Amphibian News!

July 22, 2024: Our understanding of animal light sensitivity is like an iceberg. Visual photosensitivity is the tip, while nonvisual photosensitivity makes up the often-overlooked ice mass floating below the surface. Nonvisual photosensitivity is responsible for many biologically critical functions, including the calibration of circadian rhythms, regulation of light-seeking behaviors, and initiation of seasonal reproductive changes. These processes are initiated by nonvisual opsins, transmembrane proteins, which, when paired with a light-sensitive chromophore, form the photopigments responsible for nonvisual photosensitivity. Boyette et al. (2024) explored the diversity and molecular evolution of nonvisual opsin genes in 102 frog species, representing 34 of 56 currently recognized frog families. They tested several evolutionary hypotheses. Most notably, the nocturnal ancestry of frogs is hypothesized to reduce the need for the broad spectral sensitivity provided by non-visual opsins. Therefore, they expected to find extensive nonvisual opsin gene losses across frogs, like other ancestrally nocturnal groups including mammals and snakes. Surprisingly, they recovered all 18 ancestral vertebrate nonvisual opsins at the genomic level. Frogs thus demonstrate the lowest documented level of opsin gene loss among ancestrally nocturnal tetrapods. They propose this may be due to the biphasic life history of most frogs. Although many mature frogs are nocturnal, this is not necessarily true of their tadpoles. Such biphasic life histories may subject nonvisual opsins to disparate environmental constraints and selective pressures across metamorphosis, resulting in adaptive decoupling between life stages active in different light conditions. This hypothesis is supported by differences in selective constraint detected between biphasic and direct-developing frog species. These findings indicate that many nonvisual opsins are important in species whose life histories expose them to disparate light environments across development. Such work fills an important gap in our understanding of vertebrate opsin diversity and highlights frogs as an excellent system to explore evolution across diverse environmental, developmental, and morphological adaptations. (John L Boyette)

July 15, 2024: Hybridization is a significant threat to at-risk species, especially when the hybrid offspring perform better than the parents (i.e., hybrid vigor); however, investigation into the mechanisms underlying hybrid vigor is limited. Populations of the vulnerable California Tiger Salamander (Ambystoma californiense) in Salinas Valley, California, are currently at risk of being eradicated by their hybrid offspring, and Burger et al. (2024) measured physiological traits and the interactions of these traits to better understand the success of these hybrids. They analyzed how changes in water loss affect metabolic rate using a new performance metric– the water-gas exchange ratio – that measures how well an organism can breathe while minimizing water loss, referred to as respiration efficiency. The physiological mechanisms that allow for cutaneous gas exchange (thin and highly vascularized skin) also result in high rates of water loss; therefore, organisms that physiologically reduce their water loss rates will also experience reductions in metabolic rates (a trade-off), which may limit their ability to conduct energetically demanding activities. For respiration efficiency, individuals that are more efficient (higher ratio) would be able to sustain longer bouts of energetically demanding activities while minimizing the risk of dehydration. They found that hybrids exhibited the highest respiration efficiency, potentially an explanation for their continued success. Ambystoma californiense exhibited the lowest respiration efficiency and the weakest trade-off between metabolic rate and water loss, indicating that these two traits may be decoupled in this species. By decoupling these traits, A. californiense would be able to regulate each trait separately, which may result in reduced sensitivity to environmental change. However, the increased respiration efficiency of hybrids may allow them to continue outcompeting native A. californiense. This study provides key insights into these hybrids, highlighting the potential need for management actions to maintain non-hybridized A. californiense populations while also emphasizing the importance of incorporating integrated, multitrait analyses into our investigations of species differences. (Isabella Burger)

July 8, 2024: Research has shown that individual animals can show behavioral consistency across time and/or contexts that differs from other individuals, which is sometimes referred to as “animal personality”. Bégué et al. 2024 wanted to determine if tadpoles showed consistent differences in exploration and boldness and whether those behavioral differences were maintained across the major life transition of metamorphosing from aquatic tadpole to terrestrial frog. The researchers found that these personality traits persisted in the Brilliant-Thighed Poison Frog Allobates femoralis throughout metamorphosis, despite the drastic changes in morphology, physiology, and habitat in the transition from tadpoles to metamorphs. They also found that more bold and explorative individuals tended to develop faster - took fewer days to reach metamorphosis. These results suggest a physiological and/or genetic mechanism may be causing the consistent individual behavior differences. (MWomack)

July 1, 2024: High in the mountains and the Altiplano in the Andes in South America, live the Andean water frogs of the genus Telmatobius, a group characterized by their mainly aquatic habits at predominantly high elevations. Where and when the specious water frogs evolved and acquired their adaptations to aquatic lifestyle was unknown until recently, when a new fossil species of Telmatobius was described: Telmatobius achachila. The new species, described by Gómez and collaborators in 2024, comes from the Bolivian Altiplano and is estimated to have lived 12 Ma (million years ago) in the Miocene. The fossil is a disarticulated skeleton of a male of approximately 80 to 90 mm in length. The anatomical characteristics of the skull, the vertebral column, and the limbs allowed Gómez and his team to recognize this fossil frog as a new species and establish its relationship to other Telmatobius species. They found that it is nested within other living species (its close sister species is Telmatobius marmoratus), and it is not the most ancestral one. The specific characteristics of the lower jaw and hyoid show that aquatic feeding behavior (inertial suction feeding) was already typical in this group of frogs by the Miocene. The finding of Telmatobius achachila, along with additional information from its discovery site, show that by the Miocene the Bolivian Altiplano was a humid low to mid elevation forest and Telmatobius had already acquired the diagnostic characteristics of the genus. (Maria C. Vallejo-Pareja)

June 24, 2024: The enigmatic olm, a species of amphibian that inhabits cave systems in Europe, has rarely been observed in the wild. Manenti et al. (2024) provide some of the first behavioral observations of Proteus anguinus from northeastern Italy through a 3-year survey of 10 caves and 69 springs. They show that – in contrast to prior assumptions – these cave-dwelling species regularly utilize surface habitats during the day and night. For example, during daytime surveys at one site, the authors encountered olms 64% of the time. Several individuals that were captured from surface springs regurgitated terrestrial earthworms, suggesting they may visit springs to feed. It was previously thought that olms observed in springs were only there because they had been washed out of caves by flooding. However, the data provided by the authors challenge this hypothesis as some of the surveyed areas were under drought conditions and had not experienced recent flooding. Overall, the study broadens our understanding of the ecology of cave-dwelling animals, which has long assumed a separation between communities inhabiting underground and surface habitats. (RT)

June 17, 2024: Cannibalism is a common phenomenon among tadpoles of various frog species. Poison frog tadpoles from several genera (e.g. Dendrobates, Ranitomeya) are known to be especially enthusiastic when it comes to consuming conspecifics, possibly because they are typically deposited in small pools with limited space and nutrients. A number of studies have focused on the effects of various factors on the likelihood and extent of cannibalism (e.g. nutrient availability, pool size, and type). In a recent study, Surber-Cunningham et al. (2024) carried out lab-based experiments on Dendrobates tinctorius tadpoles (well-known for their cannibalistic tendencies), to investigate the effects of various waterborne cues (in the absence of visual cues) on tadpole movement and exploratory behavior. They specifically focused on the effects of ambiguous cues (e.g., those providing information about population density and about the presence of injured conspecifics), to see whether the tadpoles displayed unique, context specific reactions to such cues. They used less ambiguous, direct waterborne cues of predator (dragonfly larvae) presence, and of food (shrimp), as controls, in addition to a standard baseline control. Using specialized software to quantify movement and exploratory behavior, the authors were able to investigate heretofore unappreciated aspects of tadpole behavior in response to such cues. Of particular interest, they found that when given an injured conspecific cue tadpoles moved less (compared to the food cue), yet explored more (compared to the baseline and predator cues). The authors interpreted this as a strategy to maximize the probability of finding food (i.e., an injured conspecific), while at the same time minimizing the probability of being detected by a (potentially larger) conspecific that may have attacked the injured conspecific (and might present a risk of predation to the focal tadpole). They also explored four possible relationships between the plasticity (variation in response to cues) and repeatability across individuals, for the different behaviors investigated. Interestingly, they found all possible combinations of high/low (plasticity) and high/low (repeatability). This has implications for the validity of assumptions made about specific behaviors, and hence provides valuable guidance for future studies of tadpole behavior. (KSummers)

June 10, 2024: If you spend enough time on social media, you may come across some variation of the phrase "heal your gut, heal your brain." While the supplements peddled under such posts may be of dubious value, there is growing scientific research on the reciprocal relationships between vertebrate gut microbiomes and neurological development and function. Emerson and Woodley (2024) investigate the presence of the microbiota-gut-brain axis (MGB) in amphibians by raising Northern Leopard Frog (Rana (Lithobates) pipiens) tadpoles in untreated and autoclaved pond water. Autoclaving reduces the diversity of microbes found in pond water, meaning that the tadpoles were exposed to a different cohort of potential gut symbiotes between the treatments. The autoclaved water treatment produced tadpoles that were bigger, slower, less responsive to stimuli, and had smaller medulla – a brain region involved in physiology. The gut microbiomes of these tadpoles showed reduced diversity and altered composition. Furthermore, microbiome characteristics were correlated with behavior and brain morphology within and across treatments. Amphibian conservation will benefit from further research into the MGB axis; these findings are relevant for determining optimal rearing conditions of captive amphibians and suggest additional unexplored links between anthropogenic changes in environmental microbiota and amphibian neurodevelopment. (Kannon Pearson)

June 3, 2024: There are many iconic amphibian species around the world, and when they disappear, people notice. The Yosemite toad (Anaxyrus canorus) is endemic to California’s Sierra Nevada mountains, and suffered mass die-offs in the late 1970s. Dodge et al (2024) investigated the historical and contemporary effects of Batrachochytrium dendrobatidis (Bd), which causes a fatal amphibian disease called chytridiomycosis on the Yosemite toad. When global amphibian declines were first noticed in the 1970s and 1980s, it was decades before Bd was discovered (1998). This study used a retrospective analysis to determine Bd presence/absence on 719 museum specimens collected between 1915 and 2005, and on an additional 1,678 samples collected from live animals in the wild (2004–2012). Their study found that: 1) Bd emerged coincident with historical declines; 2) Bd is currently widely distributed throughout the species range; 3) life stage, elevation, and precipitation regime were associated with Bd infection likelihood; and, 4) the juvenile life stage was the most highly infected, with some having Bd infection loads surpassing a mortality threshold identified in other species. Thus, Bd may have played a significant yet unrecognized role in the decline of the Yosemite toad, and may continue to affect survival, recruitment, and extinction risk. These represent key insights for efforts to recover this species across its historical range and may also be important in hundreds of other species that declined before Bd was discovered. (VV)

May 27, 2024: Biparental care is rare in amphibians, and evidence for pair-bonding between mates has only been found in a few species, one of which is the mimic poison frog, Ranitomeya imitator. A male and female will defend tightly overlapping territories, and cooperate to place and nurture tadpoles in tiny pools that form in plants (phytotelmata). Males carry tadpoles from clutches to the pools, and then periodically lead the female to the pool, where the female will lay trophic eggs that the tadpole depends on for growth and development, over the course of several months. Interactions between mates frequently involve acoustic signals from males to females, such as males calling to females as they guide them to pools. Podraza et al. (2024) set out to determine if female mimic poison frogs show a preference for the calls of their pair-bonded mate, as might be expected in monogamous and cooperative biparental care over long periods. They used male advertisement calls, as previous research had demonstrated that these calls show substantial variation between individuals, but minimal variation within individuals. The researchers set up arenas with speakers on each end and tested the females by playing male calls from one end and nothing from the other (one choice test), or by playing calls of the pair-bonded partner from one end and a stranger from the other (two-choice tests). In the second test, they tested two types of pair-bonded females, with and without a current clutch of eggs with their partner. Virgin females showed a clear preference to approach and remain near the side with male calls, confirming that females are indeed attracted to such calls. They did not, however, show a preference for any individual male calls, relative to those of other males. In the two-choice tests, females spent significantly more time on the side of the arena with the calls from their mates. Further, females actively involved in parental care responded to their mate’s call more quickly than females who were not currently engaged in parental care. This study provides important experimental evidence regarding the mechanisms underlying pair-bonding in this species. (KSummers)

May 20, 2024: Characterizing species roles in wildlife communities is challenging because most disease emergence events are unpredictable. Compounding the challenge are naive multi-host communities which include species that may differentially maintain, transmit and amplify novel pathogens. Longo, Lips, and Zamudio (2023) used field-collected data from amphibians in the cloud forest of El Cope, Panama, to investigate how species-specific attributes influenced the degree of exposure, probability of infection, and pathogen intensity, during the emergence of the fungal pathogen Batrachochytrium dendrobatidis (Bd). The ecological species traits identified in other Bd studies positively associated with infection prevalence and intensity at the species level during the outbreak. They identified hosts that disproportionately contributed to transmission dynamics and found a signature of phylogenetic history in disease responses. This study establishes a framework that could be applied in conservation efforts to identify key species driving disease dynamics under enzootics before reintroducing amphibians back into their original communities. Reintroductions of supersensitive hosts that are unable to overcome infections will limit the success of conservation programs by amplifying the disease at the community level. (VV)

May 13, 2024: Sulawesi "fanged frogs" (genus Limnonectes) are stream-dwelling dicroglossids that exhibit remarkable divergence in modes of reproduction, body size, prey acquisition, habitat use, and eco-physiology. The Sulawesi Limnonectes assemblage remains understudied, but recent research has identified many cryptic species via phylogenomic, morphometric, and acoustic analyses. Frederick et al. (2023) describes a sixth species of Sulawesi Limnonectes, the terrestrially-nesting species Limnonectes phyllofolia. At least eight additional undescribed species (and possibly many more) have been alluded to in the literature. Sulawesi fanged frogs exhibit 1000-fold variation in adult body mass, with the largest species weighing up to 2 kg; L. phyllofolia represents the smallest species with an average mass of only ~2 grams. Notably, this new species is only the second known Sulawesi exemplar to exhibit terrestrial egg deposition and male egg-guarding behavior, possibly an adaptative response to predation pressure from larger stream-inhabiting Limnonectes species. Males of the new species were observed guarding clutches of 10-20 eggs festooned on the leaves of small bushes or saplings, or on mossy boulders over small side-streams. The authors chose the specific epithet 'phyllofolia' (meaning "leaf nest") to characterize this unique breeding behavior not seen in other Sulawesi fanged frogs. (JFrederick)

May 6, 2024: Plants have a variety of strategies to disperse their seeds. For instance, many species utilize animals to help cast their seeds across larger distances than is possible by wind dispersal alone. Often this involves the production of edible fruit surrounding one or more seeds, the consumption of which by animals results in the seeds being passed some distance from the source tree. Frogs, which rarely consume vegetable matter, are among the least likely candidates for seed dispersal; surprisingly, Gould and Valdez (2024) document Australian Litoria fallax potentially serving just this role. Approximately 30% of frogs in their study population had seeds of the broad-leaved cumbungi plant, Typha orientalis, adhered to their moist skin. Individual frogs were found with up to 14 of these small seeds, which are filamentous in form and typically wind pollinated, attached to their skin. This study highlights a previously unknown plant-amphibian interaction, and showcases the small but real possibility of frog-mediated dispersal involving other plant and amphibian species. (JM)

April 29, 2024: Animal visual systems have evolved at multiple levels of the visual perception pathway according to a given species' visual needs in the light environments it inhabits. Among the most impactful adaptations are changes to the visual opsin proteins, which are the protein component of the light-sensitive visual pigments housed in the photoreceptor cells of the retina that detect and respond to light signals. Schott et al. (2024) examine the diversity and evolution of visual opsins specifically the gene duplication/ loss and sequence evolution across 122 frog species representing 34 families with a diversity of life histories and ecologies. They find most species express four visual opsins with evidence for gene loss in two lineages (Arthroleptidae and Dendrobatidae), which represents a much lower level of gene loss than that inferred in other ancestrally nocturnal vertebrate groups like mammals, snakes, geckos, and crocodilians. This relatively limited gene loss in anurans suggests they have heavily invested in their visual systems despite being predominantly nocturnal. They also find evidence for shifts in selective pressure on each visual opsin associated with differences in ecology (scansorial and aquatic lifestyles) and life history (direct development), highlighting the need for functional studies to better understand how particular substitutions may impact visual pigment function. Finally, Schott et al. measure the spectral sensitivities of visual pigments in a subset of species, greatly expanding the previously known ranges for all frog visual pigments. Surprisingly, much of this variation is not explained by mutations at known "spectral tuning sites" identified in other vertebrates, suggesting that frogs have used unique molecular pathways to achieve this high level of spectral diversity. In sum, their study furthers our understanding of adaptive evolution in frog visual systems and represents an important advance in our growing understanding of vertebrate visual evolution. (RBell)

April 22, 2024: The salamander fungus Batrachochytrium salamandrivorans (Bsal) is spreading in Europe and has the potential to invade North America. Gray et al. (2023) investigated how susceptible North American salamanders, newts, and sirens are to Bsal. They also infected some native and invasive species of frogs. The researchers found that a large portion (74%) of the species they tested could be infected, and over a third (35%) died from the infection, which included both salamanders and frogs. Newts (Salamandridae) and lungless salamanders (Plethodontidae) were among the most vulnerable salamander families, confirming earlier findings (Martel et al. 2014). The findings suggest that Bsal could cause significant salamander die-offs, particularly in the Appalachian region and along the West Coast of the United States. Larval stages (e.g., Eurycea bislineata) were infected as well. Sadly, the study predicts that over 80 salamander species in the US and 140 in all of North America could be lost due to Bsal. Of great concern, Bsal infected two species that frequently occur in the pet trade in the experiments, suggesting these species could be reservoirs of Bsal or could bring Bsal when imported from countries were Bsal occurs; one of them (Osteopilus septentrionalis) is invasive in Florida and has spread to South Carolina, further increasing the threat of disease spread should Bsal arrive to the US. (ACatenazzi)

April 15, 2024: In a recent paper documenting the results of expedition to the tepuis of Brazil – the so-called “Lost World” of Arthur Conan Doyle fame, Fouquet et al. (2024) describe two new species of direct-developing brachycephaloid frogs (the large clade of frogs mostly comprised of species once placed in the genus Eleutherodactylus but later shown through phylogenetic analysis to best be spread across five families of frogs). Remarkably, these two new species,Caligophryne doylei and Neblinaphryne mayeri, not only fall outside of all currently recognized genera of brachycephaloid frogs but they also fall outside of each of the five currently recognized brachycephaloid families! Thus, the authors erect two new families of frogs, Caligophrynidae and Neblinaphrynidae, which we now recognize on AmphibiaWeb. This finding is consistent with the controversial theory that the tepuis could be home to relatively ancient lineages left behind as the ancient plateau eroded away leaving habitat on stilts (so to speak). There may not be dinosaurs on the tepuis, but there are previously undiscovered frog families. Not surprisingly, the recent fieldwork in the Pantepui region has resulted in many new species of herps in addition to these deeply divergent new frog lineages including additional frogs, plus new lizards and snakes. (JM)

April 8, 2024: In populations with highly skewed male sex ratios, females may be overwhelmed with male suitors. In these situations, female choice may be nullified. However, Chen et al. (2024) recently documented a strategy that maximizes Odorrana tormota female choice. These frogs live in noisy, waterfall environments with a 10:1 male to female sex ratio. Both males and females call to attract partners, but field observations and laboratory mate trials both indicate that females show their willingness to mate by blinking at a particular male. To further test the importance of female blinking, males were given preference tests with two simultaneous videos, one of a blinking female and one without blinking. Those tests showed a clear male preference for blinking females. All together, these results indicate that blinking is an effective form of private communication for this species with intense male competition, and this may be the first time blinking has been shown as a social signal in a non-primate species. (AChang)

April 1, 2024: Many lineages of aposematic organisms exhibit high species diversity and high speciation rates, but what causes these groups to diversify more rapidly remains unknown. Medina et al. (2024) investigated whether species with aposematic anti-predator defenses (e.g. bright coloration in toxic frogs) exhibit higher levels of genetic divergence between populations, which may be a first step in the speciation process, compared to non-aposematic species. Analyzing over 3,800 pairwise values of genetic differentiation from more than 750 populations of over 60 frog species, they uncovered that frog species with warning coloration show greater genetic divergence over small distances (at the scale of single-generation gene flow) compared to those without. This suggests that aposematic coloration may somehow contribute to restricted dispersal, potentially leading to increased opportunities for speciation. (Ian Wang)

March 24, 2024: Various frog species have long been used as cell and developmental biology model systems, which makes understanding their genome of particular importance. The first amphibian genome was sequenced in 2010 (Hellsten et al 2010) and the second in 2015 (Sun et al 2015). More recently, Bredeson et al. (2024) reported a high-quality genome assembly for Xenopus tropicalis, which serves as a model for comparative genomics of frogs. Based on short DNA sequencing reads and chromosome conformation capture data, the authors also were able to generated chromosome-scale genome maps for several frog species, notably Eleutherodactylus coqui, Engystomops pustulosus, and Hymenochirus boettgeri. Within chromosomes, they found that the arrangement of genes was conserved across related frog species (i.e., synteny). By comparing gene arrangements across different frog species and performing phylogenetic analysis of interchromosomal rearrangements, they inferred the ancestral genome organization and speed of evolution. And by mapping the 3D genome organization using chromosome conformation capture, the authors were able to rationalize how spatial variation in recombination rates varies across genomes. Given the conservation and stability of the X. tropicalis genome organization, this high-quality genome assembly will help researchers understand genomic variation within anurans, which is crucial for deciphering the molecular basis of development, disease, tissue regeneration, among other non-molecular research questions in this vertebrate model system. (Scott Hansen)

March 18, 2024: Convergent evolution, the independent development of similar phenotypic traits in different lineages, is a widespread phenomenon in nature. Examples range from image-forming eyes in diverse organisms to the repeated evolution of wings in tetrapods. Convergent evolution among close relatives is less-studied and often thought to be generated from shared (homologous) mechanisms, but this is not necessarily always the case. Twomey et al. (2023) studied color convergence in Ranitomeya, a relatively young, color-diverse group of Neotropical poison frogs. By combining phylogenetic analysis with examination of skin pigments and spectral reflectance data, they identified several instances of color convergence based on independent gains and losses of carotenoid and pterin pigments. In one case, red coloration evolved independently via distinct pathways: in one lineage through an increase in the red pterin pigment drosopterin, and in another lineage through red ketocarotenoids. These results demonstrate that convergent evolution can occur through “same” or “different” pathways even when the species involved are only recently diverged. (Evan Twomey)

March 11, 2024: Chemical signalling in frogs is only poorly understood but is expected to be far more common than currently known. Thus far, all cases of proven or suggested chemical communication in frogs are based on skin-derived chemical cues; however, internal tissues may likewise be involved in sequestering communication chemicals in frogs. Schäfer et al. (2024) analysed the volatile chemical composition and the general anatomy of a fatty strand, embedded in the lower jaw of both sexes of West African Saber-toothed Frogs (Odontobatrachidae) and discovered a previously unknown, internal structure which produces sex-, species- and mating related chemical cues. The chemical properties leave little doubt about the breeding related signalling function of the strand’s secretions. Just how the five Odontobatrachus species, use and excrete these cues remains a mystery. Given the anatomical placement and close association with calling related structures it is likely that the chemical cues complement the acoustic signals that both sexes emit. Though preliminary, the Odontbatrachidae add a new dimension to frog communication, highlighting that a deeper look, beyond the salient most obvious signals can be worthwhile. (Marvin Schäfer)

March 4, 2024: Frogs and toads are often known for their acoustic communication, yet many lineages of frogs and toads (anurans) have lost their tympanic middle ears that are vital to airborne hearing in most four-legged animals. Womack and Hoke (2023) used phylogenetic comparative methods to examine whether particular geographic ranges, microhabitats, activity patterns, or aspects of acoustic communication are associated with the many instances of anuran tympanic middle ear loss. They found plenty of overlap between the geographic distributions of eared and earless species and no relationship between a species’ microhabitat (e.g., arboreal, burrowing, etc.) and earlessness. Additionally, they found no noticeable differences in the call frequencies of earless species when compared to eared species. However, they did find a higher prevalence of diurnality in earless species, which could indicate increased importance of visual systems in diurnal species or selection to be acoustically cryptic in daylight. But not all earless species were diurnal, leaving the researchers with no single, clear adaptive explanation that was shared by all earless lineages. The puzzling lack of a universal, adaptive explanation for anuran middle ear loss motivates discussion of alternative hypotheses, including genetic or developmental constraints, and the possibility that anura earlessness is maladaptive. (MWomack)

February 26, 2024: Those trying to understand global amphibian declines in the context of the fossil record are probably out of luck. It’s not that the fossils aren’t there; rather, it’s that the fossils couldn’t be there. That’s the conclusion Krone et al. (2023) draw from a novel analysis of fossilization potential that includes nearly all modern tetrapods. To reach this rather jarring conclusion, the authors measured the area of overlap between the geographic ranges of modern tetrapods and areas of current sediment deposition. If no sediments are being deposited somewhere, no sedimentary rocks from our time period will exist there, which means that the animals living there won't have the opportunity to leave behind fossils. Among major tetrapod groups, amphibians have, by far, the poorest preservation potential, with only 40% of amphibian species having more than 1 km^2 of their geographic range in a sedimentary basin. Amphibians with a large amount of sedimentary basin overlap are even rarer. Additionally, more phylogenetically unique lineages of amphibians tend to be excluded from the fossil record. The authors link all of this to the particular affinity of amphibians for mountainous environments, which are areas of net erosion, rather than sedimentation. If this regime of under-preservation has affected amphibians throughout deep time, fluctuations in their diversity may be in principle impossible to recover. For instance, they show that, were the 40% of currently endangered amphibian species to go extinct, the fossil record would record, at best, a 13.6% drop in amphibian diversity, and more realistically, a drop of less than 5%. While these results suggest that the vast majority of amphibian history has gone unfossilized, their model can help point amphibian paleontologists away from hopeless dead-ends and remind us how precious and ephemeral modern amphibian species are. (Isaac Krone)

February 19, 2024: Nine of the 10 modern families of salamanders occur today in North America. But often overlooked are several other families of salamanders that occurred during the Mesozoic and Cenozoic of North America. One of those, the Batrachosauroididae, occurred along the coastal plain of the Western Interior Seaway during the Late Cretaceous and then persisted along the Southern coastal plain into the Miocene. Bourque and colleagues (2023) describe newly discovered fossils of Batrachosauroides from the Late Miocene of Florida. This reveals that this now extinct family persisted in the Florida peninsula until 9 or 10 million years ago, a time of global cooling. Although Batrachosauroides is now extinct, it co-occurred with other salamanders that still live today in Florida (Ambystoma, Siren), which adds new insight into the timing of turnover of the North American salamander fauna. (DCBlackburn)

February 12, 2024: The caecilian fossil record is remarkably scarce. Although time-calibrated molecular phylogenies suggest that caecilians have existed for more than 200 million years, there has been named fossil referred to any of the lineages alive today (i.e., part of the crown group). Otávio Santos and colleagues (2024) have described a new extinct caecilian, Ymboirana acrux, from the Oligocene (approximately 25 million years ago) of Brazil and that they refer to the living family Typhlonectidae. This extinct caecilian was likely aquatic and was fossilized in what was then a lake. The remarkable preservation of both its vertebral column and much of its skull promises that this fossil will be an important resource for understanding the evolution of caecilians in South America. (DCBlackburn)

February 5, 2024: A whopping 59% of frogs and toads lack data on larval stages. Vera Candioti et al. (2024) quantify these gaps in knowledge of amphibian larvae. Of note is Brachycephaloidea (also known as the Terrarana) with larval stages described in only 3% of 1,228 species and a general lack of information regarding fossorial versus lentic/lotic tadpoles. In general, very few endotrophic species are known (226 species), but they are broadly distributed across the amphibian tree of life and are likely much more widespread than currently described. The Tropical Andes and New Guinea were identified as regions with particularly large knowledge gaps; the Andes is also a hot spot of new species descriptions, suggesting that specific efforts to describe larval stages will be increasingly necessary (Womack et al. 2022). In contrast, the Brazilian Atlantic forest and Madagascar have relatively high proportions of known larval stages. The authors propose that more focus on larval stage descriptions could reveal novel and highly specialized life stages equally exciting for researchers and local communities in addition to more general knowledge that is critical for successful conservation initiatives. (RTarvin)

January 29, 2024: Animals that live underground have to deal with long periods with low oxygen and sometimes high carbon dioxide within burrows. Burrowing mammals often handle this challenge by having lower metabolisms than species that stay above ground. Many amphibians spend lots of time in burrows but it was not clear whether they had lower metabolisms like burrowing mammals. Giacometti and Tattersall (2023) compared metabolic rates among 185 amphibian species with different lifestyles including burrowing, but found that burrowing amphibians did not have lower metabolic rates than non-burrowing amphibians. Instead, they found that species living at higher latitudes generally had higher metabolic rates than species at lower latitudes, regardless of lifestyle. It is possible that having relatively low energy requirements, small body sizes, and multiple respiratory surfaces (skin and lungs) helps amphibians avoid negative respiratory effects of life underground. (MWomack)

January 22, 2024: When toads invade an environment, they arrive armed with a chemical weapon: bufadienolides (BDs). Toads synthesize these potent cardiotoxins and store them in their lumpy skin as a defense against predators. Sawada et al. (2023) demonstrate for the first time that invasive toads can serve as a toxin source for a sequestering predator. The Tiger Keelback, Rhabdophis tigrinus, is a poisonous snake that eats toads and concentrates the consumed BDs in specialized glands that run along its back. R. tigrinus living on Sado island in Japan have been isolated from toad prey for 120,000 to 800,000 years, until the introduction of the Eastern Japanese Common Toad, Bufo formosus (formerly Bufo japonicus formosus) in 1966. The researchers detected bufadienolides in the gland extracts of more than half of the snakes sampled from toad-infested areas of Sado, but found no poison in the snakes sampled from parts of the island not yet invaded by toads. Intriguingly, the BD composition largely matched that of keelbacks which predate native Japanese Common Toad in other regions of Japan, and differed from keelbacks which eat a different toad species, Bufo praetextatus (formerly Bufo japonicus japonicus). This strengthens the case that B. formosus is indeed the source of BDs in Sado island keelbacks. The Tiger Keelback snakes from historically nontoxic populations exhibit different antipredator behaviors than historically poisonous ones, thus the re-toxicification of Sado island keelbacks may have interesting effects on fitness and the microevolution of behavior. While its frequency of occurrence is yet unclear, the phenomenon of invasive species as toxin sources is a novel paradigm for the study of chemical ecology and evolution in a changing world. (Kannon Pearson)

January 15, 2024: Many frog enthusiasts have noticed that some frogs tap their toes on the ground fairly regularly. However we still do not know why most frogs exhibit this "toe tapping" behavior. To better characterize this toe tapping behavior, Vergara-Herrera et al. (2023) created a vibration-sensitive arena and examined toe tapping patterns during feeding in both males and females of the Yellow-striped Poison Frog, Dendrobates truncatus. The researchers found no differences between tapping behavior in males and females but they did find that tapping often increased before frogs attacked prey. And interestingly, frogs with longer third toes were more likely to increase their taps before attack. The patterns of toe tapping provided in this study provide an excellent starting point for asking more questions about the evolution and purpose (if any) of frog toe tapping. (Molly Womack)

January 8, 2024: Microplastics are becoming ubiquitous in waterways used by amphibians, and consequently tadpoles are ingesting those microplastics. There is growing concern of the effects of this environmental pollutant, however, few studies have quantified their effects. Ruthsatz et al. (2023) examined the effects of microplastics and climate change in lab experiments on the development of Xenopus laevis, African Clawed Frog. They found that microplastics increased larval metabolic and developmental rate as well as increased their corticosterone levels. The result of these changes led to juveniles that had wider bodies and longer limbs. Some of these changes were counteracted by the temperature treatments, but the authors noted that in other organisms the degree of temperature change can have opposing effects. Although the biological implications for these changes, particularly in amphibian species with more traditional life histories, is still murky, the illustration of this study that microplastics can cause sublethal and permanent changes to amphibian physiology and morphology is worth further investigation. (AChang)

January 1, 2024: Happy New Year’s! The AmphibiaWeb Team wishes you all a safe and happy year in 2024. We are grateful for the wonderful year we had in 2023 thanks to the enthusiasm and work of our users, contributors, and volunteers. We successfully launched our new initiative Species Account Live Training for AmphibiaWeb (SALTA) to expand our network of experts. So far we had two SALTA workshops and now have 39 new experts who will mentor students and other contributors to AmphibiaWeb. We also recorded 131 new species in 2023, over 680 new photos and 107 new species accounts. However, the main reason for launching AmphibiaWeb over 20 years ago, the alarming global decline of amphibians, has not abated but has since deepened. The recent news highlights have been a sober reminder that our mission to "connect people around the world by synthesizing and sharing information about amphibians to enable research, education, and conservation" is as important as ever.