Development of the subdigital adhesive pads of Ptyodactylus guttatus (Reptilia: Gekkonidae)

Subdigital adhesive pads play an important role in the locomotion of many species of gekkonid lizards. These pads consist of integrated components derived from the epidermis, dermis, vascular system, subcuticular tendons, and phalanges. These components become intimately associated with each other during the developmental differentiation of the digits and the sequence of this integration is outlined herein in Ptyodactylus guttatus. The pads initially appear as paired swellings at the distal tips of the digits. Subsequently, a fan-like array of naked scansors develops on the ventral surface of each digit, at about the same time that scales differentiate over the surface of the foot as a whole. At the time of appearance of the naked scansors, the vascular sinus system of the pad also differentiates, along with subcuticular connective tissue specializations. At this stage the digits, along with the rest of the body, are clad in an embryonic periderm. Only after hatching and as the periderm is shed, do the epidermal setae and spines appear. The developmental sequence described here is consistent with predictions previously advanced about the evolutionary origin and elaboration of subdigital pads in gekkonid lizards. The paucity of available staged embryonic material leaves many questions unresolved.     

Arcs: Curved microfilament bundles beneath the dorsal surface of the leading lamellae of moving chick embryo fibroblasts

Curved microfilamentous structures are frequently found in the leading lamellae of cultured fibroblasts. These structures, termed arcs, form parallel to, and about 8 μm from, the lamellar margin. Arcs move centripetally through the lamella beneath the dorsal surface at speeds of 1.5 to 3.0 μm min⁻¹ and they disappear in front of the nucleus. The movement of arcs is related to the movement of particles transported on the cell surface. Arcs show some structural and biochemical similarities to the actomyosin stress fibres, but arcs are not obviously functional in applying force against the substratum during cell locomotion. Arcs provide clues to the organisation and regulation of the microfilament system for movement.     

Changes in fibroblast contractility, morphology, and adhesion in response to a phorbol ester tumor promoter

We have studied the effects of the phorbol ester tumor promoter 12-O-tetradecanoyl-phorbol-13-acetate (TPA) on the contractility, locomotion, morphology, and adhesion of two mammalian fibroblastic cell lines. Using the silicone rubber substratum technique, we have found that the first observable response to the tumor promoter is a rapid weakening of cell contractility (8-15 min). This is followed by gradual morphological changes, characterized by a hyperextension of the cells' leading lamellae, which stretch out to an unlimited degree, and occasionally even detach from the cell bodies. Treated cells also become able to crawl onto hydrophobic substrata which are insufficiently adhesive to support the spreading of untreated fibroblasts. We suggest that both the hyperextension and the ability to spread on nonadhesive surfaces can be explained as consequences of the reduced contractility, and that this reduced contractility may also help to explain the increased invasiveness and loss of anchorage dependence by transformed cells.     

The structure of anoline (Reptilia: Dactyloidae: Anolis) toe pads in relation to substratum conformity

Adhesive toe pads of geckos house modified components of vascular and/or connective tissues that promote conformity of the setal fields with the locomotor substratum. Similar modifications have been claimed for the digits of Anolis, but evidence for them is not compelling. Angiographic and histological investigations of Anolis failed to identify any evidence of either an intralamellar vascular reticular network or a central sinus. Instead, their vascularity more closely resembles that of lizards in general than that of pad‐bearing geckos. The loose connective tissue of the toe pads likely contributes to their general pliability and flexibility, promoting localized compliance with the substratum. Through the shedding cycle, the lamellae change shape as the replacing setae elongate. The outer epidermal generation lacunar cells on the inner lamellar faces simultaneously hypertrophy, providing for compatibility between overlapping lamellae, enabling reciprocity between them. This contributes to continuing compliance of the setal fields with the substratum. Overall, digital structure and attachment and release kinematics of the toe pads of Anolis are very similar to those of geckos exhibiting an incipient adhesive mechanism. Both lack major anatomical specializations for promoting conformity of the setae with the locomotor substratum beyond those of the seta‐bearing portions of the epidermis.     

Emigration of bilayered epidermal cell sheets from tadpole tails (Xenopus laevis)

Summary Migration of bilayered epidermal cell sheets out of explants of tadpole tails (Xenopus laevis) were investigated with time-lapse cinemicrography using reflection-contrast optics. Cell-sheet formation begins beneath the explant in a region where it is closely attached to the coverslip. A single basal cell extends a lamellipodium through the outer (surface) epidermal layer and starts moving in a direction free of attached cells. This cell remains connected to the following basal cell, which the also extends a lamellipodium onto the glass. The cell sheet develops as increasingly more adjacent basal cells start to migrate. Surface cells do not actively locomote but they remain attached to the basal cells and to adjacent surface cells. Thus, they are transported as an intact cell layer, and consequently the in situ arrangement of the tadpole epidermis is largely preserved in the cell sheet, i.e., basal cells adhere to the substratum and are covered by outer cells (surface cells) which face the culture medium. Basal cells extend lamellae beneath the rear end of the preceding cell, which is slightly fifted off the substratum. The direction of locomotion is determined by the frontal cells. Cell-sheet enlargement and locomotion cease when all the epidermal cells facing the coverslip have left the explant, and the cell sheet and epidermis covering the explant form a continuous layer.     

Underwater locomotion strategy by a benthic pennate diatom Navicula sp.

The mechanism of diatom locomotion has been widely researched but still remains a hypothesis. There are several questionable points on the prevailing model proposed by Edgar, and some of the observed phenomena cannot be completely explained by this model. In this paper, we undertook detailed investigations of cell structures, locomotion, secreted mucilage, and bending deformation for a benthic pennate diatom Navicula species. According to these broad evidences, an updated locomotion model is proposed. For Navicula sp., locomotion is realized via two or more pseudopods or stalks protruded out of the frustules. The adhesion can be produced due to the pull-off of one pseudopod or stalk from the substratum through extracellular polymeric substances. And the positive pressure is generated to balance the adhesion because of the push-down of another pseudopod or stalk onto the substratum. Because of the positive pressure, friction is generated, acting as a driving force of locomotion, and the other pseudopod or stalk can detach from the substratum, resulting in the locomotion. Furthermore, this model is validated by the force evaluation and can better explain observed phenomena. This updated model would provide a novel aspect on underwater locomotion strategy, hence can be useful in terms of artificial underwater locomotion devices.     

Morphology of the adhesive tail tips of carphodactyline geckos (Reptilia: Diplodactylidae)

Members of the carphodactyline gekkonoid genera Naultinus, Hoplodactylus, Bavayia, Eurydactylodes, Rhacodactylus, and Pseudothecadactylus possess tails that are both prehensile and adhesive. In New Caledonian and Australian species of this group, the adhesive apparatus forms a discrete and grossly observable scansorial pad. The caudal scansorial system appears to show a phylogenetic trend towards increasing complexity. The caudal scansors closely parallel the subdigital scansors in surface morphology and bear branched setae and mechanoreceptive sensillae. Internal morphology also resembles that of the toe, although a tendinous system is absent and the mechanism of pressurization of the vascular network of the tail tip remains unclear. Despite obvious differences in basic organization of tails and toes, the caudal and digital scansors in these taxa appear to be iterative homologues of one another. J. Morphol. 235:41–58, 1998. © 1998 Wiley-Liss, Inc.     

Evidence of force exchanges during the six-legged walking of the bottom-dwelling fish, Chelidonichthys lucerna

Locomotion in terrestrial vertebrates is supposed to be derived from preadaptation in bottom-dwelling fish. A few fish species have been assumed to walk on the substratum, on the basis of coordinated movements of their paired fins. However, the validity of this assumption has remained uncertain, because of a lack of evidence that their fin rays actually exert a force on the substratum. Here, we provide the first conclusive evidence that a benthic teleost fish, the gurnard, Chelidonichthys lucerna (Triglidae), exerts forces on the substratum during its temporary bottom-dwelling hexapod locomotion. This demonstration was achieved by the use of a photoelastic gel technique combined with a force calibration device. The movement patterns of the three first pairs of rays of the pectoral fins were analysed in relation to the forces exerted on the substratum, by measuring deformations of the photoelastic gel substratum produced by the rays. The rays were shown to produce a force pattern that confirmed the existence of a hexapod locomotion in a vertebrate that was consistent with body propulsion and voluntary substratum walking.     

Morphology and vascular anatomy of the gills of a primitive air-breathing fish,the bowfin (Amia calva)

Summary The morphology of the gills of a primitive air breather (Amia calva) was examined by light microscopy of semithin sections of gill filaments, and gill perfusion pathways were identified by scanning-electron microscopic analysis of corrosion replicas prepared by intravascular injection of methyl methacrylate. The arrangement of gill filaments and respiratory lamellae is similar to that of teleosts with the exception of an interfilamental support bar that is fused to the outer margins of lamellae on adjacent filaments. The prebranchial vasculature is also similar to that of teleosts, whereas the postbranchial circulation of arches III and IV is modified to permit selective perfusion of the air bladder. Gill filaments contain three distinct vascular systems: (1) the respiratory circulation which receives the entire cardiac output and perfuses the secondary lamellae; (2) a nutrient system that arises from the postlamellar circulation and perfuses filamental tissues; (3) a network of unknown function consisting of subepithelial sinusoids surrounding afferent and efferent margins of the filament and traversing the filament beneath the interlamellar epithelium. Prelamellar arteriovenous anastomoses (AVAs) are rare, postlamellar AVAs are common especially at the base of the filament where they form a dense network of small tortuous vessels before coalescing into a large filamental nutrient artery. Unlike in most teleosts, the outer vascular margins of the lamellae are embedded in the interfilamental support bar and become the sole vasculature of this tissue. Arterial-arterial lamellar bypass vessels were not observed. Previously observed decreases in oxygen transfer across the gills during air breathing can be explained only by redistribution of blood flow between or within the respiratory lamellae.Supported by NSF Grant No. PCM 79-23073The author wishes to thank Miss K. Drajus and D. Kullman for their excellent technical assistance and Dr. W. Gingerich, Mr. J. Crowther and D. Zurn for help in obtaining bowfin     

Crawling-like movements and polarisation in non-adherent leucocytes

Leucocytes, in an appropriate medium, are polarized and show movements both when floating in suspension and when settled on, but not attached to, a substratum. These movements are similar to those performed during locomotion but significant active locomotion on a plain surface is invariably accompanied by adhesion to the substratum as detected by reflection contrast microsopy. The results suggest that polarisation and crawling-type movements represent a fixed action pattern which is performed independently of adhesion to the substratum.     

Does autonomic blockade reveal a potent contribution of nitric oxide to locomotion-induced vasodilation?

We sought to test the role of nitric oxide (NO) in governing skeletal muscle (iliac) vascular conductance during treadmill locomotion in dogs (n = 6; 3.2 and 6.4 km/h at 0% grade, and 6.4 km/h at 10% grade). As seen previously, the increase in muscle vascular conductance accompanying treadmill locomotion was little influenced by NO synthase inhibition alone with N(omega)-nitro-L-arginine methyl ester (L-NAME, 10 mg/kg iv), but the absolute value of conductance achieved during locomotion was reduced. Such ambiguous results provide an unclear picture regarding the importance of NO during locomotion. However, muscle vasodilation is normally restrained by the sympathetic system during locomotion. Thus a significant contribution by NO to the increase in vascular conductance that accompanies locomotion could be masked by partial withdrawal of the competing influence of sympathetic vasoconstrictor nerve activity secondary to the rise in arterial pressure following systemic L-NAME administration. To test this possibility, we compared the rise in muscle vascular conductance before and after L-NAME treatment while ganglionic transmission was blocked by hexamethonium. Under these conditions, L-NAME significantly reduced both the rise in vascular conductance (by 32%, P < 0.001) and the absolute level of vascular conductance (by 30%, P < 0.001) achieved during locomotion with no effect on blood flow. Thus augmented NO production normally provides a significant drive to relax vascular smooth muscle in active skeletal muscle during locomotion. Potential deficits stemming from the absence of NO following L-NAME treatment are masked by less intense sympathetic restraint when autonomic function is intact.     

Knuckle-walking anteater: a convergence test of adaptation for purported knuckle-walking features of African Hominidae

Appeals to synapomorphic features of the wrist and hand in African apes, early hominins, and modern humans as evidence of knuckle-walking ancestry for the hominin lineage rely on accurate interpretations of those features as adaptations to knuckle-walking locomotion. Because Gorilla, Pan, and Homo share a relatively close common ancestor, the interpretation of such features is confounded somewhat by phylogeny. The study presented here examines the evolution of a similar locomotor regime in New World anteaters (order Xenarthra, family Myrmecophagidae) and uses the terrestrial giant anteater (Myrmecophaga tridactyla) as a convergence test of adaptation for purported knuckle-walking features of the Hominidae. During the stance phase of locomotion, Myrmecophaga transmits loads through flexed digits and a vertical manus, with hyperextension occurring at the metacarpophalangeal joints of the weight-bearing rays. This differs from the locomotion of smaller, arboreal anteaters of outgroup genera Tamandua and Cyclopes that employ extended wrist postures during above-branch quadrupedality. A number of features shared by Myrmecophaga and Pan and Gorilla facilitate load transmission or limit extension, thereby stabilizing the wrist and hand during knuckle-walking, and distinguish these taxa from their respective outgroups. These traits are a distally extended dorsal ridge of the distal radius, proximal expansion of the nonarticular surface of the dorsal capitate, a pronounced articular ridge on the dorsal aspects of the load-bearing metacarpal heads, and metacarpal heads that are wider dorsally than volarly. Only the proximal expansion of the nonarticular area of the dorsal capitate distinguishes knuckle-walkers from digitigrade cercopithecids, but features shared with digitigrade primates might be adaptive to the use of a vertical manus of some sort in the stance phase of terrestrial locomotion. The appearance of capitate nonarticular expansion and the dorsal ridge of the distal radius in the hominin lineage might be indicative of a knuckle-walking ancestry for bipedal hominins if interpreted within the biomechanical and phylogenetic context of hominid locomotor evolution.     

Role of the prehensile tail during ateline locomotion: experimental and osteological evidence

The dynamic role of the prehensile tail of atelines during locomotion is poorly understood. While some have viewed the tail of Ateles simply as a safety mechanism, others have suggested that the prehensile tail plays an active role by adjusting pendulum length or controlling lateral sway during bimanual suspensory locomotion. This study examines the bony and muscular anatomy of the prehensile tail as well as the kinematics of tail use during tail-assisted brachiation in two primates, Ateles and Lagothrix. These two platyrrhines differ in anatomy and in the frequency and kinematics of suspensory locomotion. Lagothrix is stockier, has shorter forelimbs, and spends more time traveling quadrupedally and less time using bimanual suspensory locomotion than does Ateles. In addition, previous studies showed that Ateles exhibits greater hyperextension of the tail, uses its tail to grip only on alternate handholds, and has a larger abductor caudae medialis muscle compared to Lagothrix. In order to investigate the relationship between anatomy and behavior concerning the prehensile tail, osteological data and kinematic data were collected for Ateles fusciceps and Lagothrix lagothricha. The results demonstrate that Ateles has more numerous and smaller caudal elements, particularly in the proximal tail region. In addition, transverse processes are relatively wider, and sacro-caudal articulation is more acute in Ateles compared to Lagothrix. These differences reflect the larger abductor muscle mass and greater hyperextension in Ateles. In addition, Ateles shows fewer side-to-side movements during tail-assisted brachiation than does Lagothrix. These data support the notion that the prehensile tail represents a critical dynamic element in the tail-assisted brachiation of Ateles, and may be useful in developing inferences concerning behavior in fossil primates.     

Insights from ecological niche modeling on the taxonomic distinction and niche differentiation between the black‐spotted and red‐spotted tokay geckoes (Gekko gecko)

The black‐spotted tokay and the red‐spotted tokay are morphologically distinct and have largely allopatric distributions. The black‐spotted tokay is characterized by a small body size and dark skin with sundry spots, while the red‐spotted tokay has a relatively large body size and red spots. Based on morphological, karyotypic, genetic, and distribution differences, recent studies suggested their species status; however, their classifications remain controversial, and additional data such as ecological niches are necessary to establish firm hypotheses regarding their taxonomic status. We reconstructed their ecological niches models using climatic and geographic data. We then performed niche similarity tests (niche identity and background tests) and point‐based analyses to explore whether ecological differentiation has occurred, and whether such differences are sufficient to explain the maintenance of their separate segments of environmental ranges. We found that both niche models of the black‐ and the red‐spotted tokay had a good fit and a robust performance, as indicated by the high area under the curve (AUC) values (“black” = 0.982, SD = ± 0.002, “red” = 0.966 ± 0.02). Significant ecological differentiation across the entire geographic range was found, indicating that the involvement of ecological differentiation is important for species differentiation. Divergence along the environmental axes is highly associated with climatic conditions, with isothermality being important for the “black” form, while temperature seasonality, precipitation of warmest quarter, and annual temperature range together being important for the “red” form. These factors are likely important factors in niche differentiation between the two forms, which result in morphological replacement. Overall, beside morphological and genetic differentiation information, our results contribute to additional insights into taxonomic distinction and niche differentiation between the black‐ and the red‐spotted tokay.     

Focal adhesion sites and the removal of substratum-bound fibronectin

Fibronectin was not removed from the substratum beneath focal adhesion sites when fibroblasts spread in serum-free medium on adsorbed fibronectin substrata, or when fibroblasts spread in serum-containing medium on covalently cross-linked fibronectin substrata. Under these conditions, there was colocalization between 140-kD fibronectin receptors and focal adhesion sites. It was concluded that removal of adsorbed fibronectin from beneath focal adhesion sites was a mechanical process that required serum. The effect of serum was nonspecific since serum could be replaced by equivalent concentrations of serum albumin, ovalbumin, or gamma globulins. Quantitative measurements indicated that the presence of proteins in the incubation medium weakens the interaction of fibronectin with the substratum, thereby allowing the adsorbed protein to be removed from the substratum at sites of high stress. After removing fibronectin from the substratum, cells reorganized this material into patches and fibrils beneath cells, and the reorganized fibronectin colocalized with fibronectin receptors. Some of the patches of fibronectin were phagocytosed. The fibronectin fibrils were observed to be in register with actin filament bundles and sometimes translocated to the upper cell surfaces. It is proposed that removal of fibronectin from beneath focal adhesion sites is an example of how cells can modify their extracellular matrices through contractile activity.     

Behavior of cultured cells on substrata of variable adhesiveness

The locomotory behavior of tissue cells cultured on various artificial substrata was studied by time-lapse cinemicrography. Cells were able to spread more completely on certain more wettable substrata and to accumulate preferentially on these substrata according to a consistent hierarchy of cell-substratum affinity, which was the same for all cell types. Cell responses to variations in substrata suggest that substratum adhesiveness is the determining factor, but that cells accumulate on more adhesive substrata as the result of unequal competition between several actively locomotory ruffled lamellae around their margin. The increased overlapping between cells cultured on less adhesive substrata was found to be attributable to factors other than a decrease of contact inhibition of locomotion.     

Locomotion and adhesion of neutrophil granulocytes : Effects of albumin, fibrinogen and gamma globulins studied by reflection contrast microscopy

Proteins as well as materials of low molecular weight have marked effects on the rate of locomotion, adhesion and cell shape of human neutrophil granulocytes in vitro. Plasma protein preparations differ qualitatively with respect to their chemokinetic activity. Human serum albumin (HSA), fibrinogen and acid-treated gamma globulin without polymers have a positive chemokinetic effect on neutrophils suspended in Gey's solution. Standard gamma globulin (SGG) or acid-treated gamma globulin with polymers have marked negative chemokinetic activity. Three different mechanisms are presumably responsible for the low rate of locomotion observed in Gey's solution alone, Gey's solution containing acid-treated gamma globulin with polymers or SGG, respectively: (a) too firm adhesion to the substratum; (b) lack of adhesion to the substratum; and (c) impaired capacity to perform shape changes. The relationship between attachment of cells to the substratum and the rate of neutrophil locomotion has been investigated. It appears that the pattern of adhesion rather than cell attachment as measured by the proportion of neutrophils adhering to the substratum is a meaningful correlate to locomotion. Two different patterns of adhesion can be distinguished by means of reflection-contrast microscopy: (a) the pattern characterized by uniform grey areas is compatible with efficient locomotion; (b) a pattern characterized by large black areas at the cell periphery. It is associated with neutrophils in Gey's solution which fail to displace themselves efficiently. This suggests that reflection-contrast microscopy may be helpful in distinguishing contacts allowing locomotion to occur from contacts impeding neutrophil locomotion.     

Adhesion to the substratum improves the motility ofAmoeba proteus in the absence of a cell nucleus

Summary Anucleated fragments ofAmoeba proteus obtained by dissection and kept on an untreated glass surface fail to adhere to this substratum, lose motor polarity, and stop moving, at least for several hours. If they are transferred after the operation to a highly adhesive surface (polylysine-coated glass), they adhere to the substratum, although locomotion is not spontaneously restored. However, after exposure to a light-shade difference along their body they start moving towards the shaded area and continue locomotion as long as the photic stimulus is acting. Disorganisation of the F-actin cytoskeleton of anucleated fragments was observed on the untreated glass but reorganization on the polylysine-coated surface. The anucleated fragments can show transient recovery of slight spontaneous motor activity and react promptly to external stimuli after up to several days on untreated glass. These intermittent activity periods are enabled by reconstruction of F-actin cytoskeleton in the anucleated fragments during their temporary adhesion to the glass. It is concluded that the injurious effect of cell nucleus removal on the locomotor capacity of amoebae can be compensated by the simultaneous enhancement of cell adhesion and application of a stimulus restoring the motor polarity of the cell. The compensation is achieved by cytoskeletal reorganization.     

Changes in the ventral dermis and development of iridophores in the anadromous sea lamprey, Petromyzon marinus, during metamorphosis: an ultrastructural study.

The ultrastructural changes that take place in the ventral dermis along with the development of iridophores were examined in the anadromous sea lamprey, Petromyzon marinus, during metamorphosis. There is a disruption of all components of the ventral dermis and a reformation that results in a structure very similar to that prior to metamorphosis. Although not a dermal component, a layer of iridophores develops directly beneath the dermis during late metamorphosis. The dermal endothelium is lost by mid metamorphosis (stage 4) and the highly organized collagenous lamellae making up the bulk of the dermis become disrupted by the migration of fibroblasts into the region. Many of these fibroblasts are involved in the degradation of the lamellae. By stage 5 of metamorphosis some fibroblasts become highly active collagen synthesizing cuboidal shaped cells that align to form a layer above the reformed dermal endothelium. New lamellae are formed by these cuboidal cells which then divide and migrate into the lamellae where they assume the characteristic attenuated appearance of fibroblasts in the adult dermal lamellae region. Iridophores first appear during stage 5 directly beneath the dermal endothelium. Reflecting platelets develop from double membraned vesicles associated with the Golgi apparatus. By late metamorphosis, stacks of trapezoidal shaped platelets fill the cytoplasm of the iridophores. The significance of the changes in the dermis during metamorphosis are discussed. This work is part of a continuing series of studies on the connective tissues in the anadromous sea lamprey.     

Amoeboid locomotion of Acanthamoeba castellanii with special reference to cell-substratum interactions

The amoeboid locomotion of Acanthamoeba castellanii has been studied by observation of individual cells moving on a planar glass substratum. Cell-substratum interactions involved in traction have been observed by reflexion interference microscopy. A variable part of the ventral surface of A. castellanii formed a protean platform, the 'associated contact', from which filopodia were subtended; these established stable, focal adhesions (approximately 0.4 micron diameter) on the substratum beneath. Surprisingly, acanthopodia, a prominent feature of this protozoon, did not play an obvious role in traction. The dimensions of the cell-substratum gap in the associated contact could be modulated by the concentration of ambient electrolyte. Dilution of electrolyte from 50 mM-KC1 to 2mM resulted in (i) an increase in the cell-substratum gap, (ii) a marked decrease in cell motility, (iii) reduced cell adhesion to glass.