Showing papers in "Journal of Morphology in 1996"
TL;DR: Comparing and contrasting the morphologic patterns of nasal structures across species representing every extant odontocete superfamily reveals probable homologous relationships, which suggests that all toothed whales may be making their biosonar signals by a similar mechanism.
Abstract: The site and physiologic mechanism(s) responsible for the generation of odontocete biosonar signals have eluded investigators for decades. To address these issues we subjected postmortem toothed whale heads to interrogation using medical imaging techniques. Most of the 40 specimens (from 19 species) were examined using x-ray computed tomography (CT) and/or magnetic resonance imaging (MR). Interpretation of scan images was aided by subsequent dissection of the specimens or, in one case, by cryosectioning. In all specimens we described a similar tissue complex and identified it as the hypothetical biosonar signal generator. This complex includes a small pair of fatty bursae embedded in a pair of connective tissue lips, a cartilaginous blade, a stout ligament, and an array of soft tissue air sacs. Comparing and contrasting the morphologic patterns of nasal structures across species representing every extant odontocete superfamily reveals probable homologous relationships, which suggests that all toothed whales may be making their biosonar signals by a similar mechanism.
437 citations
TL;DR: Developmental information on the structure and composition of the zebrafish skull, pectoral, and pelvic girdle, and paired fins from a large series of cleared and Alizarin red‐stained specimens is provided.
Abstract: Because of the genetic and developmental information available, Danio rerio stands out as a vertebrate model system in which significant progress in the areas of development and evolution can be made. Despite its increasing popularity, little research has been done on skeletal development. In this report, we provide developmental information on the structure and composition of the zebrafish skull, pectoral, and pelvic girdle. We describe the sequence of ossification of the skull and paired fins from a large series of cleared and Alizarin red-stained specimens at larval and adult stages. The most commonly followed developmental sequence in Danio rerio is described. Chondrocranial development is noted from Alcian blue-stained specimens. General trends in ossification patterns are examined from developmental, phylogenetic, and functional contexts. No clear pattern in ossification order of dermal versus cartilage bones is evident. Ossification sequence conforms to functional need in a general way, but there are inconsistencies in the details of order. Selected phylogenetic comparisons of ossification sequence within cranial regions are made among Danio rerio, Betta splendens, Oryzias latipes, and Barbus barbus. Greater sequence conservation is apparent between D. rerio and Barbus barbus, the ostariophysans, than among other taxon pairs. Intraspecific variation in ossification order is apparent, most of which involves small adjustments in timing. © 1996 Wiley-Liss, Inc.
372 citations
TL;DR: The development of the chondrocranium and the relative timing of ossification of the osteocranium is described in the teleost fish Betta splendens from a large series of cleared and differentially stained specimens.
Abstract: The development of the chondrocranium and the relative timing of ossification of the osteocranium is described in the teleost fish Betta splendens from a large series of cleared and differentially stained specimens. General trends in ossification patterns are examined from developmental, phylogenetic, and functional contexts. As in many other vertebrates, dermal bones form before cartilage bones. Ossification sequence conforms to functional need in a very general way, but there are many inconsistencies in the details of order. For example, some bones that are directly involved in feeding ossify no earlier than bones more indirectly involved. Comparisons of ossification sequence within specific cranial regions are made among Betta splendens, Oryzias latipes (Atherinomorpha), and Barbus barbus (Ostariophysi) within a phylogenetic framework. Many evolutionary changes in relative sequence of ossification are evident within regions among these taxa, yet many other sequences are conserved. The logistic difficulty of comparing entire cranial ossification sequences (vs. regional sequences) makes evident the need for new methods for identifying and quantifying sequence changes. Intraspecific variation in order of ossification is described for the first time in teleost fishes. To the extent that ossification sequence varies intraspecifically, conclusions drawn from previous interspecific comparisons are compromised. Understanding the importance of changes in ossification order within and among taxa will require experimental, functional, and evolutionary work. © 1996 Wiley-Liss, Inc.
127 citations
TL;DR: The avian eggshell is an excellent vehicle for the study of biomineralization processes and the role of the organic matrix in the mineral‐matrix composite.
Abstract: The avian eggshell is a composite structure of organic matrix and mineral (calcium carbonate) that is rapidly and sequentially fabricated in the oviduct in <24 hr. The eggshell is an excellent vehicle for the study of biomineralization processes and the role of the organic matrix in the mineral-matrix composite. The organic matrix components of eggshells from White Leghorn chickens (Gallus gallus) were examined by transmission electron microscopy (TEM) and optical microscopy. The mineral phase was analyzed by TEM, scanning electron microscopy (SEM), X-ray compositional microanalysis, and electron diffraction. Ultrastructural examination of the matrices within the calcified eggshell reveals a complex architecture that differs within each of the major zones of the eggshell: the shell membranes, the mammillary zone, the palisade region, and the cuticle. The mammillary layer consists of the calcium reserve assembly (CRA) and crown region, each with a unique substructure. TEM images show that the matrix of the CRA consists of a dense, flocculent material partially embedded within the outer shell membrane (a mostly noncalcified region of the shell). The mantle of the collagen fibers of the shell membranes is rich in polyanions (cuprolinic blue-positive), as is the CRA matrix. The CRA is capped by a centrally located calcium reserve body sac (CRB sac) that contains numerous 300-400 nm, electron-dense, spherical vesicles. Directly above the CRB sac is a zone of matrix consisting of stacks of interconnected vesicles (similar in morphology to CRA vesicles) that are interspersed with a granular material. The palisade region, the largest of the mineralized zones, contains hollow vesicles ∼450 nm (s.d. = 75 nm) in diameter, with a crescent-shaped, electron-dense fringe. An interconnecting matrix material is also found between the vesicles in the palisades region. The cuticle is composed of two layers, a mineralized inner layer and an outer layer consisting of only organic matrix. The bulk of the mineral within the eggshell is calcite, with small amounts of needlelike hydroxyapatite in the inner cuticle and occasionally, vaterite micro crystals found at the base of the palisade (cone) region. The well-crystallized calcite crystals within the palisade are columnar, typically ∼20 μm wide by 100-200 μm long; aside from numerous entrapped vesicles and occasional dislocations, they are relatively defect-free. The bulk of the matrix found in the palisade and crown regions are thought to be residual components of the rapid mineralization process. The unique matrix structure within the CRB corresponds to the region of preferentially solubilized calcite used by the developing embryo and the hydroxyapatite found in the inner cuticle may play a role in the cessation of mineral growth. © 1996 Wiley-Liss, Inc.
119 citations
TL;DR: It is concluded that birds, whose homeothermic control depends so much on CWL, cannot possess a permanent “good barrier,” as such would compromise the heat loss mechanism.
Abstract: The ultrastructure of naked neck epidermis from the ostrich (Struthio camelus) and ventral apterium from watered, and water-deprived, Zebra finches (Taeniopygia [Poephila] guttata castanotis) is presented. The form and distribution of the fully differentiated products of the lipid-enriched multigranular bodies are compared in biopsies post-fixed with osmium tetroxide or ruthenium tetroxide. The fine structure of ostrich epidermis suggests it is a relatively poor barrier to cutaneous water loss (CWL). The fine structure from watered, and 16-hr water-deprived Zebra finches, considered in conjunction with measurements of CWL, confirms previous reports of "facultative waterproofing," and emphasizes the rapidity of tissue response to dehydration. The seemingly counterintuitive facts that one xerophilic avian species, the ostrich, lacks a "good barrier" to CWL, whereas another, the Zebra finch, is capable of forming a good barrier, but does not always express this capability, are discussed. An explanation of these data in comparison to mammals centers on the dual roles of the integument of homeotherms in thermoregulation and conserving body water. It is concluded that birds, whose homeothermic control depends so much on CWL, cannot possess a permanent "good barrier," as such would compromise the heat loss mechanism. Facultative waterproofing (also documented in lizards) protects the organism against sudden reductions in water availability. In birds, and probably in snakes and lizards, facultative waterproofing involves qualitative changes in epidermal cell differentiation. Possible control mechanisms are discussed.
106 citations
TL;DR: A revision of a classic model for the evolution of placentation among Reptilia, which predicts specific relationships among reproductive characteristics and thus is testable by comparative analysis among other species within the Eugongylus group of Australian skinks.
Abstract: A prominent model for the evolution of placentation among Reptilia is based on placental structure among species in the Eugongylus group of Australian lygosomatine skinks. We studied the development of the extraembryonic membranes of an oviparous species, Bassiana duperreyi, and a viviparous species, Pseudemoia entrecasteauxii, within this taxonomic group. We observed differences in the timing of development of shared features and in the structure of extraembryonic membrane epithelia in the two species. In the viviparous species, there is earlier vascularization of the yolk sâc and increased vascular support for the abembryonic yolk sac splanchnopleure. Structural differences between species result in partitioning of the egg into two distinct hemispheres and produce epithelia which appear functionally histotrophic in both the chorioallantoic membrane and the bilaminar omphalopleure of the viviparous species. We propose that the evolution of placentation in P. entrecasteauxii involved a combination of heterochrony and structural innovation. Further, because our interpretation of placental structure of this species provides new information relevant to placental function, we propose a revision of a classic model for the evolution of placentation among Reptilia. This model predicts specific relationships among reproductive characteristics and thus is testable by comparative analysis among other species within the Eugongylus group of Australian skinks. © 1996 Wiley-Liss, Inc.
100 citations
TL;DR: Overall, feeding and respiratory needs are met by changes in form and function during larval fish growth and are correlated with demands of energy acquisition essential to survival.
Abstract: Cranial development in larval Atlantic cod Gadus morhua was studied throughout ontogeny using specimens treated by staining and clearing, scanning electron microscopy and histology. Newly hatched cod larvae have closed mouths, no operculii, five well-developed branchial arches, and transversii ventralis muscles. During the endogenous feeding (yolk-sac) stage, viscerocranial structures remain simple and nonarticulated. Six days after hatching at 5°C, articulation occurs between the quadrate/Meckel's cartilage and the hyomandibula/cranium. Integration of skeletal elements results in a functional jaw that facilitates the transition from endogenous to exogenous feeding. During later ontogenetic stages, the opercular apparatus and levator-operculi coupling develops, facilitating the transition of cutaneous to branchial respiration. Overall, feeding and respiratory needs are met by changes in form (including composition) and function during larval fish growth and are correlated with demands of energy acquisition essential to survival. © 1996 Wiley-Liss, Inc.
90 citations
TL;DR: In this paper, the authors compared carpal joint size and curvature among strepsirhine primates that differ significantly in their positional behaviors and hand postures: vertical clingers, active arboreal quadrupeds, and slow cautious climbers.
Abstract: Theoretical and empirical evidence suggest that limb joint surface morphology is mechanically related to joint mobility, stability, and strength. This study tests hypotheses relating aspects of joint surface shape to joint function by comparing carpal joint size and curvature among strepsirhine primates that differ significantly in their positional behaviors and hand postures: vertical clingers, active arboreal quadrupeds, and slow cautious climbers. Joints that are very mobile are expected to have increased size and curvature of male joint mating surfaces, whereas those that function primarily in weight-bearing are expected to have relatively expanded female joint mating surfaces. Results show that 1) high male joint mating surface curvature is related to increased joint mobility and 2) increased female joint mating surface curvature is related to increased joint stability under loads of different orientation. Arc lengths of both male and female joint mating surfaces do not differ significantly between locomotor groups. Moreover, carpal joint curvature is not significantly correlated with either joint size (arc length) or body size, but carpal joint size and body size are highly correlated with one another. Relative to body size, articular arc lengths scale close to isometry (geometric similarity) both within and among groups. These results suggest that structural changes leading to increased joint mobility involve modifying joint surface curvature, and in the case of the carpal joints do not include altering joint size. Curvature of female joint mating surfaces appears related to variation in load orientation, but not necessarily load magnitude and frequency.
89 citations
TL;DR: A model of the ancestral pattern of embryonic head development in anuran amphibians is provided and can serve as a basis for examining the ontogenetic mechanisms that underlie the diversity of cranial morphology and development displayed by living frogs, as well as the evolutionary consequences of this diversity.
Abstract: We assess cranial neural-crest cell migration and contributions to the larval chondrocranium in the phylogenetically basal and morphologically generalized anuran Bombina orientalis (Bombinatoridae). Methods used include microdissection, scanning electron microscopy, and vital dye labeling, in conjunction with confocal and fluorescence microscopy. Cranial neural-crest cells begin migrating before neural-fold closure and soon form three primary streams. These streams contribute to all cranial cartilages except two medial components of the hyobranchial skeleton (basihyal and basibranchial cartilages), the posterior portion of the trabecular plate, and the otic capsule, the embryonic origin of which is unknown. Chondrogenic fate is regionalized within the cranial neural folds, with the anterior regions contributing to anterior cartilages and the posterior regions to posterior cartilages. A neural-crest contribution also was consistently observed in several cranial nerves and the connective tissue component of many cranial muscles. Notwithstanding minor differences among species in the initial configuration of migratory streams, cranial neural-crest migration and chondrogenic potential in metamorphosing anurans seem to be highly stereotyped and evolutionarily conservative. This includes a primary role for the neural crest in the evolutionary origin of the paired suprarostral and infrarostral cartilages, two prominent caenogenetic features of the rostral skull unique to anuran larvae. Our results provide a model of the ancestral pattern of embryonic head development in anuran amphibians. This model can serve as a basis for examining the ontogenetic mechanisms that underlie the diversity of cranial morphology and development displayed by living frogs, as well as the evolutionary consequences of this diversity. © 1996 Wiley-Liss, Inc.
86 citations
TL;DR: To provide a quantitative study of mandibular form and function in Eocene primates, the scaling of jaw dimensions and the development of symphyseal fusion was considered in a broad sample of North American and European Adapidae and Omomyidae.
Abstract: Previous experimental and comparative studies among a wide variety of primate and nonprimate mammals provide a unique source of information for investigating the functional and phylogenetic significance of variation in the masticatory apparatus of Eocene primates. To provide a quantitative study of mandibular form and function in Eocene primates, the scaling of jaw dimensions and the development of symphyseal fusion was considered in a broad sample of North American and European Adapidae and Omomyidae. Statistical analyses indicate a significant size-related pattern of symphyseal fusion across Eocene primates, with larger taxa often having a greater degree of fusion than smaller species; this trend is also evident at the family level. As adapids are mostly larger than omomyids and these taxa show allometry of symphyseal fusion, this may explain why no omomyids evince complete fusion. Controlling for jaw size, species with greater symphyseal fusion tend to have more robust jaws than those with a lesser amount of fusion. Upon further examination, a primary reason why adapids have more robust mandibles than omomyids is associated with the presence of taxa with fused symphyses, and thus more robust jaws, in the adapid sample, whereas no omomyids have fused symphyses. In addition, there is little indication of a dietary effect, as measured by molar shear-crest development, on symphyseal fusion. Moreover, as there is no correlation between molar shear-crest development and skull size, this also points to the absence of a size-related pattern of dietary preference underlying the allometry of symphyseal fusion. Based on the interspecific and ontogenetic allometry of symphyseal ossification in Eocene primates, jaw-scaling patterns are used to further examine the functional determinants of fusion in this group. This study indicates that greater dorsoventral shear during mastication is a more likely factor than lateral transverse bending ("wishboning") in the evolution of symphyseal fusion among "late-fusing" mammals like adapids and omomyids. Given that wishboning is an important functional determinant of symphyseal form in recent anthropoids, apparently the evolutionary development of marked wishboning occurs only in taxa that shift the timing of fusion to a growth stage preceding the onset of weaning (before adult masticatory patterns are fully developed) and perhaps first ossified the symphysis to counter elevated dorsoventral shear stress. As early anthropoids probably consisted of members varying interspecifically and ontogenetically in the degree of ossification, it is especially informative to analyze the adaptive setting in which anthropoid symphyseal fusion evolved from a similar primitive "prosimian" perspective. Finally, since taxa with fused symphyses are widely distributed across mammals, a similar analytical framework could be directed profitably at unraveling the functional and evolutionary significance of symphyseal fusion in other mammalian clades.
86 citations
TL;DR: Cumulative data from all four behaviors suggest that the Di muscles can be activated independently relative to the myomeric musculature rather than having a single phase relationship with the myomersic muscle common to all of the observed behaviors.
Abstract: The median fins of fishes are key features of locomotor morphol- ogy which function as complex control surfaces during a variety of behaviors. However, very few studies have experimentally assessed median fin function, as most workers focus on axial structures. In particular, the dorsal fin of many teleost fishes possesses both spiny anterior and soft posterior portions which may function separately during locomotion. We analyzed the function of the soft region of the dorsal fin and of the dorsal inclinator (Di) muscles which are the primary muscles responsible for lateral flexion. We used electromyography to measure in vivo Di activity, as well as activity of the red myomeric muscles located at a similar longitudinal position. We quantified motor patterns during four locomotor behaviors: braking and three propulsive behaviors (steady swimming, kick and glide swimming, and C-starts). During the three propul- sive swimming behaviors, the timing of Di activity was more similar to that of ipsilateral red myomeric muscle rather than to contralateral myomeric activ- ity, whereas during braking the timing of activity of the Di muscles was similar to that of the contralateral myomeric musculature. During the three propul- sive behaviors, when the Di muscles had activity, it was consistent with the function of stiffening the soft dorsal fin to oppose its tendency to bend as a result of the body being swept laterally through the water. In contrast, activity of the Di muscles during braking was consistent with the function of actively flexing the soft dorsal fin towards the side of the fish that had Di activity. Activity of the Di muscles during steady speed swimming was generally sufficient to resist lateral bending of the soft dorsal fin, whereas during high speed kick and glide swimming and C-starts, Di activity was not sufficient to resist the bending caused by resistive forces imposed by the water. Cumulative data from all four behaviors suggest that the Di muscles can be activated independently relative to the myomeric musculature rather than having a single phase relationship with the myomeric muscle common to all of the observed behaviors. o 1996 Wiley-Liss, Inc. The median fins of most fishes are large, conspicuous structures whose evolutionary origin within the chordate clade probably preceded that of appendicular structures, and yet we presently know remarkably little about how the median fins function during fish locomotion. This is unfortunate because hy- drodynamic modeling suggests that interspe- cific variation in median fin morphology is related to differences in the longitudinal dis- tribution of surface area that tend to corre- late with different locomotor tasks such as fast steady swimming, rapid acceleration, and maneuvering (Webb, '84). Our current knowl- edge of the median fins of teleosts is derived mainly from a small number of studies which are mostly structural and evolutionary in nature, such as Winterbottom's ('74) com- parative descriptions of the median fin muscles. With the exceptions of the papers by Arita ('71) and Roberts ('69), the overview of Harris ('53), and the work of Geerlink and Videler ('87), who focused on the relation between fin ray structure and its mechanical
TL;DR: The hypothesized reduction of tooth replacement rate with ontogeny was supported and counts done on teeth of mean size for individuals give reasonable estimates of the mean replacement rates for the entire dentition.
Abstract: Incremental lines were found in the dentine of Alligator mississippiensis and Caiman crocodilus. Fluorochrome markers indicate that these increments form daily in juvenile alligators. By counting the total number of incremental lines in a functional tooth and subtracting the number in the successive replacement tooth, it is possible to ascertain the replacement rate for the tooth position. Counts done on teeth of mean size for individuals give reasonable estimates of the mean replacement rates for the entire dentition. The tooth replacement rates were monitored for 11 months in juvenile alligators to test this methodology. The hypothesized reduction of tooth replacement rate with ontogeny was supported. © 1996 Wiley-Liss, Inc.
TL;DR: It is suggested that small insects, which are able to walk quickly on thin rods, usually have wide microplates on the UT plate to provide quicker fixation‐release of the UT in the contact area.
Abstract: The structure of the unguitractor system of insect legs was studied using scanning and transmission electron microscopy. On the base of serial semithin sections, the 3-D reconstruction of structures of the terminal tarsomere was obtained and the arrangement of different types of cuticle was demonstrated. The membrane connects all structures of the system and divides the terminal parts of the claw flexor muscle into the external (unguitractor plate) (UT) and inner (tendon) ones. Elastic nonlayered cuticle located between the claws and the posterior wall of the terminal tarsomere is interpreted as a claw-returning string. Cuticle surrounding the apodeme of the posterior wall of the terminal tarsomere contains large porous canals. The anterior part of the terminal tarsomere has an invagination that forms a plate facing toward the UT. This plate comprises the UT anteriorly and laterally and contains a microtrichia field (MF) on its distal part. The surface of the UT has a complex microstructure providing fixation to the MF of the corresponding surface of the anterior wall of the terminal tarsomere. Microtrichia of the UT and MF are directed to opposite directions and provide anchorage of the UT whenever the flexor claw muscle contracts. The microsculpture of UT and MF for representatives of Odonata, Coleoptera, Hemiptera, Hymenoptera, and Diptera was compared. It is suggested that small insects, which are able to walk quickly on thin rods, usually have wide microplates on the UT plate to provide quicker fixation-release of the UT in the contact area. Insects using the legs to produce hollows in the soil usually have a large UT with well-developed microtrichia on its surface to produce strong friction forces in the contact area for a long period of time. © 1996 Wiley-Liss, Inc.
TL;DR: The jaw, suprahyoid, and extrinsic tongue muscles were studied in 11 genera of Old World squirrels and it is suggested that among the pygmy squirrels, the position of the anterior deep masseter suggests that it plays a more significant role in molar chewing.
Abstract: The jaw, suprahyoid, and extrinsic tongue muscles were studied in 11 genera, belonging to five tribes, of Old World squirrels. Significant variation in most of the adductor muscles is evident. The most primitive state of sciuromorphy is seen in the African tree squirrels Paraxerus and Funisciurus, especially as reflected in the anterior deep masseter. A derived state of sciuromorphy is found in five genera of Old World squirrels and perhaps evolved independently in each. Reduction of the temporalis muscle was observed in three genera, distantly related to one another. A unique arrangement of the superficial masseter is reported in the Asian giant tree squirrels, Ratufa. The arrangement of the masseter in the African pygmy squirrel, Myosciurus, is very similar to that of the South American pygmy squirrel, Sciurillus. We present hypotheses about the functional significance of these differences. In the derived state of sciuromorphy, which is found in three cases in squirrels that feed extensively on hard fruits, the anterior deep masseter is well positioned to increase the strength of the power stroke of the incisor bite. Among the pygmy squirrels, the position of the anterior deep masseter suggests that it plays a more significant role in molar chewing.
TL;DR: This study presents a model for the step cycle patterns used during both hopping and swimming by the leopard frog, Rana pipiens, and finds that the two behaviors are essentially similar in movement pattern and in the ways they are modified from quadrupedal gaits.
Abstract: This study presents a model for the step cycle patterns used during both hopping and swimming by the leopard frog, Rana pipiens. The two behaviors are essentially similar in movement pattern and in the ways they are modified from quadrupedal gaits. In hopping, there is marked hind limb extension throughout stance. The swing begins with a suspension equivalent to the leap that occurs in a galloping or bounding quadruped. Following suspension, as the frog descends from the apex of its leap, the hind limbs remain posterior and in line with the spine while they flex. Near the end of flexion, there is a rapid downward rotation of the hindquarters to bring the hind feet underneath the body. This movement utilizes the planted forelimb as a pivot. A similar pattern of movement occurs in swimming; the stance (propulsion) phase involves extension at all hind limb joints. The swing (recovery) phase begins with the hind feet fully extended and includes a protracted gliding phase, equivalent to the suspension in the hop. The hind limb then recovers to its initial position during a flexion phase. Since there is no landing and the hind limbs remain lateral rather than ventral to the pelvis, less flexion occurs in the spine or the limb joints. In both behaviors, the extensor muscles of hip (M. semimembranosus), knee (M. cruralis), and ankle (M. plantaris longus) achieve their longest lengths, when they likely can produce near maximal force, at the beginning of extension. All three muscles shorten during extension, but, because they are multiple-joint muscles, the amount of shortening is relatively small (approximately 15%). Hopping and swimming in frogs are comparable asymmetrical gaits with the same relative contact intervals (25% of stride). The step cycles in both gaits are modified from quadrupedal locomotion in the same ways: by 1) loss of knee and ankle extension toward the ground prior to landing (or end of flexion in swimming), 2) loss of a yield phase on landing (or end of flexion in swimming), and 3) inclusion of extended suspensions in both gaits.
TL;DR: The results suggest that lmax may provide a more useful scaling factor for generic models of muscle and the passive length‐tension properties of mammalian muscle appear to reflect a complex mix of structures at both the myofilament and connective tissue levels that may differ depending on muscle‐fiber architecture.
Abstract: The relationships between range of motion, optimal length for force production (lo), and passive force provide useful insights into the structure and function of muscles but are unknown for most individual muscles. We measured these values and examined their relationships in five strap-like muscles of the cat hind limb: caudofemoralis, semitendinosus, sartorius anterior, tenuissimus, and biceps femoris anterior. The range of motion relative to lo was found to vary significantly between different muscles and even between different specimens of the same muscle. The passive force-length (FL) curve was found to be correlated with both lo and lmax (maximal in situ muscle length) but was correlated more strongly with lmax. The mean passive force produced by these muscles at lmax was less than 7% of estimated maximal isometric force, suggesting that passive force may not be important in these muscles during normal activation patterns. The variance in passive FL curves between specimens of the same muscle was found to be significantly lower when length was scaled by lmax as opposed to lo. These results suggest that lmax may provide a more useful scaling factor for generic models of muscle. However, the passive length-tension properties of mammalian muscle appear to reflect a complex mix of structures at both the myofilament and connective tissue levels that may differ depending on muscle-fiber architecture and perhaps on the history of trophic influences on a particular specimen.
TL;DR: The present findings suggest that the normal progress of PCD in the hand and foot plates of rodent fetuses may prevent the formation of some limb malformations such as webbing fusion of digits, polydactyly, or cleft hand/foot.
Abstract: Apoptotic cell death in the developing limb of mouse fetuses was examined sequentially on days 11-15 of gestation by means of Nile blue (NB) sulfate staining with special reference to its relation to limb morphogenesis. With some exceptions, programmed cell death (PCD) in the hand and foot was observed in the mesenchyme but not in the surface ectoderm. We found that during digital formation PCD begins at the proximal portion of the interdigital mesenchyme and subsequently expands distally. Therefore, the initial PCD that occurs in the interdigital zones may determine the proximal ends of digital separation and also contribute to the demarcation between the palm (sole) and digits (toes). During digital separation, the areas of PCD in the interdigital zones were found to become larger and expand distally on day 13, which may be necessary for the separation of digits and for determining the interdigital area to disappear. PCD in presumptive phalangeal joints was also found to proceed from proximal to more distal joints. The PCD in presumptive joints may be required for the separation of phalanges and metacarpal (metatarsal) bones and for the formation of joint cavities. In addition, intense PCD was observed in the radial (tibial) and ulnar (fibular) margins of the hand and foot plates for 4-5 days. Such PCD at marginal areas seems to prevent the formation of supernumerary digits (preaxial and postaxial polydactyly) and other digital malformations. Therefore, the timing when PCD commences and ends, the sites where PCD occurs, and the intensity, duration, and proximo-distal progress of PCD appear to be genetically determined, and the elimination of unnecessary cells by PCD may be essential for normal limb morphogenesis. The present findings also suggest that the normal progress of PCD in the hand and foot plates of rodent fetuses may prevent the formation of some limb malformations such as webbing fusion of digits, polydactyly, or cleft hand/foot.
TL;DR: The finding that most of the red muscle is in the posterior half of the fish further supports the notion that most power for steady swimming at moderate speeds comes from posterior rather than anterior musculature.
Abstract: Because the mass-specific power generated by myotomal muscle during swimming varies along the length of the fish, a realistic assessment of total power generation by the musculature requires integrating the product of mass-specific power and muscle mass at each position over the length of the fish. As a first step toward this goal, we examined the distribution of red, pink, and white muscle along the length of Stenotomus chrysops (scup) using histochemical and image analysis techniques. The largest cross-sectional area of red fibers occurs at 60% of total fish length and declines both anteriorly and posteriorly. By contrast, white fibers have the largest cross-sectional area in the anterior and decline dramatically moving posteriorly. The proportion of the fishes' cross-section occupied by red fibers increases from 1.37% to 8.42% moving posteriorly along the length of the fish. In contrast, the proportion of cross-sectional area occupied by pink fibers is constant (1.19%), while the proportional cross-sectional area of white fibers falls from 82.5% to 66.3%. The red, pink, and white fibers comprise 2.09, 0.73, and 51.1%, respectively, of total fish weight. We also compared the distribution of muscle in 10 degrees C- and 20 degrees C- acclimated animals. The value for red fiber volume, though slightly higher (13%) in cold-acclimated fish, is not statistically different. No difference was found in pink or white fibers. Finally, the finding that most of the red muscle is in the posterior half of the fish further supports the notion that most power for steady swimming at moderate speeds comes from posterior rather than anterior musculature.
TL;DR: The functional morphology of the oviduct shows cyclical changes that are correlated with eggshell formation and the vagina consists of thick longitudinal and circular smooth muscle layers, which may serve in retention of eggs during gestation.
Abstract: Oviductal functional morphology remains poorly understood in oviparous snakes, particularly in regard to oviductal formation of albumen and the eggshell and to sperm storage. The oviduct of Diadophis punctatus was examined using histology and scanning electron microscopy to determine oviductal functional morphology throughout the reproductive cycle. The oviduct is composed of four morphologically distinct regions: infundibulum, uterine tube, uterus, and vagina. The infundibulum is thin, flaccid, and lined with simple ciliated cuboidal epithelial cells. The tube contains ciliated and secretory epithelial cells, which reach a maximum height and hypertrophy during early gravidity and produce glycosaminoglycans. The posterior portion of the tube contains temporary sperm storage receptacles. The uterus retains eggs throughout gestation and secretes the eggshell constituents. The endometrial glands of the uterus hypertrophy during vitellogenesis and become depleted of the secretory granules during gravidity. The functional morphology of the oviduct therefore shows cyclical changes that are correlated with eggshell formation. The vagina consists of thick longitudinal and circular smooth muscle layers, which may serve in retention of eggs during gestation. Furthermore, the vagina contains long furrows in the mucosa that serve as sperm storage receptacles. These receptacles store sperm following fall mating and overwintering, whereas the receptacles in the tube are utilized briefly during vitellogenesis just prior to ovulation. © 1996 Wiley-Liss, Inc.
TL;DR: For 73 cichlid species from various African lakes and covering a wide array of feeding types and adult sizes, it is demonstrated that these optimal positions for the onset of suction feeding can be attained or closely approached by species whose regular diet only requires suction feed but not by specieswhose regular diet is dominated by items requiring forceful biting.
Abstract: During suction feeding teleost fish have to start mouth opening prior to other expansion movements of the head such as operculo-suspensorium abduction. The distribution of the input force over the various expansion movements is determined by the position of the hyoid in the expansion apparatus. Based on a three-dimensional (3-D) kinematic model of this apparatus it can be calculated at which positions of the hyoid operculo-suspensorial abduction is precluded. For 73 cichlid species from various African lakes and covering a wide array of feeding types and adult sizes, it is demonstrated that these optimal positions for the onset of suction feeding can be attained or closely approached by species whose regular diet only requires suction feeding but not by species whose regular diet is dominated by items requiring forceful biting. It is argued that the suboptimality of the biters is due to an architectonic constraint, viz. an increase in head width necessary to accommodate their enlarged m. adductor mandibulae. Although it is theoretically feasible to optimize the model's parameters for every head width, the biters apparently have not achieved such an adaptive change. As these parameters also feature in the execution of other functions, it is likely that conflicting demands on their optimal value overrule their optimization for the starting position of the hyoid of biters. The results hold for cichlids of independently evolved species flocks and therefore concern general rules for biter-sucker transformations in cichlids. © 1996 Wiley-Liss, Inc.
TL;DR: Analysis of developmental processes undergone by several cranial structures during postnatal growth of wild felids shows evidence suggesting the involvement of a heterochronic process, neoteny, in the morphological differentiation of several populations and species of the genus Lynx.
Abstract: Studies on ossification patterns and other ontogenetic events associated with postnatal cranial growth of wild felids are scarce. An analysis of developmental processes undergone by several cranial structures (presphenoidal and sphenooccipital synchondroses, temporal and sagittal crests, and deciduous and permanent teeth) during postnatal growth has been conducted on a sample of 336 specimens belonging to the four Recent species of lynxes (Lynx pardinus, Lynx lynx, Lynx rufus, and Lynx canadensis). Age has been estimated based on tooth replacement, skull size, and by counting the annual lines of cementum growth. Comparison of the results obtained for each of the four species reveal (1) a single pattern for both tooth replacement and ossification of the sphenooccipital synchondrosis, (2) two ossification patterns for the presphenoidal synchondrosis, (3) a common pattern for development of temporal ridges and sagittal crest showing different degrees of morphological expression, and (4) evidence suggesting the involvement of a heterochronic process, neoteny, in the morphological differentiation of several populations and species of the genus Lynx. These data also support the hypothesis that processes involved in the replacement of carnassials are based on functional requirements.
TL;DR: It is proposed that oviparous taxa with relatively thin eggshells may be preadapted to evolve viviparity, and comparative examination of the limited data available on eggshell thickness in lizards supports this possibility.
Abstract: In reptiles, the evolutionary transition from egg-laying to live-bearing is thought to involve a gradual increase in the duration of egg retention, with progressively more development occurring prior to oviposition, and culminating in the birth of fully developed offspring. However, prolonging the retention of fully-shelled eggs within the oviducts may pose serious gas-exchange problems for the embryos. Thus, evolutionary increases in the period of intrauterine retention may require correlated decreases in the thickness of eggshells and/or their degree of calcification to allow for adequate embryonic gas exchange. To test this evolutionary model, eggs of three distinct reproductive forms of the scincid lizard Lerista bougainvillii were examined to determine the evolutionary relationships between the thickness of the shell membrane, degree of eggshell calcification, and the duration of uterine egg retention. These comparisons revealed the predicted pattern of correlated shifts in eggshell morphology and embryonic stage at oviposition. Evolutionary increases in the duration of egg retention were accompanied by decreases in the thickness of the eggshell membrane and degree of eggshell calcification. This evolutionary model suggests that there may be a tradeoff between the advantages of extended egg retention and the disadvantages of a thinner eggshell. On the basis of this tradeoff, I propose that oviparous taxa with relatively thin eggshells may be preadapted to evolve viviparity. Comparative examination of the limited data available on eggshell thickness in lizards supports this possibility. © 1996 Wiley-Liss, Inc.
TL;DR: Important morphological observations indicate that, despite some dissimilarities, the chordoid larva of the cycliophoran species, Cycliophora among protostomians is a modified trochophore.
Abstract: Developmental and free-living stages of the chordoid larva of the cycliophoran species, Symbion pandora Funch and Kristensen 1995, were studied using light and electron microscopy. In the free-living stage of the larva, about 200 μm long, four ciliated areas are found: two anterior bands, a ventral ciliated field, and a posterior unit on the ventral side of the foot. The nervous system consists of a dorsal brain and a pair of ventral longitudinal nerves. A gut is absent. A pair of protonephridia, each with a single multiciliated terminal cell and at least one duct cell, is present. Nephridiopores are not localized. A pair of corsal ciliated organs is posterior to the brain. The homology between these and the apical organ of a trochophore larva is discussed. A distinctive longitudinal rod, the chordoid organ, consists of vacuolized cells with circular myofilaments. The organ is comparable to a similar structure in gastrotrichs. In the discussion of the phylogenetic position of Cycliophora among protostomians, important morphological observations that are described in the present study indicate that, despite some dissimilarities, the chordoid larva is a modified trochophore. © 1996 Wiley-Liss, Inc.
TL;DR: The organ‐specific effectiveness of bacterial clearance was determined and found the hematopoietic nodules of the shrimp Sicyonia ingentis to be the most effective on a per gram basis and suggestions that hemocytes in the HPN are functionally mature and held in reserve until they are released into circulation are supported.
Abstract: In an earlier investigation, radiolabelled bacteria injected into the hemolymph of the shrimp Sicyonia ingentis were cleared rapidly from circulation. Most of the bacteria were localized in the gills, followed by other organs including the heart, abdominal musculature, and hematopoietic nodules (HPN). We determined the organ-specific effectiveness of bacterial clearance and found the HPN to be the most effective on a per gram basis. Light and electron microscopy were used to determine the mechanism of clearance in the HPN. The HPN are readily permeable to individual bacteria, which then are recognized and phagocytosed exclusively by small granule hemocytes. Within the first hour, the bacteria are degraded, leaving only whorls of membrane in the phagocytic vacuoles. Subsequently, the hemocytes that ingested bacteria lyse, as has been observed in vitro. These observations support earlier suggestions that hemocytes in the HPN are functionally mature and held in reserve until they are released into circulation. © 1996 Wiley-Liss, Inc.
TL;DR: This study expands the understanding of axial bending in fishes by examining extreme modifications of the musculoskeletal system associated with the evolution of unique functional capabilities within teleosts.
Abstract: Unlike most teleosts, the seahorse (genus Hippocampus) is able to bend its tail ventrally, uses its tail in a postural role as a grasping and holding appendage, and possesses heavy body plates instead of scales. To investigate seahorse axial bending mechanisms and the role of plating in those mechanisms, observations were made on seahorses curling their tails ventrally and holding a support and components of the mechanical system used for axial bending, including dermal plates, vertebrae, and axial muscles, were examined. Anatomical modifications involved in ventral tail bending include hypertrophy of the ventral region of the hypaxial muscle, ventrolateral attachment of the myomeres to plates, and modification of the infracarinalis posterior muscles so that they act in axial bending rather than in fin movement as has previously been hypothesized (Harder, '75) for other fishes. Modifications for prehension include the presence of fibers histochemically characterized as tonic in the median ventral muscles (the modified infracarinalis muscle) and in portions of the myomeres. Dermal plates are an important part of the force transmission system used in seahorse tail bending. They transmit forces from the hypaxial myomeres to bend the tail both laterally and ventrally. This study expands our understanding of axial bending in fishes by examining extreme modifications of the musculoskeletal system associated with the evolution of unique functional capabilities within teleosts. © 1996 Wiley-Liss, Inc.
TL;DR: Analysis of plasticity of skull shape and tooth morphology in prairie deer mice by feeding mice diets that differed in consistency but not nutritional quality took into account both family relationships of the animals and the large number of statistical comparisons performed.
Abstract: Morphologists and systematists have long suspected that dietary consistency can affect skull and dental form in mammals. We examined plasticity of skull shape and tooth morphology in prairie deer mice (Peromyscus maniculatus bairdii) by feeding mice diets that differed in consistency but not nutritional quality. Shape differences were analyzed qualitatively and quantitatively, using both landmark-based morphometrics and traditional distance measurements. Mice fed a gruel made of laboratory chow soaked in water differed from those fed hard blocks of chow by a slight anterior shift in the incisor tips a narrowed zygomatic plate, a reduction in size of the masseteric tubercles, an overall decrease in skull size in lateral view, and an increase in overall size in ventral view. Disparities between our results and previous studies may be due to the differences in behavior between the inbred, relatively inactive laboratory strains commonly used in experimental studies and the outbred, constantly active species used here. Also, in contrast to previous studies, the statistical analysis employed here took into account both family relationships of the animals and the large number of statistical comparisons performed. Failure to consider these factors would have resulted in an exaggerated estimate of the effects of diet on skull form and may taint other studies that have explored the same aspects of plasticity. © 1996 Wiley-Liss, Inc.
TL;DR: The ultrastructural differentiation of two muscle fiber types of the squid Sepioteuthis lessoniana was correlated with development of prey‐capture behavior and high‐speed video recordings show correlated behavioral changes.
Abstract: The ultrastructural differentiation of two muscle fiber types of the squid Sepioteuthis lessoniana was correlated with development of prey-capture behavior. Transmission electron microscopy was used to document the differentiation of the fast-contracting cross-striated muscle cells of the tentacles and the obliquely striated muscle cells of the arms of specimens sampled at one week intervals from hatching to 5 weeks. By using high-speed video recordings, the ultrastructural differentiation was correlated with changes in prey-capture behavior that occur during development and growth. The ultrastructural analysis focused on the muscle cells of the transverse muscle of the tentacles and the transverse muscle of the arms. For the first 2 weeks after hatching, the tentacle transverse muscle fibers do not show the adult ultrastructure and are indistinguishable from the obliquely striated fibers of the transverse muscle of the arms. Transverse striation of the tentacle muscle cells appears at approximately three weeks and adult ultrastructure is present by 4-5 weeks after hatching. The high-speed video recordings show correlated behavioral changes. During the first 2-3 weeks after hatching, the animals use a different prey-capture mode from the adults; they jet forward and capture the prey with splayed arms and tentacles rather than employing the rapid tentacular strike. © 1996 Wiley-Liss, Inc.
TL;DR: Morphological features of the middle and distal (ungual) phalanges that have been purported to be necessary for hyper‐retraction in felids vary considerably among digits within the manus and pes, and some of the variation in these features is associated instead with protraction.
Abstract: All carnivorans retract and protract their claws. In felids and some viverrids the claws of digits II through V of both the manus and pes have a larger arc of rotation than those of other carnivorans; the claws retract to the lateral side of the middle phalanx rather than onto its dorsal surface as in most other carnivorans. This condition should be termed hyper-retraction. Morphological features of the middle and distal (ungual) phalanges that have been purported to be necessary for hyper-retraction in felids vary considerably among digits within the manus and pes. These features include the lateral projection of the distal head and the asymmetry of the shaft of the middle phalanx, and the oblique orientation of the articular surface on the distal phalanx. None of these features is necessary in every instance for hyper-retraction, and some of the variation in these features is associated instead with protraction. Differences among digits in the orientation of the articular surface on the distal phalanx are associated with differences in the degree to which the claws must move laterally to rotate from the protracted to the retracted position. Differences in the orientation of the distal head on the middle phalanx are associated with the spreading of the claws during protraction. The manual claws are hook-shaped, whereas the pedal claws are more blade-like; this morphological difference is associated with differences in function between the manus and pes. In the manus the medial claws have a larger radius of curvature and a smaller angle of arc as compared to the more lateral claws; in the pes, the claws on digits III and IV have larger radii of curvature and smaller angles of arc. Digit I of the manus lacks the hyper-retraction mechanism; nonetheless, this digit shares many of the attributes that are associated with this mechanism.
TL;DR: It is hypothesized that this unusual activity may be present in frogs so that the hind limb remains aero(hydro)dynamically stable as the frog arches through its leap or glides in swimming following completed limb extension.
Abstract: Electromyography (EMG) was used to examine muscle activity of the major hip, knee, and ankle extensors during both hopping and swimming in leopard frogs. Chronic EMG electrodes were implanted for periods of 7-10 days. This permitted us to record EMG activities during both hopping and swimming from the same electrode, allowing a direct comparison of the timing and amplitudes of muscle activity between the two behaviors. We could then relate these activities to the kinematics of locomotion. In both behaviors, all three extensors were synchronously activated 30-50 ms before limb extension began. However, the hip extensor turned on relatively earlier in hopping than in swimming when on time was expressed as percent of stride. The hip and knee extensors were activated relatively longer in hopping and the ankle extensor relatively longer in swimming. The amplitudes of the rectified, inte- grated EMG signals were roughly twice as large in hopping as in swimming for all three muscles, supporting the notion that propulsion in hopping requires more force than in swimming. The EMG burst durations differed little between the muscles or, in relative duration, between the behaviors. As has been found in other quadrupeds, the EMG bursts began before visible movement and ceased at or before hindlimb extension was completed. In our animals, how- ever, we found a consistent, low level (10-30% of maximum amplitude) of EMG activity that continued 60-200 ms past the end of the burst and into the suspension periods in both hopping and swimming. We hypothesize that this unusual activity may be present in frogs so that the hind limb remains aero(hydr0)dynamically stable as the frog arches through its leap or glides in swimming following completed limb extension. Thus, the timing and pattern of the EMG bursts are consistent with those present in other tetrapods and support conservatism of neural control. However, the prolonged low-level activity suggests flexibility in the control pattern and variation according to specific behaviors. o 1996 Wiley-Liss, Inc Amphibians are an important group of ver- tebrates for morphologists and physiologists to examine because, within the Amphibia, extremes of pleisiomorphic and derived mor- phology and function can be found. Investiga- tors have studied neural and muscular anatomy and physiology along with the bio- mechanics of locomotion in both salamanders and frogs going back for over 100 years (e.g., Gregory and Camp, '18; Hill, '38; Schaeffer, '41; Barclay, '46; Ashley-Ross, '94; Marsh, '94). The morphology, limb and muscle me- chanics, and behavior of salamanders are likely similar to those of the earliest terres- trial vertebrates (Gans and De Gueldre, '92;
TL;DR: It is believed that the crossbridges may have greater competition for actin binding sites in simple‐lattice muscles compared to the superlattICE types, and the possible functional significance of the different lattice types is discussed.
Abstract: A survey of skeletal muscles throughout craniates shows basic kinds of myosin filament arrangement, simple-lattice and superlattice, within the A-band of each sarcomere. Distribution of simple- and superlattice arrangements across a phylogeny of craniates suggests that the superlattice arrangement is primitive and that Amia and teleosts are derived in showing simple-lattice arrangements. Two taxa examined (Scyliorhinus and Acipenser) show both lattice types within the same organism implying that there is not a simple evolutionary transformation of one to the other fiber arrangement. We discuss the possible functional significance of the different lattice types. We believe that the crossbridges may have greater competition for actin binding sites in simple-lattice muscles compared to the superlattice types. © 1996 Wiley-Liss, Inc.