SciCombinator

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Concept: Gecko

527

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

229

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

33

Animals often view humans as predators, leading to alterations in their behavior. Even nuanced aspects of human activity like clothing color affect animal behavior, but we lack an understanding of when and where such effects will occur. The species confidence hypothesis posits that birds are attracted to colors found on their bodies and repelled by non-body colors. Here, we extend this hypothesis taxonomically and conceptually to test whether this pattern is applicable in a non-avian reptile and to suggest that species should respond less fearfully to their sexually-selected signaling color. Responses to clothing color could also be impacted by habituation to humans, so we examine whether behavior varied between areas with low and high human activity. We quantified the effects of four T-shirt colors on flight initiation distances (FID) and on the ease of capture in western fence lizards (Sceloporus occidentalis), and we accounted for detectability against the background environment. We found no differences in lizard behavior between sites. However, lizards tolerated the closest approaches and were most likely to be captured when approached with the T-shirt that resembled their sexually-selected signaling color. Because changes in individual behavior affect fitness, choice of clothing color by people, including tourists, hikers, and researchers, could impact wildlife populations and research outcomes.

Concepts: Psychology, Human, Species, Natural environment, Mammal, Gecko, Chimpanzee, Western fence lizard

33

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

28

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

25

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

15

Ecomorphology links microhabitat and morphology. By comparing ecomorphological associations across clades, we can investigate the extent to which evolution can produce similar solutions in response to similar challenges. While Anolis lizards represent a well-studied example of repeated convergent evolution, very few studies have investigated the ecomorphology of geckos. Similar to anoles, gekkonid lizards have independently evolved adhesive toe pads and many species are scansorial. We quantified gecko and anole limb length and microhabitat use, finding that geckos tend to have shorter limbs than anoles. Combining these measurements with microhabitat observations of geckos in Queensland, Australia, we observed geckos using similar microhabitats as reported for anoles, but geckos with relatively longer limbs were using narrower perches, differing from patterns observed in anoles and other lizards. We also observed arboreal geckos with relatively shorter proximal limb segments as compared to rock-dwelling and terrestrial geckos, similar to patterns observed for other lizards. We conclude that although both geckos and anoles have adhesive pads and use similar microhabitats, their locomotor systems likely complement their adhesive pads in unique ways and result in different ecomorphological patterns, reinforcing the idea that species with convergent morphologies still have idiosyncratic characteristics due to their own separate evolutionary histories.

Concepts: Evolution, Gecko, Squamata, Anolis, Lizard, Polychrotidae, Carolina anole, Arboreal locomotion

15

Tails are an intricate component of the locomotor system for many vertebrates. Leopard geckos (Eublepharis macularius) possess a large tail that is laterally undulated during steady locomotion. However, the tail is readily shed via autotomy, resulting in the loss of tail function, loss in body mass, and a cranial shift in the center of mass. To elucidate the function of tail undulations, we investigated changes in limb kinematics after manipulating the tail artificially by restricting tail undulations and naturally by removing the tail via autotomy. Restricting tail undulations resulted in kinematic adjustments similar to those that occur following tail autotomy, characterized by more flexed hind limb joints. These data suggest that effects of autotomy on locomotion may be linked to the loss of tail movements rather than the loss of mass or a shift in center of mass. We also provide empirical support for the link between lateral tail undulations and step length through the rotation of the pelvic girdle and retraction of the femur. Restriction and autotomy of the tail limits pelvic rotation, which reduces femur retraction and decreases step length. Our findings demonstrate a functional role for tail undulations in geckos, which likely applies to other terrestrial vertebrates.

Concepts: Mass, Gecko, Vertebra, Human anatomy, Classical mechanics, Eublepharis, Gekkonidae, Leopard gecko

13

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