Amphibian News!

June 5, 2023: Foam nests are a unique reproductive strategy used by frogs providing eggs and larva protection from desiccation, predation, and suffocation while also aiding in fertilization and providing a food source for developing larvae. More recently, the protein and carbohydrate rich foam also has been associated with the vertical transfer of beneficial microbial communities in rhacophorid frogs. Monteiro et al. (2023) characterized the protein composition and microbiome of the nests of three Leptodactylid species: Adenomera hylaedactyla, Leptodactylus vastus, and Physalaemus cuvieri, with each representing a different spawning habitat type. They found that protein composition was species-specific and was influenced more by spawn habitat type and nest size than phylogenetic relatedness. Many of these proteins were previously unidentified. Additionally, the microbiome community of the nest was unique from the surrounding environment and the adult skin microbiome. These findings show that foam nests have a key functional role in reproduction and highlight the need for conservation efforts to protect nests from anthropic pressures, as each nest has a unique microenvironment. (AChang)

May 29, 2023: De-Oliveira-Nogueira et al (2023) reports a new behavior and relationship between an amphibian and plant: the South American tree frog Xenohyla truncata has been observed feeding on nectar and flowers of the Brazilian milk fruit tree Cordia taguahyensis. The flower structure of this tree species allows the frog to enter and exit the flower easily. During their feeding activity, the pollen grains adhere to the frog’s back and are transported to other flowers while visiting them. Based on this observation, the authors suggest that X. truncata is not only a seed disperser, but also a potential pollinator of C. taguahyensis, or even of other plant species with similar floral structure. Nectar-feeding is an unique natural history behavior among frogs and highlights the importance of fundamental natural history information for this endemic tree frog species, which exclusively lives in the rapidly disappearing Restinga habitat on the coast of Rio de Janeiro in Brazil. With expanding development and habitat destruction, it is feared that losing this frog species, currently threatened with extinction, also means the extinction of a unique amphibian-plant interaction, especially important as it is a first known for a frog. Thus, conservation of this tree frog species has heightened stakes. (UArifin)

May 15, 2023: Infectious disease has been linked to several instances of amphibian population decline and is hypothesized to contribute to worldwide amphibian declines. As a result, there is urgency to better understand host-pathogen-environment interactions in amphibian communities. Researchers can take advantage of cultured cell lines to investigate host-pathogen-environment interactions in controlled experiments that do not require the use of live animals. Amphibian cell lines thus can provide an important and more accessible first step in addressing open research questions which can be followed up with live animal studies. Douglas et al. (2023) reviewed the existing amphibian cell line resources and literature and found that the amphibian invitrome, the collection of amphibian cell lines, consists of at least 159 distinct amphibian cell lines originating from 23 species belonging to five frog families and four salamander families. Despite this impressive history of cell line resources and many curated lines, few have been used to investigate amphibian cellular immune responses. The authors propose that the amphibian invitrome has the potential to transform our understanding of amphibian immune responses at a mechanistic level while limiting use of live amphibians. (MWomack)

May 8, 2023: Neotropical poison frogs are known for their intensive parental care. Male or female parents will carry their tadpoles to bromeliads to provide them with small pools of water where they can develop, safe from fishy predators. In these nutrient poor habitats, some species have evolved egg-feeding, where females lay unfertilized eggs for the tadpoles to eat. In the Peruvian mimic poison frog, Ranitomeya imitator, parents form a pair bond and cooperate in the care of their tadpoles. In this system, Weinfurther et al. (2023) provide preliminary evidence of a symbiotic protist in the guts of the tadpole. In comparative experiments, they switched the diets of R. imitator tadpoles (eggs) with the ancestral diet (detritus) consumed by a related species (R. variabilis) without egg-feeding, and did the reverse (with control treatments for both species). Analyses of gut gene expression revealed elevated expression of proteases in the R. imitator field egg-fed treatment. These digestive proteins came from parabasalians, a group of protists known to form symbiotic relationships with hosts that enhance digestion (especially in termites). Genes encoding these digestive proteins are not present in the R. imitator genome, and phylogenetic analyses shows these mRNA sequences were from parabasalian protists. Bar-coding analyses of the tadpole eukaryotic microbiomes further confirmed this discovery. More study is necessary to confirm whether these parabasalians aid R. imitator tadpoles in protein/ lipid digestion in an egg diet. This may have enabled the exploitation of a key ecological niche (very small, nutrient-poor pools), allowing R. imitator to expand into an area with ecologically similar species (e.g., R. variabilis and R. summersi). In turn, this may have enabled a Müllerian mimetic radiation, one of only a few examples of this phenomenon in vertebrates. (KSummers)

May 1, 2023: Symbiotic skin microbial communities and skin secretions have been studied in frogs for their immunological effects for decades, however, there are still much to discover about all the other roles they may play. Brunetti et al. (2023) examined Burmeister's Treefrog, Boana prasina, for evidence of chemical signaling and found that their skin secretions contained 10 different compound classes of volatile chemicals, some of which were produced by symbiotic Pseudomonas sp. bacteria. Moreover, these odors varied by sex, which in tandem with acoustic signaling, could play a chemical signaling role in sex recognition and assessment during breeding. These findings open the door to questions that could improve our understanding of amphibian breeding behavior and symbiotic associations. (AChang)

April 24, 2023: In a 2023 study, Loeffler-Henry et al. provide new insights into the evolution of aposematism, that is, the warning coloration combined with a chemical defense. They review the apparent paradox inherent in the evolution of aposematism: How can new brightly colored mutants survive when they will attract predator attention before the predators have learned that bright coloration is associated with toxicity? While a variety of potential solutions to this puzzle have offered, none have been definitively demonstrated to apply in general. Here, they focus on the hypothesis that aposematism evolved in gradual stages involving the prior evolution of facultatively presented signals, such as bright colors concealed by limbs, or bright coloration of the underbelly of the animal (and revealed only upon the close approach of a predator). The conditions favoring the evolution of this type of coloration are likely to be much less restrictive, and yet they provide a clear pathway to the evolution of overall bright coloration. The authors carry out an extensive series of phylogenetically- controlled comparative analyses using maximum- likelihood methods, which allows them to make statistically supported inferences about the evolutionary pathways of the evolution of both coloration and defense (toxicity). The results provide support for the hypothesis that conspicuousness evolved via an indirect pathway in which facultative conspicuous coloration evolved first and provided pathways for full conspicuousness to evolve later. There is still considerable work to be done in terms of identifying the specific evolutionary mechanisms that facilitated the evolution of aposematism through each gradual step, but this study provides a valuable roadmap for those kinds of analyses. (KSummers)

April 17, 2023: In a phylogenetic analysis, Ellepola et al (2022) investigates the roles of climate, ecological opportunity and key evolutionary innovations (KEI) in the diversification of rhacophorid frogs, which represent six percent of global amphibian diversity, four distinct reproductive modes, and spans a climatically variable area across mainland Asia, associated continental islands, and Africa. Using a complete species-level phylogeny, they report 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; the study identifies these as cool-wet refugia. Starting from a center 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 favorable climate (‘niche conservatism’-dominant). (VV)

April 10, 2023: What compounds do amphibians taste? What role might taste play in the biology of amphibians as they develop from larvae to adults? Using comparative genomics, Hao et al. (2023) found unexpected diversity in the Tas2r taste receptors that detect bitter compounds, more than in any other vertebrate group. By looking at the differential expression of the nearly 200 Tas2r genes in the American Bullfrog (Rana catesbeiana), they found that tadpoles and adults differently express some genes at high levels. This suggests that variation across development in expression of these bitter receptors is related to the different foods (and presumably different preferences) between herbivorous larvae and insectivorous adults. Interesting areas for further research include how these receptors might be distributed within the mouth, including on the unusual taste “discs” of frog tongues, as well as how closely related species might differ in bitter receptors and thus preferences for different prey. (DBlackburn)

April 3, 2023: Researchers are finding amphibians move more frequently and farther across landscapes than often assumed, which has broad conservation implications. Davis et al. (2023) carried out an impressive six-year capture-mark-recapture study across 12 wetlands in Pennsylvania, US, and showed that adult Spotted Salamanders (Ambystoma maculatum) move a surprising distance both within and between breeding seasons. Six percent of males moved among wetlands each day, and in high density populations, males tended to return to the same breeding wetland year after year (had higher site fidelity). Females exhibited higher interannual site fidelity and dispersed farther than males between breeding seasons. This study and others that track amphibian movements are improving our understanding of breeding dispersal probabilities and capabilities. (MW)

March 27, 2023: Pandemics in amphibians, caused by the fungal pathogen Batrachochytrium dendrobatidis (Bd), have resulted in biodiversity loss at a global scale. Genomic data suggest a complex evolutionary history of Bd lineages that vary in pathogenicity. Africa harbors a significant proportion of global amphibian biodiversity, and multiple Bd lineages are known to occur there; yet, despite the decline of many host species, there are currently no described Bd-epizootics. Ghose et al. (2023) describes the historical and recent biogeographical spread of Bd and assess its risk to amphibians across the continent of Africa. Their study provides a 165-year view of host-pathogen interactions by (i) employing a Bd assay to test 4,623 specimens (collected 1908–2013); (ii) compiling 12,297 published Bd records (collected 1852–2017); (iii) comparing the frequency of Bd-infected amphibians through time by both country and region; (iv) genotyping Bd lineages; (v) histologically identifying evidence of chytridiomycosis, and (vi) modeling future Bd risk. They found a pattern of Bd emergence beginning largely at the turn of the century. From 1852–1999, Bd prevalence is low (3.2% overall) with limited geographic spread, but after 2000, prevalence sharply increases (18.7% overall) with wider geographic spread and multiple Bd lineages that may be responsible for emergence in different regions.They found Bd risk to amphibians to be highest in much of eastern, central, and western Africa. The study documents a largely overlooked yet significant increase in a fungal pathogen that could pose a threat to amphibians across an entire continent and emphasizes the need to bridge historical and contemporary datasets to better describe and predict host-pathogen dynamics over larger temporal scales. (VV)

March 20, 2023: New Guinea – the world’s largest tropical island – is famous for its rugged topography, with snow-capped mountains reaching 4,884 m in elevation (16,024 ft), and a multitude of deeply incised valleys that make ground-based overland travel virtually impossible. This topography is highly conducive to localized speciation and small-range endemism. Oliver et al. (2022) focused on the amphibians of this imposing landscape and find that New Guinea holds the world’s most diverse and intact insular amphibian fauna, with over 7% of global frog species (534 currently recognized species) distributed across less than 0.7% of the world’s land area. Remarkably, the scale of the New Guinea frog fauna is almost certainly substantially underestimated as the authors are aware of about 190 species in collections that have yet to be described. Furthermore, most of the known species were described from the much better surveyed eastern half of the island that represents the country of Papua New Guinea. The frog fauna of the western half of the island (Papua Province, Indonesia) remains relatively understudied and promises to hold additional species beyond the ~700 estimated by the authors. The composition of the New Guinea frog fauna is almost entirely restricted to three families (Microhylidae, Hylidae, Ceratobatrachidae), with the direct-developing microhylids dominating. New Guinea’s rugged topography has likely contributed to its amazingly diverse fauna and simultaneously prevented the sort of large-scale anthropogenic habitat destruction that has allowed the fauna to remain largely intact (only 6% of assessed species are listed as threatened). (JM)

March 13, 2023: Brazil is considered a mega-diverse country for amphibian diversity (1159 amphibian species known so far). However, it is also home to one of the global hotspots of amphibian decline, the coastal Atlantic Forest. To understand the history, nature, and response of species to the precipitous declines, Toledo and colleagues (2023) closely analysed surveys, reports, and museum records with environmental, climatic, and disease data. Their study more than doubled the number of population declines reported in previous studies, placing the Brazilian Atlantic Forest as a global hotspot of amphibian declines with one of the highest rates of declines and extinctions. The height of decline appears to be in 1979 within a decades long trend. Populations, if they recovered, sometimes took as long as 30 or more years. Their use of museum collections showed that specimen records matched the spatiotemporal patterns of declines and extinctions, including the impact of chytridiomycoses; they suspect that historic declines might have impacted many more amphibian populations and species. They also sought correlations of life history traits and phylogeny to help explore patterns of decline. They note some families were disproportionally impacted (specifically Cycloramphidae, Hylodidae, Phyllomedusidae). Their comprehensive report will be an essential guide to conservation, management, and disease surveillance to protect this important amphibian ecology. (MK)

March 6, 2023: One of the most remarkable forms of camouflage observed in nature involves transparency in glass frogs of the family Centrolenidae. These frogs, which are arboreal and typically perch on leaves, have highly transparent ventral skin through which their organs can be clearly seen, as well as green dorsal coloration and green bones that presumably enhance their camouflage. One feature that might disrupt their camouflage is the presence of red blood cells, which are easily seen through the transparent ventral skin. Recently Taboada et al. (2022) showed that the glass frog species Hyalinobatrachium fleischmanni increase their transparency while resting by two to three-fold by removing about 89% of their red blood cells from circulation and packing them within their liver. This exciting new discovery not only provides new information on the nature of transparency in glass frogs but may also inform biomedical research because the ability to densely pack red blood cells into the liver without clotting could have important human health consequences. (JM)

February 27, 2023: Evolutionary transitions in reproductive modes and life-cycles in amphibians has long been a target of study to understanding the diversity of life. Liedtke et al (2022) compares large-scale macroevolutionary patterns across the three orders of amphibians: frogs, salamanders, and caecilians, and includes reproductive and phylogenetic data for 4,025 species. Their analysis indicate aquatic larvae as ancestral for all three groups. The most frequent transitions in each group are to relatively uncommon states: live-bearing in caecilians, paedomorphosis in salamanders, and semi-terrestriality in frogs. All three groups show transitions to more terrestrial reproductive modes, but only in caecilians have these evolved sequentially from most-to-least aquatic. Diversification rates are largely independent of reproductive modes. However, in salamanders, direct development accelerates diversification whereas paedomorphosis decreases it. Overall, the study reports a widespread retention of ancestral modes, decoupling of trait transition rates from patterns of species richness, and the general independence of reproductive modes and diversification. (VV)

February 20, 2023: How do frogs swallow their food? While the mechanics of the frog tongue are well-studied for the prey capture phase of the feeding cycle, little is known of how structures in the mouth move once it is closed. Recent work by Keeffe et al. (2022) investigated the functional morphology of the hard and soft tissues involved in feeding behaviors in the Cane toad, Rhinella marina. Using a combination of high-speed X-ray video, 3D animation software, and dissection, they assessed the role of the skull, jaw, pectoral girdle, tongue, and hyoid apparatus (skeleton supporting the tongue) during a complete feeding cycle. Their results suggest the hyoid apparatus plays an important role in prey transport, potentially helping remove prey from the sticky tongue pad prior to swallowing. They also found that the tip of the tongue consistently travels behind the back of the skull during swallowing, and that tongue protrusion comprises only a small portion of a full feeding cycle. This work raises new questions about the evolution of feeding in frogs, as well as how the observed diversity across frogs in the skeleton of the shoulder and tongue may influence feeding kinematics. (Rachel Keeffe)

February 13, 2023: Poison frogs, with bright colors and potent skin toxins, represent iconic examples of aposematism in rainforests throughout South and Central America. These frogs are also known for intensive parental care– parents carry tadpoles to small pools (phytotelmata) and some species provide trophic eggs as food for their offsprings. Much interest has focused on the question of whether poison frog tadpoles can acquire toxins for protection from predators by consuming eggs from their mothers. Studies have shown two species of Oophaga provide toxins to their tadpoles via obligate trophic egg feeding. In contrast, in Ranitomeya variabilis (and related R. fantastica, R. summersi) do not provide unfertilized eggs to their tadpoles (instead, they subsist on detritus, algae, and insect larvae), although they will sometimes lay fertilized clutches in or above pools that are later cannibalized by tadpoles. Villanueva et al. (2022) investigate this issue in a third species of Oophaga (O. granulifera) and in Ranitomeya imitator and R. variabilis. They found that while O. granulifera receives toxins in its eggs (like other members of this genus), that was not true for either species of Ranitomeya. They infer the degree to which egg feeding is facultative (high in R. variabilis, low in R. imitator, not facultative in Oophaga) is related to the evolution of toxin transfer via egg feeding. This is only a single comparison between the Oophaga and Ranitomeya lineages, so further studies will be necessary for definitive conclusions, but their study provides a fascinating and promising first pass at this question. (KSummers)

February 6, 2023: Evolutionary history and biogeographic patterns give us insight into how species respond to paleogeographic and paleoclimatic changes over a shared landscape, and these in turn can provide a guide for conservation management. In southern China, the landscape is a transitional mosaic with dramatic changes in elevation ranging from an average of 4000 m a.s.l to sea level. Yuan et al. (2022) used multi-locus genetic and environmental data from 78 sites to investigate phylogeographic patterns in the southern Chinese newt genera of Cynops, Paramesotriton, and Pachytriton. Their results showed consistency with major geological events, such as the uplift of the Qinghai-Xizang (Tibet) Plateau. Furthermore, variation in summer monsoons and the complex landscape of montane/submontane forest with lowland areas resulted in barriers that act as both ‘museums’ or refugia of old lineages and ‘cradles’ for new species diversification. These findings can provide a backbone for genetically informed management plans, but education and public awareness are crucial to preventing habitat disturbance and over-harvesting of vulnerable species. (AChang)

January 30, 2023: Some amphibians are able to persist in human-modified habitats, including within cities and intensively managed lands. Which mechanisms allow persistence in such environments? Cayuela et al. (2022) conducted a comprehensive analysis of mark-recapture studies of Yellow-bellied Toad (Bombina variegata) populations across a range of anthropic habitats. These toads breed in early-succession ponds and small pools of natural or anthropic origin. Life history traits can change along the gradient from natural to anthropic habitats according to two demographic scenarios. In the first scenario, the risk of adult mortality decreases with anthropization, associated with concomitant decreases in predation and parasitism rates. In the alternative scenario, increased exposure to contaminants, invasive species, ecological mismatches and other processes promote higher adult mortality risk in human-modified habitats. In this scenario, increased recruitment can compensate for increased adult mortality. Cayuela and collaborators estimated adult recruitment, adult survival, lifespan, and senescence rate from 67 populations of the yellow-bellied toads across western Europe. They convincingly show that toads in anthropogenic habitats have lower adult survival, shorter lifespan, and accelerated senescence than toads in natural habitats. Compensatory recruitment indeed occurs in anthropogenic habitats, where average adult recruitment is 93% higher than in natural habitats. Increased human land disturbance might promote creation of breeding habitats conducive to higher adult recruitment. These findings suggest the important role of human disturbance for maintaining populations of amphibians using early-succession habitats. (ACatenazzi)

January 23, 2023: Biological reserves provide protected refugia against human-mediated habitat degradation, which is one of the strongest conservation concerns for amphibians. The Manu Biosphere Reserve is one of the most biodiverse places on earth with over 155 amphibian species. Serrano-Rojas et al. (2022) surveyed 70 of the amphibian species recorded in the Manu Biosphere Reserve within five sites that span a land-use gradient in the park buffer zone (immigrant agricultural land, forests used by three Indigenous communities, and a regenerating forest) in addition to a reference site in its core protected area. They found the richness and diversity of amphibians in the regenerating forest and the indigenous communities’ forests were similar to that of the core protected area, whereas agricultural land had lower richness and was dominated by generalist species. Their findings underscore that supporting sustainable livelihood activities, cultural practices, and forest protection, which are observed in many Indigenous communities, could help avoid a shift towards intensive agriculture, fulfilling a crucial conservation role. (MWomack)

January 16, 2023: Amphibians may be affected by climate change more than other terrestrial vertebrates, and they have the higher rates of decline in recent years. The Columbia Spotted Frog (Rana luteiventris) is a widespread North American frog that occurs across a variety of climate gradients, from subalpine forests to semi-arid deserts. Pilliod and colleagues (2022) marked 15,885 adult Columbia Spotted frogs with subdermal transponders, with 33% recaptured at least once during their long term study (11-16 years depending on site). Within each population, adult survival and recruitment rates respond uniquely to seasonal temperature and precipitation variables, especially in winter and spring. Seasonal rain is a weak predictor of adult survival but was a useful predictor of juvenile recruitment, especially in three of the populations. Recruitment rates for each population peaked with different environmental gradients, depending on the amount of winter snowfall, and fall temperature and moisture levels. Thus recruitment may be responding to local conditions independently within each population. Their work emphasizes that local conditions and climate gradients need to be accounted for when managing climate effects on populations of amphibian species with broad geographic ranges. (CS)

January 9, 2023: An important life history trait is body size, which can be affected by environmental and evolutionary factors. Acevedo et al. (2022) examined these relationships in the specious, neotropical genus Pristimantis, which has a distribution across wide latitudinal and elevational ranges. Using body size data for all 584 known Pristimantis, phylogenetic information from 257 species, and information on their environments, the authors found that the body size of males, females, and sexual size dimorphism were correlated with climatic variation associated with heat balance (temperature), water availability (precipitation), and habitat availability (elevation). Additionally, despite the majority of species displaying sexual size dimorphism, their trend ran opposite to Rensch's rule, where males are larger then females. This correlation may be the result of fecundity selection, reproductive energy requirements, or heat balancing. Although separate clades show evidence that they are experiencing different selective pressures, the rate of body size evolution appears to be decelerating as the trait reaches an optimum. As this study provides a case for bioclimatic factors in body size evolution, it is a good launching point to generate future selection and macroevolutionary hypotheses of sexual size dimorphism. (AChang)

January 2, 2023: Happy New Year’s! Reflecting on 2022, we had a particularly productive year at AmphibiaWeb. One of the most visible improvements this year is (the much needed) new home page! All of the old links are still present but much more presentable. We hope you love the new home page as much as we do. We published the first "State of the Amphibia" paper (Womack et al 2022) in which we summarize the major research and data trends on Amphibia in the last 5 years. We aim to repeat this every five years to establish a record of and facilitate amphibian research and conservation. We end the year with 152 newly described species (20 mantellids frogs alone thanks to Scherz et al 2022!), a little less than the five-year average of 158. We also nearly doubled the number of new species accounts (140) which reflects both the new editing forms and efforts by student apprentices, but we hope to release even more accounts next year. In 2023, we will launch a new program to expand our network of experts and trained authors-- look out for announcements and opportunities to connect with us. We hope to have an equally productive 2023, so please keep an eye out for new projects, new data-driven pages and graphics, and the same committment as we continue to serve as the knowledge-hub for amphibians.