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True frog

The true frogs, members of the family Ranidae within the order Anura, are a diverse group of amphibians characterized by smooth or slightly warty moist skin, long and powerful hind legs adapted for jumping, and partially to fully webbed toes that aid in swimming.^[1] They exhibit a wide range of sizes, from small species under 20 mm in snout-vent length to the goliath frog (Conraua goliath), which reaches up to 300 mm and is the largest living frog.^[1] With approximately 463 species distributed across about 25 genera, Ranidae represents one of the most species-rich frog families, though taxonomic revisions continue due to its potentially paraphyletic nature.^[2] Ranids are cosmopolitan in distribution, occurring on every continent except Antarctica, with the highest diversity in the Old World, particularly Asia, and notable presence in North America, Europe, and Africa; they are absent from most of temperate South America, much of Australia (except introduced or native species like the Australian wood frog), and oceanic islands.^[1]^[3] Habitats vary extensively, from riparian zones and wetlands to forests, montane streams, and even arid regions, with many species being semi-aquatic or terrestrial while others are arboreal or fossorial.^[1] Most ranids lack ribs, possess dentate upper jaws, eight holochordal-procoelous presacral vertebrae, and a fused astragalus-calcaneum, though these traits are not unique diagnostics.^[1] Reproduction in true frogs typically involves axillary amplexus, with eggs laid in aquatic clusters that develop into free-swimming tadpoles (type IV larval morphology), though some genera exhibit direct development without a tadpole stage.^[1] Diets primarily consist of insects and other small invertebrates, captured via a protrusible tongue, and behavior includes vocalizations for mating and territorial defense, with adaptations like torrent-specialization in genera such as Amolops.^[3]^[1] Conservation status varies, with many species listed as Least Concern by the IUCN, but others face threats from habitat loss, pollution, and invasive species, exemplified by the introduced American bullfrog (Rana catesbeiana), a model organism in amphibian research that has become invasive in many regions.^[2]^[3]

Taxonomy and Evolution

Evolutionary History

The family Ranidae, comprising true frogs, originated in Eurasia during the Eocene epoch around 50 million years ago, as evidenced by fossil records from this period. Early fossils include the ilium of an indeterminate ranid from the Vastan Lignite Mine in Gujarat, India, dated to the early Eocene (approximately 53.5–48.6 million years ago), and the genus Thaumastosaurus from late Eocene deposits in western Europe, representing an endemic European radiation. These findings suggest an initial diversification in the northern continents following the breakup of Pangaea, with Indorana-like forms indicating possible links to Asian lineages.^[4] The evolutionary origins of Ranidae have been debated, with an earlier Gondwanan hypothesis proposing a late Cretaceous diversification tied to the breakup of the supercontinent, leading to continent-scale endemism in Africa, Asia, and the Americas. However, modern molecular phylogenies refute this vicariance model, instead supporting an Eurasian cradle and Laurasian radiation, where the crown group arose in Paleogene Asia (likely Indochina) and underwent multiple dispersals. A 2017 molecular study analyzing 95% of ranid diversity estimated the crown Ranidae at approximately 48 million years ago, emphasizing dispersal over vicariance as the driver of global distribution, consistent with fossil-calibrated trees showing no pre-Eocene ranid fossils in Gondwana.^[5]^[6] By the early Miocene, around 20 million years ago, Ranidae had achieved a near-cosmopolitan distribution through a combination of vicariance via land bridges—such as the Bering and Tethys connections—and rare overwater rafting events. This dispersal enabled colonization of North America (via Beringia), Africa (possibly from Eurasian stock), and isolated regions like parts of South America, with no native species in Australia. Fossil evidence from Miocene sites in Europe and Asia corroborates this expansion, with ranids adapting to new temperate and tropical niches.^[6]^[7] During the Paleogene, Ranidae evolved key adaptations that underpinned their ecological success, including semi-aquatic to fully aquatic lifestyles tied to riparian and lentic habitats, and indirect development featuring exotrophic tadpoles with specialized herbivorous or detritivorous feeding. These traits, evident in Eocene fossils with robust ilia suited for jumping into water, allowed exploitation of freshwater ecosystems amid post-Cretaceous environmental shifts, contrasting with more terrestrial anuran clades and facilitating rapid diversification.^[5]

Classification and Systematics

The true frogs, family Ranidae, are placed within the order Anura and suborder Neobatrachia, comprising a diverse group of cosmopolitan anurans characterized by generalized morphology and broad ecological tolerances.^[2] The family includes the subfamily Raninae, encompassing core Eurasian and North American lineages such as the genus Rana; other subfamilies such as Amolopsinae, Meristogenyinae, and Stauroinae are recognized in some classifications (e.g., Amphibian Species of the World). Petropedetinae, previously included, is now treated as the separate family Petropedetidae.^[2]^[8] This classification reflects ongoing refinements based on integrated morphological and molecular evidence, with AmphibiaWeb and the IUCN Red List serving as primary references for current taxonomy, listing approximately 464 species across 25 genera.^[2] Historical revisions to Ranidae systematics began intensifying in the early 2000s, driven by molecular phylogenetic analyses that revealed extensive polyphyly within the traditional family boundaries. Former subfamilies such as Dicroglossinae (now a distinct family of Oriental ranoids) and Mantellinae (elevated to family status for Madagascan endemics) were recognized as independent lineages based on mitochondrial and nuclear DNA sequences, necessitating their separation from Ranidae to achieve monophyly. A pivotal change occurred in 2006, when Frost et al. comprehensively split the polyphyletic genus Rana into over a dozen genera, including Lithobates for New World species, Pelophylax for European water frogs, and Odorrana for East Asian cascade frogs, based on a multi-gene phylogeny that resolved deep divergences within the family. These revisions reduced Rana sensu stricto to primarily Holarctic brown frogs, fundamentally reshaping the family's internal structure.^[7] More recent taxonomic adjustments include a 2023 proposal by the Amphibian Species of the World database to tentatively synonymize several Southeast Asian genera—such as Amnirana, Chalcorana, Humerana, Hydrophylax, Indosylvirana, Papurana, Pulchrana, and Sylvirana—back into a broadly defined Hylarana, reversing some post-2006 splits to simplify nomenclature amid unresolved phylogenetic ambiguities.^[9] However, this synonymy remains controversial and not universally accepted, with some researchers advocating retention of separate genera based on morphological and ecological distinctions, highlighting persistent debates in Asian ranid systematics. For example, AmphibiaWeb maintains Hylarana with 14 species and recognizes the other genera separately.^[10]^[2] Phylogenetic challenges in Ranidae have centered on resolving historical polyphyly, particularly in Old World lineages, through analyses of mitochondrial DNA (mtDNA) and multiple nuclear genes. Early studies in the 2000s identified convergent morphological traits masking deep genetic divergences, but subsequent multi-locus phylogenies, such as those employing 12S rRNA, 16S rRNA, and RAG1 sequences, confirmed the monophyly of core Ranidae while excluding unrelated groups previously lumped within it.^[11] For instance, Yuan et al. (2016) integrated mtDNA and nuclear data to delineate Rana proper as monophyletic within Raninae, addressing prior uncertainties and providing a robust framework for subfamily boundaries that aligns with Eocene origins as a foundational divergence point in anuran evolution.^[7] These molecular approaches continue to underpin systematic stability, though ongoing sampling in understudied tropical regions may prompt further refinements.^[2]

Diversity and Genera

The family Ranidae encompasses approximately 464 species distributed across 25 genera.^[2] Key genera include Abavorana, with 3 species restricted to Southeast Asia; Amnirana, comprising 13 species mainly in Africa; and Babina, represented by 2 species in East Asia.^[2] Hylarana includes 14 species native to Asia.^[2] Lithobates contains 28 species across the Americas, while Pelophylax includes 10 species in Eurasia, and the core genus Rana accounts for about 100 species in the Holarctic realm.^[2]^[12] Certain fossil forms remain incertae sedis pending systematic revision. Diversity hotspots occur regionally, with Asia hosting over 200 species, followed by Africa and North America.^[2] These patterns reflect ongoing taxonomic refinements from molecular studies.^[13]

Physical Characteristics

Morphology

True frogs in the family Ranidae exhibit a generalized anuran body plan characterized by bilateral symmetry, a compact trunk, and the absence of a tail in adults. Their skin is typically smooth and moist, facilitating cutaneous respiration and hydration in aquatic or semiaquatic environments, though some species show slight granulation or warty textures. The hindlimbs are robust and elongated, adapted for powerful propulsion, while the forelimbs are shorter and less specialized; the hind feet feature partial to complete webbing between the toes, aiding in swimming, whereas the hands usually lack webbing.^[2]^[1] The head is broad and distinct from the body, with large protruding eyes positioned dorsolaterally and featuring horizontal pupils for enhanced binocular vision in low-light conditions. A prominent, externally visible tympanum serves as the eardrum, enabling auditory detection of conspecific calls and environmental cues. The mouth includes vomerine teeth on the roof for grasping prey and dentate maxillary teeth along the upper jaw margins, supporting a carnivorous diet in adults.^[14]^[1] Skeletal features include eight holochordal-procoelous presacral vertebrae, reflecting a derived anuran condition with reduced rib elements and a firmisternal pectoral girdle where the epicoracoid cartilages are fused medially. The ilium is notably elongated and slender, articulating with the sacrum to form a lever system that amplifies force during leaps, a key adaptation for the family's locomotor ecology. The astragalus and calcaneum of the tarsus are fused only at their proximal and distal ends, contributing to ankle flexibility.^[14]^[15] Larval stages, known as tadpoles, conform to Orton's Type IV morphology, featuring a depressed body with dorsolaterally placed eyes, a sinistral spiracle, and keratinized mouthparts including a serrated beak and labial tooth rows (typically 2/3 configuration) suited for scraping algae and detritus. These exotrophic, benthic forms possess a muscular tail for propulsion and a coiled gut for processing plant material, with most species undergoing aquatic metamorphosis.^[16] Sexual dimorphism is evident primarily during the breeding season, with males possessing paired subgular vocal sacs that inflate to amplify advertisement calls, and nuptial pads—keratinized, glandular swellings on the thumbs and sometimes other digits—for improved grasp during amplexus. Females lack these structures but may exhibit slightly larger body proportions overall.^[17]^[18]

Size, Coloration, and Adaptations

True frogs in the family Ranidae exhibit a wide range of body sizes, reflecting their diverse ecological niches across global habitats. The smallest species, such as Staurois parvus, measure approximately 20–25 mm in snout-vent length (SVL) in males.^[19] In contrast, larger species like the American bullfrog (Lithobates catesbeianus) attain 9–15 cm SVL, making it one of the largest in the family.^[20] The overall family size range spans ~20–300 mm SVL, with the goliath frog (Conraua goliath) representing the upper extreme at up to 300 mm.^[1] Coloration among true frogs varies significantly, often serving cryptic functions tied to their lifestyles. Aquatic and semi-aquatic species, such as the American bullfrog, typically display a green or olive dorsal surface with pale, light-colored ventral sides to blend with aquatic vegetation and water reflections.^[21] Terrestrial forms tend toward brown or gray hues for camouflage in leaf litter or soil, while species like the northern leopard frog (Lithobates pipiens) feature bold patterns of dark spots or blotches on a green to brown background, arranged in irregular rows along the back and legs.^[22] Specialized adaptations in Ranidae enhance survival in varied environments. Arboreal species, including some in the genus Amolops, possess expanded digital tips on their toes that provide adhesion for climbing vegetation, facilitating life in forested canopies.^[1] Burrowing forms have reinforced, hardened snouts to aid in excavating soil during dry periods, as seen in certain ground-dwelling ranids.^[1] Sexual dimorphism and ontogenetic changes further diversify appearance within the family. Males often appear darker or develop brighter throat coloration during breeding seasons to signal mates, as observed in Lithobates catesbeianus where males exhibit yellow throats.^[20] Juveniles typically display more vibrant or contrasting patterns than adults, which fade with maturation to enhance camouflage, a pattern evident in species like the northern leopard frog.^[22]

Distribution and Habitat

Global Distribution

The family Ranidae, commonly known as true frogs, exhibits a nearly cosmopolitan distribution, occurring naturally on all continents except Antarctica. They are absent from the temperate regions of South America but are present in the tropical Andes, where species such as Lithobates palmipes inhabit lowlands and Amazonian areas east of the Andes.^[23] One species, Papurana daemeli (Australian wood frog), is native to northern Australia, while introduced populations have also established in Australia and various oceanic islands, often through human activities.^[24]^[25] Key regions of diversity include the Holarctic realm, where the genus Rana is prominent with 54 species across Eurasia and parts of North America, such as Rana temporaria in Europe and Rana catesbeiana in North America. In the Afrotropical region, the genus Amnirana is prominent, comprising about 13 species primarily in sub-Saharan Africa. The Neotropical region features the genus Lithobates, which includes former Rana species and is centered in the Americas with 37 species.^[2]^[12] The dispersal history of Ranidae involves natural pathways such as crossings via the Beringian land bridge for Holarctic expansion and the Afro-Arabian plates for connections between Africa and Eurasia. Human-mediated introductions have further expanded ranges, notably the American bullfrog (Lithobates catesbeianus), which was brought to Europe starting in the 1930s and to South America in the 1980s–1990s for aquaculture and food production.^[7]^[5]^[26]^[27] As of 2025, over 90% of the 464 Ranidae species are found in the Eastern Hemisphere, reflecting the family's Asian origins and subsequent radiations, while about 50 species occur in the Americas, predominantly in Lithobates. Diversity hotspots are closely tied to major genera like Rana and Amnirana.^[2]^[8]

Habitat Preferences

True frogs, belonging to the family Ranidae, primarily inhabit lentic freshwater systems such as ponds, marshes, and slow-moving streams, where they exhibit a semiaquatic lifestyle often associated with riparian zones for breeding and foraging.^[2] These environments provide the necessary moisture for their permeable skin and support the aquatic larval stages typical of most species in the family.^[28] Dominance in such aquatic habitats is a key characteristic, with many species rarely venturing far from water bodies to avoid desiccation.^[14] Habitat variations within Ranidae reflect ecological diversity, including arboreal adaptations in some Asian species like those in the genus Hylarana, which utilize forest canopies and lowland rainforests for shelter and movement.^[29] Terrestrial preferences are evident in European genera such as Pelophylax, which occupy grasslands and forested areas adjacent to water, favoring open to semi-wooded landscapes for dispersal and refuge.^[30] In arid African regions, certain genera exhibit burrowing behaviors, estivating underground in savannas and semiarid zones during dry periods to conserve moisture.^[31] Microhabitat requirements emphasize high humidity levels and dense vegetation cover, essential for egg deposition in protected, moist sites that prevent desiccation of clutches.^[32] Species tolerate a broad elevational range, from sea level to over 2,200 meters in populations like Rana temporaria in montane areas, with some Himalayan representatives extending to higher altitudes in streamside habitats.^[33] Climate associations span temperate to tropical zones, with eurythermic species capable of enduring freezing temperatures through hibernation strategies, such as burrowing into substrate or leaf litter.^[34] Coloration in these frogs often aids camouflage against the varied substrates of their preferred moist, vegetated environments.^[31]

Behavior and Ecology

Activity and Locomotion

True frogs (family Ranidae) exhibit primarily nocturnal or crepuscular activity patterns, with individuals becoming active during twilight or nighttime hours to forage and move, particularly in warmer or wetter conditions.^[35] In some temperate species, such as the northern leopard frog (Rana pipiens), activity extends into diurnal periods, allowing day-night flexibility influenced by temperature and habitat availability.^[36] Species in regions with cold winters, like the pool frog (Rana lessonae) and edible frog (Rana esculenta), enter hibernation, burrowing into soil or leaf litter at depths of 3-7 cm to overwinter from late fall to early spring.^[37] In arid or dry climates, certain ranids undergo aestivation, a dormant state that reduces metabolic demands during periods of low oxygen or desiccation stress.^[38] Locomotion in true frogs is predominantly saltatory, relying on powerful hindlimbs for jumping as the primary mode of terrestrial movement, enabling rapid escape and navigation across varied terrains.^[39] Aquatic species utilize webbed feet for efficient swimming, generating propulsive impulses through synchronized hindlimb strokes, as observed in the edible frog (Rana esculenta).^[40] Terrestrial and semi-aquatic forms may employ walking gaits for short distances, while some ranids incorporate climbing behaviors using adhesive toe pads and elongated limbs to ascend vegetation. Sensory behaviors in true frogs include auditory and chemosensory modalities for environmental interaction. Males produce vocalizations from fixed positions at water edges to establish territory and attract mates, with calls serving as acoustic signals for conspecific communication.^[41] Chemosensory detection occurs via the skin, allowing individuals to identify prey through chemical cues released into the environment and to sense predator threats, as demonstrated by avoidance responses in species like the northern leopard frog (Rana pipiens) to conspecific skin extracts and Iberian green frog (Rana perezi) to snake odors.^[42]^[43] Socially, true frogs are generally solitary outside of breeding seasons, minimizing interactions to conserve energy in their often dispersed habitats.^[44] However, territorial defense is common among males, who use vocalizations or postural displays to repel intruders and maintain calling sites, particularly in species like the bullfrog (Lithobates catesbeianus).^[44] This territoriality ensures resource access without widespread aggregation beyond reproductive periods.^[45]

Diet and Predatory Interactions

True frogs in the family Ranidae are primarily carnivorous as adults, consuming a diverse array of invertebrates such as insects, earthworms, spiders, and beetles, with larger individuals preying on small vertebrates including fish, smaller frogs, and occasionally birds or mammals.^[46]^[31] Foraging typically employs a sit-and-wait ambush strategy, where frogs remain stationary near water edges or vegetation to strike at passing prey opportunistically, though some species actively pursue food during nocturnal activity.^[31] Larger species, such as the American bullfrog (Lithobates catesbeianus), exhibit broader opportunistic feeding, ingesting vertebrates like small mammals and birds in addition to invertebrates.^[31] In contrast, tadpoles of Ranidae are mostly herbivorous or detritivorous, grazing on algae, diatoms, plankton, bacteria, and organic detritus in aquatic environments, though some populations incorporate animal matter like dead tadpoles or insect larvae.^[47]^[48] This dietary shift supports rapid growth during the larval stage, with gut morphology adapting to process plant-based foods through longer intestines in herbivorous forms.^[49] True frogs serve as prey for a range of predators, including birds (e.g., herons), snakes, mammals (e.g., raccoons and foxes), and fish, particularly during aquatic life stages.^[50] Anti-predator defenses vary but commonly include rapid jumps to escape threats, behavioral responses like reduced activity in larval stages upon detecting predator cues, and feigning death in some species to deter further attack.^[51] Additionally, certain genera produce toxic skin secretions containing antimicrobial peptides and mild toxins that can deter predators or cause irritation upon contact.^[52]^[53] Ecologically, true frogs regulate insect populations through their carnivorous habits, acting as key predators in wetland food webs while providing a vital prey base for higher trophic levels.^[46] As invasive species, such as Lithobates catesbeianus, they disrupt native ecosystems by preying on local amphibians, reptiles, and invertebrates, often leading to declines in biodiversity and altered community structures in invaded regions.^[54]^[55]

Reproduction and Life Cycle

Mating Behaviors

Males of true frogs (family Ranidae) typically initiate courtship by producing species-specific advertisement calls, such as trills or low-frequency chuckles, from calling sites in breeding aggregations known as choruses.^[56] These calls serve to attract receptive females and deter rival males, with females often selecting mates based on call characteristics like duration, frequency, and complexity that indicate male quality and genetic fitness.^[57] Vocal sacs in males amplify these calls, enhancing their range during choruses.^[1] Once a female approaches, the male grasps her in axillary amplexus, positioning his forelimbs around her upper body near the armpits to ensure precise sperm release upon egg deposition.^[56] This embrace can last from several hours to multiple days, synchronizing with the female's oviposition and preventing premature separation.^[58] True frogs are often explosive breeders, converging in large choruses at temporary ponds, flooded fields, or slow-moving streams during rainy seasons or post-hibernation periods in temperate regions.^[57] These sites provide ephemeral aquatic habitats suitable for larval development, with choruses forming rapidly in response to environmental cues like rainfall.^[56] Most true frogs exhibit indirect development with an aquatic tadpole stage, though direct development without a tadpole stage occurs rarely in some species.^[1] Additionally, satellite males—typically smaller individuals—remain silent near active choruses and attempt to intercept females already in amplexus with calling males, exploiting the attraction provided by the primary callers without expending energy on vocalization.^[59]

Development and Parental Care

True frogs (family Ranidae) exhibit a typical anuran biphasic life cycle, beginning with egg deposition following amplexus. Females deposit clutches ranging from hundreds to over 10,000 eggs, depending on species and environmental conditions; for instance, Chalcorana labialis produces 787–2,100 eggs per clutch, while larger species like the American bullfrog (Lithobates catesbeianus) can lay up to 20,000. These eggs are encased in gelatinous, spherical masses that provide protection and oxygenation, often attached to submerged vegetation, rocks, or pond substrates in lentic waters. Incubation periods vary with temperature but generally last 1–4 weeks; in Rana temporaria, hatching occurs in about 10–14 days at 15–20°C, whereas in higher-altitude species like the mountain yellow-legged frog (Rana muscosa), it extends to 18–21 days. Upon hatching, ranid larvae emerge as tadpoles characterized by a tail for propulsion, external gills transitioning to internal ones, and a ventrally positioned oral disc. Most ranid tadpoles conform to Type IV morphology as described by Altig and McDiarmid, featuring a sinistral spiracle, dextral vent tube, and a beak with multiple rows of keratodonts (labial tooth rows) adapted for rasping algae and detritus from surfaces. This morphology supports an exotrophic, primarily herbivorous or detritivorous diet, with the oral disc functioning as a suction mechanism to cling to substrates while feeding. The larval stage lasts 1–3 months, influenced by water temperature, food availability, and pond permanence; for example, in Lithobates pipiens, metamorphosis completes in 2–3 months under optimal conditions. Metamorphosis in true frogs is hormonally regulated, primarily by surges in thyroid hormones (thyroxine and triiodothyronine), which orchestrate the resorption of the tail, gill degeneration, and development of lungs and limbs. This process transforms the aquatic tadpole into a terrestrial juvenile frog, typically occurring in shallow waters to facilitate emergence. The timing is species-specific but aligns with the larval duration, with peak thyroid hormone levels coinciding with rapid morphological changes during Gosner stages 42–46. Parental care in Ranidae is generally minimal, with most species abandoning eggs immediately after deposition, relying on the gelatinous matrix for protection against desiccation and predation. However, exceptions exist in certain genera; for example, some species in Babina and Nidirana engage in simple parental care such as egg attendance in mud nests.^[31] Post-metamorphosis, juvenile true frogs resemble miniaturized adults in morphology and behavior, dispersing from breeding sites to forage independently. Growth is rapid initially, with individuals reaching sexual maturity in 1–3 years, varying by species, latitude, and resource availability; northern leopard frogs (Lithobates pipiens) mature at 1–2 years in males and 2–3 years in females, whereas subtropical species like Rana rugosa attain maturity at 1–2 years for males and 2–3 years for females. Lifespan and maturity age are influenced by predation, climate, and habitat quality, with smaller-bodied species often maturing earlier.

Conservation

Major Threats

Habitat loss represents the primary threat to populations of true frogs (family Ranidae), driven by deforestation, agricultural expansion, urbanization, and infrastructure development, which degrade essential wetland and riparian habitats.^[60] These activities affect a large proportion of all threatened amphibian species, including 77% impacted by agriculture, 53% by logging and plant harvesting, and 40% by infrastructure development, with many Ranidae such as the northern leopard frog (Lithobates pipiens) and Chiricahua leopard frog (Lithobates chiricahuensis), leading to fragmentation and reduced breeding sites that exacerbate population declines.^[60] In regions like the southwestern United States, logging and water management have contributed to the extirpation of local populations of species like the lowland leopard frog (Lithobates yavapaiensis).^[61] Climate change poses an escalating risk to true frogs by altering breeding phenology, causing wetland desiccation through altered precipitation patterns, and increasing ultraviolet-B (UV-B) radiation exposure, which damages eggs and larvae.^[60] This threat drives 39% of recent deteriorations in amphibian conservation status globally, with Ranidae species like the mountain yellow-legged frog (Rana muscosa) experiencing habitat shifts and reduced survival in montane environments due to warming temperatures and prolonged droughts.^[60]^[62] Diseases, particularly chytridiomycosis caused by the fungus Batrachochytrium dendrobatidis (Bd), have led to severe declines in true frog populations by disrupting skin function and electrolyte balance, resulting in mass mortality.^[62] Bd has caused declines in over 500 amphibian species, including Ranidae genera such as Lithobates, with notable impacts on the Tarahumara frog (Lithobates tarahumarae) in Mexico, where infections combined with environmental stressors like cold temperatures have caused significant die-offs.^[62]^[63] Ranavirus outbreaks further compound these risks, contributing to co-infections that amplify mortality rates in species like the southern leopard frog (Lithobates sphenocephalus).^[62] Within Ranidae, disease like chytridiomycosis has contributed to declines in numerous species, aligning with global amphibian trends where 41% are threatened as of 2023, with ongoing assessments.^[60] Invasive species and pollution add to the vulnerabilities of native true frogs, with introduced American bullfrogs (Lithobates catesbeianus)—also in Ranidae—acting as predators and competitors that reduce native occurrence by up to eightfold in shared habitats, while vectoring pathogens like Bd and ranavirus.^[61] Pesticides, such as atrazine and 2,4-D, bioaccumulate in aquatic environments, impairing reproduction and development in Ranidae species by disrupting endocrine systems and increasing susceptibility to diseases, as observed in studies on northern leopard frogs where exposure led to higher mortality during breeding seasons.^[64]^[65]

Status and Protection Efforts

The conservation status of true frogs (family Ranidae) varies widely across the approximately 460 species, with the International Union for Conservation of Nature (IUCN) assessing approximately 37% as threatened in its 2025 Red List update, including 7 Critically Endangered, 6 Endangered, and 14 Vulnerable species; additionally, 12 species are classified as Data Deficient, while many others are Least Concern but exhibit declining trends in certain regions due to ongoing pressures.^[66] Notable examples include the northern leopard frog (Lithobates pipiens), which is globally Least Concern but has shown recovery in North American populations through targeted initiatives, and the mountain yellow-legged frog (Rana muscosa), listed as Critically Endangered primarily due to chytrid fungus impacts on its California habitats.^[67]^[68] Protection efforts emphasize habitat restoration, such as wetland creation projects in Europe under the EU LIFE AMPHICON initiative, which targets species like the moor frog (Rana arvalis) by restoring ponds and reducing fragmentation.^[69] Captive breeding programs support Asian endemics, including efforts for the Kao Nan stream frog (Rana kaoensis) in Taiwan, combining headstarting with disease screening to bolster wild releases.^[70] International trade regulation under the Convention on International Trade in Endangered Species (CITES) covers select species, such as the goliath frog (Conraua goliath), listed in Appendix I to curb overexploitation for food and pets. Ongoing research and monitoring rely on platforms like AmphibiaWeb for species accounts and IUCN Red List updates to track population trends, while genetic studies facilitate reintroductions, as seen in analyses of Rana muscosa populations to ensure source diversity and minimize inbreeding in California recovery efforts.^[2]^[71]^[72]

References

[1]
Ranidae (Ranid Frogs, Ranids, Riparian Frogs, True Frogs)
Most ranids lack ribs, have dentate upper jaws, eight holochordal-procoelous presacral vertebrae, and an astragalus and calcaneum that are fused only at their ...
[2]
Ranidae - AmphibiaWeb
Notable Family Characteristics. Terrestrial and aquatic; Inhabits a wide range of habitats, ecoregions and elevations; Eggs are typically laid in water and ...
[3]
Ranidae - true frogs | Wildlife Journal Junior - New Hampshire PBS
True frogs have a bony breast bone, long legs, and webbed toes. They lay their eggs in the water. Most species eat insects.
[4]
Eocene Western European endemic genus Thaumastosaurus
Aug 27, 2018 · The fossil finds of the genus from the studied localities allow to refer the previously suggested Eocene true frogs to the genus ...
[5]
Late Cretaceous Diversification Resulted in Continent-Scale ...
Phylogeny and Biogeography of a Cosmopolitan Frog Radiation: Late Cretaceous Diversification Resulted in Continent-Scale Endemism in the Family Ranidae.
[6]
Did true frogs 'dispersify'? | Biology Letters - Journals
Aug 9, 2017 · Did true frogs 'dispersify'? Kin Onn Chan. Kin Onn Chan. http://orcid ... Ranidae [9,14] but strongly conflicted with another study ...
[7]
Spatiotemporal Diversification of the True Frogs (Genus Rana)
Abstract. True frogs of the genus Rana are widely used as model organisms in studies of development, genetics, physiology, ecology, behavior, and evolution.
[8]
Hylarana Tschudi, 1838 - Amphibian Species of the World
S. Afr.: 266. Synonymies of African species of "Hylarana" (now Amnirana) provided by Perret, 1977, Rev. Suisse Zool., 84: 842-844.
[9]
Description of a new cryptic Amnirana species (Amphibia, Anura ...
This synonymy has not been universally adopted (e.g., Conradie et al. 2023 ... Rana, Sylvirana, Hylarana, Amnirana, and most recently to Indosylvirana.
[10]
Phylogeny of Raninae (Anura: Ranidae) inferred from mitochondrial ...
Phylogenetic relationships among representative species of the subfamily Raninae were investigated using approximately 2000 base pairs of DNA sequences from ...
[11]
Hylarana) from Halmahera, Northern Moluccas, with the Description ...
Aug 5, 2024 · This species has long been considered a junior synonym of Rana varians by Boulenger (1920) and R. ... Chalcorana, Humerana, Papurana, Sylvirana, ...
[12]
Lithobates Fitzinger, 1843 | Amphibian Species of the World
Lithobates Fitzinger, 1843. Class: Amphibia > Order: Anura > Family: Ranidae > Genus: Lithobates. 37 species. Lithobates Fitzinger, 1843, Syst. Rept.: 31. Type ...<|separator|>
[13]
Phylogenetic relationships of southern Wallacean ranid frogs (Anura
Aug 6, 2025 · Glandirana susurra is an endemic species of ranid frog from Sado Island in northwestern Japan. Previous phylogenetic studies indicated that this ...
[14]
Ranidae - an overview | ScienceDirect Topics
Frogs belonging to the genus Rana, often referred to as “true frogs”, are included in the family Ranidae within the suborder Neobatrachia. These amphibians ...
[15]
[PDF] Fauna of Australia 2A - Amphibia - Ranidae - DCCEEW
Australian Ranidae, or 'True frogs', are ground-dwelling frogs characterised by the following features. The pectoral girdle is firmisternal, with the sternum.Missing: anatomical | Show results with:anatomical
[16]
Larval morphology in four species of Hylarana from Vietnam and ...
Mar 25, 2009 · The tadpoles of these four species are generalized exotrophic lentic-benthic forms of Orton's Type 4 with a depressed body shape, dorsolaterally ...
[17]
Transcriptome analysis reveals the genetic basis underlying the ...
Dec 30, 2024 · Nuptial pads, a typical sexually dimorphic trait in anurans, are located on the first digit of the male forelimb in Rana chensinensis and ...
[18]
Histology and histochemistry of androgen-stimulated nuptial pads in ...
Aug 6, 2025 · Nuptial pads are digital specializations of male frogs that cycle with the reproductive season, and that are thought to function in mating.
[19]
Hylarana taipehensis | Two-striped Grass Frog
The Two-striped Grass Frog is 3-4 cm, with green-brown or pale-brown back, two golden-yellow stripes, white belly, and lives in cultivated fields, grasslands, ...
[20]
https://nas.er.usgs.gov/queries/FactSheet.aspx?SpeciesID=71
[21]
Species Profile - Lithobates catesbeianus
Adults range in size between 9 and 15.2 cm (snout vent length) (Powell et al. 2016). Lithobates catesbeianus can be identified by their green or olive ...
[22]
Northern leopard frog | Minnesota DNR
Color: Brown or green with two or three rows of irregularly spaced dark spots. Spots are rounded and have light borders. There are two color mutations of the ...
[23]
Convergent adaptive radiations in Madagascan and Asian ranid ...
The adaptive radiation on Madagascar produced more than 120 species comprising (Figs. 1 and 2): burrowing frogs, arboreal frogs, torrential frogs, and the ...Missing: brackish | Show results with:brackish
[24]
Crab-eating Frog - Fejervarya cancrivora - Ecology Asia
The species (and its tadpoles) can tolerate brackish water. Its diet will vary depending on habitat: a study in Singapore showed that in mangrove areas it ...
[25]
Salinity Acclimation Affects Survival and Metamorphosis of Crab ...
Mar 1, 2012 · Tadpoles of F. cancrivora inhabit brackish water and have been reported to tolerate 24- and 35-ppt salinity (which approaches that of seawater) ...
[26]
Lithobates palmipes (Spix, 1824) - Amphibian Species of the World
Distribution. Northern and Amazonian South America east of the Andes, including Colombia, Ecuador, Peru, Bolivia, Venezuela, Guyana, Suriname, French Guiana ...
[27]
Emerging community reports of the highly invasive American ...
Feb 6, 2023 · Elouise Mo Sydney, New South Wales, Australia ... Emerging community reports of the highly invasive American Bullfrog (Lithobates catesbeianus) in ...
[28]
Rana catesbeiana - AmphibiaWeb
Yuan et al. (2016) recognized subgenera within Rana for the major traditional species groups, with Lithobates used as the subgenus for the Rana palmipes group.Missing: count | Show results with:count
[29]
Ranidae Batsch, 1796 | Amphibian Species of the World
Ranidae Batsch, 1796. Class: Amphibia > Order: Anura > Family: Ranidae. 458 species. Ranae Laurenti, 1768, Spec. Med. Exhib. Synops. Rept.: 20. Unavailable ...
[30]
Ranidae | Frogs, Toads, Tadpoles - Britannica
Members of this group are referred to as the true frogs. Although most are aquatic or semiaquatic, a few ranids are ground burrowers or arboreal. Some species ...
[31]
Hylarana erythraea - AmphibiaWeb
This species is found throughout much of southeast Asia, at elevations up to 1,200 m above sea level (Diesmos et al. 2004). R. erythraea occurs in Brunei ...Missing: count | Show results with:count
[32]
Pelophylax ridibundus - AmphibiaWeb
This species is generally an abundant amphibian. In the rivers of the southern part of Europe, its abundance may reach more than a thousand individuals per ...Missing: count | Show results with:count
[33]
True Frogs (Ranidae) | Encyclopedia.com
Many members share several characters, including a peculiar scapular girdle with slightly overlapping coracoids, the lowest one having a slight concavity ...<|control11|><|separator|>
[34]
[PDF] Action Plan for the Conservation of the Italian Agile Frog (Rana ...
Rana latastei provides shady, constantly humid conditions and good ground vegetation cover (or at least a deep litter layer) under the canopy. The natural, ...
[35]
[PDF] INTRODUCTION The ecology and biology of the common frog ...
At 2200m, adult frogs prefer moist areas, show diurnal/nocturnal activity, while juveniles are more diurnal. Adults' night activity is linked to temperature.
[36]
Behavioural adaptations of Rana temporaria to cold climates
Our results suggest that at mid and high elevation common frogs use freeze avoidance alone to survive temperatures below 0 °C.
[37]
Northern red-legged frog | Washington Department of Fish & Wildlife
However, most individuals are found in the vicinity of standing or flowing water, even during the non-breeding terrestrial phase of the seasonal life cycle.
[38]
Northern Leopard Frog - Montana Field Guide
Sep 30, 2024 · Northern Leopard Frogs are active during the day and night. The active period extends from March to November in Colorado (Hammerson 1999).Missing: nocturnal crepuscular
[39]
[PDF] Hibernation behavior of Rana lessonae and R. esculenta in their ...
All radio-tracked animals hibernated in the woodland, 3 to 7cm below the surface in soil, under moss, fallen leaves or small branches. Soil temperatures at the ...
[40]
Sleeping beauties—how do frogs stay alive without oxygen? - PMC
Apr 30, 2020 · Frogs survive low oxygen by aestivating, choosing low-oxygen microhabitats, and rapidly lowering their metabolic rate, which is more pronounced ...
[41]
Morphological correlates of aquatic and terrestrial locomotion in a ...
Frogs, and particularly ranids, are not only jumping animals but are also frequent swimmers. Both behaviours are accomplished by the hind limbs but do not ...
[42]
[PDF] Swimming and jumping in a semi-aquatic frog
Unexpectedly, the impulse of swimming proved to be significantly smaller than the jumping impulses during locomotion in a semi-aquatic frog, Rana esculenta, ...
[43]
The Functional Morphology and Biomechanics of Arboreal ...
Jul 10, 2025 · True frogs (Ranidae) comprise the largest and most widespread family of anurans and are characterized by saltatory (i.e., hopping) locomotion.
[44]
Vocal communication in frogs - ScienceDirect.com
The robust nature of vocal communication in frogs has long attracted the attention of natural philosophers and their biologically inclined successors.
[45]
Behavioral Responses by Adult Northern Leopard Frogs to ...
Apr 8, 2020 · Our work demonstrates that Northern Leopard Frogs likely use chemical communication to detect conspecifics and that the attraction exhibited by ...
[46]
(PDF) Predator, but not conspecific, chemical cues influence pond ...
Our results suggest that frogs were able to detect the presence of chemical cues of snake predators in the water and that they avoided entering such ponds.
[47]
Territorial male bullfrogs (Rana catesbeiana) do not assess fighting ...
From within their territories, males emit advertisement calls, presumably to attract gravid females and to repel rival males, and these signals are by far the ...Missing: solitary true
[48]
https://www.scielo.br/j/rbzool/a/7tZfFB43jKvVNY6jxD8fjVJ/?lang=en&format=pdf
[49]
True Frog - an overview | ScienceDirect Topics
They are part of the family Ranidae and are characterized by slight morphological differences that complicate taxonomic classification. AI generated definition ...
[50]
Rana aurora (Northern Red-legged Frog) - Animal Diversity Web
Red-legged frogs have a highly variable diet, eating any prey they can subdue that is not distasteful. Adults feed on invertebrates, small mammals and other ...Missing: strategies | Show results with:strategies
[51]
[PDF] Diets of tadpoles - SciELO
Most tadpoles are primarily herbivorous (ALFORD 1999) con- suming a wide variety of algal taxa as well as detritus, viruses, bacteria, protists, plant ...
[52]
Ontogenetic Changes in Diet and Intestinal Morphology in Semi ...
A strong relationship exists between a tadpole's diet and its gut morphology (Toloza and Diamond, 1990). In general, herbivorous tadpoles have long intestines.
[53]
Do Bufonids Employ Different Anti-Predator Behaviors Than Ranids ...
Feb 20, 2018 · European anurans are prey for a variety of predators, against which they have evolved a range of defense behaviors.
[54]
Anti-predator behavior in two brown frogs: differences in the mean ...
Aug 15, 2023 · In this study, we describe the anti-predator behavior of two closely related brown frogs, Rana dalmatina and Rana latastei, and compare their structures of ...
[55]
Multiple antimicrobial peptides and peptides related to bradykinin ...
The skin secretions of the North American pickerel frog Rana palustris are toxic to both microorganisms and predators. A total of 22 peptides with ...
[56]
Antimicrobial peptides from the skin secretions of the South-East ...
Skin secretions from frogs belonging to the family Ranidae (“true frogs”) have proved to be a particularly rich source of antimicrobial peptides and more than ...
[57]
American Bullfrog Invasion and Impacts on Native Species in the ...
Apr 25, 2023 · The invasive American bullfrog (Lithobates catesbeianus) and a variety of non‐native sport fish commonly co‐occur in lowland lentic habitats of the western ...
[58]
Evidence of niche shift and invasion potential of Lithobates ...
Sep 27, 2017 · The American bullfrog Lithobates catesbeianus is an invasive species that can have negative impacts on native amphibian populations.
[59]
Rana temporaria - AmphibiaWeb
A large frog with a chunky body (corpulent); snout rounded. Vomerine teeth present. Posterior part of the tongue free and forked. Toes webbed.Missing: features | Show results with:features
[60]
Rana arvalis - AmphibiaWeb
In the forests of the center of European Russia, it usually prefers more open habitats than the sympatric Common Frog, and is rarer than the latter in the north ...
[61]
Rana luteiventris - AmphibiaWeb
As a female enters the breeding area, she is approached by and subsequently pairs with a male in a nuptial embrace referred to as amplexus. From several hours ...
[62]
Lithobates clamitans (Green Frog) - Animal Diversity Web
Green frogs have stable population sizes throughout their range. They are listed as a species of "Least Concern" on the IUCN Red List and have no species status ...
[63]
Ongoing declines for the world's amphibians in the face of emerging ...
Oct 4, 2023 · The 2004 baseline study identified habitat loss and degradation and over-exploitation as the main threats, contributing to the deterioration of ...Missing: Ranidae | Show results with:Ranidae
[64]
Empirical evidence for effects of invasive American Bullfrogs on ...
Dec 8, 2022 · Our results provide landscape-scale evidence that bullfrogs reduce occurrence of native amphibians and increase occurrence of pathogens.
[65]
Overview of chytrid emergence and impacts on amphibians - PMC
Impacts of chytridiomycosis on amphibians are varied; some species have been driven extinct, populations of others have declined severely, whereas still others ...
[66]
How Do Pesticides Affect Frogs? EPA Researchers Conduct Uptake ...
Jul 19, 2022 · This finding could be important because frogs would be at higher risk during their breeding season. In other research, Henderson and ...
[67]
Amphibians/Reptiles - Beyond Pesticides
These effects of 2,4-D in P. cuvieri indicate that the ecological risk observed at concentrations above 10.35 μg L−1 2,4-D may represent a threat to the health ...
[68]
[PDF] Amphibians - IUCN Red List
Oct 6, 2025 · The. Anuran families Alytidae (midwife toads and painted frogs), Pelobatidae (spadefoot toads), and Ranidae (true frogs) contain an average.
[69]
Recovery Strategy for the Northern Leopard Frog (Lithobates ...
Feb 24, 2022 · The recovery strategy sets the strategic direction to arrest or reverse the decline of the species, including identification of critical habitat ...
[70]
Mountain Yellow-legged Frog (Rana muscosa) Fact Sheet - LibGuides
Apr 29, 2025 · The Mountain Yellow-legged Frog is "Endangered" by IUCN and "Endangered" by the US, with "Largely Depleted" by Green List. By 2003, fewer than ...
[71]
LIFE AMPHICON - feeling the love for Europe's amphibians
Jul 26, 2024 · With more than 80 per cent of Europe's natural habitats in a degraded condition, the law aims to restore wetlands, rivers, forests, grasslands ...
[72]
Captive Breeding - IUCN SSC Amphibian Specialist Group
Identifying suitable candidate species that require captive breeding programs. Not all amphibians are suitable candidates for captive breeding programs. The ...
[73]
IUCN Red List of Threatened Species
The IUCN Red List, established in 1964, is the world's most comprehensive source on species conservation status, and a critical indicator of biodiversity ...About · 3.1 · Searching The IUCN Red List · Citing The IUCN Red ListMissing: Ranidae true frogs
[74]
Revisiting conservation units for the endangered mountain yellow ...
Sep 29, 2023 · Our study used two different sequencing strategies – amplicon sequencing and exome capture – to refine our understanding of the population genetics of these ...<|control11|><|separator|>