Anuran Families Research Articles

Phylogeny, historical biogeography and climate niche differentiation in extant species of Ceratophryidae (Anura, Hyloidea) frogs in South America

Ceratophryidae is a family of frogs containing twelve extant species distributed in South America. Several studies have been carried out concerning the systematics, morphology, karyotypes, and behaviour within this monophyletic family. However, little is known about the historical biogeography and the divergence in time of this group. Here, we present an updated phylogeny, along with a calibrated chronogram, to analyse the historical biogeographical pattern and climate niche differentiation among extant species of Ceratophryidae (Anura: Hyloidea) frogs in South America. A phylogeny based on morphological and genetic data was obtained from 256 morphological characters, six mitochondrial and eight nuclear genes for up to a total of 8428 characters in the homological matrix. Our results indicate that the genus Ceratophrys is sister to the clade Chacophrys + Lepidobatrachus. The divergence of the crown group of Ceratophryidae is estimated to have occurred 19.2 Ma at the beginning of the Miocene, with recent cladogenetic events related to the late Miocene (10.18–13.70 Ma) and the Pliocene (~5.3–2.6 Ma). Moreover, the Cerrado region is estimated to be the ancestral area of the family, as well for the genera Chacophrys and Lepidobatrachus. In addition, temperature seasonality and annual precipitation play a major role in the niche differentiation of extant species within Ceratophryidae. In conclusion, our data suggest multiple dispersal and vicariance events originating from the Cerrado region in the early Miocene, and recognize the role of the environment in the differentiation of the ecological niches among extant species of this family in South America. Ceratophryidae is hypothesized to have originated in the semi-arid Cerrado region in the early Miocene (~19.2 million years ago), from where species have diversified by independent dispersal and vicariance events across other South American regions. Ceratophrys frogs are phylogenetically recovered as the sister taxon to the clade comprising Chacophrys and Lepidobatrachus. Three lineages of Lepidobatrachus and four lineages from Ceratophrys diverged in the Pliocene, around 5.3 to 2.6 million years ago. Niche differentiation among extant species of Ceratophryidae appears to reflect roles for temperature seasonality and annual precipitation.

Evolutionary relationships in the African frog family Ptychadenidae, including the first molecular analysis, range extension, and distribution modelling of the monotypic genus Lanzarana

ABSTRACT The family Ptychadenidae contains three ecologically and morphologically distinct genera: the widespread, species-rich and above-ground dwelling Ptychadena, the less widespread and diverse, burrowing Hildebrandtia, and the little-known, burrowing, monotypic Lanzarana, endemic to Somalia. Previous morphological studies placed Lanzarana in a sister position to Hildebrandtia and these two genera as sister to Ptychadena. However, our analyses of mitochondrial and multilocus nuclear DNA data revealed Lanzarana as a sister lineage to Ptychadena (divergence ∼28 Mya), and Hildebrandtia sister to them (∼42 Mya). This suggests that the common ancestor of ptychadenids may have exhibited a burrowing lifestyle similar to Hildebrandtia and Lanzarana, rather than the more active, above-ground lifestyle of Ptychadena. In addition, based upon analysis of available mitochondrial DNA data, we have identified major clades within the genus Ptychadena and propose them as four species groups, with the P. mascareniensis group being the first diverging lineage (∼20 Mya). We also report four new localities of Lanzarana largeni from central Somaliland, south-western Puntland, southern Somalia and south-eastern Ethiopia, extending the presently known range of the species westward. This represents the first official record of L. largeni from Ethiopia. An ecological niche model of L. largeni for present climatic conditions identifies extensive climatically highly suitable areas in central Somalia and south-eastern Ethiopia. A model for future climatic conditions estimates a substantial extension of climatically suitable areas to northern Somalia and north-eastern Kenya, likely due to predicted more humid conditions accompanying the increase of temperatures in the western Indian Ocean.

Musculoskeletal and tendinous details of selected anomalies in the locomotor system of anurans.

Previous studies on anuran anomalies predominantly examine isolated cases or focus on external and skeletal features. Our study analyzes a comprehensive sample collected from 1991 to 2017, examining the muscle-tendon system in 24 anuran species across adult, juvenile, and metamorphic stages. This extensive sample size allows us to investigate consistent anomaly patterns across different developmental stages and anuran families, exploring potential common developmental or genetic factors. Our detailed anatomical examination, encompassing musculature, tendons, and skeletal structures, revealed that 21% of the specimens displayed anomalies, a noteworthy finding considering the extensive sample size and duration of the studied sample. Of these anomalies, 17% affected the locomotor system, predominantly in the upper limbs. Key anomalies included, forelimbs and hindlimbs brachydactyly, rotation in forelimbs, partial kyphotic lordosis, and scoliosis. Notably, the digit 4 in the forelimbs and digits 4 and 5 in the hindlimbs were particularly susceptible to teratogenic effects, indicating possible prolonged exposure during development. Our study also uncovered combinations of anomalies and identified a phenotype similar to Poland syndrome. The findings validate the "Logic of Monsters" (LoMo theory) by Alberch, although the name itself may not be deemed appropriate, showing that developmental disruptions in tetrapods are not random but follow distinct sequences and patterns. The name, while unfortunate, accurately reflects the unusual nature of these developmental anomalies. This contributes to the evolving "Evo-Devo-Path" framework, highlighting the study's importance in understanding developmental disruptions in tetrapods.

Species- and sex-specific chemical composition from an internal gland-like tissue of an African frog family.

Intraspecific chemical communication in frogs is understudied and the few published cases are limited to externally visible and male-specific breeding glands. Frogs of the family Odontobatrachidae, a West African endemic complex of five morphologically cryptic species, have large, fatty gland-like strands along their lower mandible. We investigated the general anatomy of this gland-like strand and analysed its chemical composition. We found the strand to be present in males and females of all species. The strand varies in markedness, with well-developed strands usually found in reproductively active individuals. The strands are situated under particularly thin skin sections, the vocal sac in male frogs and a respective area in females. Gas-chromatography/mass spectrometry and multivariate analysis revealed that the strands contain sex- and species-specific chemical profiles, which are consistent across geographically distant populations. The profiles varied between reproductive and non-reproductive individuals. These results indicate that the mandibular strands in the Odontobatrachidae comprise a so far overlooked structure (potentially a gland) that most likely plays a role in the mating and/or breeding behaviour of the five Odontobatrachus species. Our results highlight the relevance of multimodal signalling in anurans, and indicate that chemical communication in frogs may not be restricted to sexually dimorphic, apparent skin glands.

Skin secretions of Leptodactylidae (Anura) and their potential applications.

The skin of anuran species is a protective barrier against predators and pathogens, showing also chemical defense by substances that represent a potential source for bioactive substances. This review describes the current chemical and biological knowledge from the skin secretions of Leptodactylidae species, one of the most diverse neotropical frog families. These skin secretions reveal a variety of substances such as amines (12), neuropeptides (16), and antimicrobial peptides (72). The amines include histamine and its methylated derivatives, tryptamine derivatives and quaternary amines. The peptides of Leptodactylidae species show molecular weight up to 3364 Da and ocellatins are the most reported. The peptides exhibit commonly glycine (G) or glycine-valine (GV) as C-terminal amino acids, and the most common N-terminal amino acids are glutamic acid (E), lysine (K), and valine (V). The substances from Leptodactylidae species have been evaluated against pathogenic microorganisms, particularly Escherichia coli and Staphylococcus aureus, and the most active peptides showed MIC of 1-15 µM. Furthermore, some compounds showed also pharmacological properties such as immunomodulation, treatment of degenerative diseases, anticancer, and antioxidant. Currently, only 9% of the species in this family have been properly studied, highlighting a large number of unstudied species such as an entire subfamily (Paratelmatobiinae). The ecological context, functions, and evolution of peptides and amines in this family are poorly understood and represent a large field for further exploration.

Relicts in the mist: Two new frog families, genera and species highlight the role of Pantepui as a biodiversity museum throughout the Cenozoic

The iconic mountains of the Pantepui biogeographical region host many early-diverging endemic animal and plant lineages, concurring with Conan Doyle’s novel about an ancient “Lost World”. While this is the case of several frog lineages, others appear to have more recent origins, adding to the controversy around the diversification processes in this region. Due to its remoteness, Pantepui is challenging for biological surveys, and only a glimpse of its biodiversity has been described, which hampers comprehensive evolutionary studies in many groups. During a recent expedition to the Neblina massif on the Brazil-Venezuela border, we sampled two new frog species that could not be assigned to any known genus. Here, we perform phylogenetic analyses of mitogenomic and nuclear loci to infer the evolutionary relationships of the new taxa and support their description. We find that both species represent single lineages deeply nested within Brachycephaloidea, a major Neotropical clade of direct-developing frogs. Both species diverged >45 Ma from their closest relatives: the first is sister to all other Brachycephaloidea except for Ceuthomantis, another Pantepui endemic, and the second is sister to Brachycephalidae, endemic to the Brazilian Atlantic Forest. In addition to these considerable phylogenetic and biogeographic divergences, external morphology and osteological features support the proposition of two new family and genus-level taxa to accommodate these new branches of the amphibian tree of life. These findings add to other recently described ancient vertebrate lineages from the Neblina massif, providing a bewildering reminder that our perception of the Pantepui’s biodiversity remains vastly incomplete. It also provides insights into how these mountains acted as “museums” during the diversification of Brachycephaloidea and of Neotropical biotas more broadly, in line with the influential “Plateau theory”. Finally, these discoveries point at the yet unknown branches of the tree of life that may go extinct, due to global climate change and zoonotic diseases, before we even learn about their existence, amphibians living at higher elevations being particularly at risk.

The radiation continuum and the evolution of frog diversity

Most of life’s vast diversity of species and phenotypes is often attributed to adaptive radiation. Yet its contribution to species and phenotypic diversity of a major group has not been examined. Two key questions remain unresolved. First, what proportion of clades show macroevolutionary dynamics similar to adaptive radiations? Second, what proportion of overall species richness and phenotypic diversity do these adaptive-radiation-like clades contain? We address these questions with phylogenetic and morphological data for 1226 frog species across 43 families (which represent >99% of all species). Less than half of frog families resembled adaptive radiations (with rapid diversification and morphological evolution). Yet, these adaptive-radiation-like clades encompassed ~75% of both morphological and species diversity, despite rapid rates in other clades (e.g., non-adaptive radiations). Overall, we support the importance of adaptive-radiation-like evolution for explaining diversity patterns and provide a framework for characterizing macroevolutionary dynamics and diversity patterns in other groups.

First Eocene–Miocene anuran fossils from Peruvian Amazonia: insights into neotropical frog evolution and diversity

AbstractAnurans are one of the most diverse vertebrate groups, particularly in Amazonia, where species richness exceeds that of anywhere else. Amazonian frogs belong to three main lineages (Hyloidea, Microhylidae and Pipidae), each of which diversified during the Cenozoic. However, due to the virtual absence of an anuran fossil record in that area, the evolutionary history of modern lineages has so far remained accessible only via molecular data. In recent decades, a series of field campaigns in Peruvian Amazonia led to the discovery of an unparalleled set of anuran bone fragments, scattered across different sites spanning the Eocene–Miocene time interval. Here, we describe these first Palaeogene and early Neogene anurans from Peru with a focus on humeral and ilial morphology, identifying five humeral and five ilial morphotypes. Humeral morphotypes suggest the presence of different lineages of Brachycephaloidea in Peruvian fossil assemblages, whereas ilial morphotypes suggest the presence of Leptodactylidae, although leptodactylid‐like ilia also occur in some extant brachycephaloids. Pipids were also identified based on both humeral and ilial fragments. This study fills a major temporal and geographical gap in the evolutionary history of South American anurans, while further uncovering a lack of knowledge in the skeletal morphology of extant anuran families, as well as their inter‐ and intra‐species variability.

A new anuran family from the fossil sites of Langebaanweg and Cooper’s Cave, South Africa

ABSTRACT Enigmatic frog ilia were recovered from two geographically and temporally disparate fossil sites in South Africa, namely the Early Pliocene (5.1 Ma) fossil site of Langebaanweg (south-western Cape), and Cooper’s Cave D (Northern province), which dates to around 1.38 Ma. The fossil ilia appear to represent an extinct anuran genus that subsisted in southern Africa over several million years, had a previously undocumented mode of locomotion, and possibly exceptional jumping ability. Relative to extant anurans, the fossil ilia show a unique suite of characteristics pertaining to the acetabulum, dorsal protuberance, ventral ridge of the shaft, and dorsal crest; features which would have facilitated and stabilised jumping.

Tissue-specific in vivo transformation of plasmid DNA in Neotropical tadpoles using electroporation.

Electroporation is an increasingly common technique used for exogenous gene expression in live animals, but protocols are largely limited to traditional laboratory organisms. The goal of this protocol is to test in vivo electroporation techniques in a diverse array of tadpole species. We explore electroporation efficiency in tissue-specific cells of five species from across three families of tropical frogs: poison frogs (Dendrobatidae), cryptic forest/poison frogs (Aromobatidae), and glassfrogs (Centrolenidae). These species are well known for their diverse social behaviors and intriguing physiologies that coordinate chemical defenses, aposematism, and/or tissue transparency. Specifically, we examine the effects of electrical pulse and injection parameters on species- and tissue-specific transfection of plasmid DNA in tadpoles. After electroporation of a plasmid encoding green fluorescent protein (GFP), we found strong GFP fluorescence within brain and muscle cells that increased with the amount of DNA injected and electrical pulse number. We discuss species-related challenges, troubleshooting, and outline ideas for improvement. Extending in vivo electroporation to non-model amphibian species could provide new opportunities for exploring topics in genetics, behavior, and organismal biology.

Locomotor, ecological and phylogenetic drivers of skeletal proportions in frogs.

Frogs exhibit complex anatomical features of the pelvis, limbs and spine, long assumed to represent specialisations for jumping. Yet frogs employ a wide range of locomotor modes, with several taxa featuring primary locomotor modes other than jumping. Using a combination of techniques (CT imaging and 3D visualization, morphometrics, phylogenetic mapping), this study aims to determine the link between skeletal anatomy and locomotor style, habitat type and phylogenetic history, shedding new light on how functional demands impact morphology. Body and limb measurements for 164 taxa from all the recognised anuran families are extracted from digitally segmented CT scans of whole frog skeletons and analysed using various statistical techniques. We find that the expansion of the sacral diapophyses is the most important variable for predicting locomotor mode, which was more closely correlated with frog morphology than either habitat type or phylogenetic relationships. Predictive analyses suggest that skeletal morphology is a useful indicator of jumping but less so for other locomotor modes, suggesting that there is a wide range of anatomical solutions to performing locomotor styles such as swimming, burrowing or walking.

Five new species of the pelodryadid genus Litoria Tschudi from the southern versant of Papua New Guinea’s Central Cordillera, with observations on the diversification of reproductive strategies in Melanesian treefrogs

New Guinea has the most diverse insular frog fauna in the world, and rates of species discovery and description have increased rapidly in the last two decades. Pelodryadid treefrogs are the second most diverse family of anurans on the island but their taxonomy, relationships, and especially ecology remain poorly documented. Based on differences in morphology, advertisement calls (where available) and phylogenetic analyses of a 787 base pair alignment from the mitochondrial ND4 gene and flanking tRNA, we describe five new species of small treefrogs from hill and lower montane forests in the high rainfall belt that straddles the southern versant of Papua New Guinea's Central Cordillera. Three of these species are known only from forest growing on karst substrates, adding to the growing number of herpetofauna species currently known only from the extensive karst habitats of Papua New Guinea's South-fold Mountains. We also describe the arboreal breeding strategies of two of the new species, and report obligate treehole (phytotelm) breeding in New Guinean frogs for the first time. The new phytotelm-breeding species has juveniles with colour and patterning that closely resemble bird droppings, suggesting defensive mimicry or masquerade. A preliminary phylogeny suggests that arboreal-breeding frogs do not form a monophyletic group and that arboreal breeding has evolved multiple times within the New Guinean pelodryadid radiation. A further striking feature of the phylogeny is poor support for most basal nodes in the most diverse radiation of Melanesian Pelodryadidae, suggesting rapid ecological diversification and speciation, potentially following colonisation from Australia and/or mountain uplift. These new taxa and observations highlight previously unrecognised ecological and reproductive diversity in the Melanesian Pelodryadidae.

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.

Purification and Biological Properties of Raniseptins-3 and -6, Two Antimicrobial Peptides from Boana raniceps (Cope, 1862) Skin Secretion.

The number of multidrug-resistant pathogenic microorganisms has been growing in recent years, most of which is due to the inappropriate use of the commercial antibiotics that are currently available. The dissemination of antimicrobial resistance represents a serious global public health problem. Thus, it is necessary to search for and develop new drugs that can act as antimicrobial agents. Antimicrobial peptides are a promising alternative for the development of new therapeutic drugs. Anurans' skin glands are a rich source of broad-spectrum antimicrobial compounds and hylids, a large and diverse family of tree frogs, are known as an important source of antimicrobial peptides. In the present study, two novel antimicrobial peptides, named Raniseptins-3 and -6, were isolated from Boana raniceps skin secretion and their structural and biological properties were evaluated. Raniseptins-3 and -6 are cationic, rich in hydrophobic residues, and adopt an α-helix conformation in the presence of SDS (35 mM). Both peptides are active against Gram-negative bacteria and Gram-positive pathogens, with low hemolytic activity at therapeutic concentrations. No activity was observed for yeasts, but the peptides are highly cytotoxic against B16F10 murine melanoma cells and NIH3T3 mouse fibroblast cells. None of the tested compounds showed improvement trends in the MTT and LDH parameters of MHV-3 infected cells at the concentrations tested.

Identification and determination of the absolute configuration of amorph-4-en-10β-ol, a cadinol-type sesquiterpene from the scent glands of the African reed frog Hyperolius cinnamomeoventris.

Hyperolid reed frogs are one of the few families of Anurans known to possess glands that emit volatile compounds used in chemical communication. Hyperolius cinnamomeoventris, a model species, possesses a gular gland on its vocal sac that emits chemicals, and sends visual and auditory signals during calling. Previous investigations have shown that the glandular compounds are typically macrocyclic lactones. However, in this work, we show that another major constituent of the male specific gland is (10R,1S,6R,7R,10R)-amorph-4-ene-10β-ol [(1R,4R,4aR,8aS)-4-isopropyl-1,6-dimethyl-1,2,3,4,4a,7,8,8a-octahydronaphthalen-1-ol]. This compound was synthesized for the first time and has the opposite configuration to amorph-4-ene-10β-ol known from plants. A short synthesis using an organocatalytic approach through a tandem Mannich/intramolecular Diels-Alder reaction led to a mixture of cadinols, which was used for the assignment of the natural cadinol structures and their stereoisomers.

Body Size Estimation in Toads (Anura: Bufonidae): Applicability to the Fossil Record

Organisms’ body size is an important biological trait that is related to the environment and constrained by physiology. It is also one of few biological characteristics that can be inferred from fossil specimens. Variation in body size both within and across fossil communities can provide insight into their response to past climatic events, as well as morphological or ecological evolution in specific taxa. Among vertebrates, frogs and toads (Anura) are of particular interest given their sensitivity to environmental variation. Here, we propose a method for estimating body size in toads, one of the most ecologically and taxonomically diverse frog families (Bufonidae) that is cosmopolitan in distribution and contains aquatic, terrestrial, arboreal, and fossorial species. We used computed tomography scans (CT-scans) of 36 living species of toads to digitally segment five bones that are frequently found as fossil (ilium, sacrum, urostyle, humerus, and radioulna). We took nine different measurements on those bones to be used as proxies for body size and for each specimen collected a measurement of body size, snout–urostyle length (SUL). We used ordinary least square regression analysis (OLS) with 95% confidence and prediction intervals to determine if those measurements are useful to estimate body size from isolated bones and in the fossil record. Our regression analyses indicate that these measurements can serve as proxies to estimate body size in bufonids (with coefficients of determination between 0.80–0.95). The measurements with the highest coefficient of determinations are those of the ilium and humeri, both of which are abundant in the fossil record and taxonomically informative. Last, we tested our method on examples of living and fossils toads of North and South America. Our method is the first quantitative approach to estimate size in toads based on isolated bones and enables us to continue to explore the correlation between size and ecology in toads in the past.

Hematologic variables of free-living Leptodactylus luctator with and without hemoparasites and thrombidiform mites in southern Brazil.

It has been suggested that anuran amphibian parasites can cause clinical signs in situations of environmental imbalance. In the family Leptodactylidae, information about hematology is scarce, although these are well-known tools for the diagnosis and prognosis in clinical practice and potential bioindicators of environmental stress. The objective of this study is to describe Leptodactylus luctator hematology, to report the occurrence of hemoparasites and thrombidiform mites, and to compare the hematological variables under the presence and absence of these organisms. Ectoparasites and heparinized blood samples from 40 free-living specimens of L. luctator were collected for analysis. Hematologic variables and total plasma protein were compared between groups with and without hemoparasites and intradermal mites. As results, structures compatible with hemogregarines, Lankesterella sp., five morphotypes of Trypanosoma spp., microfilaria, Aegyptianella sp., an unidentified intraleukocytic hemoparasite, and frog erythrocytic virus (FEV) inclusion bodies were identified in the blood samples, besides Hannemania spp. intradermal mites. The hemoparasite occurrence was higher than previously reported in other anuran families and locations. Also, L. luctator has smaller red blood cells (RBCs) and white blood cells (WBCs), and a hyposegmentation of the neutrophil nucleus, when compared to many other amphibians. White blood cell, neutrophil, and monocyte counts were higher in animals parasitized by mites. There was no correlation between the number of parasitized RBCs and hematologic variables. This study provides anuran hematologic information, in addition to indicating a host reaction to infestation by Hannemania spp. mites, besides constituting the first record of the distribution of hemoparasites and intradermal mites in L. luctator of the study region.

Factors influencing fine-scale occupancy and detectability of an insular Atlantic Forest frog

Context Species of the tropical frog Family Hylodidae tend to be restricted to streams and, hence, have a small occupancy area. Hylodes fredi (Canedo and Pombal 2007), a diurnal stream-dwelling species endemic to the Atlantic Forest in Ilha Grande, south-eastern Brazil, is one such species. Because of scarce population studies, it is also categorised as Data Deficient (DD) in the IUCN Red List. Previous studies on the habitat use by this species did not account for imperfect detection, which could have led to biased results. Aims We aimed to systematically describe the microhabitats occupied by H. fredi, by generating a fine-scale occupancy model while accounting for imperfect detection. Methods We sampled six streams where the species is known to occur. Perpendicular transects were established in each stream and further subdivided into 10 sampling plots. Single-species and single-season occupancy models were created with the UNMARKED R package, and model selection was performed on the basis of the Akaike information criterion. Key results We observed the species in 70 of the 275 sampled sites, which resulted in a naïve occupancy of 0.28 and detectability of 0.25. The best models suggest that H. fredi occupancy increases positively with rock cover and inversely with leaf-litter cover. Detectability reduced with an increase in leaf litter cover and varied with the air temperature. Conclusions We conclude that H. fredi occupancy is affected by the presence of rock and leaf-litter cover. The data indicated that the species is restricted to the stream channel and does not seem to occupy forested areas that are distanced from the stream margins. Implications Considering that H. fredi and many other congeneric species are listed as ‘Data Deficient’ in the IUCN Red List, it is important to define a threat category so as to conserve them. Many stream-associated species tend to have their occupancy overestimated, leading to an underestimation of their threat risk. This study systematically demonstrated that H. fredi has a strict and reduced occupancy, mostly limited to the stream margins, that should be considered when determining conservation efforts for this and ecologically similar species.

Environment rather than character displacement explains call evolution in glassfrogs.

The acoustic adaptation hypothesis (AAH) and ecological character displacement (ECD) are two potential mechanisms shaping call evolution that can predict opposite trends for the differentiation of signals. Under AAH, signals evolve to minimize environmental degradation and maximize detection against background noise, predicting call homogenization in similar habitats due to environmental constraints on signals. In contrast, ECD predicts greater differences in call traits of closely related taxa in sympatry because of selection against acoustic interference. We used comparative phylogenetic analyses to test the strength of these two selective mechanisms on the evolution of advertisement calls in glassfrogs, a highly diverse family of neotropical anurans. We found that, overall, acoustic adaptation to the environment may outweigh effects of species interactions. As expected under the AAH, temporal call parameters are correlated with vegetation density, but spectral call parameters had an unexpected inverse correlation with vegetation density, as well as an unexpected correlation with temperature. We detected call convergence among co-occurring species and also across multiple populations from the same species in different glassfrogs communities. Our results indicate that call convergence is common in glassfrogs, likely due to habitat filtering, while character displacement is relatively rare, suggesting that costs of signal similarity among related species may not drive divergent selection in all systems.

Melanesia holds the world’s most diverse and intact insular amphibian fauna

Identifying hotspots of biological diversity is a key step in conservation prioritisation. Melanesia—centred on the vast island of New Guinea—is increasingly recognised for its exceptionally species-rich and endemic biota. Here we show that Melanesia has the world’s most diverse insular amphibian fauna, with over 7% of recognised global frog species in less than 0.7% of the world’s land area, and over 97% of species endemic. We further estimate that nearly 200 additional candidate species have been discovered but remain unnamed, pointing to a total fauna in excess of 700 species. Nearly 60% of the Melanesian frog fauna is in a lineage of direct-developing microhylids characterised by smaller distributions than co-occurring frog families, suggesting lineage-specific high beta diversity is a key driver of Melanesian anuran megadiversity. A comprehensive conservation status assessment further highlights geographic concentrations of recently described range-restricted threatened taxa that warrant urgent conservation actions. Nonetheless, by world standards, the Melanesian frog fauna is relatively intact, with 6% of assessed species listed as threatened and no documented extinctions; and thus it provides an unparalleled opportunity to understand and conserve a megadiverse and relatively intact insular biota.