Showing papers in "Journal of Morphology in 1995"

Hydrodynamic design of the humpback whale flipper.

Abstract: The humpback whale (Megaptera novaeangliae) is reported to use its elongate pectoral flippers during swimming maneuvers. The morphology of the flipper from a 9.02-m whale was evaluated with regard to this hydrodynamic function. The flipper had a wing-like, high aspect ratio planform. Rounded tubercles were regularly interspersed along the flipper's leading edge. The flipper was cut into 71 2.5-cm cross-sections and photographed. Except for sections near the distal tip, flipper sections were symmetrical with no camber. Flipper sections had a blunt, rounded leading edge and a highly tapered trailing edge. Placement of the maximum thickness placement for each cross-section varied from 49% of chord at the tip to 19% at mid-span. Section thickness ratio averaged 0.23 with a range of 0.20-0.28. The humpback whale flipper had a cross-sectional design typical of manufactured aerodynamic foils for lift generation. The morphology and placement of leading edge tubercles suggest that they function as enhanced lift devices to control flow over the flipper and maintain lift at high angles of attack. The morphology of the humpback whale flipper suggests that it is adapted for high maneuverability associated with the whale's unique feeding behavior.

Homology of facial structures in extant archosaurs (birds and crocodilians), with special reference to paranasal pneumaticity and nasal conchae.

Abstract: Homology of virtually all major components of facial anatomy is assessed in Archosauria in order to address the function of the antorbital cavity, an engimatic structure that is diagnostic for the group. Proposed functions center on its being a housing for a gland, a muscle, or a paranasal air sinus. Homology is approached in the context of the Extant Phylogenetic Bracket method of reconstructing unpreserved aspects of extinct organisms. Facial anatomy and its ontogeny was studied in extant archosaurs (birds and crocodilians) to determine the osteological correlates of each soft-tissue component; resemblances between birds and crocodilians comprised the similarity test of homology. The congruence test of homology involved surveying phylogenetically relevant fossil archosaurs for these bony signatures. The facial anatomy of extant birds and crocodilians is examined in detail to provide background and to discover those apomorphic aspects that contribute to the divergent specialization of these two groups and thus obscure homologies. Birds apomorphically show enlarged eyeballs, expanded nasal vestibules, and reduced maxillae, whereas crocodilian faces are dorsoventrally flattened (due to nasal rotation) and elongated. Most facial attributes of archosaurs are demonstrably homologous and in fact characterize much more inclusive groups. Special emphasis has been placed on the nasal conchae and paranasal air sinuses. Within Amniota, the following conchal structures are homologous, and all others are neomorphs: Avian caudal concha, crocodilian concha + preconcha, Sphenodon caudal concha, squamate concha, and probably the mammalian crista semicircularis. The avian antorbital paranasal air sinus is homologous with the crocodilian caviconchal sinus; the maxillary sinus of placental mammals is not homologous with the archosaurian paranasal sinus. With regard to the function of the antorbital cavity, archosaurs possess homologous nasal glands, dorsal pterygoideus muscles, and paranasal air sinuses, but the osteological correlates of only the paranasal sinus involve the antorbital fenestrae and fossae. Thus, the antorbital cavity is best interpreted as principally a pneumatic structure. © 1995 Wiley-Liss, Inc.

Mechanical properties of aponeurosis and tendon of the cat soleus muscle during whole-muscle isometric contractions.

Abstract: Recent studies have suggested that the mechanical properties of aponeurosis are not similar to the properties of external tendon. In the present study, the lengths of aponeurosis, tendon, and muscle fascicles were recorded individually, using piezoelectric crystals attached to the surface of each structure during isometric contractions in the cat soleus muscle. We used a surgical microscope to observe the surface of the aponeurosis, which revealed a confounding effect on measures of aponeurosis length due to sliding of a thin layer of epimysium over the proximal aponeurosis. After correcting for this artifact, the stiffness computed for aponeurosis was similar to tendon, with both increasing from around 8 F0/Lc (F0 is maximum isometric force and Lc is tissue length) at 0.1 F0 to 30 F0/Lc at forces greater than 0.4 F0. At low force levels only (0.1 F0), aponeurotic stiffness increased somewhat as fascicle length increased. There was a gradient in the thickness of the aponeurosis along its length: its thickness was minimal at the proximal end and maximal at the distal end, where it converged to form the external tendon. This gradient in thickness appeared to match the gradient in tension transmitted along this structure. We conclude that the specific mechanical properties of aponeurosis are similar to those of tendon. © 1995 Wiley-Liss, Inc.

In vivo strain in the humerus of pigeons (Columba livia) during flight

Abstract: Longitudinal and principal strain recordings were made in vivo at three sites (dorsal, anterior, and ventral) on the humeral midshaft of pigeons executing five modes of free flight: Take-off, level flight, landing, vertical ascent, and near-vertical descent. Strains were also recorded while the birds flew carrying weights that were 33%, 50%, or 100% of their body weight. The relative distribution of strain measured at the three surface midshaft sites and across the bone's cortex was found to be similar for all flight modes. Principal strains recorded in the dorsal and ventral humerus indicated considerable torsion produced by aerodynamic loading of the wing surface posterior to the bone. Measured torsional shear strains (maximum: 2,700–4,150 μ e during level flight) were 1.5 times greater than longitudinal strains. In addition to torsion, the humerus is also subjected to significant dorsoventral bending owing to lift forces acting on the wing during the downstroke. Analysis of the cross-sectional distribution of longitudinal strains at the humeral midshaft cortex shows that the orientation of bending shifts in a regular manner during the downstroke, indicating that the wing generates progressively more thurst (vs. lift) later in the downstroke. This shift is less during take-off and vertical ascent when greater lift is required. Peak principal and longitudinal strains increased by an average of only 50% from landing to vertical ascending flight and take-off (e.g., dorsal humerus: −1,503 to −2,329 μ e) and did not exceed −2,600 μ epsiv; at any site, even when the birds flew carrying twice their body weight. Strains recorded when birds flew at two times their body weight (100% BW load) were similar in magnitude to those recorded during vertical ascent and take-off and likely represent those developed during maximal performance. Strains developed within the midshaft were maximal in the anterodorsal and posteroventral cortices, not at the dorsal, ventral, and anterior sites at which strain was recorded. Consequently, maximum strains experienced by the bone are probably 20–25% greater than those recorded (ca. 3,200 μ e), indicating a safety factor of about 3.5 for compressive strain failure. The much higher shear strains, however, indicate a lower safety factor (1.9), in which the bone's torsional strength is its most critical design feature. Finally, the magnitude and distribution of strains developed in the humerus of pigeons are generally similar to those recorded in the humerus of large fruit-eating bats during flight. © 1995 Wiley-Liss, Inc.

Incubation temperature and gonadal sex affect growth and physiology in the leopard gecko (Eublepharis macularius), a lizard with temperature-dependent sex determination.

Abstract: Temperature-dependent sex determination (TSD), in which the temperature at which an egg incubates determines the sex of the individual, occurs in egg-laying reptiles of three separate orders. Previous studies have shown that the embryonic environment can have effects lasting beyond the period of sex determination. We investigated the relative roles of incubation temperature, exogenous estradiol, and gonadal sex (testis vs. ovary) in the differentiation of adult morphological and physiological traits of the leopard gecko, Eublepharis macularius. The results indicate that incubation temperature, steroid hormones, and gonads interact in the development of morphological and physiological characters with incubation temperature resulting in the greatest differences in adult phenotype. Incubation temperature did not affect reproductive success directly, but may influence offspring survival in natural situations through effects on adult female body size. Postnatal hormones seem to be more influential in the formation of adult phenotypes than prenatal hormones. These results demonstrate that TSD species can be used to investigate the effects of the physical environment on development in individuals without a predetermined genetic sex and thus provide further insight into the roles of gonadal sex and the embryonic environment in sexual differentiation. © 1995 Wiley-Liss, Inc.

Internal fertilization, testis and sperm morphology in glandulocaudinae fishes (Teleostei: Characidae: Glandulocaudinae).

Abstract: In this report, the gonads of 32 glandulocaudine species, representing 18 genera, are compared with 11 outgroup characiform species. Through the presence of spermatozoa within the ovarian cavity, internal fertilization of the female is confirmed for the 16 genera for which mature ovaries were available. No outgroup ovary studied contains spermatozoa. All mature glandulocaudine testes have a large portion of the posterior testis, which is devoid of developing germ cells and spermatocysts (aspermatogenic), devoted to sperm storage, with the degree of partitioning in that region varying greatly within the group. All outgroup species examined have spermatozoa with spherical nuclei. With the exception of the species of the genus Planaltina, which also have spherical nuclei, all glandulocaudines have elongated nuclei, which vary among the species from 3.6 μm to 31.6 μm in length. Distinct sperm packets (spermatozeugmata) are formed in five genera by two different methods. In the genera Xenurobrycon, Tyttocharax, and Scopaeocharax, all of the tribe Xenurobryconini, the spermatozeugmata are formed within the spermatocysts and released fully formed. In all genera of the tribe Glandulocaudini, which includes Glandulocauda and Mimagoniates, loose spermatozoa are released which cluster into spermatozeugmata within the posterior storage areas. These morphological specializations are discussed within a phylogenetic framework as adaptations for internal fertilization and are hypothesized to be independently derived. © 1995 Wiley-Liss, Inc.

Comparative and functional myology of the prehensile tail in new world monkeys

Abstract: The caudal myology of prehensile-tailed monkeys (Cebus apella, Alouatta palliata, Alouatta seniculus, Lagothrix lagotricha, and Ateles paniscus) and nonprehensile-tailed primates (Eulemur fulvus, Aotus trivirgatus, Callithrix jacchus, Pithecia pithecia, Saimiri sciureus, Macaca fascicularis, and Cercopithecus aethiops) was examined and compared in order to identify muscular differences that correlate with osteological features diagnostic of tail prehensility. In addition, electrophysiological stimulation was carried out on different segments of the intertransversarii caudae muscle of an adult spider monkey (Ateles geoffroyi) to assess their action on the prehensile tail. Several important muscular differences characterize the prehensile tail of New World monkeys compared to the nonprehensile tail of other primates. In atelines and Cebus, the mass of extensor caudae lateralis and flexor caudae longus muscles is more uniform along the tail, and their long tendons cross a small number of vertebrae before insertion. Also, prehensile-tailed monkeys, especially atelines, are characterized by well-developed flexor and intertransversarii caudae muscles compared to nonprehensile-tailed primates. Finally, Ateles possesses a bulkier abductor caudae medialis and a more cranial origin for the first segment of intertransversarii caudae than do other prehensile-tailed platyrrhines. These myological differences between nonprehensile-tailed and prehensile-tailed primates, and among prehensile-tailed monkeys, agree with published osteological and behavioral data. Caudal myological similarities and differences found in Cebus and atelines, combined with tail-use data from the literature, support the hypothesis that prehensile tails evolved in parallel in Cebus and atelines.

Allometry and developmental integration of body growth in a piranha, Pygocentrus nattereri (Teleostei: Ostariophysi).

Abstract: Piranhas, like many teleosts, change their diets on both ontogenetic and phylogenetic time scales. Prior studies have suggested that pervasive morphological changes in body form on a phylogenetic time scale may be related to changes in diet, but previous reports have found little shape change in piranhas on an ontogenetic time scale. We re-examine the post-transformational allometry of body form in one piranha, Pygocentrus nattereri (Kner), using the method of thin-plate splines decomposed by their partial warps. We find substantial evidence of allometry, primarily elongation of the mid-body relative to the more anterior and posterior regions, elongation of the postorbital and nape regions relative to the more anterior head and posterior body, and deepening of the head relative to the body. In addition to these pervasive changes throughout the body, there are some that are more localized, especially elongation of the postorbital region relative to eye diameter and snout, and an even more localized elongation of the snout relative to eye diameter. Initial dietary transitions are associated with changes in head and jaw proportions, but rates of shape change decelerate through growth, so that the final transition to a diet increasingly dominated by small whole fish appears associated with change largely in overall body size. © 1995 Wiley-Liss, Inc.

Cranial features of dendrobatid larvae (Amphibia: Anura: Dendrobatidae).

Abstract: The larval neurocranium and visceral arches of seven dendrobatid species representing four genera are described, based on cleared-and-stained and serially sectioned specimens. A variety of characters is shared by all seven species. Larval features do not substantiate the assumption of close ranoid affinities of the Dendrobatidae. Instead dendrobatid larvae share features such as the special quadripartite cartilago suprarostralis, the lack of the larval processus oticus, the presence of three foramina acustica, and the lack of a foramen perilymphaticum accessorius with many bufonoid larvae. The first of these characters is unique to bufonids, hylids, dendrobatids, and some New World leptodactylids; the other characters also occur in pelobatids and are presumably plesiomorphic for the Neobatrachia. The free proximal ends of Ceratobranchialia II and III are an autapomorphy of the Dendrobatidae supporting the monophyly of the family. Some features of the cranium are paedomorphic: low cartilago orbitalis, lack of connection between cartilage orbitalis and otic capsule (most species), and vestigal taeniae tecti. New anatomical terms are introduced. © 1995 Wiley-Liss, Inc.

Comparative embryology of teleostean fishes. I. Development and staging of the american shad, Alosa sapidissima (Wilson, 1811)

Abstract: A new approach to devising embryological staging systems allows improved phylogenetic comparisons of developmental patterns. As in traditional approaches, morphological features provide the defining criteria for stages, but unlike traditional normal tables, each stage is defined by no more than one or two morphological criteria that are fundamental developmental features of all teleosts. Additional developmental features that occur concurrently with the defining criteria of a stage are treated as variables potentially uncoupled from the defining criteria for that stage. This system is well suited to detect phylogenetic heterochrony and promises to increase our understanding of conserved vs. labile features in teleostean embryology. In this study, I explain the defining criteria for American shad and then make comparisons with other clupeoids. The development of American shad includes 35 stages extending from fertilization to metamorphosis. Comparisons with other clupeoids indicate that the developmental pattern of shad is representative of the early ontogeny of many clupeoids during the embryonic and yolk sac periods and may be conservative for the group. However, several concurrent features, particularly hatching, formation of neuromasts, and opercular development, vary in developmental timing among clupeoids. Comparisons indicate that shad embryos delay the development of these concurrent features relative to other clupeoids. Modifications of the developmental pattern for different species of clupeoids are heterochronic but their phylogenetic and adaptive significance is unknown. © 1995 Wiley-Liss, Inc.

Jaw muscles of new world squirrels

Abstract: The jaw, suprahyoid, and extrinsic tongue muscles are described for eight species of New World squirrels, spanning more than an order of magnitude in body mass Anatomical differences are discussed in the light of body size, natural history, and phylogeny The relative sizes of different muscles, their orientations, and the shapes and positions of their areas of attachment vary but show few trends in relation to body size The anatomical differences are likewise not readily explained by the mechanical requirements of the animals' diets, which are similar The most marked anatomical differences occur in Sciurillus (the pygmy tree squirrel), as well as those genera--Glaucomys (the flying squirrel) and Tamias (the chipmunk)--that are taxonomically most distinct from the tree squirrels Sciurillus is noteworthy for its unusually small temporalis and an anterior deep masseter that is oriented to assist in retraction of the jaw Tamias has a more vertically oriented temporalis and greater inclination in the anterior masseter muscles than the other squirrels, features that may be associated with its large diastema and relatively posteriorly situated cheek teeth, which in turn may relate to its having cheek pouches Our results form a valuable database of information to be used in further studies of functional morphology and phylogeny

Anatomy of the feeding apparatus of the lemon shark, Negaprion brevirostris.

Abstract: The anatomy of the feeding apparatus of the lemon shark, Negaprion brevirostris, is investigated by gross dissection, computer axial tomography, and histological staining. The muscles and ligaments of the head associated with feeding are described. The upper and lower jaws are suspended by the hyoid arch, which in turn is braced against the chondrocranium by a complex series of ligaments. In addition, various muscles and the integument contribute to the suspension and stability of the jaws. The dual jaw joint is comprised of lateral and medial quadratomandibular joints that resist lateral movement of the upper and lower jaws on one another. This is important during feeding involving vigorous head shaking. An elastic ethmoplatine ligament that unites the anterior portion of the upper jaw to the neurocranium is involved with upper jaw retraction. The quadratomandibularis muscle is divided into four divisions with a bipinnate fiber arrangement of the two large superficial divisions. This arrangement would permit a relatively greater force per unit volume and reduce muscle bulging of the jaw adductor muscle in the spatially confined cheek region. Regions of relatively diffuse integumental ligaments overlying the adductor mandibulae complex and the levator palatoquadrati muscle, interspersed with localized regions of longer tendonlike attachments between the skin and the underlying muscle, permit greater musculoskeletal movement relative to the skin. The nomenclature of the hypobranchial muscles is discussed. In this shark they are comprised of the unsegmented coracomandibularis and coracohyoideus, and the segmented coracoarcualis. © 1995 Wiley-Liss, Inc.

Incisal biting in the mountain beaver (Aplodontia rufa) and woodchuck (Marmota monax).

Abstract: Analysis of synchronously recorded cine-radiographs and electromyograms in two rodents (Aplodontia rufa and Marmota monax) demonstrates that jaw movements and muscle activities during incisal functions are distinctly different from those found during mastication. Movements during incisal biting are primarily along the midline, accompanied by symmetrical activity of the jaw adductor muscles. Most biting cycles do not end in contact between upper and lower incisors. When contact does occur, the lower incisors are dragged along the lingual surfaces of the upper incisors. Cropping, or tip-to-tip occlusion of upper and lower incisors, was not observed. Sharpening of the lower incisors, a behavior which may be unique to the Rodentia, was recorded in both A. rufa and M. monax. During sharpening, the lingual surface of the lower incisor is dragged across the tip of the upper incisor producing a lingual wear facet. Like incisal biting, sharpening movements are primarily confined to the midline, although there may be lateral movements in some sharpening cycles. Sharpening cycles are among the most rapid cyclic movements recorded in mammals, as the mean frequencies of sharpening are 11 cycles/s in A. rufa and 8 cycles/s in M. monax.

Mechanical properties of the skin of Xenopus laevis (Anura, Amphibia).

Abstract: The skin of the aquatic pipid frog, Xenopus laeuis, was examined for specific biomechanical features: 1) thickness, 2) maximal strain at break (~f), 3) tensile strength (urn), 4) modulus of elasticity (E, stiffness), and 5) the area under the stress-strain curve (W) (breaking energy, toughness). Skin freshly removed from dorsal, ventral, and lateral areas of the body was subjected to uniaxial tension. In both sexes, the dorsal skin is thicker than the ventral. The skin of male frogs was consistently thinner in all body regions than that of females. Most biomechanical parameters showed a considerable range of values in both males (~f = 59-63%, a, = 15-16.5 MPa, E = 33.5-38.4 MPa, W = 3.84.5 MJ/m3) and females (E( = 102-126%, u, = 11.5 MPa, E = 10.4-12 MPa, W = 5.2-6.7 MJ/m3). The disparate Efvalues in males (low) and females (high) might reflect sexual dimorphism. Static stress-strain curves were typically J-shaped; with the exception of a "toe," the curves rose approxi- mately linearly with increasing strain. The skin ofX. laeuis, although heteroge- neous in structure, possesses features similar to those found in tissues with aligned collagen fibers such as tendons or fish skin. However, in anurans, the skin seems to play a more passive mechanical role during locomotion than in fish. Q 1995 Wiiey-Liss, Inc. The skin of vertebrates has many func- tions. It is an organ for protection, for admit- ting sensory reception, and it contributes to locomotion and osmoregulation. These func- tions are reflected in its morphological com- plexity as well as in the physiological and biochemical properties of its components. The morphology and biochemistry of amphibian skin, including that of the anurans, has been described in detail (Fox, '86 and references therein), but data on its biomechanical prop- erties are rare. The basic constituents of anuran skin (epi- dermis and dermis) are identical with those in other vertebrates. In the dermis, which consists mainly of a framework of collagen and elastic fibers, two strata can be distin- guished. The superficial layer has a loose network of collagen fibers (stratum spongio- sum) and the compact deep layer contains collagen fibers arranged in a crisscrossed manner (stratum compactum). This layer rep- resents the most conservative element in the vertebrate dermis and characterizes mainly the mechanical properties of the skin (e.g.,

Lectin histochemical identification of carbohydrate moieties in opossum chemosensory systems during development, with special emphasis on VVA‐identified subdivisions in the accessory olfactory bulb

Abstract: Lectins, sugar-binding molecules of nonimmune origin, were used in this study to describe the development of the main olfactory and vomeronasal systems in the Brazilian gray short-tailed opossum, Monodelphis domestica. A battery of seven lectins of the N-acetylgalactosamine/galactose-binding group was used. Of the seven lectins, only two, Vicia villosa agglutinin (VVA) and Griffonia (Bandeiraea) simplicifolia lectin I-isolectin B4 (GS I-B4), were specific to the vomeronasal system. The other five lectins recognized carbohydrates in both chemosensory systems, although the binding was more intense in the accessory olfactory system. Furthermore, whereas six of the lectins stained the adult opossum accessory olfactory bulb (AOB) homogeneously, the VVA lectin distinguished two regions of the AOB. Similar to the expression of olfactory marker protein (OMP) (Shnayder et al. [1993] Neuroreport 5:193-196), the rostral half of the AOB stained much darker with VVA than the caudal half, and the onset of the restricted pattern of staining at age 45 days also coincided. We conclude that 1) GS I-B4 and VVA recognize cell surface carbohydrate moieties specific to the vomeronasal, but not to the main olfactory, system, and 2) the carbohydrate moiety that is recognized by the VVA lectin, presumably terminal N-acetyl-galactosamine, is both temporally and spatially restricted in the opossum AOB. These results are discussed in the framework of other known spatially restricted molecules of the two major nasal chemosensory systems.

Intratendinous ossification in birds: A review.

Abstract: Intratendinous ossification (tenostosis; Tendo ossificans) is a distinct structural form feature of the avian musculoskeletal system with different definitions in terms of morphogenesis, resultant morphology, and functional role(s). Interpretation of these structural elements and their pattern(s) among avian taxa at different systematic levels is reviewed with regard to age-related changes in tendon, form features in avian phylogeny, and adaptive features in biomechanics and kinematics of locomotion. Specific examples of patterns in the musculoskeletal elements of the head and hyolingual system, axial (vertebral) system, and the limbs in several avian taxa are given. A series of questions is formulated as a prospectus for further study. © 1995 Wiley-Liss, Inc.

Prey capture in the lizard Agama stellio.

Abstract: Prey capture in Agama stellio was recorded by high-speed video in combination with the electrical activity of both jaw and hyolingual muscles. Quantification of kinematics and muscle activity patterns facilitated their correlation during kinematic phases. Changes in angular velocity of the gape let the strike be subdivided into four kinematic phases: slow open (SO1 and SOII), fast open (FO), fast close (FC), and slow close-power stroke (SC/PS). The SO1 phase is marked by initial activity in the tongue protractor, the hyoid protractor, and the ring muscle. These muscles project the tongue beyond the anterior margin of the jaw. During the SO11 phase, a low level of activity in the jaw closers correlates with a decline of the jaw-opening velocity. Next, bilateral activity in the jaw openers defines the start of the FO phase. This activity ends at maximal gape. Simultaneously, the hyoid retractor and the hyoglossus become active, causing tongue retraction during the FO phase. At maximal gape, the jaw closers contract simultaneously, initiating the FC phase. After a short pause, they contract again and the prey is crushed during the SC/PS phase. Our results support the hypothesis of tongue projection in agamids by Smith (( 19881 J. Morphol. 196:157-171), and show some striking similarities with muscle activity patterns during the strike in chameleons (Wainwright and Bennett ( 1992al J. Exp. Biol. 168:l-21). Differences are in the activation pattern of the hyoglossus. The agamid tongue projection mechanism appears to be an ideal mechanical precursor for the ballistic tongue projection mechanism of chameleonids; the key derived feature in the chameleon tongue projection mechanism most likely lies in the changed motor pattern controlling the hyoglossus muscle. B 1995 Wiley-Liss, Inc. Lizards capture prey by means of lingual or jaw prehension (Smith, '84, '88). Some authors argue that jaw-mediated prey cap- ture might be the primitive condition in squa- mates (Bels and Goosse, '90; referring to the plesiomorphic condition of jaw prehension in Amphibia, Thexton et al., '77; Lauder and ShafTer, '88; Findeis and Bemis, '90; Nishi- kawa and Cannatella, '91; Anderson, '931, but lingual prey capture is considered by most authors to be more primitive than jaw capture (Schwenk, '88; Schwenk and Bell, '88; Schwenk and Throckmorton, '89). Most functional morphological studies con- cerning prey capture in lizards have empha- sized a few groups belonging to the Iguania (Agamidae: Schwenk and Throckmorton, '89; Kraklau, '91; Iguanidae: Schwenk and Throckmorton, '89; Bels, '90; Bels and Go- osse, '90; Delheusy and Bels, '92; and Cha- maeleonidae: Gnanamuthu, '30; Zoond, '33; Bels and Baltus, '87; Bell, '89, '90; Wain-

Cytological and morphological ontogenesis and involution of the thymus in cichlid fishes (Cichlidae, Teleostei).

Abstract: The ontogenesis and involution of thymus in cichlid fishes was studied with the aim of comparing development in the bottom-spawning species Tilapia zillii and T. tholloni, and in the mouth-brooding species Oreochromis auratus, O. niloticus, O. mossambicus, and Sarotherodon galilaeus. For comparison, data are also given on bottom-spawning Cichlasoma spp. from America and mouth-brooding Pseudotropheus auratus and Aulonocara nyassae from Africa. Developmental changes were followed histologically by means of light and electron microscopy of sections, beginning with embryos 24 h after fertilization, up to 14-year-old specimens of O. auratus. In all these fish, the anlagen of the thymus glands begins from the third and fourth gill pouches, and their development shows a high correlation with the pace of general organogenesis, which differs greatly in the bottom-spawning and mouth-brooding cichlids. In juveniles of bottom-spawners of 20-40 mm total length and in mouth-brooders of 40-60 mm total length, three cell types are present in the thymus: thymocytes, with large, dense nuclei; epitheliocytes, with long cell extensions containing bundles of tonofibrils; and reticulocytes, with short, granulated cell extensions. Hassall's corpuscles start to develop in larvae of T. zillii at 20-35 mm total length, and in specimens of 40 mm and more total length the corpuscles are typical, formed by inner and outer rings of epitheliocytes. At 30-45 mm total length, cell debris starts to accumulate in the interior of the corpuscles as an early sign of regression. As involution continues, macrophages accummulate within and around the Hassall's corpuscles. The epitheliocyte rings are eventually completely broken down. Isles of thymocytes persist in tilapias from the age of 1-14 years, but most of the thymus volume is occupied by blood lacunae and pigmented macrophage aggregations. The morphology is similar in the mouth-brooding species Pseudotropheus beginning at 1.5 years of age. © 1995 Wiley-Liss, Inc.

Flagellar basal apparatus and its utility in phylogenetic analyses of the porifera

Abstract: A broadly based comparative study was initiated to assess components of the flagellar basal apparatus as a character set in phylogenetic analyses of poriferans. The flagellated (monociliated) epidermal cells of sponge larvae were selected for study. Taken together, they create a field of locomotory cells analogous to a multiciliated surface. Larvae of six species in four orders of the Demospongiae were examined by transmission electron microscopy. Results are compared with findings taken from the literature on larvae of five additional species of demosponges and four species of calcareans. Data were assembled on six components of the basal apparatus: (1) basal body, (2) basal foot, (3) accessory centriole, (4) transverse cytoskeletal system, (5) longitudinal cytoskeletal system, and (6) association with Golgi body. Where evidence permits assessment, all have Type II basal bodies. Basal feet are diverse and are subdivided into three categories based on structural complexity. The most anatomically intricate (Type III) is found only in larvae of Mycale spp. Accessory centrioles are present or absent depending on the species, but their occurrence is without overall taxonomic pattern. When present, accessory centrioles are oriented perpendicularly to the long axis of the basal body, but as ascertained from relationship to the anterior-posterior axis of the larvae they are without consistent orientation with regard to the plane of effective beat of the flagellum. Transverse and longitudinal cytoskeletal systems are also diverse among larvae. The existence of cross-striated rootlets is convincingly established only in larvae of calcareans, and such rootlets are present in larvae of all four calcareans studied to date. Three apparently new rootlet structures are described: lateral arms of the transverse cytoskeletal system from larvae of Aplysilla sp. and Haliclona tubifera; laminar sheets of the longitudinal system from larvae of Aplysilla sp. and M. cecilia; and paraxial rootlet in larvae of H. tubifera. A robust similarity in structure of the basal appartus is observed among the three species of halichondrids reported here for the first time. In comparison with the flagellar basal apparatus found in adults, those of larvae are more complex and more diverse. Review of studies on adult sponges that include information on the basal apparatus reveals the absence of a longitudinal rootlet system in all cases. Additionally, there exists a high degree of concordance between properties of the basal apparatus in the one sclerosponge and the one hexactinellid studied to date. These basal apparatus are also the simplest in construction of those found in sponges. Conversely, the basal apparatus of demosponges are varied. Although consistent presentation of the basal apparatus is evident in certain taxa, any discernable systematic pattern in their overall configuration remains obscure. Finally, we conclude that the flagellar basal apparatus of sponges is more similar to that found in choanoflagellates than it is to that observed in eumetazoans. © 1995 Wiley-Liss, Inc.

Convergent evolution of the vestibular organ in the subterranean mole‐rats, Cryptomys and Spalax, as compared with the aboveground rat, Rattus

Abstract: The membranous labyrinth of the vestibular organ (examined in toto) in two unrelated species of subterranean rodents, Cryptomys sp from Zambia and Spalax ehrenbergi from Israel, was in many parameters (streamline length, curvature radius, and cross-sectional area of the lumen) relatively or even absolutely (especially the cross-sectional area) larger than in the laboratory Norway rat The mechanical sensitivity of the vestibular organ (estimated according to the mathematical model of Oman et al, [1987] Acta Otolaryngol (Stockh) 103:1–13) was similar in both subterranean rodent species and significantly higher than that in the laboratory rat The most pronounced differences in morphometry and the resulting mechanical sensitivity between the subterranean forms and the rat occurred in the lateral (ie, phylogenetically and ontogenetically most recent and presumably most plastic) semicircular duct The area of the sensory epithelia, and density and total numbers of vestibular receptors, were estimated on surface specimens for both maculae and for all three cristae for all three species While the density of hair cells in comparable sensory epithelia was similar in all three species, the sensory area and thus, also, the total receptor counts were significantly larger in both subterranean forms The peripheral vestibular organ in subterranean rodents is, in comparison to a generalized aboveground dwelling form, ie, the rat, progressively specialized, and in any case cannot be denoted as degenerate © 1995 Wiley-Liss, Inc

Diversification of brain morphology in antarctic notothenioid fishes: Basic descriptions and ecological considerations

Abstract: The Notothenioidei, a perciform suborder of 120 species, dominates the ichthyofauna of the Southern Ocean around Antarctica. Unlike most teleost groups, notothenioids have undergone a corresponding ecological and phyletic diversification and therefore provide an excellent opportunity to study the divergence of the nervous system in an unusual environment. Our goal is to evaluate notothenioid brain variation in light of this diversification. To provide a baseline morphology, we examine the gross morphology and histology of the brain of Trematomus bernacchii, a generalized member of the family Nototheniidae. We then examine the variation in brain gross anatomy (32 species) and histology (10 species) of other notothenioids. Our sample represents about 27% of the species in this group and includes species from each of the six families, as well as species representing diverse ecologies. For comparison we reference the well-studied brains of two species of temperate perciformes (Perca flavescens and Lepomis humilis). Our results show that, in general, notothenioid brains are more similar to the brains of temperate perciforms than to the unusual brains of cave-dwelling and deep-sea fishes. Interspecific variation in gross brain morphology is comparable to that in Old World cyprinids and is illustrated for 17 species. Variation is especially noteworthy in the ecologically and geographically diverse family Nototheniidae. Measurements indicate that sensory regions (olfactory bulbs, eminentia granularis, and crista cerebellaris) exhibit the most pronounced variation in relative surface area. Association areas, including the corpus cerebelli and the telencephalon, exhibit moderate variation in size, shape, and lobation patterns. Regulatory areas of the brain, including the saccus vasculosus and the subependyma of the third ventricle, are also variable. These regions are best developed in species living in the subfreezing water close to the continent. In some species the expanded ependymal lining forms ventricular sacs, not previously described in any other vertebrate. Three species, including two nototheniids (Eleginops maclovinus and Pleuragramma antarcticum) and the only artedidraconid in our sample, have distinctive brains. The unique brain morphology of Pleuragramma is probably related to a sensory (lateral line) specialization for feeding. Within the Nototheniidae, a phyletic effect on cerebellar morphology is evident in the Coriiceps group and in the Pleuragramminae. Neither phyletic position nor ecological factors (water temperature, position in the water column, dietary habits) alone fully explain the pattern of notothenioid brain diversification.

Cephalometric correlates of echolocation in the chiroptera: II. Fetal development.

Abstract: Cephalometry was used to detect patterns of cranial growth in fetal bats that were stained differentially for bone and cartilage. Three developmental features distinguish embryos of taxa that echolocate nasally from embryos of taxa that echolocate orally: (1) the basicranium is retained ventral to the cervical axis, (2) the rostrum is retained below the basicranial axis, and (3) the lateral semicircular canals are rotated caudally. Together, the first two actions align the fetal nasal cavity with what will be the long axis of the adult body in flight. The third action aligns the lateral semicircular canals with the horizontal. In contrast, skulls of oral-emitting taxa are constructed such that the oral cavity is aligned with the long axis of the body in flight. The evolution of head posture and skull form in microchiropteran bats has been constrained by the demands of vocalization, i.e., ultrasonic echolocation. Accordingly, the ontogeny of the microchiropteran skull has been canalized along two distinct developmental paths—oral-emitting and nasal-emitting Bauplane. © 1995 Wiley-Liss, Inc.

Structure of atympanate tibial organs in legs of the cave-living ensifera, Troglophilus neglectus (Gryllacridoidea, Raphidophoridae).

Abstract: Troglophilus neglectus (Gryllacridoidea, Raphidophoridae) is a nocturnal Ensifera which can be found in caves of Slovenia. The anatomy of the tibial organs in the fore-, mid-, and hindlegs, as well as the external morphology of the proximal fore-tibia and the prothoracic tracheal system, is described comparatively. In the prothorax and in the forelegs, no sound-conducting structures such as an acoustic trachea, enlarged spiracles, or tympana are developed. A group of 8-10 campaniform sensillae is located in the dorsal cuticle of the proximal tibia. In each leg, the tibial organ complex is built up by two scolopale organs, the subgenual organ and the intermediate organ; the structure and the number of scolopidia is similar in each leg. No structure resembling the crista acoustica is found. The subgenual organ contains around 30 scolopidia; the intermediate organ is subdivided into a proximal part containing 8-9 scolopidia and a distal part with 5-6 scolopidia. The two groups of scolopidia are not directly connected to the tracheal system. The tibial organs in the forelegs are insensitive to airborne sound, and they appear to be more primitive compared to those found in members of the Tettigoniidae and the Gwllidae. The results indicate that the complex tibial organs in all legs of T. neglectus are primarily vibrosensitive. © 1995 Wiley-Liss, Inc.

Skeletal morphogenesis in the urodele skull: III. Effect of hormone dosage in TH-induced remodeling.

Abstract: This study examines the dosage dependency of thyroid hormone (TH)-mediated remodelling in the cranial skeleton of the hemidactyliine plethodontid urodele, Eurycea bislineata. One set of experiments quantifies morphogenetic responses in 21 tissues for four size-age classes of larvae immersed in four different T4 concentrations. A second set varies both the period and concentration of T4 treatment to evaluate the effect of different TH profiles on adult tissue shape. The tissues surveyed in this study exhibit a 100-fold range in TH sensitivity. Those in regressive morphogenesis have tissue-specific sensitivities which correlate with the timing of their remodelling in natural development: bone resorption is more sentitive than cartilage resorption and is initiated earlier in metamorphosis. In contrast, the TH sensitivities of tissues in progressive morphogenesis vary within each tissue type and even within some tissues, and they do not correlate with timing in natural development. Some explanation for this discrepancy is offered by the constant spatial and temporal relationships between nasal cartilage and dermal bone, which suggest that some TH-mediated ossification may additionally require induction by cartilage. Also, the failure of nasolacrimal duct morphogenesis at all but the lowest dosage correlates with the inductdion of integumentary changes that may preclude duct formation. Variable T4 treatments produce no effect upon the adult skull, other than loss of the nasolacrimal duct and/or foramen. These results have two developmental implicatons. First, the dosage dependencies of the nasolacrimal duct, ossification sequences, and cranial remodelling patterns all support a TH profile with exceptionally low levels at larval stages and at least a 100-fold increase at metamorphosis. Second, a small change in the rate of TH activity has the potential to effect a large-scale rearranggement and restructuring of TH-dependent remodelling. The lack of such transformations in metamorphic plethodontids suggests that TH activity is highly conserved in this group. © 1995 Wiley-Liss, Inc.

Microstructure, evolution, and ontogeny of scale surfaces in cordylid and gerrhosaurid lizards.

Abstract: The distal oberhautchen and proximal beta layer of 41 species and every genus of cordylid and gerrhosaurid lizard were examined with a scanning electron microscope. Scale organs in these families are concentrated on the face, and scale organs occur singly or in pairs below the keel on the dorsals of cordylids but not gerrhosaurids. Most species examined possess primitive, lenticular scale organs. Unique and previously unknown, projecting scale organs occur in two species of Cordylus. Scale organs appear to be absent in species of Chamaesaura. The scale surfaces of cordylids are covered in macrohoneycomb. Individual compartments of cordylid macrohoneycomb are not intracellular structures but may be overlain by apparent oberhautchen cells. In some cordylid species, part of each cell is free and projects away from the scale surface as a pointed flap. Gerrhosaurids lack macrohoneycomb. Instead, their scale surfaces are covered in lamellae without dentate borders, 50-100 times as long as wide. The epidermis of Platysaurus is unique among cordylids in possessing lamellae 1-8 times as wide as long that overlap macrohoneycomb in some regions of the body. The scale surfaces of Cordylus cordylus undergo an ontogenetic change similar to that recently described for the xenosaurid genus Shinisaurus. Phylogenetic analysis of scale surface features allows the partitioning of Cordylus into three species groups and Chamaesaura into two species groups. Synapomorphies of the species of Chamaesaura, the species of Platysaurus, and the genera of the gerrhosaurids are also described. © 1995 Wiley-Liss, Inc.

Seasonal-variation in ovarian histology of the viviparous lizard sceloporus-torquatus-torquatus

Abstract: Changes in ovarian histology during the reproductive cycle of the viviparous lizard Sceloporus torquatus torquatus are described. In general, the variation in follicular histology observed during the seasonal cycle is similar to that of other lizards. Sceloporus t. torquatus exhibits a cycle in which small, previtellogenic follicles exist in the ovary from December to August. Vitellogenesis occurs between September and November, followed by ovulation from late November to early December. Parturition occurs the following spring. After ovulation, the remaining follicular cells form the corpus luteum and luteolysis did not occur until April-May. Follicular atresia is commonly observed in previtellogenic follicles with polymorphic granulosa, but occurs less frequently in follicles during late vitellogenesis. There are two germinal beds in each ovary. The yolk nucleus is evident in young oocytes as is a vacuolated ooplasma prior to vitellogenesis. Extensive polymorphism is observed in yolk platelets. Mast cells and secretory cells are observed in the thecal layer of the follicular wall as are melanocytes in the ovarian stroma. © 1995 Wiley-Liss, Inc.

Microanatomical organization of hepatic stroma of the brown trout, Salmo trutta fario (Teleostei, Salmonidae): A qualitative and quantitative approach

Abstract: Despite the absence of lobulation, light microscopy of serial sections of the liver of brown trout, Salmo trutta fario, reveals that the stromal elements are spatially organized as venous-biliary-arteriolar tracts (VBAT), venous-arteriolar tracts (VAT), biliary-arteriolar tracts (BAT), venous-biliary tracts (VBT), biliary tracts (BT), arteriolar tracts (AT), and isolated veins. These components are not two- but three-dimensional entities, and the anatomical interrelationships among all entities are displayed. The VBAT, VAT, and VBT are considered portal tracts; the adjacent parenchymal zones are viewed as periportal areas. The veins emerging from those tracts are regarded as afferent, and related with periportal zones. The veins that do not communicate with the VBAT, VAT, or VBT are viewed as efferent. Only serial sectioning allows a definite recognition of afferent from efferent isolated veins. The morphometric study discloses that isolated veins occupy around 60% of the stromal areas. Nevertheless, the VBAT, VAT, and BT are also considerably important, occupying variable proportions of the stromal areas (8-12%). The VBT and BAT are less important in quantitative terms. No sexual diffences appear in either qualitative or quantitative terms. There is no structural support for an eventual macroorganization of hepatic tissues. It is suggested that the quantitative data can be useful, as standards for the normal hepatic architecture of brown trout. The paper emphasizes the importance of a general structural model for the fish liver and of the use of an internationally acceptable nomenclature. © 1995 Wiley-Liss, Inc.

Distribution of cranial and rostral spinal nerves in tadpoles of the frog Discoglossus pictus (Discoglossidae).

Abstract: We studied the peripheral nervous system of early tadpoles of the frog Discoglossus pictus using whole-mount immunohistochemistry. Double-labeling of muscles and nerves allowed us to determine the innervation of all cranial muscles supplied by the trigeminal, facial, glossopharyngeal, vagal, and hypoglossal nerves. The gross anatomical pattern of visceral, cutaneous, and lateral-line innervation was also assessed. Most muscles of the visceral arches are exclusively supplied by posttrematic rami of the corresponding branchiomeric nerves, the only exceptions being some ventral muscles (intermandibular, interhyoid, and subarcual rectus muscles). In the mandibular arch, the pattern of motor ramules of the trigeminal nerve prefigures in a condensed form the adult pattern, but the muscles of the hyoid arch are innervated by ramules of the facial nerve in a pattern that differs from that of postmetamorphic frogs. With respect to the nerves of the branchial arches, pretrematic visceral rami, typical of other gnathostomes, are absent in D. pictus. Instead, we find a separate series of posttrematic profundal visceral rami. Pharyngeal rami of all branchial nerves contribute to Jacobson's anastomosis. We provide a detailed description of the lateral-line innervation and describe a new ramus of the middle lateral-line nerve (ramus suprabranchialis). We confirm the presence of a first spinal nerve and its contribution to the hypoglossal nerve in D. pictus tadpoles.

Skeletal morphogenesis in the urodele skull: I. Postembryonic development in the hemidactyliini (Amphibia: Plethodontidae)

Abstract: The metamorphic species Eurycea bislineata is presented as a standard for evaluating the relationship between cranial ontogeny and life history in hemidactyliine plethodontid urodeles. Past and present descriptions are combined into a comprehensive summary of postembryonic skull development for this species, and the sequence, sizes of onset, and morphogenetic pathways are documented for all major remodelling events. Developmental series are also compared intraspecifically, between two populations of E. bislineata that differ in metamorphic size, and interspecifically, with species having different larval periods (Hemidactylium scutatum, Gyrinophilus porphyriticus, Pseudotriton ruber, E. wilderae, E. longicauda guttolineata) and with epigean (E. tynerensis, E. nana, and E. neotenes) and subterranean perennibranchiates (Haideotriton wallacei and Typhlomolge rathbuni). Cranial ontogeny is largely conserved in these hemidactyliines despite their disparate life histories. Outside the dichotomy of metamorphic and perennibranchiate development, variation is limited to interspecific differences involving the nasolacrimal duct, the repeated loss of the scleral cartilage, and minor dissociation of several metamorphic and postmetamorphic remodelling events. Some, but not all, of this variation is consistent with evolutionary differences in metamorphic size and age. The comparison of metamorphic and perennibranchiate hemidactyliines reveals a unique cranial ontogeny for urodeles, characterized by the abrupt and synchronous timing of almost all postembryonic remodelling, including the nasal skeleton, and the complete absence of these events in perennibranchiate forms. © 1995 Wiley-Liss, Inc.

Marginal tooth-bearing bones in the lower jaw of the recent australian lungfish, Neoceratodus forsteri (Osteichthyes, Dipnoi).

Abstract: Developmental studies of the Recent Australian lungfish, Neoceratodus forsteri, show that this species has two sets of functional tooth-bearing bones in the lower jaw of young hatchlings. These coincide with an early stage in the life history when the fish is strictly carnivorous. In N. forsteri, a paired tooth-bearing dentary and an unpaired symphyseal bone and tooth develop slightly later than the permanent vomerine, prearticular, and pterygopalatine tooth plates, which appear at stage 44 of development, and erupt with the permanent dentition between stages 46 and 48, when the hatchling first starts to feed on small aquatic invertebrates. At these stages of development, all of the teeth are long, sharp, and conical and help to retain prey items in the mouth. Disappearance of the transient dentition coincides with complete eruption of the permanent tooth plates and precedes the change to an omnivorous diet. Existence of a transient marginal dentition in this species of lungfish suggests that the presence of an apparently similar marginal dentition in adults of many species of Palaeozoic dipnoans should be considered in phylogenetic analyses of genera within the group, and when analysing the relationships of dipnoans with other primitive animals. © 1995 Wiley-Liss, Inc.