SciCombinator

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Concept: Gecko

525

The gecko genus Geckolepis, endemic to Madagascar and the Comoro archipelago, is taxonomically challenging. One reason is its members ability to autotomize a large portion of their scales when grasped or touched, most likely to escape predation. Based on an integrative taxonomic approach including external morphology, morphometrics, genetics, pholidosis, and osteology, we here describe the first new species from this genus in 75 years: Geckolepis megalepissp. nov. from the limestone karst of Ankarana in northern Madagascar. The new species has the largest known body scales of any gecko (both relatively and absolutely), which come off with exceptional ease. We provide a detailed description of the skeleton of the genus Geckolepis based on micro-Computed Tomography (micro-CT) analysis of the new species, the holotype of G. maculata, the recently resurrected G. humbloti, and a specimen belonging to an operational taxonomic unit (OTU) recently suggested to represent G. maculata. Geckolepis is characterized by highly mineralized, imbricated scales, paired frontals, and unfused subolfactory processes of the frontals, among other features. We identify diagnostic characters in the osteology of these geckos that help define our new species and show that the OTU assigned to G. maculata is probably not conspecific with it, leaving the taxonomic identity of this species unclear. We discuss possible reasons for the extremely enlarged scales of G. megalepis in the context of an anti-predator defence mechanism, and the future of Geckolepis taxonomy.

Concepts: Biology, Taxonomy, Reptile, Gecko, Madagascar, Taxonomic rank, Zoological nomenclature, Gekkonidae

227

Modern tropical forests harbor an enormous diversity of squamates, but fossilization in such environments is uncommon and little is known about tropical lizard assemblages of the Mesozoic. We report the oldest lizard assemblage preserved in amber, providing insight into the poorly preserved but potentially diverse mid-Cretaceous paleotropics. Twelve specimens from the Albian-Cenomanian boundary of Myanmar (99 Ma) preserve fine details of soft tissue and osteology, and high-resolution x-ray computed tomography permits detailed comparisons to extant and extinct lizards. The extraordinary preservation allows several specimens to be confidently assigned to groups including stem Gekkota and stem Chamaleonidae. Other taxa are assignable to crown clades on the basis of similar traits. The detailed preservation of osteological and soft tissue characters in these specimens may facilitate their precise phylogenetic placement, making them useful calibration points for molecular divergence time estimates and potential keys for resolving conflicts in higher-order squamate relationships.

Concepts: Evolution, Medical imaging, Phylogenetics, Gecko, Squamata, Fossil, Preservation, Lizard

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Fabricated adhesives are demonstrated to support high loads while maintaining easy release on a variety of “real world” surfaces. These adhesives consist of simple elastomers and fabrics without nano or micron scale features, yet they surpass the adhesive force capacity of live Tokay geckos and can be scaled to large sizes.

Concepts: 2002 albums, Gecko, Polyurethane, Elastomer, Universe, Adhesion, Adhesive, Tokay gecko

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In the past, toxinological research on reptiles has focused principally on clinically important species. As a result, our understanding of the evolution of the reptile venom system is limited. Here, for the first time, we describe the structural and molecular evolutionary features of the mandibular toxin-secreting gland of Abronia graminea, a representative of one of the poorly known and entirely arboreal lineages of anguimorph lizards. We show that the mandibular gland is robust and serous, characters consistent with those expected of a toxin-secreting gland in active use. A wide array of transcripts were recovered that were homologous to those encoded by the indisputably venomous helodermatid lizards. We show that some of these toxin transcripts are evolving under active selection and show evidence of rapid diversification. Helokinestatin peptides in particular are revealed to have accumulated residues that have undergone episodic diversifying selections. Conversely, the natriuretic peptides have evolved under tremendous evolutionary constraints despite being encoded in tandem with helokinestatins by the same gene precursor. Of particular note is the sequencing for the first time of kunitz peptides from a lizard toxin-secreting gland. Not only are kunitz peptides shown to be an ancestral toxicoferan toxin, the ancestral state of this peptide is revealed to be a dual domain encoding precursor. This research provides insight into the evolutionary history of the ancient toxicoferan reptile venom system. In addition, it shows that even ‘clinically irrelevant’ species can be a rich source of novel venom components, worthy of investigation for drug design and biomedical research.

Concepts: DNA, Natural selection, Evolution, Biology, Evolutionary biology, Gecko, Squamata, Komodo dragon

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Since the discovery of the mechanism of adhesion in geckos, many synthetic dry adhesives have been developed with desirable gecko-like properties such as reusability, directionality, self-cleaning ability, rough surface adhesion and high adhesive stress. However, fully exploiting these adhesives in practical applications at different length scales requires efficient scaling (i.e. with little loss in adhesion as area grows). Just as natural gecko adhesives have been used as a benchmark for synthetic materials, so can gecko adhesion systems provide a baseline for scaling efficiency. In the tokay gecko (Gekko gecko), a scaling power law has been reported relating the maximum shear stress σmax to the area A: σmax ∝ A(-¼). We present a mechanical concept which improves upon the gecko’s non-uniform load-sharing and results in a nearly even load distribution over multiple patches of gecko-inspired adhesive. We created a synthetic adhesion system incorporating this concept which shows efficient scaling across four orders of magnitude of area, yielding an improved scaling power law: σmax ∝ A(-1/50). Furthermore, we found that the synthetic adhesion system does not fail catastrophically when a simulated failure is induced on a portion of the adhesive. In a practical demonstration, the synthetic adhesion system enabled a 70 kg human to climb vertical glass with 140 cm(2) of adhesive per hand.

Concepts: Gecko, Shear stress, Scale, Adhesion, Adhesive, Gekkonidae, Invasive animal species, Tokay gecko

23

The tropical savannah landscapes of Australia’s north, though previously overshadowed by the biodiverse rainforests of the Wet Tropics, are themselves now attracting interest for their biological significance and uniqueness. The Einasleigh Uplands region of north-east Queensland is home to a diverse group of mammals and reptiles and was previously recognised for its importance in shaping speciation in birds. Here we add a small saxicoline gecko to a growing list of recently described reptiles that are endemic to this region. Phylogenetic analyses including Gehyra species from the arid zone and the monsoonal tropics reveal that small Gehyra geckos in this area, while closely resembling Gehyra nana from the Top End and Kimberley, form a clade that is geographically isolated and phylogenetically distant from the G. nana complex. Instead, the Einasleigh Uplands taxon is sister to a large, arboreal species within the arid zone clade. It is readily distinguished from all lineages within the G. nana complex, its closest relative G. purpurascens, and all other rock-dwelling species from the arid zone by a combination of its very small body size, few subdigital lamellae, and mid tan to golden dorsal coloration with a pattern of scattered pale ocelli and irregular dark-brown blotches on a stippled background. We therefore describe this taxon as a new Australian species of Gehyra, Gehyra einasleighensis sp. nov., based on a combination of phylogenetic separation, morphological characters and discrete geographic distribution.

Concepts: Biodiversity, Evolution, Species, Phylogenetic nomenclature, Phylogenetics, Cladistics, Gecko, Australia

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Geckos are well known for their extraordinary clinging abilities and many species easily scale vertical or even inverted surfaces. This ability is enabled by a complex digital adhesive mechanism (adhesive toepads) that employs van der Waals based adhesion, augmented by frictional forces. Numerous morphological traits and behaviors have evolved to facilitate deployment of the adhesive mechanism, maximize adhesive force and enable release from the substrate. The complex digital morphologies that result allow geckos to interact with their environment in a novel fashion quite differently from most other lizards. Details of toepad morphology suggest multiple gains and losses of the adhesive mechanism, but lack of a comprehensive phylogeny has hindered efforts to determine how frequently adhesive toepads have been gained and lost. Here we present a multigene phylogeny of geckos, including 107 of 118 recognized genera, and determine that adhesive toepads have been gained and lost multiple times, and remarkably, with approximately equal frequency. The most likely hypothesis suggests that adhesive toepads evolved 11 times and were lost nine times. The overall external morphology of the toepad is strikingly similar in many lineages in which it is independently derived, but lineage-specific differences are evident, particularly regarding internal anatomy, with unique morphological patterns defining each independent derivation.

Concepts: Biology, Species, Van der Waals force, Anatomy, Gecko, Friction, Adhesion, Adhesive

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Geckos are among the most species-rich reptile groups and the sister clade to all other lizards and snakes. Geckos possess a suite of distinctive characteristics, including adhesive digits, nocturnal activity, hard, calcareous eggshells, and a lack of eyelids. However, one gecko clade, the Eublepharidae, appears to be the exception to most of these ‘rules’ and lacks adhesive toe pads, has eyelids, and lays eggs with soft, leathery eggshells. These differences make eublepharids an important component of any investigation into the underlying genomic innovations contributing to the distinctive phenotypes in ‘typical’ geckos.

Concepts: Reptile, Gecko, Squamata, Lizard, Eublepharis, Gekkonidae, Leopard gecko, Pet lizards

10

One of the central controversies regarding the evolution of adhesion concerns how adhesive force scales as animals change in size, either among or within species. A widely held view is that as animals become larger, the primary mechanism that enables them to climb is increasing pad area. However, prior studies show that much of the variation in maximum adhesive force remains unexplained, even when area is accounted for. We tested the hypothesis that maximum adhesive force among pad-bearing gecko species is not solely dictated by toepad area, but also depends on the ratio of toepad area to gecko adhesive system compliance in the loading direction, where compliance © is the change in extension (Δ) relative to a change in force (F) while loading a gecko’s adhesive system (C = dΔ/dF). Geckos are well-known for their ability to climb on a range of vertical and overhanging surfaces, and range in mass from several grams to over 300 grams, yet little is understood of the factors that enable adhesion to scale with body size. We examined the maximum adhesive force of six gecko species that vary in body size (~2-100 g). We also examined changes between juveniles and adults within a single species (Phelsuma grandis). We found that maximum adhesive force and toepad area increased with increasing gecko size, and that as gecko species become larger, their adhesive systems become significantly less compliant. Additionally, our hypothesis was supported, as the best predictor of maximum adhesive force was not toepad area or compliance alone, but the ratio of toepad area to compliance. We verified this result using a synthetic “model gecko” system comprised of synthetic adhesive pads attached to a glass substrate and a synthetic tendon (mechanical spring) of finite stiffness. Our data indicate that increases in toepad area as geckos become larger cannot fully account for increased adhesive abilities, and decreased compliance must be included to explain the scaling of adhesion in animals with dry adhesion systems.

Concepts: Mass, Ratio, Gecko, Scale, Adhesion, Adhesive, Phelsuma, Gold dust day gecko

7

The lizards of the family Agamidae are one of the most prominent elements of the Australian reptile fauna. Here, we present a genomic resource built on the basis of a wild-caught male ZZ central bearded dragon Pogona vitticeps.

Concepts: Gecko, Squamata, Komodo dragon, Tuatara, Lizards, Agamidae, Central Bearded Dragon, Pogona