Widely used, short 16S rRNA mitochondrial gene fragments yield poor and erratic results in phylogenetic estimation and species delimitation of amphibians

High speciation in the cryptic Pristimantis celator clade (Anura: Strabomantidae) of the Mira river basin, Ecuador-Colombia

Over the past decade, research in the montane forests of the Mira River basin, spanning Ecuador and Colombia, has identified it as crucial for the adaptive radiation of flora and fauna, shaped by its complex geological and climatic history. This study focuses on the phylogenetic and systematic revision of a frog clade initially labeled as Pristimantis verecundus, revealing significant cryptic diversity. Through detailed analyses of type material and expanded molecular sampling, we found that the original description actually included specimens representing two additional species, which are described herein. In this work, we discovered and formally described four new species within montane forests at elevations from 1,600 to 2,300 meters. Genetic distances of 3.34% to 14% and clear morphological differences underscore the clade's hidden diversity. We propose renaming the group Pristimantis celator clade within Pristimantis myersi species group and subgenus Trachyphrynus, aligning with phylogenetic evidence and resolving taxonomic ambiguities using the oldest available name, Pristimantis celator (Lynch, 1976). This reclassification includes 14 species, seven formally described, and seven as candidates, distributed across northwestern Ecuador and southwestern Colombia, particularly in Mira and Esmeraldas River basins. The study highlights the Andean orogeny's role in species diversification within Pristimantis celator clade, with geographic barriers like Cerro Golondrinas influencing genetic isolation. Genetic divergences exceeding 3.34% indicate evolutionary isolation across these landscapes. Our findings provide insights into montane ecosystem speciation, emphasizing vicariance, niche adaptation, and altitudinal gradients in shaping biodiversity. A polytomy among three well-supported clades within Pristimantis myersi species group is noted due to incomplete genetic data, yet distinctiveness and evolutionary relationships are affirmed. Cryptic diversity within Pristimantis celator clade links to unique orogenic and climatic conditions, highlighting conservation needs. Lastly, we provide a redescription of Pristimantis verecundus and species identification key to aid future research and conservation in this biogeographically influential region.

A multi-gene phylogeny of the Asian kukri snakes (Oligodon Fitzinger, 1826): Sharpening the blade of the second largest serpent radiation (Reptilia: Squamata: Colubridae)

With 90 recognized species, kukri snakes in the genus Oligodon Fitzinger constitute the second largest snake radiation in the world. Oligodon species are collectively distributed across the Asian continent and possess several ecological and morphological attributes that are unique amongst other snakes. Despite their high levels of species richness, evolutionary relationships within Oligodon are poorly understood due to a limited number of samples and genetic markers available in earlier phylogenies. In this study, we assembled the largest molecular dataset of Oligodon to date, which we use to assess the systematics and biogeography of the entire genus. Based on a combination of maximum likelihood and Bayesian phylogenies using fragments of three mitochondrial genes (12 s, 16 s, CytB) and three nuclear genes (Rag1, C-mos, BDNF), we identify eight deeply divergent clades within Oligodon, of which only two correspond with species groupings that were recognized by previous morphological classifications. Four species delimitation methods employed on the mitochondrial portion of the dataset resulted in dramatically divergent estimations of molecular operational taxonomic units (mOTUs). When combined, all four methods support the existence of unrecognized species-level lineages, but also indicate that several other Oligodon species are poorly differentiated genetically and require additional integrative taxonomic research to properly resolve. Based on divergence dating, we demonstrate that Oligodon began to diversify during the early Neogene and hypothesize that the most recent common ancestor of the genus originated in mainland Southeast Asia. We conclude by recognizing eight phylogenetically defined species groups and identify sampling gaps that require further investigation once new data becomes available. This study contributes to a greater understanding of snake evolution on the Asian continent and acts as a baseline for future studies of this speciose genus.

The small and inconspicuous majority: Revealing the megadiversity and historical biogeography of the Pristimantis unistrigatus species group (Anura, Strabomantidae)

With more than 600 recognized species, the genus Pristimantis is already the most diverse among vertebrates, but described species only represent a fraction of the actual diversity in this clade. This genus is widely distributed throughout the Neotropics and represents an interesting model for biogeographic studies because Pristimantis spp. are direct developing and generally have narrow ecological niches and low dispersal abilities. The P. unistrigatus species group is one of the most important components in the genus (ca. 200 recognized species) and has been supported by morphological but not by molecular evidence. We assessed the species boundaries and distribution in the P. unistrigatus species group and infer spatiotemporal patterns of diversification related to historical landscape changes in the Neotropics. We gathered three mitochondrial, and two nuclear DNA loci from 416 specimens throughout the range of the group, and including 68 nominal species. We redefine the group based on the obtained phylogeny and found 151 candidate species that composes it, with 83 of these remaining undescribed. We recovered 11 major clades within the group that diverged before 13 Ma. The diversification of the group started during the early Miocene most likely in northwestern South America, currently corresponding to western Amazonia and northern Andes. The other neotropical areas subsequently acted as sinks, receiving lineages mostly during the last 10 Ma, after the demise of the Pebas System and the setup of the modern Amazonian hydrographic system.

A new species of frog of the genus Noblella Barbour, 1930 (Amphibia: Strabomantidae) from the Cordillera del Cóndor, Ecuador

We describe a new species of leaflitter frog of the genus Noblella from southern Ecuador, province of Zamora Chinchipe. The new species is diagnosed from all its congeners by having one or two tubercles on the upper eyelids; distal phalanges strongly T-shaped; phalangeal formula on hands 2-2-3-3; phalangeal formula on feet 2-2-3-4-3; heel with a small subconical tubercle; disc on all toes with papillae; dorsum brown or brown with gray, with V-shaped inverted or scattered irregular darker marks. We include a detailed description of its osteology and a study of its phylogenetic relationships. Finally, we evaluate its conservation status and discuss the threats that are currently impacting at the type locality.

A new species of Dainty Frog (Anura: Pyxicephalidae: Cacosternum) and the first endemic anuran to the Cederberg region of South Africa

Within the genus Cacosternum, the species C. capense and C. namaquense form a clade defined by their robust morphology, large size, and distinct dorsolateral glands. In this study, we describe a third member of the group endemic to the Cederberg region of South Africa. Specimens from this area have historically been assigned to C. karooicum, but here we show that this population is genetically unrelated. Using a combination of molecular, morphological, and acoustic data, we provide evidence to show that the Cederberg population of C. karooicum represents an undescribed species within the C. capense group. The new species can be diagnosed from its closest phylogenetic relatives, C. capense and C. namaquense, by the absence of a dark streak running downwards from the pupil into the iris, the presence of large rictal glands that form an uninterrupted arc with the angle of the jaw, heart-shaped palmar tubercles, and an advertisement call with a dominant frequency below 2 kHz. We further discuss their natural history, distribution, and conservation.

Analysis of the Mitochondrial COI Gene and Genetic Diversity of Endangered Goose Breeds

The mitochondrial cytochrome c oxidase subunit I (COI) genes of six endangered goose breeds (Xupu, Yangjiang, Yan, Wuzong, Baizi, and Lingxian) were sequenced and compared to assess the genetic diversity of endangered goose breeds. By constructing phylogenetic trees and evolutionary maps of genetic relationships, the affinities and degrees of genetic variations among the six different breeds were revealed. A total of 92 polymorphic sites were detected in the 741 bp sequence of the mtDNA COI gene after shear correction, and the GC content of the processed sequence (51.11%) was higher than that of the AT content (48.89%). The polymorphic loci within the populations of five of the six breeds (Xupu, Yangjiang, Yan, Baizi, and Lingxian) were more than 10, the haplotype diversity > 0.5, and the nucleotide diversity (Pi) > 0.005, with the Baizi geese being the exception. A total of 35 haplotypes were detected based on nucleotide variation among sequences, and the goose breed haplotypes showed a central star-shaped dispersion; the FST values were -0.03781 to 0.02645, The greatest genetic differentiation (FST = 0.02645) was observed in Yan and Wuzong breeds. The most frequent genetic exchange (Nm > 15.00) was between the Wuzong and Yangjiang geese. An analysis of molecular variance showed that the population genetic variation mainly came from within the population; the base mismatch differential distribution analysis of the goose breeds and the Tajima's D and Fu's Fs neutral detection of the historical occurrence dynamics of their populations were negative (p > 0.10). The distribution curve of the base mismatches showed a multimodal peak, which indicated that the population tended to be stabilised. These results provide important genetic information for the conservation and management of endangered goose breeds and a scientific basis for the development of effective conservation strategies.

Head in the clouds: two new microendemic tepui-summit species of Stefania (Anura: Hemiphractidae)

In addition to the type locality (the summit of Aprada-tepui, Bolívar State of Venezuela), the distribution of the egg-brooding frog Stefania satelles was long thought to include several isolated tabletop mountain (tepui) summits surrounding the large Chimantá Massif in Bolívar State (hence the Latin name "satelles"). However, multilocus molecular phylogenetic analyses have revealed that this taxon includes several undescribed morphologically cryptic species, and that S. satelles should be restricted to its type locality. Two tepui-summit species confused under that name in the literature remain to be named, and the present paper aims at describing these populations previously referred to as Stefania sp. 3 and S. sp. 5. Stefania sp. 3 is only known from the small summit of Angasima-tepui, while S. sp. 5 is only reported from the small summit of Upuigma-tepui, both mountains being located south of the Chimantá Massif. These new, phylogenetically distinct species are described based on external morphology and osteology and in comparison to close relatives in the S. ginesi clade, which consists exclusively of tepui summit species. Both new species have highly restricted geographic ranges (less than 3 km2) and should be listed as Critically Endangered according to IUCN criteria.

The efficacy of single mitochondrial genes at reconciling the complete mitogenome phylogeny-a case study on dwarf chameleons

Although genome-scale data generation is becoming more tractable for phylogenetics, there are large quantities of single gene fragment data in public repositories and such data are still being generated. We therefore investigated whether single mitochondrial genes are suitable proxies for phylogenetic reconstruction as compared to the application of full mitogenomes. With near complete taxon sampling for the southern African dwarf chameleons (Bradypodion), we estimated and compared phylogenies for the complete mitogenome with topologies generated from individual mitochondrial genes and various combinations of these genes. Our results show that the topologies produced by single genes (ND2, ND4, ND5, COI, and COIII) were analogous to the complete mitogenome, suggesting that these genes may be reliable markers for generating mitochondrial phylogenies in lieu of generating entire mitogenomes. In contrast, the short fragment of 16S commonly used in herpetological systematics, produced a topology quite dissimilar to the complete mitogenome and its concatenation with ND2 weakened the resolution of ND2. We therefore recommend the avoidance of this 16S fragment in future phylogenetic work.

A new species of Amolops (Amphibia, Anura, Ranidae) from Guizhou Province, China

The Torrent frogs of the genus Amolops are widely distributed in Nepal and northern India eastwards to southern China and southwards to Malaysia. The genus currently contains 84 species. Previous studies indicated underestimated species diversity in the genus. In the context, a new species occurring from the mountains in the northwestern Guizhou Province, China is found and described based on morphological comparisons and molecular phylogenetic analyses, Amolopsdafangensissp. nov. Phylogenetic analyses based on DNA sequences of the mitochondrial 16S rRNA and COI genes supported the new species as an independent lineage. The uncorrected genetic distances between the 16S rRNA and COI genes in the new species and its closest congener were 0.7% and 2.6%, respectively, which are higher than or at the same level as those among many pairs of congeners. Morphologically, the new species can be distinguished from its congeners by a combination of the following characters: body size moderate (SVL 43.2-46.8 mm in males); head length larger than head width slightly; tympanum distinct, oval; vocal sacs absent; vomerine teeth present; dorsolateral folds weak formed by series of glands; nuptial pads present on the base of finger I; heels overlapping when thighs are positioned at right angles to the body; tibiotarsal articulation reaching the level far beyond the tip of the snout when leg stretched forward.

Description of a new Asian Leaf Litter Toad of the genus Leptobrachella Smith, 1925 (Anura, Megophryidae) from southern Guizhou Province, China

Background

The Asian leaf litter toads of the genus Leptobrachella Smith, 1925 (Anura, Megophryidae) inhabit the forest floor and rocky streams in hilly evergreen forests and are widely distributed from southern China, west to north-eastern India and Myanmar, through mainland Indochina to Peninsular Malaysia and the Island of Borneo.

New information

A new species of the Asian leaf litter toad genus Leptobrachella from Guizhou Province, China is described. Molecular phylogenetic analyses, based on mitochondrial 16S rRNA and COI genes and nuclear RAG1 gene sequences indicated that the new species is genetically divergent from its congeners. The new species could be distinguished from its congeners by a combination of the following characters: (1) body of medium size in males (SVL 31.9 - 32.9 mm); (2) distinct black spots present on flanks; (3) toes rudimentarily webbed, with wide lateral fringes; (4) skin on dorsum shagreened with fine tiny granules and short ridges; (5) heels overlapped when thighs are positioned at right angles to the body; (6) tibia-tarsal articulation reaching interior corner of the eye.A new species of the Asian leaf litter toad genus Leptobrachella from Guizhou Province, China is described. Molecular phylogenetic analyses, based on mitochondrial 16S rRNA and COI genes and nuclear RAG1 gene sequences indicated that the new species is genetically divergent from its congeners. The new species could be distinguished from its congeners by a combination of the following characters: (1) body of medium size in males (SVL 31.9 - 32.9 mm); (2) distinct black spots present on flanks; (3) toes rudimentarily webbed, with wide lateral fringes; (4) skin on dorsum shagreened with fine tiny granules and short ridges; (5) heels overlapped when thighs are positioned at right angles to the body; (6) tibia-tarsal articulation reaching interior corner of the eye.

Unexpected diversity and co-occurrence of phytotelmic frogs (Guibemantis) around Andasibe, one of the most intensively surveyed amphibian hotspots of Madagascar, and descriptions of three new species

The area around the Malagasy village of Andasibe, which includes Analamazaotra-Mantadia National Park as well as other protected areas, is characterized by very species-rich and well-studied communities of animals and plants, but new species are still regularly discovered. Three species of phytotelmic frogs of the subgenus Pandanusicola in the genus Guibemantis are known from this area, G. flavobrunneus, G. liber, and G. pulcher. Further Pandanusicola frogs from this area have been provisionally assigned to G. bicalcaratus or G. albolineatus, pending detailed taxonomic review. During preliminary exploration of the ecology of these specialized frogs that live and reproduce in the leaf axils of Pandanus screw pines, we noticed the syntopic presence of two differently colored and differently sized Pandanusicola in Andasibe that could not be unambiguously assigned to any known species. A genetic screening revealed that these correspond to yet two further species in the area. Based on our data, seven species of Pandanusicola occur in Andasibe and nearby forests: (1) G. liber, the only non-phytotelmic species of the subgenus in the region; (2) G. flavobrunneus which is the largest species and characterized by a diagnostic yellowish brown dorsal pattern; (3) G. pulcher, characterized by translucent-green color with purplish brown spotting not observed in any other species in the area; (4) G. methueni, a brownish species usually lacking contrasted dorsolateral bands that differs from the other species in the area by emitting a characteristic trill-like advertisement call series (rather than clicks or chirps) and according to our data is widespread along Madagascars east coast; as well as three new species: (5) G. ambakoana sp. nov., a brownish species, typically with contrasted incomplete light dorsolateral bands and with single click-like advertisement calls; (6) G. vakoa sp. nov., a species that is equally brownish but lacks contrasted light dorsolateral bands and that has single click-like advertisement calls of very short duration; and (7) G. rianasoa sp. nov., a species that is smaller sized and has less distinct femoral glands than all the others, and emits a short series of soft chirp-like advertisement calls. All these species are genetically highly distinct, with >5% uncorrected pairwise distances in the mitochondrial 16S rRNA gene, and lack of haplotype sharing in two nuclear-encoded genes. The co-occurrence of seven Pandanusicola frogs in a relatively small geographic area is unprecedented in Madagascar and calls for in-depth studies of a possible differentiation in habitat use and life history.

DNA Barcoding in Species Delimitation: From Genetic Distances to Integrative Taxonomy

Over the past two decades, DNA barcoding has become the most popular exploration approach in molecular taxonomy, whether for identification, discovery, delimitation, or description of species. The present contribution focuses on the utility of DNA barcoding for taxonomic research activities related to species delimitation, emphasizing the following aspects:(1) To what extent DNA barcoding can be a valuable ally for fundamental taxonomic research, (2) its methodological and theoretical limitations, (3) the conceptual background and practical use of pairwise distances between DNA barcode sequences in taxonomy, and (4) the different ways in which DNA barcoding can be combined with complementary means of investigation within a broader integrative framework. In this chapter, we recall and discuss the key conceptual advances that have led to the so-called renaissance of taxonomy, elaborate a detailed glossary for the terms specific to this discipline (see Glossary in Chap. 35 ), and propose a newly designed step-by-step species delimitation protocol starting from DNA barcode data that includes steps from the preliminary elaboration of an optimal sampling strategy to the final decision-making process which potentially leads to nomenclatural changes.

Distinguishing fanged frogs (Limnonectes) species (Amphibia: Anura: Dicroglossidae), from Thailand using high resolution melting analysis

Morphologically, species of fanged frogs (Limnonectes) are exceedingly similar, making it difficult to distinguish them within the complex. In Thailand, it has been difficult to distinguish between the sympatric species L. bannaensis and L. taylori, particularly among tadpoles, adolescents, and adult females. A precise identification contributes to a greater understanding of biodiversity, particularly for assessing distributions and population dynamics. Therefore, a novel approach is required. The objective of this study was to develop a high resolution melting analysis (HRM) for the rapid and accurate identification of six species of Limnonectes of the L. kuhlii complex found in Thailand, particularly the two sympatric fanged frogs. Here, HRM assays using 16S rRNA mitochondrial primers were designed and developed. There was as much as a 25.3% variation in the nucleotide sequence of the fragment amplified by HRM16S primers among the six species of Limnonectes. Prior to conducting an in vitro HRM, the DNA sequences were used in a simulation HRM, uMELT Quartz, to predict the melting curve for each species of Limnonectes. There were discrepancies between the predicted melting curves of each species generated by the programme. Consequently, in vitro HRM tests were conducted. The obtained melting curve and Tm values were consistent with those predicted, albeit with a slightly different Tm value and a more distinct melting curve. All evaluated species of Limnonectes could be easily distinguished from one another by comparing the melting curve shapes. The HRM assay was then used to confirm the species of 18 Limnonectes samples in comparison to the reference samples (confidence interval > 90%). In addition, the results of HRM were consistent with those of experts who used morphological analysis to identify species. The HRM was found to be useful, and therefore the method would also contribute to future ecological and systematic studies on the target species.

Genomic phylogeography illuminates deep cyto-nuclear discordances in midwife toads (Alytes)

The advent of genomic methods allows us to revisit the evolutionary history of organismal groups for which robust phylogenies are still lacking, particularly in species complexes that frequently hybridize. In this study, we conduct RAD-sequencing (RAD-seq) analyses of midwife toads (genus Alytes), an iconic group of western Mediterranean amphibians famous for their parental care behavior, but equally infamous for the difficulties to reconstruct their evolutionary history. Through admixture and phylogenetic analyses of thousands of loci, we provide the most comprehensive phylogeographic framework for the A. obstetricans complex to date, as well as the first fully resolved phylogeny for the entire genus. As part of this effort, we carefully explore the influence of different sampling schemes and data filtering thresholds on tree reconstruction, showing that several, slightly different, yet robust topologies may be retrieved with small datasets obtained by stringent SNP calling parameters, especially when admixed individuals are included. In contrast, analyses of incomplete but larger datasets converged on the same phylogeny, irrespective of the reconstruction method used or the proportion of missing data. The Alytes tree features three Miocene-diverged clades corresponding to the proposed subgenera Ammoryctis (A. cisternasii), Baleaphryne (A. maurus, A. dickhilleni and A. muletensis), and Alytes (A. obstetricans complex). The latter consists of six evolutionary lineages, grouped into three clades of Pliocene origin, and currently delimited as two species: (1) A. almogavarii almogavarii and A. a. inigoi; (2) A. obstetricans obstetricans and A. o. pertinax; (3) A. o. boscai and an undescribed taxon (A. o. cf. boscai). These results contradict the mitochondrial tree, due to past mitochondrial captures in A. a. almogavarii (central Pyrenees) and A. o. boscai (central Iberia) by A. obstetricans ancestors during the Pleistocene. Patterns of admixture between subspecies appear far more extensive than previously assumed from microsatellites, causing nomenclatural uncertainties, and even underlying the reticulate evolution of one taxon (A. o. pertinax). All Ammoryctis and Baleaphryne species form shallow clades, so their taxonomy should remain stable. Amid the prevalence of cyto-nuclear discordance among terrestrial vertebrates and the usual lack of resolution of conventional nuclear markers, our study advocates for phylogeography based on next-generation sequencing, but also encourages properly exploring parameter space and sampling schemes when building and analyzing genomic datasets.

Easternmost distribution of Bufo bufo (Linnaeus, 1758) in Türkiye: implications for the putative contact zone between B. bufo and B. verrucosissimus

The geographic range of a species is crucial for obtaining information on the exact distribution of the species. The geographic data are important for delimiting distinct species or exploring the degree of differentiation among different populations of a species. The local details of species boundaries facilitate the study of the importance of phylogeographic background, secondary contacts, and hybrid zones, along with the relations between the species and its extrinsic environmental factors. In the present study, the range boundaries of Bufo bufo and Bufo verrucosissimus in the north-eastern region of Türkiye were delineated using an integrative taxonomic approach that utilized a combination of molecular and morphological data. According to the mtDNA results of the present study, B. bufo inhabits a single distribution from İyidere town to Çayeli town in Rize, while B. verrucosissimus is distributed from Şavşat town of Artvin to Ardeşen town in Rize. In addition, the two species coexist in Pazar, Hemşin, and Çamlıhemşin towns in Rize. The demographic analyses indicated a distinct population expansion for the B. verrucosissimus species after the Last Glacial Maximum, while the same did not occur for B. bufo. The univariate and multivariate statistical analyses conducted for the morphological data of the two species corroborated the presence of a putative contact zone between B. bufo and B. verrucosissimus. In summary, the present study resolved the non-distinct geographic boundaries between B. bufo and B. verrucosissimus species and also revealed the easternmost distribution of B. bufo in Türkiye. In addition, important evidence on the putative contact zone between the two species was indicated using an integrative taxonomic approach.

Systematic position of the Clicking Frog (Kassinula Laurent, 1940), the problem of chimeric sequences and the revised classification of the family Hyperoliidae

The systematics of the African frog family Hyperoliidae has undergone turbulent changes in last decades. Representatives of several genera have not been genetically investigated or with only limited data, and their phylogenetic positions are thus still not reliably known. This is the case of the De Witte's Clicking Frog (Kassinula wittei) which belongs to a monotypic genus. This miniature frog occurs in a poorly studied region, southeastern Democratic Republic of the Congo, northern Zambia, Angola. So far it is not settled whether this genus belongs to the subfamily Kassininae as a relative of the genus Kassina, or to the subfamily Hyperoliinae as a relative of the genus Afrixalus. Here we present for the first time a multilocus phylogenetic reconstruction (using five nuclear and one mitochondrial marker) of the family Hyperoliidae, including Kassinula. We demonstrate with high confidence that Kassinula is a member of Hyperoliinae belonging to a clade also containing Afrixalus (sub-Saharan Africa), Heterixalus (Madagascar) and Tachycnemis (Seychelles). We find that Kassinula represents a divergent lineage (17-25 Mya), which supports its separate genus-level status, but its exact systematic position remains uncertain. We propose to name the clade to which the above four genera belong as the tribe Tachycnemini Channing, 1989. A new taxonomy of the family Hyperoliidae was recently proposed by Dubois et al. (2021: Megataxa 5, 1-738). We demonstrate here that the new taxonomy was based on a partially erroneous phylogenetic reconstruction resulting from a supermatrix analysis of chimeric DNA sequences combining data from two families, Hyperoliidae and Arthroleptidae (the case of Cryptothylax). We therefore correct the erroneous part and propose a new, revised suprageneric taxonomy of the family Hyperoliidae. We also emphasize the importance of inspecting individual genetic markers before their concatenation or coalescent-based tree reconstructions to avoid analyses of chimeric DNA sequences producing incorrect phylogenetic reconstructions. Especially when phylogenetic reconstructions are used to propose taxonomies and systematic classifications.