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The tree frog is a prominent amphibian among terrestrial vertebrates known for its ability to adhere to various surfaces through the capillary forces of water in the microchannels between micropillars on its disc‐shaped toe pads, a phenomenon known as wet adhesion. However, the secretion pattern of mucus on the attachment surface of living tree frog toe pads and the distribution of active mucus pores (AMPs) have not yet been fully elucidated. In this study, we utilized synchrotron X‐ray micro‐computed tomography and interference reflection microscopy to obtain the spatial distribution of the entire population of ventral mucus glands on the toe pads of living tree frogs and the real‐time mucus secretion patterns from the ventral mucus pores on the contact surface under different environmental conditions. We observed that the number and secretion frequency of AMPs on the toe pad are regulated according to environmental conditions. Such dynamic mucus secretion on the tree frog's toe pad could contribute to the understanding of capillary force regulation for wet adhesion and the development of adhesive surfaces by mimicking the mucus‐secreting toe pad. [ABSTRACT FROM AUTHOR]

Investigations of mate choice continue to address fundamental questions about the mechanisms and evolution of animal behaviour. A common behavioural assay used to study acoustically guided mate choice with playback experiments is phonotaxis, a typically robust response in which a chooser approaches acoustic signals, such as courtship songs or mating calls. Robust empirical studies of phonotaxis often require substantial laboratory facilities, such as a dedicated and sound-treated room or enclosure, in which the acoustic environment is controlled and in which animals are freely able to move about. The financial and space resources required to outfit a research laboratory to investigate phonotaxis may be sufficiently prohibitive such that some researchers are excluded from undertaking bioacoustic behavioural research. Here, we validate a new device designed to measure animal movements related to phonotaxis using an inertial measurement unit (IMU). The device is small and portable; it can be constructed for less than $300 USD (£ 238 GBP); and the build instructions and code for operation are freely available. In a series of four experiments with treefrogs, we demonstrate using the device that an IMU-based approach to measuring animal movement can replicate a broad range of findings from traditional phonotaxis experiments on species recognition and sexual selection. We conclude by discussing several possible uses for IMU-based measurements of phonotaxis. • Phonotaxis is a key assay in many behavioural studies. • Inertial measurement units (IMUs) provide new tools to measure phonotaxis. • An IMU is validated to study acoustically mediated mate choice in frogs. • The IMU produced results similar to those obtained in traditional phonotaxis tests. • IMUs are inexpensive alternatives to study species recognition and mate choice. [ABSTRACT FROM AUTHOR]

Some frog species have a unique skeletal element, referred to as the intercalary element (IE), in the joints between the terminal and subterminal phalanges of all digits. IEs are composed of cartilage or connective tissue and have a markedly differ shape than the phalanges. IEs are highly related to the arboreal lifestyle and toe pads. The IE is found only in neobatrachian frogs among anurans, suggesting that it is a novelty of Neobatrachia. IEs are widely distributed among multiple neobatrachian lineages and are found in the suborders Hyloides and Ranoides (the two major clades in Neobatrachia). However, it is unclear whether the IEs found in multiple linages resulted from convergent evolution. Therefore, in this study, we aimed to examine how similar or different the developmental trajectories of the IEs are between Hyloides and Ranoides. To that end, we compared the osteological and histological developmental processes of the IEs of the hyloid frog Dryophytes japonicus and the ranoid frog Zhangixalus schlegelii. Both species shared the same IE‐initiation site and level of tissue differentiation around the IE when it began to form in tadpoles, although the IE developments initiated at different stages which were determined by external criteria. These results suggest that similar mechanisms drive IE formation in the digits of both species, supporting the hypothesis that the IEs did not evolve convergently. [ABSTRACT FROM AUTHOR]

The influence of desiccation on metamorphic traits (larval duration and size at emergence) was studied in Polypedates maculatus under laboratory conditions. Gosner Stage 23 tadpoles were exposed to decreasing water levels (gradual or rapid) until the beginning of metamorphic climax (Stage 42). A control group was reared in constant water levels. Tadpoles reared in decreasing water levels reached the metamorphic climax earlier and metamorphosed at a smaller size than those reared in constant water levels. Further, tadpoles experiencing rapid depletion of water reached the metamorphic climax earlier and metamorphosed at a smaller size than those experiencing gradual depletion of water levels. Tadpoles of P. maculatus showed adaptive plasticity in metamorphosis to pond drying. Survival of tadpoles in treatments and the control was 100%. The study revealed that tadpoles of P. maculatus have plastic development in response to water levels; the trade-off between growth and development favors development, which results in early metamorphosis at a small size.

The strong adhesion on dry and wet surfaces and the durability of bioinspired hierarchical fibrillar adhesives are critical for their applications. However, the critical design for the strong adhesion normally depends on fine sub-micron structures which could be damaged during repeat usage. Here, we develop a tree frog-inspired gradient composite micropillars array (GP), which not only realizes a 2.3-times dry adhesion and a 5.6-times wet adhesion as compared to the pure polydimethylsiloxane (PDMS) micropillars array (PP), but also shows excellent durability over 200 repeating cycles of attachment/detachment and self-cleaning ability. A GP consists of stiffer tips and softer roots by incorporating gradient dispersed CaCO3 nanoparticles in PDMS micropillar stalks. The modulus gradient along the micropillar height facilitates the contact formation and enhances the maximum stress during the detaching. The study here provides a new design strategy for robust adhesives for practical applications in the fields of robotics, electronics, medical engineering, etc. [ABSTRACT FROM AUTHOR]

Recently, Rhacophorus sensu lato was divided into three genera. In addition, Rhacophorus laoshan and Zhangixalus yinggelingensis were placed in the genus Rhacophorus sensu stricto and Zhangixalus, respectively, only based on morphological characters. The research on the genus Rhacophorus sensu lato faces major challenges due to their complex interspecies relationships, and the phylogenetic status of many species are still unclear, which hampered the taxonomy and protection of these species. In this study, we investigated the molecular phylogenetic status of R. laoshan and Z. yinggelingensis using mitochondrial DNA (12S rRNA, tRNAVal, 16S rRNA and Cyt b) fragments and nuclear DNA (RAG-1, RHOD, TYR) fragments. Our results revealed that Rhacophorus laoshan is closely related to R. verrucopus, R. orlovi and R. calcaneus, and Zhangixalus yinggelingensis should indeed be placed under Zhangixalus. This research clarified the phylogenetic positions of two species within the genus Rhacophorus sensu lato, and it also has an impact on the protection and biogeographic analysis of these species. [ABSTRACT FROM AUTHOR]

We used three-dimensional micro-computed tomography to compare the skeletal features of two species of male tree frogs with similar morphologies: the globally prevalent Hyla japonica and critically endangered Hyla suweonensis. One of the most prominent differences between the two species was the angle of the alary processes of the premaxilla. In H. suweonensis, the alary processes were inclined posteriorly at an angle of 77.05°, whereas in H. japonica, they were deflected at an angle of 93.27° (a difference of more than 16°). This difference accounts for the more protruded shape of H. suweonensis compared with that of H. japonica. Sizes and proportions related to skeletal compartments (e.g. skull, forelimb, vertebrae, and hindlimb) also differed between the two species, which is consistent with the general exterior observation that compared with H. japonica, H. suweonensis has a more acuminate snout and a more slender body. The full skeletal configuration could provide classification keys for the two sympatric species that will be applicable to ecological field surveys and conservation activities.

The roles of bactericidal cathelicidins against bacterial infection have been extensively studied. However, the antibacterial property and mechanism of action of non-bactericidal cathelicidins are rarely known. Herein, a novel naturally occurring cathelicidin (PopuCATH) from tree frog (Polypedates puerensis) did not show any direct anti-bacterial activity in vitro. Intriguingly, intraperitoneal injection of PopuCATH before bacterial inoculation significantly reduced the bacterial load in tree frogs and mice, and reduced the inflammatory response induced by bacterial inoculation in mice. PopuCATH pretreatment also increased the survival rates of septic mice induced by a lethal dose of bacterial inoculation or cecal ligation and puncture (CLP). Intraperitoneal injection of PopuCATH significantly drove the leukocyte influx in both frogs and mice. In mice, PopuCATH rapidly drove neutrophil, monocyte/macrophage influx in mouse abdominal cavity and peripheral blood with a negligible impact on T and B lymphocytes, and neutrophils, monocytes/macrophages, but not T and B lymphocytes, were required for the preventive efficacy of PopuCATH. PopuCATH did not directly act as chemoattractant for phagocytes, but PopuCATH obviously drove phagocyte migration when it was cultured with macrophages. PopuCATH significantly elicited chemokine/cytokine production in macrophages through activating p38/ERK mitogen-activated protein kinases (MAPKs) and NF-κB p65. PopuCATH markedly enhanced neutrophil phagocytosis via promoting the release of neutrophil extracellular traps (NETs). Additionally, PopuCATH showed low side effects both in vitro and in vivo. Collectively, PopuCATH acts as a host-based immune defense regulator that provides prophylactic efficacy against bacterial infection without direct antimicrobial effects. Our findings reveal a non-bactericidal cathelicidin which possesses unique anti-bacterial action, and highlight the potential of PopuCATH to prevent bacterial infection.

The strong adhesion on dry and wet surfaces and the durability of bioinspired hierarchical fibrillar adhesives are critical for their applications. However, the critical design for the strong adhesion normally depends on fine sub-micron structures which could be damaged during repeat usage. Here, we develop a tree frog-inspired gradient composite micropillars array (GP), which not only realizes a 2.3-times dry adhesion and a 5.6-times wet adhesion as compared to the pure polydimethylsiloxane (PDMS) micropillars array (PP), but also shows excellent durability over 200 repeating cycles of attachment/detachment and self-cleaning ability. A GP consists of stiffer tips and softer roots by incorporating gradient dispersed CaCO3 nanoparticles in PDMS micropillar stalks. The modulus gradient along the micropillar height facilitates the contact formation and enhances the maximum stress during the detaching. The study here provides a new design strategy for robust adhesives for practical applications in the fields of robotics, electronics, medical engineering, etc.

Vasa, an RNA binding protein with an ATP-dependent helicase domain, is one of the critical germ cell factors. In this study, we reported cloning of a full-length vasa cDNA from tree frog F. palpebralis. The predicated F. palpebralis Vasa shares eight conserved regions with Vasa proteins from other vertebrates. Furthermore, we confirmed germline specific expression of the vasa RNA by RT-qPCR. These results suggest that vasa is involveed in germ cell specification in F. palpebralis. Our observation provides a new tool to study germ cell formation in amphibians. [ABSTRACT FROM AUTHOR]

Abstract Background: Amphibians inhabit the terrestrial environment, a conquest achieved after several evolutionary steps, which were still insufficient to make them completely independent of the aquatic environment. These processes gave rise to many morphological and physiological changes, making their skin (and cutaneous secretion) rich in bioactive molecules. Among the tree frogs, the secretion is composed mainly of peptides; but alkaloids, proteins and steroids can also be found depending on the species. The most known class of biologically active molecules is the antimicrobial peptides (AMPs) that act against bacteria, fungi and protozoans. Although these molecules are well-studied among the hylids, AMPs ontogeny remains unknown. Therefore, we performed peptidomic and proteomic analyses of Pithecopus nordestinus (formerly Phyllomedusa nordestina) in order to evaluate the peptide content in post-metamorphosed juveniles and adult individuals. Methods: Cutaneous secretion of both life stages of individuals was obtained and analyzed by LC-MS/MS after reduction and alkylation of disulfide bonds or reduction, alkylation and hydrolysis by trypsin. Results: Differences in the TIC profile of juveniles and adults in both treatments were observed. Moreover, the proteomic data revealed known proteins and peptides, with slight differences in the composition, according to the life stage and the treatment. AMPs were identified, and bradykinin-potentiating peptides were observed in trypsin-treated samples, which suggests a protein source of such peptide (cryptide). Conclusion: In general, skin secretion contents were similar between juveniles and adults, varying in quantity, indicating that the different stages of life are reflected in the number of molecules and not on their diversity.

Abstract Background: Argenteohyla siemersi (red-spotted Argentina frog) is a casque-headed tree frog species belonging to the Hylidae family. This species has a complex combination of anti-predator defense mechanisms that include a highly lethal skin secretion. However, biochemical composition and biological effects of this secretion have not yet been studied. Methods: The A. siemersi skin secretion samples were analyzed by mass spectrometry and chromatographic analysis (MALDI-TOF/MS, RP-HPLC and GC-MS). Proteins were also studied by SDS-PAGE. Among the biological activities evaluated, several enzymatic activities (hemolytic, phospholipase A2, clotting, proteolytic and amidolytic) were assessed. Furthermore, the cytotoxic activity (cytolysis and fluorescence staining) was evaluated on myoblasts of the C2C12 cell line. Results: The MALDI-TOF/MS analysis identified polypeptides and proteins in the aqueous solution of A. siemersi skin secretion. SDS-PAGE revealed the presence of proteins with molecular masses from 15 to 55 kDa. Steroids, but no alkaloids or peptides (less than 5 KDa), were detected using mass spectrometry. Skin secretion revealed the presence of lipids in methanolic extract, as analyzed by CG-MS. This secretion showed hemolytic and phospholipase A2 activities, but was devoid of amidolytic, proteolytic or clotting activities. Moreover, dose-dependent cytotoxicity in cultured C2C12 myoblasts of the skin secretion was demonstrated. Morphological analysis, quantification of lactate dehydrogenase release and fluorescence staining indicated that the cell death triggered by this secretion involved necrosis. Conclusions: Results presented herein evidence the biochemical composition and biological effects of A. siemersi skin secretion and contribute to the knowledge on the defense mechanisms of casque-headed frogs.

We re-examined the holotype of Polypedates chlorophthalmus, the only specimen of the species that has ever been collected. Detailed comparison to recently collected specimens of Philautus hosii revealed that the two taxa are identical in general habitus, shape of snout, hands and feet, extent of toe webbing, presence and shape of hand and foot tubercles, size and shape of vomerine teeth, dorsal and ventral colouration and pattern, iris colouration, as well as body size and proportions. We refer Polypedates chlorophthalmus to the synonymy of Philautus hosii. [ABSTRACT FROM AUTHOR]

Our artificial bioinspired adhesive patch is inspired by two different biological creatures in one design, which consists of a densely packed hexagonal tree-frog pad embedded with vulgaris octopuses' microscopic suckers. This work focuses on the creation of a new microscopic sucker design that takes inspiration from the structure of real octopus' suckers to improve adhesion and overcome potential issues related to the existing micro-sucker design. Theoretical analysis, simulations, and experimental studies demonstrated that this new-designed microscopic sucker exhibits robust adhesion under various conditions (dry, moist, underwater, and under oil). Several factors that influence adhesion performance, including compressive preloading force, time of attachment, number of contact cycles, and surface roughness, are investigated. It showed stronger adhesion than previous sucker designs and proved its ability to remain attached for up to 24 h, withstand a large number of contact cycles, and adhere to high- and low-roughness surfaces. It reached 57.3–116.4 kPa of normal adhesion strength and 29.8–93.47 kPa of shear adhesion strength. Based on these results, our adhesive patch design could pave the way for future skin-conforming patches in medical devices. [ABSTRACT FROM AUTHOR]

Tree frogs need to adhere to surfaces of various roughnesses in their natural habitats; these include bark, leaves and rocks. Rough surfaces can alter the effectiveness of their toe pads, due to factors such as a change of real contact area and abrasion of the pad epithelium. Here, we tested the effect of surface roughness on the attachment abilities of the tree frog Litoria caerulea. This was done by testing shear and adhesive forces on artificial surfaces with controlled roughness, both on single toe pads and whole animal scales. It was shown that frogs can stick 2–3 times better on small scale roughnesses (3–6 µm asperities), producing higher adhesive and frictional forces, but relatively poorly on the larger scale roughnesses tested (58.5–562.5 µm asperities). Our experiments suggested that, on such surfaces, the pads secrete insufficient fluid to fill the space under the pad, leaving air pockets that would significantly reduce the Laplace pressure component of capillarity. Therefore, we measured how well the adhesive toe pad would conform to spherical asperities of known sizes using interference reflection microscopy. Based on experiments where the conformation of the pad to individual asperities was examined microscopically, our calculations indicate that the pad epithelium has a low elastic modulus, making it highly deformable.

In this study, three types of bionic texture surfaces were designed, based on the microstructure of tree frog and gecko feet, for two typical prosthetic substrates: silicone rubber and thermoplastic polyurethane elastomer (TPU). The surface energy of all bionic texture surfaces, and the relative displacement and energy dissipation of the reciprocating friction between these bionic surfaces and skin, were investigated. The results revealed that the bionic texture of the prosthetic socket surface had an obvious influence on the surface characteristics and reciprocating characteristics of friction with the skin. According to the comprehensive weight rating method, the optimal bionic textures for the silicone rubber substrate were a regular hexagonal prism and a quadrangular prism; for the TPU substrate, only the regular quadrangular prism texture was optimal. These textures can effectively increase the surface energy of the surface of the prosthetic socket, thereby increasing its adhesion to skin and reducing the dissipation of friction energy when it interacts with the stump. This bionic prosthetic socket surface design helps improve the adaptation between the prosthetic socket and the stump.

Due to excessive use or abuse in the food industry, agriculture, and medicine, many pathogens are developing resistance against conventional antibiotics. Antimicrobial peptides (AMPs) hold promise as effective therapeutic options for the treatment of bacterial infections. Herein, a novel cathelicidin antimicrobial peptide (Zs-CATH) was identified from the tree frog Zhangixalus smaragdinus . Zs-CATH mainly adopted an amphipathic β-sheet structure in a membrane-mimetic environment. It showed broad-spectrum antibacterial activity against Gram-positive and Gram-negative bacteria in vitro and significantly protected mice from lethal infections induced by Gram-negative bacteria Escherichia coli ATCC 25922 or Gram-positive bacteria Staphylococcus aureus ATCC 25923 in vivo . In addition, Zs-CATH exerted a strong anti-inflammatory effect by neutralizing lipopolysaccharide (LPS) and lipoteichoic acid (LTA) and promoting macrophage M2 polarization, thus inhibiting the secretion of proinflammatory cytokines (TNF-α, IL-6, and IL-1β) and enhancing the production of M2 macrophage markers IL-10, IL-4, and CD206. The MAPK and NF-κB inflammatory signaling pathways and transcriptional activator 6 (STAT6) were involved in this effect. In mice, Zs-CATH rapidly recruited neutrophils and monocytes/macrophages to the abdominal cavity but not T and B lymphocytes. Zs-CATH did not exhibit a direct chemoattractant effect on phagocytes but significantly promoted phagocyte migration in the presence of macrophages. Zs-CATH stimulated macrophages to secrete chemokines CXCL1, CXCL2, and CCL2, which mediated the recruitment of phagocytes. Furthermore, Zs-CATH promoted the production of reactive oxygen species (ROS) and neutrophil extracellular traps (NETs), which are oxygen-dependent and oxygen-independent mechanisms of the microbicidal activity of neutrophils, respectively. Zs-CATH exhibited no toxic side effects on mammalian cells and mice. These findings show that in addition to direct antibacterial activity, Zs-CATH also possesses the ability to modulate immune and inflammatory processes during bacterial infection, showing potential for development as anti-infective and/or anti-inflammatory agents.

Enlarged adhesive toe pads on the tip of each digit allow tree frogs to climb smooth vertical and overhanging surfaces, and are effective in generating reversible adhesion under both dry and wet conditions. In this review, we discuss the complexities of the structure of tree frog toe pads in relation to their function and review their biomimetic potential. Of particular importance are the (largely) hexagonal epithelial cells surrounded by deep channels that cover the surface of each toe pad and the array of nanopillars on their surface. Fluid secreted by the pads covers the surface of each pad, so the pads adhere by wet adhesion, involving both capillarity and viscosity-dependent forces. The fabrication and testing of toe pad mimics are challenging, but valuable both for testing hypotheses concerning tree frog toe pad function and for developing toe pad mimics. Initial mimics involved the fabrication of hexagonal pillars mimicking the toe pad epithelial structure. More recent ones additionally replicate the nanostructures on their surface. Finally we describe some of the biomimetic applications that have been developed from toe pad mimics, which include both bioinspired adhesives and friction-generating devices. This article is part of the theme issue 'Bioinspired materials and surfaces for green science and technology (part 2)'. [ABSTRACT FROM AUTHOR]

We determined the complete mitochondrial genome of the tree frog, Polypedates braueri using next generation sequencing (NGS) and Sanger sequencing. The mitogenome of P. braueri was 19,904 bp in length, which contained 12 protein-coding genes, 22 tRNAs, two rRNAs, and two control regions (D-Loop). A noncoding sequence (NC) was discovered between tRNALys and ATP6 gene, as well as replaced the original position of ATP8 gene. The ND5 gene was found between the two control regions. More mitochondrial genomic information will contribute to revealing the phylogenetic relationships among species of the genus Polypedates.

Wet clutch of heavy tractor is an important executive component of power shift gearbox. The wear failure of the friction pair is one of the main reasons for the overall performance degradation of the transmission system. To reduce the huge resource and economic loss caused by it, a wear-resistant clutch friction plate was designed. In this paper, from the perspective of bionics, the big tree frog was used as the experimental research object, and the toe end was observed by scanning electron microscopy. The microstructure of the toad end of the tree frog is quadrilateral, pentagon, hexagonal, and the hexagonal structure is mostly. The structure is uniform in size and has a diameter of about 10 μm. The microstructures have a groove between the outlines and a groove width of about 1 μm. Studies have shown that the mucus secreted by the body surface of the tree frog circulates in the groove surrounding the hexagonal structure, enhancing its adhesion, which is the coefficient of friction, in a humid environment. Tree frogs exhibit strong adhesion and friction when in contact with slippery substrates. With these characteristics, the bionic friction linings can better meet the requirements of transmission motion and torque. The toad parameters of the tree frog were extracted, the surface structure of the friction lining was optimized, and the dense hexagonal groove division structure of the toad end of the tree frog was further highlighted and simplified. The oil sump structure on the surface of the wet clutch friction plate of the heavy tractor was similarly designed. Nine kinds of bionic samples were designed for the design idea and the samples were made by laser processing technology. The friction and wear tests were carried out on a micro-friction and wear tester, and the differences of friction and wear with different hexagonal diameters and different groove widths were studied. The test results showed that the bionic non-smooth structure has better wear resistance than the smooth structure, and the regular hexagon has a diameter of 12mm. When the groove width is 1.5mm, the wear amount is the lowest and the friction coefficient is relatively high. The combined shape diameter and groove width can minimize wear and improve the service life of the friction plate, thus achieving the requirement of improving the wear resistance of the clutch. [ABSTRACT FROM AUTHOR]

Abstract: Skeletal morphology is directly associated with habitat characteristics. To investigate the arboreal adaptation, we studied the osteological morphology of the forelimbs and the third metacarpals of arboreal frogs (Rhacophoridae and Hylidae) and non‐arboreal frogs (Bombinatoridae, Bufonidae, Megophryidae, Ranidae, and Microhylidae) using transparent specimens or X‐rays of skeletons. Our results revealed that the bony knob on the third metacarpal, which formed by a dilated and elongated lateral articular cartilage (AL) through endochondral ossification, occurred only in species of Rhacophorinae. The results of the phylogenetic comparative methods and correlation analysis strongly supported the conclusion that the bony knob is a phylogenetic independent evolution trait and had a significant correlation with the arboreal habitat. Furthermore, anatomical observation showed that a muscle adhered to the bony knob. Therefore, we speculated that the bony knob might act as an enlarged attachment point for larger or more musculatures to help with grasping. In addition, the relative length of the hand showed a significant difference between arboreal and non‐arboreal species (p = .007), suggesting that longer hands might be an arboreal adaptive trait. Overall, this study leads to a deeper understanding of the arboreal adaptation. [ABSTRACT FROM AUTHOR]

This paper examines the pre-industrial historical record of Britain's anuran species. The records examined include especially the writings of naturalists and physicians, most notably Gerald of Wales (1188), John of Gaddesden (c.1314), Edward Wotton (1552), Timothie Bright (1580), Thomas Brown (1646), Robert Lovell (1660), Christopher Merrett (1667), Robert Sibbald (1684) and John Morton (1712). The common frog is attested as present throughout the period. Several reliable historical records are located that describe the presence or absence of a water frog species (Peloyphylax spp.: two records of presence, two of absence) and the tree frog (Hyla arborea: five records of presence, three of absence). The moor frog (Rana arvalis) and agile frog (Rana dalmatina) are not described separately - if present in the time period, they may have been considered varieties of the common frog. The evidence of presence comes exclusively from England. The records taken together confirm the presence of populations of water frogs between (at least) the fifteenth and eighteenth century, and provide new evidence attesting to populations of tree frogs between the sixteenth century (when the species may have been introduced) and the eighteenth century (when the species seems to have become locally extinct/locally distributed). [ABSTRACT FROM AUTHOR]

As of February 2017, approximately 7639 amphibian species have been described in the AmphibiaWeb database. However, only 20 cathelicidin-like antimicrobial peptides have been identified to date from 10 amphibian species. Half of these peptides were identified from genome sequences and have not yet been functionally characterized. In this study, a novel cathelicidin-like peptide designated cathelicidin-PP was purified from the skin of tree frog Polypedates puerensis. Cathelicidin-PP is a 32 residue peptide of sequence ASENGKCNLLCLVKKKLRAVGNVIKTVVGKIA. Circular dichroism spectroscopy indicated that cathelicidin-PP mainly adopts a β-sheet structure in membrane-mimetic solutions. Cathelicidin-PP exhibits potent antimicrobial activity against bacteria and fungi, especially Gram-negative bacteria. Meanwhile, it shows low cytotoxicity toward mammalian cells. Scanning electron microscopy analysis indicated that cathelicidin-PP kills bacteria through the disruption of the bacterial cell membrane integrity. Furthermore, cathelicidin-PP exerts significant anti-inflammatory functions by inhibiting the lipopolysaccharide (LPS)-mediated generation of nitric oxide and pro-inflammatory cytokines, tumor necrosis factor-α, interleukin-1β, and interleukin-6. The MAPKs (ERK, JNK, and p38) and NF-κB signaling pathways are involved in the anti-inflammatory effect. Cathelicidin-PP caused partial neutralization of LPS in a dose-dependent manner. Quantitative PCR indicated that infection of tree frogs with bacteria causes increased expression of cathelicidin-PP in immune-related tissues. Taken together, cathelicidin-PP is the first identified cathelicidin-like peptide from tree frogs. Our findings demonstrate that in addition to direct bactericidal capacity, cathelicidin-PP also possesses immunomodulatory properties, including partial neutralization of LPS, and inhibiting the production of inflammatory cytokines. [ABSTRACT FROM AUTHOR]

Sexual selection has been widely explored from numerous perspectives, including behavior, ecology, and to a lesser extent, energetics. Hormones, and specifically androgens such as testosterone, are known to trigger sexual behaviors. Their effects are therefore of interest during the breeding period. Our work investigates the effect of testosterone on the relationship between cellular bioenergetics and contractile properties of two skeletal muscles involved in sexual selection in tree frogs. Calling and locomotor abilities are considered evidence of good condition in Hyla males, and thus server as proxies for male quality and attractiveness. Therefore, how these behaviors are powered efficiently remains of both physiological and behavioral interest. Most previous research, however, has focused primarily on biomechanics, contractile properties or mitochondrial enzyme activities. Some have tried to establish a relationship between those parameters but to our knowledge, there is no study examining muscle fiber bioenergetics in Hyla arborea . Using chronic testosterone supplementation and through an integrative study combining fiber bioenergetics and contractile properties, we compared sexually dimorphic trunk muscles directly linked to chronic sound production to a hindlimb muscle (i.e. gastrocnemius ) that is particularly adapted for explosive movement. As expected, trunk muscle bioenergetics were more affected by testosterone than gastrocnemius muscle. Our study also underlines contrasted energetic capacities between muscles, in line with contractile properties of these two different muscle phenotypes. The discrepancy of both substrate utilization and contractile properties is consistent with the specific role of each muscle and our results are elucidating another integrative example of a muscle force-endurance trade-off. [ABSTRACT FROM AUTHOR]

Lek mating systems are characteristic of anurans that use oviposition sites that cannot be easily monopolized by individual males. The dynamics of the chorus structure in leks is not well known. Here, we examine the relationship between the movement activity of individual males during the breeding season and their size. According to our observations, the site fidelity of males is not completely random, with the larger males moving significantly shorter distances than smaller males. However, this difference applies only to the distance between the first and second captures. Whether higher site fidelity contributes to higher mating success needs further investigation. [ABSTRACT FROM AUTHOR]

Most studies on the adhesive mechanisms of climbing animals have addressed attachment against flat surfaces, yet many animals can climb highly curved surfaces, like twigs and small branches. Here we investigated whether tree frogs use a clamping grip by recording the ground reaction forces on a cylindrical object with either a smooth or anti-adhesive, rough surface. Furthermore, we measured the contact area of fore and hindlimbs against differently sized transparent cylinders and the forces of individual pads and subarticular tubercles in restrained animals. Our study revealed that frogs use friction and normal forces of roughly a similar magnitude for holding on to cylindrical objects. When challenged with climbing a non-adhesive surface, the compressive forces between opposite legs nearly doubled, indicating a stronger clamping grip. In contrast to climbing flat surfaces, frogs increased the contact area on all limbs by engaging not just adhesive pads but also subarticular tubercles on curved surfaces. Our force measurements showed that tubercles can withstand larger shear stresses than pads. SEM images of tubercles revealed a similar structure to that of toe pads including the presence of nano-pillars, though channels surrounding epithelial cells were less pronounced. The tubercles' smaller size, proximal location on the toes and shallow cells make them probably less prone to buckling and thus ideal for gripping curved surfaces. [ABSTRACT FROM AUTHOR]