Subarticular Tubercles Research Articles

Digging out another cryptic species: A new sand frog (Anura: Pyxicephalidae: Tomopterna) from Mozambique

A new species of Tomopterna is described from Banhine National Park, southern Mozambique. It differs from all other sand frogs by an uncorrected p-distance of 4.9–8.7% for 16S rRNA. The new species can be distinguished from all other described species of sand frogs by: males 37 mm SVL or less, undivided subarticular tubercles, more than three phalanges free of webbing on the fourth toe, a continuous glandular ridge below the tympanum, a distinct tympanic membrane, the nostrils closer to the snout tip than the eye, the rounded canthus rostralis, a round tympanum, the absence of an outer metatarsal tubercle, an interrupted inter-orbital bar, small dorsal warts, the absence (or weakness) of vomerine teeth, the solid pigmented throat in mature males, the distinct palmar tubercles, the smooth ventral surface, and barring on the limbs. This description adds a further amphibian to the list of Mozambican frogs, which has increased significantly in recent years.

Scanning electron microscopy and light microscopy of tongue, fingers, toes, nuptial pad, and humeral gland in Sylvirana nigrovittata (Anura: Ranidae)

The micromorphology and histology of anuran skin, particularly in Thai species, remain relatively understudied. Anurans use their tongues for prey capture and their hands and feet for adhesion and mating, suggesting a close relationship between micro-surface features and histological structure. Information on Sylvirana nigrovittata is particularly limited. This study provides a detailed examination of the micro-surface and histological characteristics of the tongue, fingers, toes, nuptial pad, and humeral gland in S. nigrovittata. Specimens collected from Phu Luang Wildlife Sanctuary in Loei province, northeastern Thailand, were studied using scanning electron microscopy (SEM) for micro-surface features and H&E staining for histological details. SEM micrographs revealed that the tongue was cordate-shaped, with about 75% of its surface covered by filiform papillae and 25% by fungiform papillae housing taste buds. Filiform papillae were trapezoidal, averaging 23.88±5.68 µm in width and 38.83±6.57 µm in length, while fungiform papillae were disc-like, averaging 52.95±14.64 µm in width and 66.70±15.88 µm in length. Digital pads on fingers and toes presented prismatic cells, with fingertip cells averaging 7.09±0.97 µm in width and 11.81±1.24 µm in length, and toe cells averaging 8.40±1.37 µm in width and 11.28±1.63 µm in length. Subdigital surfaces were smoother, containing squamous cells with dimensions of 10.65±3.21 µm in width and 21.29±4.35 µm in length. Subarticular tubercles were composed of prismatic cells with hexagonal or pentagonal surfaces, averaging 10.02±2.85 µm in width and 13.08±1.94 µm in length. Nuptial pad displayed cylindrical structures with dome-like tips, averaging 24.01±3.96 µm in width and 21.16±4.37 µm in length, and feature mucous openings. They consisted of a thick keratinized stratified squamous epithelium and a dense dermis with specialized mucous glands. Humeral gland exhibited rough surfaces with squamous cells and microridges, showing both small and large mucous openings, with average cell dimensions of 16.23±1.70 µm in width and 19.11±2.05 µm in length. Histological analysis confirmed that these structures were predominantly composed of keratinized stratified squamous epithelium, with variations in dermal collagen density and mucous gland distribution. This study enhances our understanding of the skin and gland morphology in S. nigrovittata, highlighting on its anatomical and functional adaptations.

THE RELATIONSHIPS OF AN ENSEMBLE OF GUATEMALAN AND MEXICAN FROGS (ELEUTHERODACTYLUS: LEPTODACTYLIDAE: AMPHIBIA)

Eleutherodactylus daryi and E. greggi are shown to be species of the Eleutherodactylus gollmeri group which is defined on the basis of having a synapomorphy (fusion of sacrum and presacral vertebrae). Eleutherodactylus omiltemanus is a species of the rhodopis Series rather than thefitzingeri Series. The Eleutherodactylus omiltemanus group disappears because ali of its contained members are placed in other species groups. Eleutherodactylus saltator is a synonym of E. mexicanus. Eleutherodactylus rhodopis sensu lato contains two species, a larger upland E. rhodopis and the more widely distibuted lowland E. loki. The rhodopis Series, containing the rhodopis group, is not definable because no synapomorphies are apparent. Eleutherodactylus occidentalis and E. omiltemanus are assigned to this "group. " Within this "group " there is a cluster of species having black mesorchia (E. hobartsmithi, E. mexicanus, E. pygmaeus, and E. sarton), one having a shortened inner toe (E. jota and E. podiciferus), and one having conical subarticular tubercles (E. bransfordii, E. lauraster, E. loki, E. occidentalis, E. omiltemanus, E. rhodopis, and E. stejnegerianus). Sixty of the 84 essentially Mesoamerican species of the subgenus Craugastor are placed in a monophyletic subunit based on the common presence of marked sexual dimorphism in tympanum size. The subunit includes the nine species ofthe gollmeri group, the thirteen species of the rhodopis group, and 38 additional species (the three species of the biporcatus group, the eleven species of the milesi group, eight species of thefitzingeri group, 15 species of the rugulosus group, and E. uno). The 24 species of Craugastor not included in that clade are the 13 species of the alfredi group (including E. bocourti), the two species of the augusti group, the two species of the bufoniformis group, three species removed from thefitzingeri group (E. andi, E. cuaquero, and E. emcelae), and four species removed from the rugulosus group (E. anatipes, E. anomalus, E. cheiroplethus, and E. zygodactylus).

A New Species of Nanorana (Anura: Dicroglossidae) from Northwestern Yunnan, China, with Comments on the Taxonomy of Nanorana arunachalensis and Allopaa.

The genus Nanorana contains three subgenera, namely Nanorana, Paa, and Chaparana, and currently, there are four species known to science in Nanorana (Nanorana). In this study, we describe a new species belonging to the subgenus Nanorana from northwestern Yunnan, China. Phylogenetically, the new species, Nanorana laojunshanensissp. nov., is the sister to the clade of N. pleskei and N. ventripunctata. Morphologically, the new species can be distinguished from known congeners by the combination of following characters: present tympanum, equal fingers I and II, small body size, yellow ventral surface of limbs, distinct vomerine teeth, indistinct subarticular tubercles, head width greater than head length, slender supratympanic fold, absent dorsolateral fold, nuptial spines present on fingers I and II in adult males, absent vocal sac, and paired brown spines on the chest. Moreover, we suggest moving the genus Allopaa into Nanorana (Chaparana) and consider that N. arunachalensis is neither an Odorrana species nor a member of the subfamily Dicroglossinae (therefore Nanorana), but probably represents a distinct genus closely related to Ingerana or belongs to Ingerana, pending more data. Additionally, we consider that Nanorana minica deserves the rank of an independent subgenus, and we suggest assigning N. arnoldi, N. blanfordii, N. ercepeae, N. polunini, N. rarica, N. rostandi, N. vicina, N. xuelinensis, and N. zhaoermii into the subgenus Paa and placing N. kangxianensis, N. phrynoides, and N. sichuanensis in the subgenus Chaparana.

Alternate morphological pathways involved in climbing ability in ten Neotropical anuran species

Abstract Convergent evolution has been shown to be a prominent feature of anuran evolutionary history. Studying the morphological pathways involved in the evolution of a convergent character allows us to test whether deterministic or contingent forces drive the evolution of characters. Here, we have assessed the morphological pathways associated with arboreal habits in species of six families of anurans (Hylidae, Eleutherodactylidae, Strabomantidae, Centrolenidae, Bufonidae and Hemiphractidae) through a comparative analysis of 19 phenotypic characters related to climbing ability. All species showed differences in the assessed characters, exhibiting variations in the distribution of their states and different ranges in all limb lengths. These variations implied a wide distribution across the morphospace as defined by a non-metric multidimensional scaling analysis (NMDS), with Rhinella paraguas (Bufonidae) being the most distinctive species, presenting unique characters such as the absence of intercalary elements, adhesive pads, subarticular tubercles and interphalangealis muscles of the hands. Our findings demonstrate that the morphological mechanisms involved in climbing ability of the ten species are different, suggesting distinct morphological pathways. Consequently, we advocate that historical contingency has an essential role in the evolution of arboreal habits among the species studied.

A new cryptic species in the Thelodermarhododiscus complex (Anura, Rhacophoridae) from China-Vietnam border regions.

We describe a new species of Theloderma from southern Yunnan, China and northern Vietnam based on morphological and molecular evidence. Thelodermahekouense sp. nov., which had been recorded as T.rhododiscus, is the sister to T.rhododiscus. The new species differs genetically from T.rhododiscus by 4.2% and 10.7% in 16S rRNA and COI genes, respectively, and it can be morphologically distinguished from T.rhododiscus by having more densely spaced white warts on the dorsal surface, red subarticular tubercles, red metacarpal tubercles, a red metatarsal tubercle, and black dorsal and ventral surfaces in preservative. Currently the new species is only known from the China-Vietnam border regions of Yunnan and Ha Giang, while T.rhododiscus has a wide distributional range in China including Guangxi, Guangdong, Hunan, Fujian, Jiangxi, and presumably Guizhou and eastern Yunnan. Including the new species, there are currently 10 Theloderma species in China and seven Theloderma species in Yunnan, where more species will probably be found.

A new slippery frog (Amphibia, Conrauidae, Conraua Nieden, 1908) from the Fouta Djallon Highlands, west-central Guinea

We describe a new species of the genus Conraua from the Fouta Djallon Highlands in Guinea. The species is recognised as distinct from nominotypical C. alleni, based on morphological evidence and is supported by a recent species delimitation analysis, based on DNA sequence data. The new species is distinguished from its congeners by the unique combination of the following characters: medium body size, robust limbs, only one instead of two palmar tubercles, the first finger webbed to below the first subarticular tubercle, presence of a lateral line system, indistinct tympanum, two subarticular tubercles on fingers III and IV, venter in adults white with dark brown spots or dark brown with grey or whitish spots. The new species differs from all congeners by more than 6% in the DNA sequence of mitochondrial ribosomal 16S. We discuss isolation in Pliocene and Pleistocene forest refugia as a potential driver of speciation in the C. alleni complex. We also emphasise the importance of conserving the remaining forest fragments in the Fouta Djallon Region for the preservation of both its unique biodiversity and its valuable water sources for local people.

A new critically endangered slippery frog (Amphibia, Conrauidae, Conraua) from the Atewa Range, central Ghana.

Forty-nine years after the last description of a slippery frog, we describe a seventh species of the genus Conraua. The new Conraua is endemic to the Atewa Range Forest Reserve, central Ghana, and is described based on genetic, bioacoustics, and morphological evidence. Recent molecular phylogenetic and species delimitation analyses support this population as distinct from nominotypical C. derooi in eastern Ghana and adjacent Togo. The new species is sister to C. derooi, from which it differs ~4% in the DNA sequence for mitochondrial ribosomal 16S. Genetic divergences in 16S to other species of Conraua range from 412%. The new species is distinguished morphologically from its congeners, including C. derooi, by the combination of the following characters: medium body size, robust limbs, lateral dermal fringing along edges of fingers, cream ventral color with brown mottling, the presence of a lateral line system, indistinct tympanum, the presence of inner, outer, and middle palmar tubercles, and two subarticular tubercles on fingers III and IV. We compare the advertisement calls of the new species with the calls from C. derooi and find that they differ by duration, frequency modulation, and dominant frequency. We discuss two potential drivers of speciation between C. derooi and the new species, including river barriers and fragmentation of previously more widespread forests in West Africa. Finally, we highlight the importance of the Atewa Range Forest Reserve as a critical conservation area within the Upper Guinean biodiversity hotspot.

A New Species of the Genus Adelophryne (Anura: Eleutherodactylidae: Phyzelaphryninae) from the Atlantic Forest of Northeastern Brazil

Species in the Adelophryne genus consist of diminutive, agile, and secretive frogs that inhabit forest leaf litter and have direct development. Species richness within Adelophryne was previously underestimated, and several new species have recently been described. Here, we describe a new species of Adelophryne from the Atlantic Forest in the Brazilian states of Alagoas, Pernambuco, and Paraiba. The new species is characterized by its small body size, small and distinct tympanum, toes with subarticular tubercles, fingers mucronate, three phalanges in the Finger IV, and an advertisement call composed of one single pulsed note with a high dominant frequency. The new species is phylogenetically related to other Adelophryne species of the Northern Atlantic Forest Clade and is endemic to the “Pernambuco Endemism Center” in the Atlantic Forest biodiversity hotspot.

New Species of Leaf-litter Toad of the Rhinella margaritifera Species Group (Anura: Bufonidae) from Amazonia

We describe through integrative taxonomy a new Amazonian species of leaf-litter toad of the Rhinella margaritifera species group. The new species inhabits open lowland forest in southwest Amazonia in Brazil, Peru, and Bolivia. It is closely related to a Bolivian species tentatively identified as Rhinella cf. paraguayensis. Both the new species and R. paraguayensis share an uncommon breeding strategy among their Amazonian congeners: each breeds in moderate to large rivers instead of small streams or ponds formed by rainwater. The new species is easily differentiated from other members of the R. margaritifera species group by having a strongly developed bony protrusion at the angle of the jaw, a snout–vent length of 63.4–84.7 mm in females and 56.3–72.3 mm in males, well-developed supratympanic crests with the proximal portion shorter than the parotoid gland in lateral view, a divided distal subarticular tubercle on finger III, and multinoted calls composed of groups of 7–9 pulsed notes and a dominant frequency of 1,012–1,163 Hz. Recent studies have shown that the upper Madeira Basin harbors a megadiverse fauna of anurans, including several candidate species. This is the first member of the R. margaritifera species group to be described from this region in recent years, and at least two additional unnamed species await formal description.

Three new species of frogs of the genus Pristimantis (Anura, Strabomantidae) with a redefinition of the P. lacrimosus species group.

A new phylogeny for the Pristimantis lacrimosus species group is presented, its species content reviewed, and three new species described from the eastern slopes of the Ecuadorian Andes. Our phylogeny includes, for the first time, samples of P. aureolineatus, P. bromeliaceus, and P. lacrimosus. The morphology of hyperdistal subarticular tubercles is also assessed among 21 species of Pristimantis. The P. lacrimosus species group is composed of 36 species distributed in the Chocó, Guiana, and Amazon regions of tropical South America with a single species reaching Central America. Ancestral area reconstruction indicates that, despite its high diversity in the Amazon region, the P. lacrimosus group originated in the Pacific basin, Chocó region of Ecuador and Colombia. Pristimantis amaguanaesp. nov. is most closely related to P. bromeliaceus. It differs from P. bromeliaceus by being smaller, having transversal dark bands in the hindlimbs (absent or faint in P. bromeliaceus) and the absence of discoidal fold (present in P. bromeliaceus). Pristimantis nankintssp. nov. and P. romeroaesp. nov. are part of a clade of predominantly light-green frogs that includes P. acuminatus, P. enigmaticus, P. limoncochensis, and P. omeviridis. Pristimantis nankintssp. nov. and P. romeroaesp. nov. can be distinguished from all of them by the presence of a dark dorsolateral stripe that borders a light green band on a green background. Hyperdistal tubercles are present in all examined species of the P. lacrimosus species group and its sister clade. Species with hyperdistal tubercles are characterized by having relatively long terminal phalanges and narrow T-shaped expansion at the end of the terminal phalange. We discuss the phylogenetic distribution of these characters and their potential diagnostic significance.

Out of Bound: A New Threatened Harlequin Toad (Bufonidae, Atelopus) from the Outer Borders of the Guiana Shield in Central Amazonia Described through Integrative Taxonomy

We used integrative taxonomy to describe a new species of Atelopus from the lowlands of Central Amazonia in the region of Manaus, Amazonas, Brazil. The new species is geographically isolated from the southernmost species of Atelopus of the Guiana Shield. Atelopus manauensis species nova (sp. nov.) is characterized by the combination of the following characteristics: male snout-vent length range (SVL = 19.1–26.4 mm; n = 11); dorsal and lateral skin smooth; ventral surface entirely white or white with cream-colored gular region; fingers and toes lacking subarticular tubercles and fringes. The advertisement call of the new species has a call duration of 689–840 ms, contains 15–26 pulses, is emitted at an average pulse rate of 25.5 pulses per second, and has a dominant frequency ranging 3088–3610 Hz. The genetic divergence between the new species and its morphologically most similar congeners (A. spumarius and A. pulcher) is greater than 4%. Atelopus manauensis sp. nov. is closely related to species of the A. hoogmoedi complex inhabiting the Guiana Shield. The new species has a small geographic distribution (approximately 4500 km2) in a landscape that is strongly threatened by the growth of Manaus, the largest city in Brazilian Amazonia. The new species is considered critically endangered and in need of urgent conservation measures.

A New Species of Pristimantis (Anura: Strabomantidae) from the Eastern Slope of the Cordillera Oriental, Arauca, Colombia

We describe a new species of Pristimantis from one of the most isolated regions of Colombia, at elevations of 700–800 m in the Tame River basin at the eastern slope of the Cordillera Oriental in Colombia (Department of Arauca). This locality has been in the grasp of guerrilla groups and right-wing paramilitaries, and as a consequence, this region has been historically inaccessible or risky for researchers. The new species is a diurnal forest dweller, similar to Pristimantis savagei and P. vilarsi. It is distinguished from its congeners by having finely shagreened dorsum skin, areolate ventral skin, moderate tympanic membrane size (length = 37.2–58.8% of eye length), long hind limbs (tibia length = 53.6–63.6% of snout–vent length), and an advertisement call composed of a short single note, while lacking ridges on scapula, tubercles on upper eyelid and heel, and basal webbing in toes. In addition to the new species described herein, we demonstrate that subarticular tubercles display more variation than what is commonly described in taxonomic studies of terraranan frogs.

A new nurse frog from Southwestern Amazonian highlands, with notes on the phylogenetic affinities of Allobates alessandroi (Aromobatidae)

ABSTRACT Few studies have focused on the diverse fauna of southwestern Brazilian Amazonia. This region, spared from large-scale human occupation until the second half of the twentieth century, has been threatened by expanding agriculture, logging, and mining. Here, we describe a new nurse frog (Allobates, Aromobatidae) from the open highland habitats of Serra dos Pacaás Novos, one of the few large remnants of relatively intact native vegetation in the Brazilian state of Rondônia. The new species is diagnosed by its metallic orange dorsal colouration, weakly expanded discs on hands, and presence of two subarticular tubercles on Finger IV. A phylogenetic analysis based on DNA sequence data recovered the new species as more closely related to nurse frogs from the Madeira and Tapajós River basins; this pattern may reflect a history of dispersal uphill from a lowland ancestor. Our results also indicate that the generic assignment of Allobates alessandroi (Grant and Rodriguez, 2001), a high-elevation species from the Andes of Peru, needs to be reassessed; we discuss the phylogenetic affinities of this species based on morphological attributes. http://www.zoobank.org/urn:lsid:zoobank.org:act:79131D82-B1B6-455D-AD9A-676D7E0783BC

Two New Species of Pristimantis (Amphibia: Anura: Strabomantidae) from Southwestern Colombia

We describe two new species of Pristimantis from southwestern Colombia. The first new species inhabits the humid Pacific slopes of the Cordillera Occidental, Valle del Cauca; it is most similar to three allopatric Ecuadorian species—P. eugeniae (Lynch and Duellman 1997), P. nyctophylax (Lynch 1976), and P. subsigillatus (Boulenger 1902). It is distinguished, however, by having subarticular tubercles beneath the joint between distal phalanges, basal webbing on outer edge of toe IV, papilla at the tip of snout, and uniform cream-brown coloration on the anterior surfaces of thighs and in the groin. The second new species inhabits the high mountains of the Cordillera Central, Cauca, and it is most similar to P. boulengeri (Lynch 1981) and two Peruvian species—P. deyiLehr et al. 2013 and P. schultei (Duellman 1990). However, it differs by having subarticular tubercles beneath the joint between distal phalanges, dorsal skin with low warts, papilla at the tip of snout, and by lacking tympanic membranes, dentigerous processes of the vomer, and vocal slits.

Description of a new species of Pseudophilautus (Amphibia: Rhacophoridae) from southern Sri Lanka

We describe a new Pseudophilautus species, P. conniffae sp. nov. from southern Sri Lanka. It was previously confused with Pseudophilautus rus (Manamendra-Arachchi & Pethiyagoda). The new species differs from the latter by the combination of the following characters: fourth toe webbing to penultimate subarticular tubercle on inner and outer sides (vs. fourth toe webbing in between penultimate and anetpenultimate subarticular tubercles on inner and outer sides), presence of conical median lingual process (vs. absent), and black patches on the posterior flank, anterior and posterior edges of the thigh (vs. black patches on the anterior surface of the thigh). Pseudophilautus conniffae sp. nov. may be sympatric with P. limbus (Manamendra-Arachchi & Pethiyagoda), which shares certain characters with the new species. The new species is, however, distinguished from P. limbus by the following characters: having supernumerary tubercles on manus (vs. lacking), absence of frontoparietal ridges (vs. presence), fourth toe webbing to penultimate subarticular tubercle on both sides (vs. fourth toe webbing between penultimate and anetpenultimate subarticular tubercle on both sides), third toe webbing to distal subarticular tubercle on both sides (vs. distal subarticular tubercle on outer side and below penultimate subarticular tubercle on inner side), and having the dorsum light brown with dark brown patches (vs. black and yellow variegated pattern on dorsum). The new species may be restricted to the southwestern wet zone of Sri Lanka. It is compared with all known Pseudophilautus species and also provided with a field key to identify it from those species that are sympatric with it or inhabit the southwestern wet zone.

A new species of Craugastor (Anura: Craugastoridae) from the montane rainforest of the Cordillera de Talamanca, Costa Rica

A new species of Craugastor (Anura: Craugastoridae) from the montane rainforest of the Cordillera de Talamanca, Costa Rica. A new dirt frog of the Craugastor podiciferus Species Group is described from Costa Rica; it is restricted to elevations between 2330 and 2700 m a.s.l. in the montane rainforest of the Cordillera de Talamanca. Analysis of DNA sequences of the mitochondrial 16S rRNA (16S) and cytochrome oxidase I (COI) genes reveals a distinct lineage within the C. podiciferus Species Group. Additional morphological and morphometric analyses support the distinctiveness of this lineage that is described as a new species herein. The species is distinguished from other members of the C. podiciferus Species Group by its unique coloration: a violet-brown to blackish brown venter with white pigment forming blotches, and dark brown palmar surfaces with prominent white folds between subarticular tubercles in the adults. The genetic divergence of the species from other members of the C. podiciferus Species Group is signifcant (higher than 9.2% in 16S and 13.3% in COI). Although not closely related, it resembles C. podiciferus morphologically, a species that also inhabits montane rainforest. The discovery of this new species highlights the importance of montane rainforest as a center of species richness and endemism.

A New Species ofFritzianaMello-Leitão 1937 (Amphibia: Anura: Hemiphractidae) from the Atlantic Forest, Brazil

Abstract We describe a new species of the genus Fritziana, historically identified as Fritziana fissilis or F. aff. fissilis. Using adult and tadpole morphology, as well as molecular analyses, we found the new species to be characterized by having the following traits: a mucronate snout tip, a black stripe on the wrist, round subarticular tubercles on the fingers and toes, a closed dorsal egg-pouch in females, tadpoles deposited in bromeliads, and a different mitochondrial transfer RNA gene order, when compared to the general orders already recognized for anurans. This new species occurs in the Atlantic Forest of Brazil, in the states of Sao Paulo, Parana, Santa Catarina, and Rio Grande do Sul, and has the largest geographic distribution recorded for a species of Fritziana.

Sticky tree frogs can also get a grip

A self-cleaning reusable adhesive that works in the wet and sticks to pretty much anything is the holy grail of many materials engineers, yet a charismatic group of frogs beat them to it when several families ascended into the trees to make their homes. They evolved sticky toe pads that never wear out, and Jon Barnes, from the University of Glasgow, UK, has been mesmerised by the minute amphibians since the early 1990s. Discovering that these frogs depend on a thin layer of fluid exuded from the toes for attachment to smooth surfaces and that they detach their feet by peeling them away, Barnes has also learned that repeated use self-cleans the toes to keep them in tip-top condition. However, many other species are equally adept at scaling heights without the benefits of adhesives. ‘We wanted to find out whether tree frogs could also use gripping forces’, says Barnes, who was curious to find out how the diameter of the structures that the amphibians ascend affects their ability to get a grip.Teaming up with Iain Hill from Glasgow and visitors from the Nanjing University of Aeronautics and Astronautics, China – Benzheng Dong and Aihong Ji – Barnes tested how well White's tree frogs (Litoria caerulea) and Cuban tree frogs (Osteopilus septentrionalis) coped when climbing Perspex cylinders ranging in diameter from simulated stout branches (120 cm), which were too wide for the frogs to encircle with their legs, to medium branches (44 mm), which the frogs could span with their forelimbs, and thick twigs (13 mm), which they could wrap their toes around. ‘Both [species] are excellent climbers’, says Barnes, who recalls that the Cuban tree frogs trotted up the narrowest cylinder at average speeds around 14 cm s−1, while ascending the medium curved cylinder at sprightly walks of around 13 cm s−1 and walking up the broadest cylinders at more sedate speeds of 12 cm s−1.However, the frogs struggled when the team coated the Perspex cylinders with sandpaper to force them to rely on grip alone. Neither of the two species was able to grip on to the broadest cylinder: ‘Basically, they would try to cling to the surface and immediately fall into our hands’, recalls Barnes. Although both species only managed to scale the medium cylinder on four occasions, they were always able to grasp on to the narrowest cylinder by wrapping their toes around it to ascend with ease.Barnes, Hill and Thomas Endlein then analysed how the frogs used the adhesive structures on their feet to stick to the smooth surfaces, and were impressed to see that the tiny climbers were increasingly using the subarticular tubercles, adhesive structures that are found on the toes, as the curvature of the cylinders increased. Explaining that the subarticular tubercles rarely contribute to adhesion when the frogs ascend flat plates of glass, the team was impressed to see that they contributed increasingly as the cylinders became more curved, contributing up to 57% of the footprint area on the medium-sized cylinder in contrast to 25% on the largest cylinder.So tree frogs can use a combination of strategies when manoeuvring through their complex arboreal homes, using adhesive structures on their feet to cling on to smoother structures, gripping with their flexible toes when the surface is too rough and using a combination of the two on smooth slender structures. ‘The way they climb in response to changes in both surface texture and diameter demonstrates just how adaptable they are to the challenges they face’, says Barnes, who is keen to build a generation of versatile climbing robots that ascend as nimbly as tree frogs.

The biomechanics of tree frogs climbing curved surfaces: a gripping problem.

The adhesive mechanisms of climbing animals have become an important research topic because of their biomimetic implications. We examined the climbing abilities of hylid tree frogs on vertical cylinders of differing diameter and surface roughness to investigate the relative roles of adduction forces (gripping) and adhesion. Tree frogs adhere using their toe pads and subarticular tubercles, the adhesive joint being fluid-filled. Our hypothesis was that on an effectively flat surface (adduction forces on the largest 120 mm diameter cylinder were insufficient to allow climbing), adhesion would effectively be the only means by which tree frogs could climb, but on the 44 and 13 mm diameter cylinders, frogs could additionally utilise adduction forces by gripping the cylinder either with their limbs outstretched or by grasping around the cylinder with their digits, respectively. The frogs' performance would also depend on whether the surfaces were smooth (easy to adhere to) or rough (relatively non-adhesive). Our findings showed that climbing performance was highest on the narrowest smooth cylinder. Frogs climbed faster, frequently using a 'walking trot' gait rather than the 'lateral sequence walk' used on other cylinders. Using an optical technique to visualise substrate contact during climbing on smooth surfaces, we also observed an increasing engagement of the subarticular tubercles on the narrower cylinders. Finally, on the rough substrate, frogs were unable to climb the largest diameter cylinder, but were able to climb the narrowest one slowly. These results support our hypotheses and have relevance for the design of climbing robots.