Marsh frog
Species of frog
From Wikipedia, the free encyclopedia
The marsh frog (Pelophylax ridibundus) is a species of water frog native to Europe and parts of western Asia.[4]
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| Marsh frog | |
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| Adult in Kampinos Forest, Poland | |
Scientific classification  | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Amphibia |
| Order: | Anura |
| Family: | Ranidae |
| Genus: | Pelophylax |
| Species: | P. ridibundus |
| Binomial name | |
| Pelophylax ridibundus (Pallas, 1771) | |
| Subspecies | |
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See text | |
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| Distribution | |
| Synonyms[3] | |
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List
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Taxonomy and evolution
History of naming
The first scientific description of the marsh frog was published in 1771 and written by Prussian zoologist Peter Simon Pallas, who gave it the scientific name Rana ridibunda after collecting specimens of it during an expedition through the Russian Empire. Pallas did not precisely specify the type locality (where he found the frogs), only noting it as "versus mare Caspium; Volgae et Iaico" (opposite to the Caspian Sea, Volga, and on the Yaik River).[5] A more precise location of "Gurjew" on the north coast of the Caspian Sea (now the city of Atyrau in Kazakhstan) was given in a 1928 publication written by German herpetologists Robert Mertens and Lorenz Müller.[6] However, a 1994 paper by herpetologists Alain Dubois and Annemarie Ohler noted that because Pallas never designated a holotype specimen, a neotype needs to be selected for the species. The restriction of the type locality done by Mertens and Müller is therefore invalid unless a specimen from Atyrau is designated as the neotype, which Dubois and Ohler suggest should be done.[7]
Though Pallas initially considered the marsh frog to be a species in the genus Rana, later authors would move it into other genera or treat it as a variant of other species. French naturalist Pierre Joseph Bonnaterre was the first to do so, moving it into Bufo under the name Bufo ridibundus in an encyclopedia published in 1789, and the same classification was used in a book written by German naturalist Johann Gottlob Theaenus Schneider in 1799.[8][9] The species would later be moved back into Rana but treated as a variant of the edible frog (which formerly had the scientific name Rana esculenta), with Belgian-British zoologist George Albert Boulenger addressing it as Rana esculenta var. ridibunda in works published in 1885 and 1898.[10][11] The marsh frog would be listed as a species separate from other frogs again in 1891, when German herpetologist Erwin Schulze established a subgenus of Rana called Baliopygus and listed the marsh frog as a species of it, thus naming it Rana (Baliopygus) ridibunda.[12]
In a 1986 paper, Alain Dubois stated that frogs of the edible frog species group should be moved into the subgenus Rana, which means the scientific name of the marsh frog would be Rana (Rana) ridibunda.[13] However, Dubois would later divide Rana into 33 subgenera and place this species in the subgenus Pelophylax under the name Rana (Pelophylax) ridibunda.[14] A study published in 2005 further divided the species placed in the genus Rana at the time into several different genera, with those of the subgenus Pelophylax being assigned to the genus Hylarana, thus the marsh frog was considered to be part of this genus under the name Hylarana ridibunda.[15] In 2006, another publication on amphibian taxonomy elevated the rank of Pelophylax from subgenus to genus, a revision which is further supported by a study published the following year, so the scientific name of the marsh frog was recombined once again into Pelophylax ridibundus.[16][17]
Obsolete names
In addition, some marsh frog specimens were formerly thought to represent distinct, separate forms. They have since been found to represent the same species and the taxa erected based on them are thus considered synonymous.[7] German naturalist Johann Friedrich Gmelin established the name Rana gigas in 1789 for a species of frog found in Persia (now known as Iran), but without designating a holotype or even listing what specimens he studied.[18] In a book printed in 1814 (but whose publication was delayed to 1831), Pallas would erect the names Rana cachinnans and Rana caucasica without listing the specimens studied for any of these supposed species. Additionally, he states that his description of R. caucasica is copied from manuscript notes written by Baltic German explorer Johann Anton Güldenstädt, who referred to it as Rana bufoides instead. Because Güldenstädt's notes were never formally published and the two names refer to the same specimens, R. bufoides is objectively a junior synonym of R. caucasica.[7][19] Baltic German polymath Karl Eichwald declared R. gigas to be a junior synonym of R. cachinnans in 1842, which itself and R. caucasica were synonymised with R. ridibunda by George Albert Boulenger in 1898.[11][20]
In 1837, Russian zoologist Johann Krynicki erected the species Rana dentex based on multiple specimens found along the Podkumok River in Russia, of which two still exist but were noted to be in "bad condition" in 2009.[21][22] This species would then be lumped with Rana ridibunda by Boulenger in 1898.[11] The name Rana taurica was first published as a synonym of the Rana esculenta (the edible frog) by French biologist Charles Lucien Bonaparte in 1840, who read the name on a label in the Wien Museum, though a 1994 publication considered it to represent the marsh frog instead.[7][23] Boulenger established the species Rana fortis in 1884 based on his study of German specimens, but would synonymize it with Rana ridibunda the following year.[24][25] The species Rana florinskii and Rana mangischlakensis were erected in 1913 and 1925 respectively, the former based on specimens from Tomsk, Russia and the latter based on ones from Mangyshlak, Kazakhstan, but both were synonymized with Rana ridibunda in 1994.[7][26][27]
Subspecies
There is much debate among herpetologists regarding how many subspecies the marsh frog has. Several similar types of frogs have been named and described as separate species, with proponents for their validity considering them to form a species complex. However, some argue that they should be treated as subspecies of Pelophylax ridibundus instead. A phylogenetic study published in 2024 recovered the following subspecies:[28]
| Subspecies | Trinomial authority | Description | Range |
|---|---|---|---|
| Eurasian marsh frog (P. r. ridibundus) | (Pallas, 1771) | Most of Europe | |
| Levant water frog (P. r. bedriagae) | (Camerano, 1882) | Levant | |
| Beyşehir frog (P. r. caralitanus) | (Arikan, 1988) | Southern Anatolia | |
| Karpathos frog (P. r. cerigensis) | (Beerli, Hotz, Tunner, Heppich & Uzzell, 1994) | Southwest coast of Anatolia and offshore islands | |
| Cyprus water frog (P. r. cypriensis) | Plötner, Baier, Akn, Mazepa, Schreiber, Beerli, Litvinchuk, Bilgin, Borkin, and Uzzell, 2012 | Cyprus | |
| Balkan frog (P. r. kurtmuelleri) | (Gayda, 1940) | Balkans | |
| P. r. persicus | (Schneider, 1799) | Iran | |
| Terentjev's frog (P. r. terentievi) | (Mezhzherin, 1992) | Uzbekistan | |
Evolution
The marsh frog is a member of Pelophylax, a genus which is widely distributed across Eurasia. Many forms (which may be either subspecies or separate species) related to the nominate form of the marsh frog are known from across Europe and west Asia, with the most closely related being the Balkan frog (P. kurtmuelleri), which are collectively referred to as the marsh frog complex. This complex has been estimated to have already evolved about 3.5 million years ago during the Late Pliocene, with the last common ancestor of all its members living at around that time. The closest living relative of the marsh frog complex as a whole is the Cretan frog (P. cretensis), and these two lineages have been suggested to have diverged about 5.2 million years ago during the Early Pliocene. This roughly coincides with the end of the Messinian salinity crisis, an event which may have triggered the divergence. The following cladogram shows the position of the marsh frog among its closest living relatives according to Dufresnes et al. (2024):[28]
| Pelophylax |
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| Western Palearctic |
Fossilised remains indicate that frogs of the genus Pelophylax were already widespread across Europe during the Early Oligocene, as specimens dating back to this period have been found in France, Germany and Romania, suggesting that the ancestors of the marsh frog arrived to the continent over 33.9 million years ago. In particular, a complete skeleton (with the specimen number MAB19654) from the Early Oligocene-aged site of Marnes du Bois d’Asson, France has been noted to closely resemble the marsh frog, though it has not been formally assigned to any species.[29] The oldest fossils attributed to the modern marsh frog species itself originate from Nurnus, Armenia and date back to the Early Pliocene. These have been reported under the name Pelophylax cf. ridibundus and suggest that the species already existed between 5.3 and 3.6 million years ago, with additional fossils reported under this name having been found at other Pliocene and Pleistocene-aged sites in Armenia.[1][30][31]
Description
The marsh frog is the largest type of frog in most of its range, capable of reaching a snout–vent length of up to 15 cm (5.9 in).[32] Females typically grow slightly larger than males, and anthropogenic activity can also affect the size of individuals in a population; for example, commercial harvesting likely caused average body sizes in a Turkish population to decrease between 1999 and 2008.[33] The skin of a marsh frog is relatively rough as it bears warts and ridges, and forms distinctive folds on the sides of its back. There is a large variation in colour and pattern, ranging from dark green or even black to lighter green, brown or grey, often with a bright green line running down the back.[32] Dark roundish or square patterns are typically present (but sometimes absent) on the back and sides, which may be dense or scant, and the legs usually have barred patterning of a similar colour. The arms and legs can be partly brown, while the thighs and underside are usually white or cream, but may also be yellow or green. Dense black or grey spots are typically present on the underside of the lower body.[32][34] Adult males have a pair of vocal sacs, one under each tympanum, which are often folded internally but inflate and become visible during vocalisation. These sacs are usually dark grey or black, a feature often distinguishing the marsh frog from the edible frog (which has lighter grey vocal sacs) and the pool frog (which has white vocal sacs). However, the vocal sacs of some marsh frogs are known to be exceptionally pale.[32]
The snout of a marsh frog is long and has a sharp tip, differing from some related species it lives alongside (namely the edible, pool and Epirus water frogs) which have shorter, blunter snouts.[32] The marsh frog also has long hind legs, with the heel joint often reaching past the snout when the leg is pulled forwards along the body; in contrast, the heel of the edible frog tends to only just reach the snout when the leg is pulled that way, and those of the pool frog and Epirus water frog reach only the eye. Each foot bears a hardened lump called the metatarsal tubercle, which is low and asymmetrical, with the highest point near the toe and its height decreasing towards the leg.[32][34] As revealed in a study published in 2020, the size and shape of this tubercle is the most reliable and important feature for distinguishing marsh frogs from edible or pool frogs; this tubercle is higher in the latter two species, and while that of an edible frog is similarly asymmetrical, a pool frog's metatarsal tubercle instead has a symmetrical shape resembling a semi-circle.[35] Marsh frogs have webbed feet, and the webbing extends to the tip of the fourth toe. This feature distinguishes them from the Perez's frog and Graf's Hybrid Frog, in which the webbing does not reach that toe tip, though it nearly does in the latter.[32]
Some of a marsh frog's bones are distinguishable from those of other frog species, with the most diagnostic being skull bones called the frontoparietals. These are formed by fusing the frontal and parietal bones, and European Pelophylax species have ridges on their frontoparietals that start from a projection at the hind part of the bone (near where the skull connects to the vertebrae). Each species has a distinctly different ridge formation, with the marsh frog having very pronounced ridges that form sharp bulges, such that a tooth-like formation named the "dens frontoparietalis ridibundae" is present at the hind part of the bone. Furthermore, the frontoparietal bones themselves are very robust in a marsh frog. In contrast, the corresponding bones in a pool frog have a slender build with ridges reduced to a slight bulge, and those of the edible frog are intermediate between those of marsh frogs and pool frogs. In addition, the ilium (part of the hip bone) is also usable for identification; that of a marsh frog has a flattened tubercle on the front part, whereas this tubercle protrudes much further outward in a pool frog.[36] However, because edible frogs show a wide range of gradual variation intermediate between pool and marsh frogs, identifying a single ilium to species level is impossible. Instead, a larger sample of over five ilia could be used to determine whether a population of frogs consists purely of pool or marsh frogs, or if edible frogs are also present.[31] All three species have ilia which are notably thicker in the part where the ilium is joined to the ischium (another part of the hip bone), which distinguishes them from those of frogs in the genus Rana.[37]
Tadpoles can reach up to 190 mm (7.3 in) in length,[4] but this usually occurs in places with long winters where the tadpole has time to grow.
Female
Showing vocal sac.
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Distribution and habitat
A widespread animal, the marsh frog occurs in large parts of Europe and is also present in Asia as far east as Kazakhstan, Iran and Afghanistan. Additionally, an isolated relict population is present in southern Hadhramaut, Saudi Arabia. Reports of marsh frogs in China and Iraq are now believed to represent the Terentjev's frog and Levant water frog respectively, which may be subspecies of the marsh frog, though some consider them to be separate species instead.[2] Though present in much of Europe, being native to the central, eastern and southeastern parts, it is notably absent from Scandinavia.[32] It is known to have been introduced to many areas outside of its native range, though the extent of its native range is not entirely certain; for example, it remains unclear if it is native to parts of western Europe such as France, or whether isolated colonies in Bahrain were introduced.[2] Known introduced populations are present in Switzerland, Belgium, Spain, Sardinia, the Kamchatka Peninsula in Far Eastern Russia, the United Kingdom and the Al-Kharj region of Saudi Arabia.[2][32][38]
The marsh frog typically inhabits large bodies of water such as deep ponds and active rivers, but is highly adaptable and can occur in a wide range of environments. Individuals are more closely tied to the aforementioned habitat types in areas where the pool frog is also present (a form of niche partitioning via habitat selection), and young frogs are particularly versatile in habitat choice.[32][39] Both stagnant and flowing bodies of water, ranging from small puddles to large lakes, are known to host marsh frogs, especially if they are warm and have plenty of herbaceous vegetation. Even areas modified by human activity such as fish ponds can serve as suitable habitat, and such activity can even make an area more favourable; introduced populations in Kamchatka survive thanks to electric power stations discharging warm water into reservoirs. Marsh frogs inhabit water bodies in many types types of habitat up to an altitude of 2,500 m (8,200 ft), including forests, grasslands, steppes and even deserts, colonising dry areas via river channels and valleys.[2] Unusually for an amphibian, the marsh frog is tolerant of saltwater, having been reported inhabiting and even breeding in brackish pools along the shores of the Caspian Sea and Black Sea.[2][40]
Behaviour and biology
Hibernation
Marsh frogs generally hibernate during the winter, as the low temperatures and reduced food availability force them to do so in order to conserve energy. The typical hibernation period is from October to February but varies based on regional climate; frogs in Greece (a warmer area to the south of their range) often only begin hibernation in late November, with subadults beginning even later and sometimes still active on sunny December days.[32][41] Some populations in Romania do not hibernate at all, as the presence of thermal water allows them to remain active throughout the year.[42][43] Hibernation usually occurs underwater, typically within mud at the bottom of water bodies, though holes in river banks may also be used.[32][44]
The weight of a marsh frog's liver increases prior to hibernation as the frog actively feeds to reach the metabolic requirements to survive the winter, and decreases during hibernation as liver glycogen is used, reaching a minimum weight soon after hibernation ends.[45] Body fat is also used as an energy source during dormancy, so the mass of fat bodies and the lipid content of body tissues both decrease during hibernation.[46] Marsh frogs are tolerant of the low temperatures they face during hibernation, capable of surviving even if they are frozen for over 24 hours, but die if more than 58% of their body's water content becomes ice.[47] However, this species has no cryoprotective system, unlike the related pool frog and edible frog whose blood lactate, blood glucose, liver glucose and liver alanine levels increase in response to freezing temperatures. As a result, marsh frogs accumulate ice at a higher rate than these two relatives.[48] Prolactin concentration in the frog's skin increases during hibernation, allowing the skin to thicken in response to low temperatures and prevent water loss from the body, as well as regulating the function of the granular glands.[49]
When temperatures increase and the frog arouses from hibernation, its metabolism and rate of oxygen consumption increase. This causes an increase in oxidative stress, so the level of antioxidant enzymes in its organs and muscles also elevates as a form of defence against this.[50] This antioxidative defence system therefore shows the highest response in spring, and is not significantly affected by the amount of heavy metals accumulated in the frog's body, as evidenced by how frogs from polluted and unpolluted areas show the same seasonal fluctuations in antioxidant levels.[51] In addition, the levels of certain proteins also increases when the frog recovers from hibernation, providing the stamina needed to become active again.[52][53]
Reproduction
Marsh frogs typically breed during late spring or early summer, but may do so throughout the year if conditions are suitable.[32] The breeding period depends on various abiotic factors such as precipitation and temperature, and generally begins only when the water temperature exceeds 18 °C (64 °F).[54] Breeding occurs in ponds or flooded land within a few hundred meters of their hibernation sites, and the frogs of both sexes are able to use the magnetic field of the Earth to locate breeding sites, arriving at about the same time (in contrast to some other amphibians in which one sex arrives at breeding sites before the other).[55] Records have revealed that the breeding period of at least some populations now begins earlier in the year than before, likely due to global warming; a phenological study on frogs in Saratov Oblast, Russia revealed that while the date of the beginning of spawning migrations was relatively stable from 1892 to 1960, this date then shifted earlier by five days from 1961 to 2020. By 2025, this process accelerated suddenly and the date shifted earlier by an extra ten days.[56]
_сидять_на_колоді_у_річці_Лопань_у_Харкові.jpg)
During the breeding season, adult male marsh frogs produce mating calls to attract females. When one approaches, the male uses his forelimbs to grasp onto the area behind her forelimbs, a behaviour known as amplexus which continues while the female lays her eggs.[32] Male frogs generally breed with females that are larger than themselves, with a study conducted in Turkey finding that 37 of the 40 amplexed pairs observed involved a male smaller than the female he was grasping onto. Because the breeding period of the marsh frog overlaps with that of some other amphibians, interspecific amplexus sometimes occurs, with this Turkish study noting that a male European green toad was seen amplexed onto a female marsh frog.[54] The eggs of the marsh frog are laid in several clumps and fixed to underwater plants at the shallow edges of the breeding ponds, with each clump having between 144 and 645 eggs.[32][54] A female may lay eggs two to seven times in one breeding season, resulting in as many as 16,400 eggs laid. However, the average number is far lower, with one study calculating a mean fecundity of 3853 eggs. Each individual egg measures about 1.73 mm (0.068 in).[54]
Embryos of the marsh frog develop quickly, capable of hatching as aquatic tadpoles just 2 to 4 days after the eggs are laid, though the timing varies depending on temperature. The rate of metamorphosis is similarly affected by temperature and thus varies between different populations; one study found that wild tadpoles in the Turkish provinces of Adana and Mersin can complete metamorphosis in 45 to 65 days, whereas those in Anatolia require a much longer duration of 90 to 120 days.[54] Light also affects tadpole development, with experiments revealing that compared to those in normal lighting, tadpoles reared under red light are smaller while those under blue light show increased growth. Blue light also leads to faster development, whereas total darkness slows it.[57] Newly metamorphosed juveniles measuring 20–25 mm (0.79–0.98 in) emerge onto land over the course of the summer, but can grow to 26–47 mm (1.0–1.9 in) after their first hibernation.[54]
Hybridogenesis
There are known three hybridogenetic hybrids of the marsh frog:
- edible frog Pelophylax kl. esculentus (usually genotype RL):
pool frog P. lessonae (LL) × P. ridibundus (RR)[58][59] - Graf's hybrid frog Pelophylax kl. grafi (PR):
Perez's frog P. perezi (PP) × P. ridibundus (RR) or
Perez's frog P. perezi (PP) × edible frog P. kl. esculentus (RE)
(it is unclear which one crossing was the primary hybridization)[59] - Italian edible frog Pelophylax kl. hispanicus (RB):
Italian pool frog P. bergeri (BB) × P. ridibundus (RR)
Their populations are maintained however through other crossings by hybridogenesis.[59] In places where they were introduced, marsh frogs may pose a threat to the native Pelophylax by diluting the gene pool, but there is evidence that although they may hybridize they do not affect the overall population that greatly.[38][60]
Diet
Adult marsh frogs have a large head that is able to devour a wide variety of prey, mostly arthropods and other invertebrates, as well as small fish, other amphibians (including conspecifics), reptiles, small birds, and rodents.[4] In an analysis of 53 adults in Thrace, flies made up 40% and beetles 20% of their diet.[61] These frogs have been found to climb onto water buffalo so they could eat the flies attracted to it, hinting at a possible mutualistic relationship.[62]
As tadpoles, they eat a wide range of organic matter including algae, detritus, decaying plants, invertebrates, and dead animals.[4]
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