Does Clade Density Constrain Geographical Range Evolution?

The role of biotic interactions, such as interspecific competition, in driving geographical range evolution is still poorly understood. For instance, lineages distributed across regions with a large number of potential competitors might experience some level of geographical packing of their range limits, so that changes in their geographical distributions are hampered. Conversely, a large number of competitors could instead lead to accelerated rates of geographical range evolution, with lineages shifting their ranges to avoid competition. We recently introduced the concept of clade density (CD; the sum of the areas of overlap between a species and other members of its higher taxon, weighted by their phylogenetic distance) as a proxy of the potential for interspecific competition across the geographical distribution of a given species. In this study, we used a large dataset with 5936 terrestrial vertebrate species to test whether CD is significantly associated with variation in the rate of geographical range evolution using two alternative approaches. First, we tested if there is a significant relationship between CD and the geographical distance between sister species. In addition, we estimated tip rates of geographical range evolution and tested if they were consistently associated with variation in CD. We found no evidence for an effect of CD on geographical range evolution in either of the tested approaches, even after accounting for phylogenetic uncertainty. These results are inconsistent with equilibrial models of species diversification and suggest that interspecific competition might not play a pervasive role in geographical range evolution of terrestrial vertebrates.

Range size positively correlates with temperature and precipitation niche breadths but not with dietary niche breadth in triatomine insects, vectors of Chagas disease.

Ecological theory predicts that species that can utilise a greater diversity of resources and, therefore, have wider niche breadths should also occupy larger geographic areas (the 'niche breadth-range size hypothesis'). Here, we tested this hypothesis for a blood-sucking group of insects of medical significance: the Triatominae (aka 'kissing bugs') (Hemiptera: Reduviidae). Given that niches can be viewed from different perspectives, we tested this hypothesis based on both dietary and climatic niches. We assembled the most complete dataset of triatomine feeding patterns to date by reviewing 143 studies from the literature up to 2021 and tested whether the niche breadth-range size hypothesis held for this group for both dietary and climatic components of the niche. Temperature and precipitation niche breadths were estimated from macro-environmental variables, while diet breadth was calculated based on literature data that used PCR and/or ELISA to identify different types of hosts as blood sources per triatomine species. Our results showed that temperature and precipitation niche breadths, but not dietary breadth, were positively correlated with range sizes, independent of evolutionary history among species. These findings support the predictions from the range size-niche breadth hypothesis concerning climate but not diet, in Triatominae. It also shows that support for the niche breadth-range size hypothesis is dependent upon the niche axis under consideration, which can explain the mixed support for this hypothesis in the ecological literature.

Wall-following - Phylogenetic context of an enhanced behaviour in stygomorphic Sinocyclocheilus (Cypriniformes: Cyprinidae) cavefishes.

With 75 known species, the freshwater fish genus Sinocyclocheilus is the largest cavefish radiation in the world and shows multiple adaptations for cave-dwelling (stygomorphic adaptations), which include a range of traits such as eye degeneration (normal-eyed, micro-eyed and eyeless), depigmentation of skin, and in some species, the presence of "horns". Their behavioural adaptations to subterranean environments, however, are poorly understood. Wall-following (WF) behaviour, where an organism remains in close contact with the boundary demarcating its habitat when in the dark, is a peculiar behaviour observed in a wide range of animals and is enhanced in cave dwellers. Hence, we hypothesise that wall-following is also present in Sinocyclocheilus, possibly enhanced in eyeless species compared to eye bearing (normal-/micro-eyed species). Using 13 species representative of Sinocyclocheilus radiation and eye morphs, we designed a series of assays, based on pre-existing methods for Astyanax mexicanus behavioural experiments, to examine wall-following behaviour under three conditions. Our results indicate that eyeless species exhibit significantly enhanced intensities of WF compared to normal-eyed species, with micro-eyed forms demonstrating intermediate intensities in the WF distance. Using a mtDNA based dated phylogeny (chronogram with four clades A-D), we traced the degree of WF of these forms to outline common patterns. We show that the intensity of WF behaviour is higher in the subterranean clades compared to clades dominated by normal-eyed free-living species. We also found that eyeless species are highly sensitive to vibrations, whereas normal-eyed species are the least sensitive. Since WF behaviour is presented to some degree in all Sinocyclocheilus species, and given that these fishes evolved in the late Miocene, we identify this behaviour as being ancestral with WF enhancement related to cave occupation. Results from this diversification-scale study of cavefish behaviour suggest that enhanced wall-following behaviour may be a convergent trait across all stygomorphic lineages.

Selection on Visual Opsin Genes in Diurnal Neotropical Frogs and Loss of the SWS2 Opsin in Poison Frogs.

Amphibians are ideal for studying visual system evolution because their biphasic (aquatic and terrestrial) life history and ecological diversity expose them to a broad range of visual conditions. Here, we evaluate signatures of selection on visual opsin genes across Neotropical anurans and focus on three diurnal clades that are well-known for the concurrence of conspicuous colors and chemical defense (i.e., aposematism): poison frogs (Dendrobatidae), Harlequin toads (Bufonidae: Atelopus), and pumpkin toadlets (Brachycephalidae: Brachycephalus). We found evidence of positive selection on 44 amino acid sites in LWS, SWS1, SWS2, and RH1 opsin genes, of which one in LWS and two in RH1 have been previously identified as spectral tuning sites in other vertebrates. Given that anurans have mostly nocturnal habits, the patterns of selection revealed new sites that might be important in spectral tuning for frogs, potentially for adaptation to diurnal habits and for color-based intraspecific communication. Furthermore, we provide evidence that SWS2, normally expressed in rod cells in frogs and some salamanders, has likely been lost in the ancestor of Dendrobatidae, suggesting that under low-light levels, dendrobatids have inferior wavelength discrimination compared to other frogs. This loss might follow the origin of diurnal activity in dendrobatids and could have implications for their behavior. Our analyses show that assessments of opsin diversification in across taxa could expand our understanding of the role of sensory system evolution in ecological adaptation.

Clade density and the evolution of diversity-dependent diversification.

The assumption of an ecological limit to the number of species in a given region is frequently invoked in evolutionary studies, yet its empirical basis is remarkably meager. We explore this assumption by integrating data on geographical distributions and phylogenetic relationships of nearly six thousand terrestrial vertebrate species. In particular, we test whether sympatry with closely-related species leads to decreasing speciation rates. We introduce the concept of clade density, which is the sum of the areas of overlap between a given species and other members of its higher taxon, weighted by their phylogenetic distance. Our results showed that, regardless of the chosen taxon and uncertainty in the phylogenetic relationships between the studied species, there is no significant relationship between clade density and speciation rate. We argue that the mechanistic foundation of diversity-dependent diversification is fragile, and that a better understanding of the mechanisms driving regional species pools is sorely needed.

The evolutionary history of bees in time and space.

Bees are the most significant pollinators of flowering plants. This partnership began ca. 120 million years ago, but the uncertainty of how and when bees spread across the planet has greatly obscured investigations of this key mutualism. We present a novel analysis of bee biogeography using extensive new genomic and fossil data to demonstrate that bees originated in Western Gondwana (Africa and South America). Bees likely originated in the Early Cretaceous, shortly before the breakup of Western Gondwana, and the early evolution of any major bee lineage is associated with either the South American or African land masses. Subsequently, bees colonized northern continents via a complex history of vicariance and dispersal. The notable early absences from large landmasses, particularly in Australia and India, have important implications for understanding the assembly of local floras and diverse modes of pollination. How bees spread around the world from their hypothesized Southern Hemisphere origin parallels the histories of numerous flowering plant clades, providing an essential step to studying the evolution of angiosperm pollination syndromes in space and time.

Phylogenetic diversity and the structure of host-epiphyte interactions across the Neotropics.

Understanding the mechanisms driving community assembly has been a major focus of ecological research for nearly a century, yet little is known about these mechanisms in commensal communities, particularly with respect to their historical/evolutionary components. Here, we use a large-scale dataset of 4,440 vascular plant species to explore the relationship between the evolutionary distinctiveness (ED) (as measured by the 'species evolutionary history' (SEH)) of host species and the phylogenetic diversity (PD) of their associated epiphyte species. Although there was considerable variation across hosts and their associated epiphyte species, they were largely unrelated to host SEH. Our results mostly support the idea that the determinants of epiphyte colonization success might involve host characteristics that are unrelated to host SEH (e.g., architectural differences between hosts). While determinants of PD of epiphyte assemblages are poorly known, they do not appear to be related to the evolutionary history of host species. Instead, they might be better explained by neutral processes of colonization and extinction. However, the high level of phylogenetic signal in epiphyte PD (independent of SEH) suggests it might still be influenced by yet unrecognized evolutionary determinants. This study highlights how little is still known about the phylogenetic determinants of epiphyte communities.

Mechanical demands of bite in plane head shapes of ant (Hymenoptera: Formicidae) workers.

Food processing can exert significant evolutionary pressures on the morphological evolution of animal appendages. The ant genus Pheidole displays a remarkable degree of morphological differentiation and task specialization among its workers. Notably, there is considerable variation in head shape within worker subcastes of Pheidole, which could affect the stress patterns generated by bite-related muscle contraction. In this study, we use finite element analysis (FEA) to investigate the effect of the variation in head plane shape in stress patterns, while exploring the morphospace of Pheidole worker head shapes. We hypothesize that the plane head shapes of majors are optimized for dealing with stronger bites. Furthermore, we expect that plane head shapes at the edges of each morphospace would exhibit mechanical limitations that prevent further expansion of the occupied morphospace. We vectorized five head shapes for each Pheidole worker type located at the center and edges of the corresponding morphospaces. We conducted linear static FEA to analyze the stresses generated by mandibular closing muscle contraction. Our findings indicate that plane head shapes of majors exhibit signs of optimization to deal with stronger bites. Stresses are distinctly directed along the lateral margins of the head, following the direction of muscle contraction, whereas the stresses on the plane head shapes of minors tend to concentrate around the mandibular articulations. However, the comparatively higher stress levels observed on majors' plane head shapes suggest a demand for cuticular reinforcement, like increased cuticle thickness or sculpturing pattern. Our results align with the expectations regarding the main colony tasks performed by each worker subcaste, and we find evidence of biomechanical limitations on extreme plane head shapes for majors and minors.

Sensory evolution in a cavefish radiation: patterns of neuromast distribution and associated behaviour in Sinocyclocheilus (Cypriniformes: Cyprinidae).

The genus Sinocyclocheilus, comprising a large radiation of freshwater cavefishes, are well known for their presence of regressive features (e.g. variable eye reduction). Fewer constructive features are known, such as the expansion of the lateral line system (LLS), which is involved in detecting water movements. The precise relationship between LLS expansion and cave adaptation is not well understood. Here, we examine morphology and LLS-mediated behaviour in Sinocyclocheilus species characterized by broad variation in eye size, habitat and geographical distribution. Using live-staining techniques and automated behavioural analyses, we examined 26 Sinocyclocheilus species and quantified neuromast organ number, density and asymmetry within a phylogenetic context. We then examined how these morphological features may relate to wall-following, an established cave-associated behaviour mediated by the lateral line. We show that most species demonstrated laterality (i.e. asymmetry) in neuromast organs on the head, often biased to the right. We also found that wall-following behaviour was distinctive, particularly among eyeless species. Patterns of variation in LLS appear to correlate with the degree of eye loss, as well as geographical distribution. This work reveals that constructive LLS evolution is convergent across distant cavefish taxa and may mediate asymmetric behavioural features that enable survival in stark subterranean microenvironments.

Semicircular canal size constrains vestibular function in miniaturized frogs.

Miniaturization has evolved repeatedly in frogs in the moist leaf litter environments of rainforests worldwide. Miniaturized frogs are among the world's smallest vertebrates and exhibit an array of enigmatic features. One area where miniaturization has predictable consequences is the vestibular system, which acts as a gyroscope, providing sensory information about movement and orientation. We investigated the vestibular system of pumpkin toadlets, Brachycephalus (Anura: Brachycephalidae), a clade of miniaturized frogs from Brazil. The semicircular canals of miniaturized frogs are the smallest recorded for adult vertebrates, resulting in low sensitivity to angular acceleration due to insufficient displacement of endolymph. This translates into a lack of postural control during jumping in Brachycephalus and represents a physical constraint resulting from Poiseuille's law, which governs movement of fluids within tubes.

Alpha and beta phylogenetic diversities jointly reveal ant community assembly mechanisms along a tropical elevational gradient.

Despite the long-standing interest in the organization of ant communities across elevational gradients, few studies have incorporated the evolutionary information to understand the historical processes that underlay such patterns. Through the evaluation of phylogenetic α and ß-diversity, we analyzed the structure of leaf-litter ant communities along the Cofre de Perote mountain in Mexico and evaluated whether deterministic- (i.e., habitat filtering, interspecific competition) or stochastic-driven processes (i.e., dispersal limitation) were driving the observed patterns. Lowland and some highland sites showed phylogenetic clustering, whereas intermediate elevations and the highest site presented phylogenetic overdispersion. We infer that strong environmental constraints found at the bottom and the top elevations are favoring closely-related species to prevail at those elevations. Conversely, less stressful climatic conditions at intermediate elevations suggest interspecific interactions are more important in these environments. Total phylogenetic dissimilarity was driven by the turnover component, indicating that the turnover of ant species along the mountain is actually shifts of lineages adapted to particular locations resembling their ancestral niche. The greater phylogenetic dissimilarity between communities was related to greater temperature differences probably due to narrow thermal tolerances inherent to several ant lineages that evolved in more stable conditions. Our results suggest that the interplay between environmental filtering, interspecific competition and habitat specialization plays an important role in the assembly of leaf-litter ant communities along elevational gradients.

The role of climate and islands in species diversification and reproductive-mode evolution of Old World tree frogs.

Large diversifications of species are known to occur unevenly across space and evolutionary lineages, but the relative importance of their driving mechanisms, such as climate, ecological opportunity and key evolutionary innovations (KEI), remains poorly understood. Here, we explore the remarkable diversification of rhacophorid frogs, which represent six percent of global amphibian diversity, utilize four distinct reproductive modes, and span a climatically variable area across mainland Asia, associated continental islands, and Africa. Using a complete species-level phylogeny, we find near-constant diversification rates but a highly uneven distribution of species richness. Montane regions on islands and some mainland regions have higher phylogenetic diversity and unique assemblages of taxa; we identify these as cool-wet refugia. Starting from a centre of origin, rhacophorids reached these distant refugia by adapting to new climatic conditions ('niche evolution'-dominant), especially following the origin of KEIs such as terrestrial reproduction (in the Late Eocene) or by dispersal during periods of favourable climate ('niche conservatism'-dominant).

Geographical range overlap networks and the macroecology of species co-occurrence.

Direct interactions among species are only possible if there is some overlap in their geographical distributions. However, despite intense focus of macroecological research on species geographical ranges, relatively little theoretical and empirical work has been done on the evolution of range overlap. In this study we explore a simple model of range overlap based on a log-normal distribution of species range sizes along a one-dimensional domain, with or without absorbing boundary conditions. In particular, we focus on the mean and variance of range overlap distributions, as well as the topology of the resulting overlap networks with respect to their degree distribution, evenness, and betweenness scores. According to the model, there is an approximately linear relationship between many aspects of the distribution of range overlaps and their underlying species distributions, such as their mean and variance. However, the expected mean number of non-zero range overlaps for a given species varied from linear to convex depending on the variance of the underlying geographical range distribution. The expected topology of range overlap networks varied substantially depending on the mean and variance in the corresponding geographical distributions, particularly in the case of the degree and closeness distributions. Finally, we test the expectations of our model against five datasets of altitudinal distributions of Neotropical birds. We found strong departures from the expectations based on our model, which could potentially result from phylogenetic niche conservatism related to altitudinal gradients in environmental conditions, or from the asymmetric colonization of mountains by species from lowlands. Potential applications of range overlap networks to a variety of ecological and evolutionary phenomena are discussed.

Evolving in the darkness: Phylogenomics of Sinocyclocheilus cavefishes highlights recent diversification and cryptic diversity.

Troglomorphism-any morphological adaptation enabling life to the constant darkness of caves, such as loss of pigment, reduced eyesight or blindness, over-developed tactile and olfactory organs-has long intrigued biologists. However, inferring the proximate and ultimate mechanisms driving the evolution of troglomorphism (stygomorphism) in freshwater fish requires a sound understanding of the evolutionary relationships between surface and stygomorphic lineages. We use Restriction Site Associated DNA Sequencing (RADseq) to better understand the evolution of the Sinocyclocheilus fishes of China. With a remarkable array of derived stygomorphic traits, they comprise the largest cavefish diversification in the world, emerging as a multi-species model system to study evolutionary novelty. We sequenced a total of 120 individuals throughout the Sinocyclocheilus distribution. The data comprised a total of 646,497 bp per individual, including 4378 loci and 67,983 SNPs shared across a minimum of 114 individuals at a given locus. Phylogenetic analyses using either the concatenated RAD loci (RAxML) or the SNPs under a coalescent model (SVDquartets, SNAPP) showed a high degree of congruence with similar topologies and high node support (>95 for most nodes in the phylogeny). The major clades recovered conform to a pattern previously established using Sanger-based mt-DNA sequences, with a few notable exceptions. We now recognize six major clades in this group, elevating the blind cavefish S. tianlinensis and the micro-eyed S. microphthalmus as two new distinct clades due to their deep divergence from other clades. PCA plots of the SNP data also support the recognition of six major clusters of species congruent with the identified clades in ordination space. A Bayes factor delimitation (BFD) analysis showed support for 21 species, recognizing 19 previously described species and two putative new cryptic ones. Two species whose identities were previously disputed, S. furcodorsalis and S. tianeensis, are supported here as distinct species. In addition, our multi-species calibrated tree in SNAPP suggests that the genus Sinocyclocheilus originated around 10.16 Mya, with most speciation events occurring in the last 2 Mya, likely favored by the uplift of the Qinghai-Tibetan Plateau and cave occupation induced by climate-driven aridification during this period. These results provide a firm basis for future comparative studies on the evolution of Sinocyclocheilus and its adaptations to cave life.

Arrested diversification? The phylogenetic distribution of poorly-diversifying lineages.

Rapidly-diversifying lineages have been a major focus of modern evolutionary biology, with many hypotheses seeking to explain how they contribute to the uneven distribution of species in space and among taxa. However, an alternative view that is rarely explored is that some lineages evolve to become depauperate clades and show disproportionately low diversification, in a phenomenon we here call arrested diversification. In this study, we analyse several large-scale datasets including amphibian, squamate, mammal, and seed plant species to assess the extent to which poorly-diversifying lineages show distinct phylogenetic and spatial distributions in relation to other lineages. We found significant evidence that clades with low diversification rates tend to be more phylogenetically overdispersed than expected and show more idiosyncratic spatial distributions. These results suggest that arrested diversification is a real phenomenon that might play an important (yet largely overlooked) role in explaining asymmetries in the distribution of species across lineages.

Head and mandible shapes are highly integrated yet represent two distinct modules within and among worker subcastes of the ant genus Pheidole.

Ants use their mandibles for a wide variety of tasks related to substrate manipulation, brood transport, food processing, and colony defense. Due to constraints involved in colony upkeep, ants evolved a remarkable diversity of mandibular forms, often related to specific roles such as specialized hunting and seed milling. Considering these varied functional demands, we focused on understanding how the mandible and head shape vary within and between Pheidole subcastes. Using x-ray microtomography and 3D geometric morphometrics, we tested whether these structures are integrated and modular, and how ecological predictors influenced these features. Our results showed that mandible and head shape of majors and minor workers tend to vary from robust to slender, with some more complex changes related to the mandibular base. Additionally, we found that head and mandible shapes are characterized by a high degree of integration, but with little correlation with feeding and nesting habits. Our results suggest that a combination of structural (allometric) constraints and the behavioral flexibility conferred by subcaste dimorphism might largely buffer selective pressures that would otherwise lead to a fine-tuning between ecological conditions and morphological adaptation.

Mandibular morphology, task specialization and bite mechanics in Pheidole ants (Hymenoptera: Formicidae).

Ants show remarkable ecological and evolutionary success due to their social life history and division of labour among colony members. In some lineages, the worker force became subdivided into morphologically distinct individuals (i.e. minor versus major workers), allowing for the differential performance of particular roles in the colony. However, the functional and ecological significance of these morphological differences are not well understood. Here, we applied finite element analysis (FEA) to explore the biomechanical differences between major and minor ant worker mandibles. Analyses were carried out on mandibles of two Pheidole species, a dimorphic ant genus. We tested whether major mandibles evolved to minimize stress when compared to minors using combinations of the apical tooth and masticatory margin bites under strike and pressure conditions. Majors performed better in pressure conditions yet, contrary to our expectations, minors performed better in strike bite scenarios. Moreover, we demonstrated that even small morphological differences in ant mandibles might lead to substantial differences in biomechanical responses to bite loading. These results also underscore the potential of FEA to uncover biomechanical consequences of morphological differences within and between ant workers.

Morphological and genetic evidence supports the separation of two Tapinoma ants (Formicidae, Dolichoderinae) from the Atlantic Forest biome.

The taxonomic boundaries of many Neotropical ant species of the genus Tapinoma are still unclear. Tapinoma atriceps and T. atriceps breviscapum are two morphologically similar taxa which occur sympatrically in the southern Atlantic Forest of Brazil. Some characters such as the scape length and head shape suggest that these taxa may be different species. We used DNA analysis and morphological evidence, including scanning electron microscopy, to evaluate the taxonomic validity of these taxa. We found distinct morphological characteristics that allow separating them as two different species, Tapinoma atriceps and Tapinoma breviscapum status novo, and this decision is supported by the DNA results, where Tapinoma atriceps was recovered as a lineage independent of T. breviscapum.

Buccopharyngeal morphology of the tadpoles of Scinax v-signatus/, with comments on larval characters of the S. perpusillus/ species group (Amphibia: Anura: Hylidae).

The Neotropical genus Scinax Wagler currently comprises 127 species of small treefrogs distributed from southern Mexico to Argentina and Uruguay, including some islands such as Trinidad and Tobago, and St. Lucia (Frost 2020). Two major clades are recognized within Scinax, the S. catharinae and the S. ruber clades. The former is composed of two species groups, the S. catharinae and the S. perpusillus groups (Faivovich 2002; Faivovich et al. 2005). The S. perpusillus species group currently comprises 13 species: S. alcatraz (Lutz); S. arduous Peixoto; S. atratus (Peixoto); S. belloni Faivovich, Gasparini Haddad; S. cosenzai Lacerda, Peixoto Feio; S. faivovichi Brasileiro, Oyamaguchi Haddad; S. insperatus Silva Alves-Silva; S. littoreus (Peixoto); S. melloi (Peixoto), S. peixotoi Brasileiro, Haddad, Sawaya Martins; S. perpusillus (Lutz Lutz); S. tupinamba Silva Alves-Silva; and S. v-signatus (Lutz). These species are endemic of the Brazilian Atlantic Forest and are recognized by their intimate association with bromeliads (Fig. 1), in which adults breed and lay their eggs, and tadpoles develop (Peixoto 1987, 1995; Alves-Silva Silva 2009).

A review of the diagnosis and geographical distribution of the recently described flea toad Brachycephalus sulfuratus in relation to B. hermogenesi (Anura: Brachycephalidae).

BACKGROUND: The flea toad Brachycephalus sulfuratus was recently described from southeastern and southern Brazil. In its description, the authors overlooked previous records of flea toads that had been identified as "Brachycephalus sp. nov." and B. hermogenesi occurring in the same regions, which could suggest the possibility of up to three flea toads coexisting in southern Brazil. In addition, B. sulfuratus is characterized by substantial phenotypic variability, to an extent that compromises its current diagnosis with respect to its congener B. hermogenesi. Therefore, the current state-of-affairs regarding the geographical distribution of these two species and the identification of previously known populations is hitherto uncertain. Our goals are to reassess previous records of flea toads attributable to B. hermogenesi, B. sulfuratus and "Brachycephalus sp. nov.", considering the description of B. sulfuratus, and to review the diagnosis of B. sulfuratus. METHODS: A critical analysis of the species identity of flea toad specimens attributable to B. hermogenesi, B. sulfuratus, or to a potentially undescribed species from southeastern and southern Brazil was based either on the analysis of morphology or on their advertisement calls. These analyses include our independent examinations of specimens and, when not possible, examinations of published descriptions. To allow for a consistent comparison of advertisement calls between B. hermogenesi and B. sulfuratus, we made recordings of both species, including in the type locality of the former. RESULTS: We found that morphological and call characters originally proposed as diagnostic for B. sulfuratus in relation to B. hermogenesi vary intraspecifically. Live individuals with ventral yellow spots correspond to B. sulfuratus; individuals without yellow spots can be either B. sulfuratus or B. hermogenesi. In preservative, they are indistinguishable. Previous records of Brachycephalus sp. nov. correspond to B. sulfuratus. We propose that the reduced number of notes per call and the presence of only isolated notes in the call of B. sulfuratus, as opposed to a high number of notes per call with isolated notes and note groups in the call of B. hermogenesi, as the only diagnostic characters between them. Regarding their distributions and based in our assessment, only B. sulfuratus occurs in southern Brazil, without any overlap with B. hermogenesi. There is a narrow gap between the distributions of these species around the southeast of the city of São Paulo. Our revision also revealed that some records previously attributed to B. hermogenesi in Rio de Janeiro and north São Paulo represent a distinct, unidentified flea toad that is not B. sulfuratus. Both species occur side by side in Corcovado, São Paulo, a locality from where five paratypes of B. hermogenesi were obtained. Biogeographic events that might have led to vicariance between B. hermogenesi and B. sulfuratus are discussed.