The Experts below are selected from a list of 255 Experts worldwide ranked by ideXlab platform
Stanislav N. Gorb - One of the best experts on this subject based on the ideXlab platform.
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long term low friction maintenance and wear reduction on the Ventral Scales in snakes
Materials Letters, 2021Co-Authors: J C Sanchezlopez, Clemens F Schaber, Stanislav N. GorbAbstract:Abstract Snake skins evolved to withstand permanent friction and wear during sliding. Here, the microstructure of Ventral Scales of the snake Lampropeltis getula californiae was analyzed using scanning electron microscopy, and the long-term dynamic friction behavior was investigated by reciprocating sliding friction tests. A smooth epoxy resin with similar elasticity modulus and hardness was used for comparison purposes. Strong differences in frictional and wear mechanisms between the two materials were revealed in spite of similar mechanical properties. Snake skin showed a considerably lower frictional coefficient that kept stable over several thousands of sliding cycles. A reduction of the stick-slip behavior was also denoted by analyzing the variation of the friction coefficient in the forward and reverse motion influencing the wear mechanism. This frictional behavior can be explained by three different but complementary mechanisms: fibrous layered composite material of the skin with a gradient of material properties, surface microstructure, and the presence of ordered layers of lipid molecules at the skin surface.
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Anisotropic Friction of the Ventral Scales in the Snake Lampropeltis getula californiae
Tribology Letters, 2014Co-Authors: Martina J. Baum, Alexander E. Kovalev, Jan Michels, Stanislav N. GorbAbstract:Since the Ventral body side of snakes is in almost continuous contact with the substrate during undulating locomotion, their skin is presumably adapted to generate high friction for propulsion and low friction to slide along the substrate. In this study, the microstructure of Ventral Scales was analyzed using scanning electron microscopy, atomic force microscope and confocal laser scanning microscopy. Dynamic friction was investigated by a microtribometer. The Ventral Scales demonstrated anisotropic frictional properties. To analyze the role of the stiffness of underlying layers on the frictional anisotropy, two different types of scale cushioning (hard and soft) were tested. To estimate frictional forces of the skin surface on rough substrates, additional measurements with a rough surface were performed. Frictional anisotropy for both types of scale cushioning and rough surfaces was revealed. However, for both types of surface roughness, the anisotropy was stronger expressed in the soft-cushioned sample. This effect could be caused by (1) the stronger interaction of the microstructure with the substrate in soft-cushioned samples due to larger real contact area with the substrate and (2) the composite character of the skin of this snake species with embedded, highly ordered fiber-like structures, which may cause anisotropy in material properties.
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surface structure and frictional properties of the skin of the amazon tree boa corallus hortulanus squamata boidae
Journal of Comparative Physiology A-neuroethology Sensory Neural and Behavioral Physiology, 2009Co-Authors: R A Berthe, Guido Westhoff, Horst Bleckmann, Stanislav N. GorbAbstract:The legless locomotion of snakes requires specific adaptations of their Ventral Scales to maintain friction force in different directions. The skin microornamentation of the snake Corallus hortulanus was studied by means of scanning electron microscopy and the friction properties of the skin were tested on substrates of different roughness. Skin samples from various parts of the body (dorsal, lateral, Ventral) were compared. Dorsal and lateral Scales showed similar, net-like microornamentation and similar friction coefficients. Average friction coefficients for dorsal and lateral Scales on the epoxy resin surfaces were 0.331 and 0.323, respectively. In contrast, Ventral Scales possess ridges running parallel to the longitudinal body axis. They demonstrated a significantly lower friction coefficient compared to both dorsal and lateral Scales (0.191 on average). In addition, Ventral Scales showed frictional anisotropy comparing longitudinal and perpendicular direction of the ridges. This study clearly demonstrates that different skin microstructure is responsible for different frictional properties in different body regions.
Thomas Ziegler - One of the best experts on this subject based on the ideXlab platform.
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a new species of lycodon boie 1826 serpentes colubridae from central laos
Revue Suisse De Zoologie, 2020Co-Authors: Vinh Quang Luu, T Q Nguyen, Michael Bonkowski, Thomas Calame, Thomas ZieglerAbstract:We describe a new species of the genus Lycodon Boie based on an adult male specimen from Khammouane Province, central Laos. Lycodon banksisp. nov. is distinguished from its congeners by a combination of the following characters: (1) dorsal Scales in 17-17-15 rows, dorsal Scales on the anterior 2/3 of the body length smooth, the six central dorsal scale rows of the posterior 1/3 of the body length feebly keeled; (2) supralabials 8; (3) infralabials 10; (4) loreal in contact with the eye; (5) cloacal single; (6) Ventral Scales 241; (7) dorsal surface of body with 87 greyish yellow blotches; (8) Ventral surface of body and tail uniformly grey cream. Based on the molecular comparison, Lycodon banksisp. nov. is placed in a clade with other species previously considered to be members of the genus Dinodon. The new species is at least 9% genetically divergent from other species within this clade as shown by a fragment of the mitochondrial cytochrome b. This discovery increases the number of Lycodon species known from Laos to eleven.
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a new species of lycodon boie 1826 serpentes colubridae from northern vietnam
ZooKeys, 2019Co-Authors: Helen Yvonne Janssen, T Q Nguyen, Cuong T Pham, Hanh Thi Ngo, Thomas ZieglerAbstract:A new species of the genus Lycodon is described from Cao Bang Province, Vietnam, based on three individuals with distinct differences in morphology and molecular data. The new species is differentiated from its congeners by a combination of the following characters: dorsal Scales in 17-17-15 rows, smooth throughout; supralabials usually eight (rarely nine); infralabials ten; one elongated loreal on each side, in contact with the eye; precloacal plate single; Ventral Scales 212-218 (plus one or two preVentral Scales); subcaudals 90 or 91; maxillary teeth 13 or 14; dorsal surface of body with 28 or 29 light body bands; dorsal surface of tail with 13 cream bands, forming a distinct blotch in the vertebral region. Based on phylogenetic analyses of mitochondrial cytochrome b sequence data, the new species is recovered as the sister species to a clade containing L. multizonatus and L. liuchengchaoi with strong support from the Bayesian analysis. The new species is at least 7.5% divergent from other species within this clade in uncorrected pairwise distance calculated using a fragment of more than 1000 bp of the mitochondrial cytochrome b. This discovery increases the number of Lycodon species known from Vietnam to 16.
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a new species of lycodon boie 1826 serpentes colubridae from thanh hoa province vietnam
Zootaxa, 2019Co-Authors: Vinh Quang Luu, Thomas Ziegler, Nghia Van Ha, Tuoi Thi HoangAbstract:We describe a new species of the genus Lycodon based on an adult male specimen from Thanh Hoa Province, Vietnam. Lycodon namdongensis sp. nov. is differentiated from its congeners by a combination of the following characters: dorsal Scales in 17-17-15 rows, all smooth; supralabials 8; infralabials 10; one large loreal on each side, separated from the eye; cloacal single; Ventral Scales 218 (plus two preVentral Scales); subcaudals 85, paired; a total length of 723 mm; tail / total length ratio 0.205; dorsal head pattern whitish grey; dorsal surface of body with 23 narrow greyish cream bands; dorsal surface of tail with 14 cream bands; Ventral surface of body mostly cream with a few small dark spots posteriorly; Ventral surface of tail dark grey. Based on molecular comparisons, Lycodon namdongensis sp. nov. is recovered as a sister species to L. futsingensis with strong support values from all three analyses. The new species is at least 6.5% genetically divergent from other species within this clade as shown by a fragment of more than 1000 pbs of the mitochondrial cytochrome b. This discovery increases the number of Lycodon species known from Vietnam to 15.
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a new species of the natricine snake genus amphiesma from the indochinese region squamata colubridae natricinae
Zootaxa, 2007Co-Authors: Patrick David, Raoul H Bain, Nguyen Quang Truong, Nikolai L Orlov, Gernot Vogel, Vu Ngoc Thanh, Thomas ZieglerAbstract:A new species of the natricine snake genus Amphiesma is described from Central Vietnam and possibly Thailand. Amphiesma leucomystax spec. nov. is distinguished from other species of the Indochinese Region by the combination of a bright, broad white stripe extending below the eye from the tip of the snout to posterior supralabials and the neck, dorsolateral series of aligned, transversally elongated or divided spots, 19 dorsal scale rows at midbody, two first rows of dorsal scale rows smooth, moderately sized eyes, a high number of Ventral Scales (at least 154), and 1 anterior temporal. Its relationships with other Amphiesma species with 19 dorsal scale rows are discussed. Amphiesma leucomystax spec. nov. seems to be close to A. boulengeri. A key to the species of Amphiesma from the Indochinese Region is provided.
Xavier Parellada - One of the best experts on this subject based on the ideXlab platform.
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morphological variability of the lataste s viper vipera latastei and the atlas dwarf viper vipera monticola patterns of biogeographical distribution and taxonomy
Amphibia-reptilia, 2006Co-Authors: Jose Carlos Brito, Xavier Santos, Juan M Pleguezuelos, Gema Álvarez Llorente, Soumia Fahd, Xavier ParelladaAbstract:The Lataste's viper Vipera latastei is a medium-sized viper distributed throughout almost the entire Iberian Peninsula and north-west of Africa. Former morphological studies noted the existence of two subspecies, V. l. gaditana and V. l. latastei, as well as a full species, V. monticola, in the High Atlas, corresponding to the prior overall range described for V. latastei. However, some results remained unclear in these former studies, e.g. the specific status of the Medium Atlas populations, the intra-subspecific differences in V. l. gaditana and, the true status of some isolated populations of the northern range. For this reason, 45 morphological characters were analysed in 672 preserved specimens covering the entire range. Categorical Principal Components Analysis (CATPCA) and Discriminant Function Analysis (DFA) were used to assess geographic variability, treating specimens individually or assigning them ap riorito groups, respectively. Geographic groups were established according to the origin of specimens in isolated areas of mountain chains. As the percentage of correct assignment was low in DFA, initial groups were combined to maximize the percentage. The results from the multivariate analysis suggest morphological differentiation between populations. Some variables accounted for geographic variability: e.g. rows of dorsal Scales at mid-body are taxonomically stable and clearly separate the African populations; and number of Ventral Scales showed a clinal variation from 126 to 143 Ventrals in extreme populations. The three African groups manifested clear morphological differences, and especially specimens from the High Atlas (V. monticola) and Alger. On the contrary, a large number of initial Iberian groups were merged because of the low scores in the correct classification. The final groups showed a vast central area with low morphological differentiation as well as isolated populations in the NW, NE and SW Iberian Peninsula. This conclusion matches well with allopatric speciation processes during the Quaternary ice ages, which contributed to the contraction/expansion of range, isolation events, and peripheral population refugia. Morphological differentiation in external characters of V. latastei exhibited similar results with respect to V. aspis and V. ammodytes, the vipers occupying other southern European peninsulas. Molecular markers will contribute to elucidate the relationships between V. latastei populations and the history of colonisation across the Strait of Gibraltar.
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morphological variability of the lataste s viper vipera latastei and the atlas dwarf viper vipera monticola patterns of biogeographical distribution and taxonomy
Amphibia-reptilia, 2006Co-Authors: Jose Carlos Brito, Xavier Santos, Juan M Pleguezuelos, Gema Álvarez Llorente, Soumia Fahd, Xavier ParelladaAbstract:The Lataste's viper Vipera latastei is a medium-sized viper distributed throughout almost the entire Iberian Peninsula and north-west of Africa. Former morphological studies noted the existence of two subspecies, V. l. gaditana and V. l. latastei, as well as a full species, V. monticola, in the High Atlas, corresponding to the prior overall range described for V. latastei. However, some results remained unclear in these former studies, e.g. the specific status of the Medium Atlas populations, the intra-subspecific differences in V. l. gaditana and, the true status of some isolated populations of the northern range. For this reason, 45 morphological characters were analysed in 672 preserved specimens covering the entire range. Categorical Principal Components Analysis (CATPCA) and Discriminant Function Analysis (DFA) were used to assess geographic variability, treating specimens individually or assigning them ap riorito groups, respectively. Geographic groups were established according to the origin of specimens in isolated areas of mountain chains. As the percentage of correct assignment was low in DFA, initial groups were combined to maximize the percentage. The results from the multivariate analysis suggest morphological differentiation between populations. Some variables accounted for geographic variability: e.g. rows of dorsal Scales at mid-body are taxonomically stable and clearly separate the African populations; and number of Ventral Scales showed a clinal variation from 126 to 143 Ventrals in extreme populations. The three African groups manifested clear morphological differences, and especially specimens from the High Atlas (V. monticola) and Alger. On the contrary, a large number of initial Iberian groups were merged because of the low scores in the correct classification. The final groups showed a vast central area with low morphological differentiation as well as isolated populations in the NW, NE and SW Iberian Peninsula. This conclusion matches well with allopatric speciation processes during the Quaternary ice ages, which contributed to the contraction/expansion of range, isolation events, and peripheral population refugia. Morphological differentiation in external characters of V. latastei exhibited similar results with respect to V. aspis and V. ammodytes, the vipers occupying other southern European peninsulas. Molecular markers will contribute to elucidate the relationships between V. latastei populations and the history of colonisation across the Strait of Gibraltar.
Akiyoshi Takahashi - One of the best experts on this subject based on the ideXlab platform.
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expression of genes for melanotropic peptides and their receptors for morphological color change in goldfish carassius auratus
General and Comparative Endocrinology, 2017Co-Authors: Kanta Mizusawa, Yutaka Yamamura, Satoshi Kasagi, Jose Miguel Cerdareverter, Akiyoshi TakahashiAbstract:To evaluate the association of the melanotropic peptides and their receptors for morphological color change, we investigated the effects of changes in background color, between white and black, on xanthophore density in the Scales and expression levels of genes for hormonal peptides and corresponding receptors (MCH-R2, MC1R, and MC5R) in goldfish (Carassius auratus). The xanthophore density in both dorsal and Ventral Scales increased after transfer from a white to black background. However, xanthophore density in dorsal Scales increased after transfer from a black to white background, and that of Ventral Scales decreased after transfer from a black to black background, which served as the control. In the white-reared fish, melanin-concentrating hormone (mch) mRNA content in the brain was higher than that in black-reared fish, whereas proopiomelanocortin a (pomc-a) mRNA content in the pituitary was lower than that in the black-reared fish. Agouti-signaling protein (asp) mRNA was detected in the Ventral skin but not in the dorsal skin. No difference was observed in the asp mRNA content between fish reared in white or black background, suggesting that ASP might not be associated with background color adaptation. In situ hybridization revealed that both mc1r and mc5r were expressed in the xanthophores in Scales. The mRNA content of mc1r in Scales did not always follow the background color change, whereas those of mc5r decreased in the white background and increased in the black background, suggesting that mc5r might be a major factor reinforcing the function of MSH in morphological color changes. White backgrounds increased mch mRNA content in the brain, but decreased mch-r2 mRNA content in the Scales. These altered expression levels of melanotropin receptors might affect reactivity to melanotropins through long-term adaptation to background color.
Hendrik Holscher - One of the best experts on this subject based on the ideXlab platform.
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variation of the frictional anisotropy on Ventral Scales of snakes caused by nanoscale steps
Bioinspiration & Biomimetics, 2020Co-Authors: Paul Schreiber, Antje Dollmann, Christian Lutz, Guillaume Gomard, Christian Greiner, Hendrik HolscherAbstract:The Ventral Scales of most snakes feature micron-sized fibril structures with nanoscale steps oriented towards the snake's tail. We examined these structures by microtribometry as well as atomic force microscopy (AFM) and observed that the nanoscale steps of the micro-fibrils cause a frictional anisotropy, which varies along the snake's body in dependence of the height of the nanoscale steps. A significant frictional behavior is detected when a sharp AFM tip scans the nanoscale steps up or down. Larger friction peaks appear during upward scans (tail to head direction), while considerably lower peaks are observed for downward scans (head to tail direction). This effect causes a frictional anisotropy on the nanoscale, i.e. friction along the head to tail direction is lower than in the opposite direction. The overall effect increases linearly with the step height of the micro-fibrils. Although the step heights are different for each snake, the general step height distribution along the body of the examined snakes follows a common pattern. The frictional anisotropy, induced by the step height distribution, is largest close to the tail, intermediate in the middle, and lower close to the head. This common distribution of frictional anisotropy suggests that snakes even optimized nanoscale features like the height of micro-fibrils through evolution in order to achieve optimal friction performance for locomotion. Finally, Ventral snake Scales are replicated by imprinting their micro-fibril structures into a polymer. As the natural prototype, the artificial surface exhibits frictional anisotropy in dependence of the respective step height. This feature is of high interest for the design of tribological surfaces with artificial frictional anisotropy.
