Amphibian News!

April 21, 2025: In some animals, individuals of the same sex adopt one of several distinct mating strategies—a phenomenon known as alternative reproductive tactics. For amphibians, alternative reproductive tactics are typically environmentally determined, plastic (and reversible), and without accompanying morphological differentiation. A striking exception can be found in the Two-lined Salamander (Eurycea bislineata) species complex, in which some populations exhibit two distinct male phenotypes. "Searching" males use elongate cirri and mental glands for mate location and courtship on land, while “guarding” males develop hypertrophied jaw musculature used in mate-guarding at nesting sites. Kalki and Pierson (2025) analyzed genome-wide SNP data from Eurycea cf. wilderae of known sex and reproductive and provide evidence for XY sex determination and for a Y-linked polymorphism underlying alternative reproductive tactics. They also developed and validated a PCR-based genotyping assay for characterizing the sex ratio and relative frequency of male tactics from a sample of larvae, providing intriguing avenues for future research. (Todd Pierson)

April 14, 2025: Predicting how populations will respond to environmental change is an inherently complex problem often simplified due to the limitations of particular research approaches. For example, conservation genomics studies often lack insight into phenotypic traits important to environmental tolerance, while physiological studies are often limited to individuals from a single population and lack insight into population variation and the capacity for traits to evolve. Forester et al. (2025) combine conservation genomics and physiological ecology to gain important insights into the climate change vulnerability of two cold water stream frogs (Ascaphus montanus and Ascaphus truei). They developed the first annotated reference genome for A. truei and took advantage of a large data set quantifying thermal tolerance across populations of both species from a diversity of thermal environments. The authors first showed evidence for local adaptation to temperature in both species and a genetic basis to critical thermal maximum temperature (CTmax), a common metric to assess thermal tolerance. Importantly, by examining population variation, they were able to conclude that Ascaphus montanus populations appear to exhibit adaptive divergence in CTmax, such that populations have similar vulnerability to future warming. In contrast, Ascaphus truei showed only genomic evidence for local adaptation and no divergence in CTmax. A similar sensitivity to high temperatures across populations means that A. truei populations occupying warmer streams (e.g., low elevation) are closer to their upper tolerance limits and thus more vulnerable to future warming compared to populations occurring in colder streams (e.g., high elevation). The real-world implications of these results mean that management decisions used to mitigate the impacts of future warming on Ascaphus montanus may differ for Ascaphus truei, although both species appear to have high levels of evolutionary potential based on the genomic and physiological data. (Chris Funk)

April 7, 2025: Considering their body size, habitat needs, and modes of dispersal, some amphibian species undergo migrations equally as staggering as those of Caribou or Sandhill cranes. Most migrating amphibians are aquatic-breeding species, moving seasonally between their breeding habitats and their foraging and/or sheltering habitats. 'Habitat split' is a term to describe the situation when those habitats become severed by human development, like roads or farms, potentially making the migration more challenging, risky, or even impossible. Carvalho et al. (2025) investigated how habitat split might impact the occurrence and abundance of amphibians using individual-based models. Focusing on the Brazilian Atlantic Forest and a series of hypothetical landscapes representing different degrees of habitat split, they simulated occurrence and abundance over time for aquatic- and terrestrial-breeding species. They validated their models by comparing their results with field survey data for 18 endemic amphibian species from the focal study area. They found that both terrestrial- and aquatic-breeding amphibians decline in disturbed areas with high habitat split, but that declines were disproportionately higher for aquatic-breeding amphibians. Their work draws attention to the need for land-based conservation strategies that reduce the distance seasonally-migrating amphibians must cross, and reduce their risk in cases where they must cross intervening development. (Emma Steigerwald)

March 31, 2025: Our sense of taste is determined by a set of genes that encode taste receptors. In response to different types of compounds, these proteins initiate cascades of signals that result in behavioral or physiological reactions. For example, while sweet and salty compounds tend to stimulate appetites, bitter and sour ones tend to evoke aversion. In a review of bitter taste receptor genes (the TAS2R gene family) in 661 vertebrate genomes, Higgins et al. (2025) find that amphibians have a uniquely large number of these genes – up to 248 in Rana sylvatica – while other vertebrates may only have a handful. The number of TAS2R genes could not be explained by genome size expansion, or by nearby transposable element content. Instead, the relatively large number of TAS2R genes seems to be related to their physical location on the ends of chromosomes, where recombination events are frequent and can cause duplications, as well as their tendency to be in gene clusters, which could also promote gene duplication during recombination events. They also find that TAS2R genes are expressed in the brain, liver, stomach, and skin, and that some are sensitive to bitter compounds such as toad toxins. Thus, amphibians could be using these proteins as general chemoreceptors throughout their entire body and the TAS2R gene family may act as a previously unrecognized physiological regulator system in amphibians and other animals. Their results reveal future research avenues into how TAS2R genes might help regulate toxin production and metabolism or responses to toxin exposure, providing insights both into how amphibians modulate their own toxicity and why certain compounds produce adverse or allergic reactions. (RTarvin)

March 24, 2025: Sexual differentiation – the developmental process by which an embryo matures into one or the other phenotypic sex – is consequential from an evolutionary perspective because it is generally a requirement for reproduction in species with separate male and female individuals. In most mammals, sexual differentiation is triggered by the presence or absence of a male-specific gene called Sry that is located on the Y chromosome. This trigger for sexual differentiation has remained almost invariant during dozens of millions of years of mammalian diversification, and its stability is a hallmark of purifying selection and biological importance. Surprisingly, however, the genetic basis of sexual differentiation evolves incredibly rapidly in some groups, including amphibians. For example, Evans et al. 2024 discovered unexpected diversity in the genetic processes that determine the sex in different species of the African clawed frog (genus Xenopus), a significant discovery in what was already one of the most widely studied amphibians. Using genomic approaches, a total of eight different sex chromosomes were identified in just 11 Xenopus species, and many or all of these may contain unique and newly evolved genes that trigger male or female sexual differentiation. Previously, researchers had known of only three different sex chromosomes in these frogs. Prevailing theory had suggested that sex-determining genes should typically arise in regions of the genome with a low rate of genetic recombination – the exchange of genetic material within each parent that creates new mixtures of traits in their offspring. Instead, the newly evolved sex determining genes in Xenopus are almost universally located in genomic regions where genetic recombination is high. These findings raise questions about how and why the genetic basis of very important biological traits – such as sexual differentiation – may evolve so quickly, how new genes and genetic function arise, and how factors such as sexual selection may drive rapid evolution. (Ben Evans)

March 17, 2025: Fossils provide us with a lot of information about early amphibian evolution. However, amphibian larva often lack bony structures, rarely fossilize, leaving gaps in our understanding of early amphibian life cycles. Chuliver et al. (2024) discovered a fossilized tadpole from the Middle Jurassic of Patagonia, representing the earliest known tadpole. The tadpole belongs to the species Notobatrachus degiustoi and shows evidence of tadpole gigantism; it’s 159 mm (over 6 inches) long. Most excitingly, this fossil tadpole provides concrete evidence that tadpoles have been on Earth for at least 161 million years and that stem anurans had tadpoles similar to the tadpoles we see today. (MWomack)

March 10, 2025: Environment affects the development of all amphibians. Even if individuals have the same genotype, they can end up looking different under different environmental conditions. In some species, distinct developmental trajectories exist, sort of like forks in the developmental road, that create really different outcomes, which scientists call polyphenisms. Kirk et al. (2024) wanted to investigate what environmental factors contributed to individuals ending up on different forks of the developmental road to better predict how changing environments may affect populations of Arizona Tiger Salamanders (Ambystoma mavortium nebulosum). Using a large data set that spanned 32 years and included larval and adult data from 717 salamanders, they were able to determine both climate and larval density affected whether an individual stayed an aquatic paedomorph or became a terrestrial metamorph (see Image of the Week). Longer growing seasons favored individuals becoming terrestrial metamorphs, while long overwintering cold spells and high larval densities promoted paedomorphic outcomes. This study provides predictions about how changing climates will affect Arizona tiger salamanders and prompts further research on how climate change could affect other species with polyphenisms. (MWomack)

March 3, 2025: When trying to distinguish one species from another we often think about differences in adult traits. However, in animals with complex life cycles, like amphibians, sometimes early life stages are equally or more helpful in discovering the evolutionary relationships among species. Dias et al. 2024 identified and named a new genus of toad - Adhaerobufo - using tadpoles (larval frogs) that were in museum collections and had been collected in past expeditions from the Eastern Pantepui uplands and highlands of Guyana. The tadpole specimens were originally identified as part of a completely different genus of toad, Atelopus, because they were suctorial and had additional adaptations for fast-flowing streams. Molecular analyses revealed they were part of the Rhaebo group of true toads, despite the fact that they looked wildly different from all tadpoles known from that clade. This unexpected result caused a re-examination of the taxonomy within the Rhaebo group and the naming of the new genus. Adults of the genus Adhaerobufo look incredibly similar to close relatives but the tadpoles are extremely distinct, making these tadpoles the key to unraveling the taxonomy of this clade. (MWomack)

February 24, 2025: Most amphibians have some kind of chemical defense to help them avoid or survive predation. Salamanders of the family Salamandridae are known for synthesizing their own defensive chemicals from cholesterol, the samandarines. These are toxic compounds that can cause death in potential predators through respiratory paralysis. Not surprisingly, we lack information regarding the chemical defenses of several lineages in Salamandridae. Eleftherakos et al. (2024) aimed to help fill this gap by surveying two species in the genus Lyciasalamandra from Greece. Using a metabolomics analysis, they confirmed the presence of samadarines in L. helverseni and L. luschani. Their analyses also identified trace amounts of pumiliotoxins, pyrrolizidine alkaloids, and decahydroquinolines, as well as other alkaloids from the same classes of compounds sequestered by poison frogs from their ant and mite prey. These data hint for the first time that some salamanders may be able to sequester toxins from their prey, although further experimental evidence will be necessary to validate this hypothesis. Such diet-derived toxin accumulation may be more widely known in amphibians than previously thought (See Tarvin et al. 2024). (RTarvin)

February 17, 2025: Traits are inheritable characteristics and can vary among individuals, a basis for selection to operate. Repeatability is one of the first quantifiable measures towards suggesting heritability and a potential response to selection. In amphibians, acoustic signals with higher repeatability has been observed to likely have high heritability values, and traits with low repeatability values are likely non-heritable. Moreno-Gómez et al. (2024) conducted a study of variation and repeatability of the calls of males of the Banded Wood Frog, Batrachyla taeniata, from the South American temperate forest. In lab-controlled conditions, they exposed male frogs for eight days to choruses recorded in the field where the animals were collected. They found that variation of acoustic properties was significantly affected by temporal blocks and days of recording, and that the three variables measured behaved differently: call rate generally increased within and throughout days; call duration decreased during these time spans and dominant frequency decreased within days but increased across days. Nonetheless, patterns of change indicate that repeatability tends to increase toward the end of any given day for the three acoustic properties. The overall increase in repeatability values within days for the three call variables analyzed indicate an increase in individual consistency and inter-individual variation, which would imply that females can exert their mate choices based on call features more effectively at later hours of a signaling day. (Leticia Ochoa Ochoa)

February 10, 2025: Social contagion, a phenomenon recorded mainly in mammals and some birds, is the often seemingly spontaneous spread of attitudes, emotions, or behaviors throughout a group from one member to others. The spread of information is analogous to the spread of disease among groups, allowing the group to react in a concerted way generating social cohesion. It is considered the most fundamental and ancestral form of empathy. Nowicki et al. (2024) tested for evidence of emotional contagion in pairs of bonding amphibians (monogamous) of the Mimic Poison frog (Ranitomeya imitator). Through a series of experiments in which the females of the pair were stressed, they measured the cortisone levels before and after the stressing episode, as a physiological biomarker of the animal’s relaxed-stressed state. They found the levels of cortisone did not increase in the females thus no emotional contagion could be observed. Nonetheless, they found that male pair-bonded poison frogs displayed hormonal states matching exclusively with female partners compared to familiar non-partner females. Pair bonded relationships display among the highest levels of key empathetic characteristics, including ingroup familiarity and selectivity, social closeness, and cooperation. Although more experiments are needed to prove emotional contagion in amphibians, this is a novel and exciting approach to explore further. (Leticia Ochoa Ochoa)

February 3, 2025: Unlike humans, when amphibians experienced their own global pandemic with Batrachochytrium dendrobatidis (Bd), isolation and vaccination was not available. We lost many species. But some highly susceptible species populations persisted despite nearby populations being extirpated. Knapp et al. (2024) investigated one such species, Rana sierrae, to see if those populations could be used as source populations for reintroductions. In their 15-year study, they identified three recovering populations of the species in Yosemite National Park, California, that still had low to moderate viral loads but higher viral resistance than naive populations. They transplanted individuals from those populations to 12 new populations and regularly surveyed the sites to estimate adult survival, reproduction, and recruitment. From those reintroductions, nine populations persisted and appear to be established despite the continued presence of Bd at viral loads similar to the source population. In fact, a major correlation to reintroduction success was site choice, with the researcher becoming better at choosing higher quality habitats later in the study. Their study demonstrates that Bd-recovering translocated frogs are able to maintain resistance to Bd in new sites and offers a glimmer of hope in amphibian recovery. (AChang)

January 27, 2025: Robert Hansen and Jackson Shedd are excited to announce the publication of a brand new, comprehensive field guide to California amphibians and reptiles. We’ve been so impressed with the advance copies and are excited to share this bountiful book, California Amphibians and Reptiles. It is the result of nearly 3 years of work and involved the collaboration of almost 300 people, all of whom are listed in the acknowledgments. Their field guide includes detailed accounts for 209 species including established exotics, range maps that reflect both current and historical distributions, 950 color photos that depict within-species and ontogenetic variation, and original color illustrations of all amphibian larvae. The authors' attention to detail and passion are reflected in every page. It will certainly be a required book for all interested in regional herpetology.
Order directly from the publisher or from your local independent bookseller (request it if it’s not there yet!) Start 2025 right with this book, both beautiful and indispensable.

January 20, 2025: The glassfrog Hyalinobatrachium valerioi, commonly known as the Reticulated Glassfrog, is a Neotropical frog that exhibits impressive levels of parental care by fathers. After amplexus and oviposition on vegetation above water, the female leaves the oviposition site and the male remains with the clutch and cares for them by hydrating and protecting them from predators continuously until they hatch. Garrido-Priego et al. (2024) found that there is individual variation in the males’ advertisement calls and that males with longer calls also obtained a higher number of clutches over the study period. Calling and having a clutch nearby also increased the males’ likelihood of mating success on a given night. Moreover, males were often observed calling while sitting on top of their clutches, and these brooding calls differed from normal advertisement calls in several acoustic parameters. If females actually use this acoustic information when choosing a mate remains to be explored in future studies. Their findings demonstrate the prominent role of acoustic communication for female choice, but also an enticement for more studies exploring the role of male parental care in female mate choice. (Eva Ringler)

January 13, 2025: Amphibians are well known to lay their eggs in all sorts of interesting places: from large ponds, rivers, and streams to tiny tree holes and snail shells. Choosing a smaller, isolated place to grow up, like small water pools in tree hollows or bamboo stumps, can keep you relatively safe from competition and predators. But what do you do when you have to poop? Ito and Okada (2024) reared the Taiwanese tree frog (Kurixalus eiffingeri), in the lab and found they do not poop as tadpoles. Instead, these tadpoles keep their feces in their guts until metamorphosis when they leave their small pools of water. Additionally, K. eiffingeri is more tolerant of ammonia than three other species tested in the study. This sanitation strategy might be more widespread, but remains to be tested in other frogs and animals that are restricted to small bodies of water. (MWomack)

January 6, 2025: The fungal pathogen Batrachochytrium salamandrivorans (Bsal) is believed to have invaded Europe from Asia via the amphibian pet trade and has severely damaged the salamander populations there. While several studies have shown that members of the genus Salamandra are highly susceptible to Bsal, few studies have surveyed for the disease broadly. A study by Böning et al (2024) sampled Alpine salamanders (Salamandra atra and S. lanzai) in the mountains of the Alps in Europe. Ecological modelling shows that the Alps and Dinarides mountains, where Alpine salamanders occur, are generally suitable for Bsal, but this study found no evidence of Bsal. They analyzed skin swabs of 818 individuals of Alpine salamanders and co-occurring amphibians at 40 sites between 2017 to 2022. In addition, the study also includes data previously collected from 319 individuals from 13 additional sites, all of them found no Bsal infections. Their study suggests that the salamander plague so far is absent from the geographic ranges of Alpine salamanders. Thus, there is still a chance to implement surveillance and conservation strategies that could help thwart the effects of Bsal on native salamanders in the European Alps and Dinarides mountains. (VV)