tissues contain elas- tin and/or elastin-like molecules. Our study demonstrates that the cellular development of denticles resembles tooth development in elasmobranchs, but that dermal denticles differ from teeth in forming from a single denticle lamina. Whether the basal tissue of denticles is bone of attachment remains undetermined. Confirmation and function of Verhoeff-positive proteins in enameloid, dentin, and deep dermal tissue remain to be determined. We discuss these issues along with an analysis of recent findings of enamel and enameloid matrices. J. Morphol. 241:61-81, 1999. r 1999 Wiley-Liss, Inc.

Morphology and function of the copulatory system in freshwater crabs of the genus Potamon.

Abstract: To understand the reproductive processes of freshwater crabs of the genus Potamon, we examined the first and second gonopod and the gonoducts of the female by histological methods. The gonopods are highly modified compared to those of other brachyuran crabs. In particular, the second gonopod is unusually long and has a special morphology, ending in a long sclerotized tube. Suggestions for the function of both gonopods and their different parts are presented. Tubulation of the first and second gonopod is observed. Rosette glands, which are abundant in the subterminal joint of the first gonopod, are connected to the sperm channel by cuticular pores. In females, the chitinous parts of the inner vulva may prove to have a more constant morphology than the external flexible structures. J. Morphol. 239:157–166, 1999. © 1999 Wiley-Liss, Inc.

Cell death in ovarioles causes permanent sterility in Frieseomelitta varia worker bees

Abstract: Departamento de Genetica Faculdade de Med. de Ribeirao Preto Universidade de Sao Paulo, Ribeirao Preto, SP

Gill-cleaning mechanisms of a dendrobranchiate shrimp, Rimapenaeus similis (Decapoda, Penaeidae): Description and experimental testing of function

Abstract: Observations on functional morphology and results from experiments demonstrate that setiferous epipods compose the major gill-cleaning mechanism in a penaeoid shrimp, Rimapenaeus similis. Epipods on the second maxillipeds and on pereopods 1–3 are equipped with long setae bearing an array of digitate scale setules. These multidenticulate setae reach to most gills and are jostled among them during limb movements. Experiments were performed in which epipods were removed from the gill chamber on one side (experimental) but not the other (control); treated animals were exposed to fouling in a recirculating water system for 2 weeks. Particulate fouling, measured by reduction in relative gill transparency, was significantly greater on experimental than control gills. The pereopodal exopods, not previously implicated in gill cleaning in any decapod, were similarly identified as important gill-cleaning structures. Equipped with long multidenticulate setae like those on the epipods, exopods sweep back and forth over the gill filaments just under the gill cover, areas not reached by the epipods. Exopod-ablation experiments were conducted that showed that exopods prevent particulate fouling on gill surfaces over which they sweep. The similarity in action of the passive gill-cleaning system of R. similis to that of crayfish (Bauer [1998] Invert Biol 117:29–143) suggests the hypothesis that the epipodal and exopodal cleaning setae of R. similis are ineffective against epibionts. The reduction in epipodal and exopodal cleaning systems that occurs in the Penaeoidea is hypothesized to be compensated for by increased development of gill-cleaning setae on the branchiostegite, scaphognathite, or other structures. J. Morphol. 242:125–139, 1999. © 1999 Wiley-Liss, Inc.

Ultrastructure of the thoracic dorso-medial field (TDM) in the elytra-to-body arresting mechanism in Tenebrionid Beetles (Coleoptera: Tenebrionidae).

Abstract: Beetles with flying ability lock their elytra (forewings) to the thorax or/and abdomen using complex locking devices. These structures are often supplemented with microtrichia fields of the inner surface of the elytra and adjacent parts of the pterothorax. The present study provides information about the ultrastructure of microtrichia of the dorso-medial fields of the thorax (TDM) in tenebrionid beetles (Tribolium castaneum, Zophobas rugipes). Epidermal cells located under the TDM field contain large electron-lucent vesicles connected to rough endoplasmic reticulum. Microtrichia and underlying cuticle of the TDM have a high density of pore channels, which are responsible for transport of an epidermal secretion onto the TDM surface. In order to show the presence of the secretion on the cuticle surface, TDM fields of air-dried specimens were compared with those in specimens after two treatments, such as (1) dehydration in ethanol and acetone, and (2) dental-wax-cast technique applied to living beetles. This revealed the presence of the nonvolatile film on the intact microtrichial surface. Possible functions of this film are suggested to be (1) the increase of adhesive forces in the contact area and (2) providing soft coupling and release of two corresponding parts of the elytra-locking device. J. Morphol. 240:101-113, 1999. © 1999 Wiley-Liss, Inc.

Embryonic development of the skeleton of amphisbaena darwini heterozonata (squamata : amphisbaenidae)

Abstract: An assemblage of amphisbaenian embryos has allowed us to characterize the external morphology of the developing embryos as well as the chondrification and ossification sequences of their skeletal elements. The external characterization of embryos serves as an incomplete developmental table. In contrast to the condition in other squamates, the premaxilla seems to arise azygously from the beginning or to represent very early fusion during embryogenesis. The tabulosphenoid forms from two cartilages to which are added extensive membranous ossifications. The two parietals engage in medial fusion at the midline, where the anterior process of the synotic tectum ossifies and forms the sagittal crest. The lateral element-X does not ossify until very late in embryogenesis and is interpreted as an epiphysial ossification. The compound mandibular bone arises from the ossification of the posterior part of Meckel's cartilage and the fusion of at least two dermal centers, interpreted as surangular and splenial. The vertebral column shows an antero-posterior gradient of vertebral differentiation. The number of vertebrae is fixed from the beginning of their differentiation. The remnants of pectoral and pelvic girdles are represented by cartilaginous rods. Some reproductive data obtained during the collection of data could be compared with those from the literature. J. Morphol. 239:1-25, 1999. © 1999 Wiley-Liss, Inc.

Pneumatic processes in the temporal bone of chimpanzee (Pan troglodytes) and gorilla (Gorilla gorilla).

Abstract: The ontogeny of human temporal bone pneumatization has been well studied from both comparative and clinical perspectives. While a difference in the extent of air cell distribution has been noted in our closest living relatives, chimpanzees and gorillas, the processes responsible have been relatively unexplored. To examine these processes, a large, age-graded series of hominoid skulls was radiographed and the progress of pneumatization recorded. Additionally, a subsample of 30 chimpanzees and 12 gorillas was subjected to high-resolution CT scanning. Neonatal specimens show a well-developed mastoid antrum, as well as a capacious hypotympanum extending into the petrous apex. In African apes, as in humans, the mastoid antrum serves as the focus for air cell expansion into the mastoid and immediately adjacent areas. In chimpanzees and gorillas, however, a pronounced lateral structure, described as the squamous antrum, serves as the focus of pneumatization for anterior structures such as the squamous and zygomatic. The diminution of this structure in Homo sapiens explains the difference in air cell distribution in these regions.

Description of the chimaerid jaw and its phylogenetic origins.

Abstract: Anatomical delineation of the holocephalan palatoquadrate has proven to be difficult and, so, has been an extensively debated topic as it relates to the evolutionary derivation of jaws, modes of jaw suspension, and the interrelationships of the hondrichthyes (Elasmobranchii and Holocephali). Embryological analyses of the chimaerid jaw and cranium are presented to provide an anatomical description of the palatoquadrate in modern chimaerids. The palatoquadrate fuses, anteriorly, to the nasal capsule early in development. This marks the first point of contact between the mandibular arch and cranium. Orbitonasal canal foramina delineate the dorsal palatoquadrate margin. The posteriormost margin is marked by fusion of the upper jaw with trabecular and parachordal cartilages in the region of the efferent eudobranchial artery foramen and by a suborbitally positioned basitrabecular cartilage. This basitrabecula generates a subocular shelf as it fuses medially to the parachordal cartilage and posteriorly to the postorbital wall and cranial otic process. The results of these analyses are related to morphological studies of Paleozoic chondrichthyan fishes, particularly the autodiastylic paraselachians that represent morphological intermediates to selachians and holocephalans. The paraselachian basitrabecular, which was mechanically fundamental to stabilizing the free autodiastylic upper jaw and a hyoid operculum, is shown to correlate with the suborbital basitrabecular of today's chimaerids. Further analyses of both extant and fossil data permit us to conclude that the primordial chondrichthyan palatoquadrate did not extend posteriorly to include a palatoquadrate-derived otic process. Rather, the posteriormost extent of this element is primitively found within the limits of the orbit and is demarcated by the highly conserved basitrabecular element. The collective analyses support autodiastyly as the ancestral condition from which all fundamental suspensorial states are derived. J. Morphol. 239:45-59, 1999. © 1999 Wiley-Liss, Inc.

On caudal prehensility and phylogenetic constraint in lizards: The influence of ancestral anatomy on function in Corucia and Furcifer.

Abstract: We examined caudal anatomy in two species of prehensile-tailed lizards, Furcifer pardalis and Corucia zebrata. Although both species use their tails to grasp, each relies on a strikingly different anatomy to do so. The underlying anatomies appear to reflect phylogenetic constraints on the consequent functional mechanisms. Caudal autotomy is presumably the ancestral condition for lizards and is allowed by a complex system of interdigitating muscle segments. The immediate ancestor of chameleons was nonautotomous and did not possess this specialized anatomy; consequently, the derived arrangement in the chameleon tail is unique among lizards. The limb functions as an articulated linkage system with long tendinous bands originating from longitudinal muscles to directly manipulate vertebrae. Corucia is incapable of autotomy, but it is immediately derived from autotomous ancestors. As such, it has evolved a biomechanical system for prehension quite different from that of chameleons. The caudal anatomy in Corucia is very similar to that of lizards with autotomous tails, yet distinct differences in the ancestral pattern and its relationship to the subdermal tunic are derived. Instead of the functional unit being individual autotomy segments, the interdigitating prongs of muscle have become fused with an emphasis on longitudinal stacks of muscular cones. The muscles originate from the vertebral column and a subdermal collagenous tunic and insert within the adjacent cone. However, there is remarkably little direct connection with the bones. The muscles have origins more associated with the tunic and muscular septa. Like the axial musculature of some fish, the tail of Corucia utilizes a design in which these collagenous elements serve as an integral skeletal component. This arrangement provides Corucia with an elegantly designed system capable of a remarkable variety of bending movements not evident in chameleon tails. J. Morphol. 239:143-155, 1999. © 1999 Wiley-Liss, Inc.

Epidermal glands in Squamata: microscopical examination of precloacal glands in Amphisbaena alba (Amphisbaenia, Amphisbaenidae).

Abstract: The femoral or cloacal region of many species of lizards and amphisbaenians exhibits epidermal glands. The pores of these glands are plugged with holocrine solid secretions that serve as semiochemical sources. Many authors assume that these glands are mainly associated with reproduction and demarcation of territory. The structure of precloacal glands in Amphisbaena alba was previously studied by Antoniazzi et al. (Zoomorphology 113:199-203, 1993; J. Morphol. 221:101-109, 1994). These authors suggested that as the animal moves inside tunnels, the secretion plugs are abraded against the substrate, releasing a secretion trail. Some aspects of the plug were difficult to interpret in fine sections due to the dense and brittle nature of the plug. The morphology of the trail, and the manner of deposition on the substrate, have never been reported. This study presents a primarily scanning electron microscopic description of A. alba precloacal glands and of the secretion plugs. It also demonstrates experimentally the formation of the trail and its fine morphology. The results show that when the plugs scrape against the substrate, their constitution helps them to fragment into tiny pieces, which are spread on the ground, thus forming a trail. Each one of the fragments corresponds to a secretion granule of the precloacal gland's secretory cells. In this way, the trail might have an extensive area for volatilization of semiochemicals, constituting an efficient means of intraspecific communication inside the tunnels.

Skull allometry in the marine toad, Bufo marinus.

Abstract: Scaling predictions pioneered by A.V. Hill state that isometric changes in kinematics result from isometric changes in size. These predictions have been difficult to support because few animals display truly isometric growth. An exception to this rule is said to be the toads in the genus Bufo, which can grow over three orders of magnitude. To determine whether skull shape increases isometrically, I used linear measurements and geometric morphometrics to quantify shape variation in a size series of 69 skulls from the marine toad, B. marinus. Toads ranged in body mass from 1.8 gm to a calculated 1,558.9 gm. Of all linear measurements (S/V length, skull width, skull length, levator mass, depressor mass, adductor foramen area), only the area of the adductor foramen increased faster than body mass; the remaining variables increased more slowly. In addition, modeling the lower jaw as a lever-arm system showed that the lengths of the closing in- and out-levers scaled isometrically with body mass despite the fact that the skull itself is changing allometrically. Geometric morphometrics discerned areas of greatest variability with increasing body mass at the rear of the skull in the area of the squamosal bone and the adductor foramen. This increase in area of the adductor foramen may allow more muscle to move the relatively greater mass of the lower jaw in larger toads, although adductor mass scales with body mass. If B. marinus feeds in a similar manner to other Bufo, these results imply that morphological allometry may still result in kinematic isometry. J. Morphol. 241:115–126, 1999. © 1999 Wiley-Liss, Inc.

Sexual dimorphism and ontogenetic allometry of soft tissues in Rattus norvegicus.

Abstract: Most studies of sexual dimorphism in mammals focus on overall body size. However, relatively little is known about the differences in growth trajectories that produce dimorphism in organ and muscle size. We weighed six organs and four muscles in Rattus norvegicus to determine what heterochronic and allometric scaling differences exist between the sexes. This cross-sectional growth study included 113 males and 109 females with ages ranging from birth to 200 days of age. All muscle and organ weights were ultimately greater in males than in females, because males grew for a longer period of time, had a greater maximum rate of growth, and spent more time near the maximum rate. No ontogenetic scaling differences existed between the sexes in organ weight except for lungs and gonads. During growth, organ weights were negatively allometric to body weight. No scaling differences relative to body weight existed between the sexes for muscles; however, there was variation in the allometric relations among muscles relative to body weight. Sexual dimorphism in muscles and organs appears to be a size difference resulting from differences in the duration and rates of growth. J. Morphol. 242:57–66, 1999. © 1999 Wiley-Liss, Inc.

Epidermal differentiation in the developing scales of embryos of the Australian scincid lizard Lampropholis guichenoti.

Abstract: Formation of the first epidermal layers in the embryonic scales of the lizard Lampropholis guichenoti was studied by optical and electron microscopy. Morphogenesis of embryonic scales is similar to the general process in lizards, with well-developed overlapping scales being differentiated before hatching. The narrow outer peridermis is torn and partially lost during scale morphogenesis. A second layer, probably homologous to the inner peridermis of other lizard species, but specialized to produce lipid-like material, develops beneath the outer peridermis. Two or three lipogenic layers of this type develop in the forming outer surface of scales near to the hinge region. These layers form a structure here termed “sebaceous-like secretory cells.” These cells secrete lipid-like material into the interscale space so that the whole epidermis is eventually coated with it. This lipid-like material may help to reduce friction and to reduce accumulation of dirt between adjacent extremely overlapping scales. At the end of their differentiation, the modified inner periderm turns into extremely thin cornified cells. The layer beneath the inner peridermis is granulated due to the accumulation of keratohyalin-like granules, and forms a shedding complex with the oberhautchen, which develops beneath. Typically tilted spinulae of the oberhautchen are formed by the aggregation of tonofilaments into characteristically pointed cytoplasmic outgrowths. Initially, there is little accumulation of β-keratin packets in these cells. During differentiation, the oberhautchen layer merges with cells of the β-keratin layer produced underneath, so that a typical syncytial β-keratin layer is eventually formed before hatching. Between one-fourth distal and the scale tip, the dermis under epidermal cells is scarce or absent so that the mature scale tip is made of a solid rod of β-keratinized cells. At the time of hatching, differentiation of a mesos layer is well advanced, and the epidermal histology of scales corresponds to Stage 5 of an adult shedding cycle. The present study confirms that the embryonic sequence of epidermal stratification observed in other species is basically maintained in L. guichenoti. J. Morphol. 241:139–152, 1999. © 1999 Wiley-Liss, Inc.

Morphological variation of hypaxial musculature in salamanders (Lissamphibia: caudata).

Abstract: Despite the acknowledged importance of the locomotory and respiratory functions associated with hypaxial musculature in salamanders, variation in gross morphology of this musculature has not been documented or evaluated within a phylogenetic or ecological context. In this study, we characterize and quantify the morphological variation of lateral hypaxial muscles using phylogenetically and ecologically diverse salamander species from eight families: Ambystomatidae (Ambystoma tigrinum), Amphiumidae (Amphiuma tridactylum), Cryptobranchidae (Cryptobranchus alleganiensis), Dicamptodontidae (Dicamptodon sp.), Plethodontidae (Gyrinophilus porphy- riticus), Proteidae (Necturus maculosus), Salamandridae (Pachytriton sp.), and Sirenidae (Siren lacertina). For the lateral hypaxial musculature, we document 1) the presence or absence of muscle layers, 2) the muscle fiber angles of layers at mid-trunk, and 3) the relative dorsoventral positions and cross-sectional areas of muscle layers. Combinations of two, three, or four layers are observed. However, all species retain at least two layers with opposing fiber angles. The number of layers and the presence or absence of layers vary within species (Necturus maculosus and Siren lacertina), within genera (e.g., Triturus), and within families. No phylogenetic pattern in the number of layers can be detected with a family-level phylogeny. Fiber angle variation of hypaxial muscles is considerable: fiber angles of the M. obliquus externus range from 20-80°; M. obliquus internus, 14-34°; M. transversus abdominis, 58-80° (acute angles measured relative to the horizontal septum). Hypaxial musculature comprises 17-37% of total trunk cross-sectional area. Aquatic salamanders show relatively larger total cross-sectional hypaxial area than salamanders that are primarily terrestrial. J. Morphol. 241:153- 164, 1999. r 1999 Wiley-Liss, Inc.

Anatomy of the laryngeal apparatus of the pygmy right whale, Caperea marginata (Gray 1846).

Abstract: The laryngeal apparatus of Caperea marginata is described for the first time and proves to be significantly different from that of any mysticete previously described This difference is especially noticeable in the position of the laryngeal sac, which is separate from the tracheal rings and lies to the right of the animal Massive ontogenetic development of the sac in adult males is demonstrated, far greater than that seen in most other mysticetes Histological analysis of the laryngeal sac shows the walls to be very muscular, abundantly innervated, and vascularized, indicating an active organ Coiled blood vessels and nerves support the hypothesis that the sac undergoes extensive expansion and contraction A possible association with the unique thoracic development of the species is suggested The roles of the laryngeal sac and arytenoid cartilages in mysticete sound production are also discussed J Morphol 242:67–81, 1999 © 1999 Wiley-Liss, Inc