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Pool frog

From Wikipedia, the free encyclopedia
(Redirected from Pool Frog)

Pool frog
Scientific classification Edit this classification
Kingdom: Animalia
Phylum: Chordata
Class: Amphibia
Order: Anura
Family: Ranidae
Genus: Pelophylax
Species:
P. lessonae
Binomial name
Pelophylax lessonae
(Camerano, 1882)
Subspecies

See text

Range of the nominate subspecies of the pool frog
Synonyms[2]
List
  • Rana lessonae Camerano, 1882
  • Rana esculenta Linnaeus, 1758[a]
  • Rana lessonae subsp. pannonica Karaman, 1948
  • Hylarana lessonae (Camerano, 1882)
  • Rana esculenta subsp. lessonae Camerano, 1882
  • Rana esculenta subsp. bolkayi Fejérváry, 1909
  • Rana esculenta subsp. hungarica Toutain, 1966
  • Rana lessonae subsp. lessonae Camerano, 1882
Audio

The pool frog (Pelophylax lessonae) is a European frog in the family Ranidae. Its specific name was chosen by the Italian herpetologist Lorenzo Camerano in 1882, in order to honour his master Michele Lessona.

Taxonomy

[edit]

The pool frog was first recognised to be different from other frogs by Italian herpetologist Lorenzo Camerano, who published a scientific description of it in 1882. However, Camerano believed that it was a variant of the edible frog (which had the scientific name Rana esculenta at the time) rather than a separate species, and gave it the scientific name Rana esculenta var. lessonae, naming it after Italian zoologist Michele Lessona.[4] Two years later, Camerano would adopt the concept of subspecies, and in an 1884 publication he refers to the pool frog as a subspecies by the name Rana esculenta lessonae.[5] Though Camerano studied several pool frog specimens, he did not designated any one of them as a holotype. Therefore, one of these specimens (a female with the specimen number MZUT An 718 kept in the Turin Museum of Natural History) was later designated as a lectotype in 1986.[6]

The possibility of the pool frog representing a separate species from the edible frog was first recognised in 1966 by Polish biologist Leszek Berger, who proposed this based on ecological and biometric data, though he did not decisively conclude so as he believed doing so was premature.[7] In 1992, French zoologist Alain Dubois divided the genus Rana into 33 subgenera, with the pool frog being placed in the subgenus Pelophylax under the name Rana (Pelophylax) lessonae.[8] 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 pool frog was considered to be part of this genus under the name Hylarana lessonae.[9] 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 pool frog was recombined once again into Pelophylax lessonae.[10][11]

In addition, some pool frog specimens were formerly thought to represent distinct, separate forms. Hungarian general Géza Fejérváry established the name Rana esculenta var. bolkayi in 1909 for a type of frog found along the Rhône river, but does not designate a holotype specimen.[12] Similarly, Yugoslav biologist Stanko Karaman erected a new subspecies of pool frog given the name Rana lessonae pannonica in 1948 without specifying a type specimen.[13] Both of these names were declared as junior synonyms of Rana lessonae in 1994.[14]

Subspecies

[edit]

The pool frog has historically been considered a monotypic species with no subspecies. However, some authors believe that the Italian pool frog (historically deemed a separate species by the name of Pelophylax bergeri) represents a subspecies within the same species as "typical" Pelophylax lessonae individuals. This was first proposed in 2004 based on a study involving electrophoretic data, which shows that the two types of frog exhibit very little divergence.[15] A phylogenetic study published in 2008 further supported this.[16] Under this classification, the pool frog includes the following two named subspecies:

Subspecies Trinomial authority Description Range
European pool frog (P. l. lessonae)

(Nominate subspecies)

 (Camerano, 1882) Identical in appearance and only distinguishable by location[17] Northern Italy and elsewhere in Europe[15]
Italian pool frog (P. l. bergeri) Günther, in Engelmann, Fritzsche, Günther & Obst, 1986 Most of peninsular Italy[15]

DNA analysis indicates that P. l. lessonae can be further split into two genetically distinct sub-populations, namely a northern clade found in Sweden, Norway and England, and a southern clade that is more widespread throughout the rest of Europe.[18][19][20][21]

In addition, individuals from Sicily and Calabria have been suggested to represent a third subspecies which is currently unnamed and closely related to P. l. bergeri.[15][16] A genetic study published in 2024 found that the Sicilian frogs are more closely related to one another than to frogs on the Italian mainland, but still considered them to be part of the bergeri subspecies.[22]

Evolution

[edit]

The pool frog is a member of Pelophylax, a genus which is widely distributed across Eurasia, and genetic analysis has revealed that it is more closely related to other European members of this genus than to any of the Asian species. A study published in 2024 found that European pool frogs (P. l. lessonae) and Italian pool frogs (P. l. bergeri) are each other's closest known relatives, supporting the idea that they are subspecies of the same species, and suggests that they split from each other about 2.7 million years ago during the Late Pliocene. The closest living relative of the pool frog species as a whole is the Albanian water frog (P. shqipericus), and the last common ancestor of these two species is estimated to have lived 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 of these lineages. The following cladogram shows the position of the pool frog among its closest living relatives according to Dufresnes et al. (2024):[22]

Pelophylax
Western Palearctic

Description

[edit]

The pool frog is a medium-sized frog which typically grows 4–7 cm (1.6–2.8 in) long.[17] Its skin is smooth and shiny, and forms distinctive folds on the sides of its back. The colouration of these frogs is highly variable, often a shade of light or dark green, though some females and juveniles are mostly brown. Dark blotches are often present on the back, legs and flanks, and a bright green stripe runs down the middle of the frog's back. The legs often have yellowish and dark barred patterning, and the head and upper body may become bright yellow, especially in males during the breeding season.[23] 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 white, a feature distinguishing the pool frog from the edible frog (which has grey vocal sacs) and the marsh frog (which has dark grey to black vocal sacs).[17][23]

The snout of a pool frog is short and blunt, differing from the related edible and marsh frogs whose snouts are more elongated and form a sharper tip.[23] The hind legs of a pool frog are also shorter than those of related species, with the heel joint reaching only up to the eyes when the leg is pulled forwards along the body; by comparison, most other European species of the same genus (such as the Perez's frog, Graf's hybrid frog, marsh frog and edible frog) have heels that reach or extend past the snout when the leg is pulled that way. Each foot bears a hardened lump called the metatarsal tubercle, which is large and forms a symmetrical, semi-circular shape.[17][23] A study published in 2020 revealed that the size and shape of the metatarsal tubercle is the most important and reliable feature for distinguishing pool frogs from edible or marsh frogs; in the latter two species, this tubercle is much smaller and asymmetrical, with the highest point near the toe and its height decreasing towards the leg.[24]

Distribution and habitat

[edit]

The pool frog is found across most of central Europe from the west coast of northern France to the Ural Mountains in western Russia. Though absent from most of Scandinavia, there are also small populations of pool frogs in Sweden and Norway, as well as in the East Anglia region of England.[1] Pool frogs were previously thought to be a non-native species in England, partly because individuals are known to have been introduced from southern Europe (though not from Scandinavia). However, genetic evidence has shown that English pool frogs are closely related to Scandinavian frogs, not to frogs from further south. In addition, subfossil remains show that pool frogs were present in East Anglia before the oldest known introductions, and thus are likely native.[19][20] Introduced populations of pool frogs are also present in parts of Spain such as the Province of Cáceres, Galicia, Catalonia and the Valencian Community.[1]

The pool frog typically occurs in stagnant and shallow bodies of water such as ditches, ponds and lakes, often with dense vegetation. It can be found in such water bodies in a wide range of habitats including forests, steppe, heathland, meadows and fens. During winter, it sometimes hibernates further away from the water. It can tolerate some level of habitat modification and may occur in agricultural land.[1][23] The range of habitats that this species is present in varies depending on location; it is mostly restricted to oligotrophic (low-nutrient) ponds and fens towards the north of its range, whereas further south it becomes more widespread and can occur from sea level up to an altitude of 1,500 m (4,900 ft).[23]

According to Amphibiaweb populations of this frog survive in urban areas and even fisheries. The creation of new ponds and other bodies of water leads to increased dispersal and a growth in the population of these frogs.[25]

Biology

[edit]

A cathemeral animal, the pool frog is active during both day and night. It is a largely aquatic species that spends much of its time in water, but may spread out into the surrounding land to feed at night. This frog is active between March and October, while the winter months are spent hibernating on land.[23] The exact time of year that pool frogs spend hibernating varies from year to year based on temperatures, with less time spent hibernating on warmer years. Compared to that of the related edible frog, the pool frog's hibernation lasts longer, with pool frogs often leaving water earlier in autumn and returning to ponds later in spring than edible frogs do. Pool frogs typically hibernate 3–7 cm (1.2–2.8 in) below the surface of woodland soil, usually under plant matter in areas warmer than surrounding soil. They do not hibernate continuously throughout the whole winter, and instead often move between multiple hibernation sites throughout the season. Such movements are most common during the first half of winter (when it is relatively warmer), but can happen even at temperatures under 1 °C (34 °F). During hibernation, pool frogs typically lose weight, with females usually losing more than males do, and warmer winters lead to increased weight loss.[26]

To cope with the cold during hibernation, the pool frog has adaptations that make it resistant to freezing. When exposed to subzero temperatures, its blood glucose level increases significantly, preventing its cells from shrinking and suffering from osmotic shock. This increased glucose is likely synthesised mainly from the liver rather than the muscles, as indicated by the liver glycogen level dropping when this happens.[27] Similarly, blood lactate, liver glucose and liver alanine all accumulate when the frog is in freezing temperatures. Thanks to these adaptations, the pool frog accumulates ice at a much lower rate than the related marsh frog and edible frog do, allowing it to survive freezing for longer durations than its relatives. Though pool frogs still die if frozen for extended periods, their cold tolerance is enough to survive overnight freezing between 8 and 12 hours, allowing the frog to move to a warmer hibernation site if the one in use becomes cooler.[28]

Pool frogs in Britain

[edit]

Pelophylax lessonae was one of only four amphibian species recognised by the UK government as protected under its Biodiversity Action Plan, however on 2007 this was revisited,[29] adding all of the UK's extant, native herpetofauna to this plan; with a notable exception of the Aesculapian snake due to its complicated re-establishment. The reasons for declining populations are decreased pond habitat from human encroachment and air pollution leading to over-nitrification of pond waters.

The Herpetological Conservation Trust website states that "The Pool Frog is a European frog and was formerly recorded from two sites in East Anglia although it was lost from one of these in the middle of the 19th century. It was presumed extinct in the wild at the last remaining site by 1995. A single individual known from this population survived in captivity until 1999. Other populations have become established in the UK and it is known that some of these included individuals of British origin in their founding stock."

An English Nature reintroduction project is underway in Breckland, where pool frogs were introduced to a single site in 2005.

Hybridogenesis

[edit]

The edible frog Pelophylax kl. esculentus is a hybridogenetic hybrid of the pool frog Pelophylax lessonae and the marsh frog P. ridibundus. Its populations are maintained however through other crossings by hybridogenesis.[30]

Notes

[edit]
  1. ↑ Apparently describing a specimen representing a Pelophylax lessonae × Pelophylax ridibundus hybridogen, not a true taxonomic synonym[3]

References

[edit]
  1. 1 2 3 4 IUCN SSC Amphibian Specialist Group. (2022). "Pelophylax lessonae". IUCN Red List of Threatened Species. 2022 e.T58643A177068753. doi:10.2305/IUCN.UK.2022-1.RLTS.T58643A177068753.en. Retrieved 16 October 2022.
  2. ↑ "Pelophylax lessonae (Camerano, 1882)". Integrated Taxonomic Information System. Retrieved 1 August 2024.
  3. ↑ "Rana esculenta Linnaeus, 1758". Integrated Taxonomic Information System. Retrieved 1 August 2024.
  4. ↑ Camerano, Lorenzo (1882). "Recherches sur les variations de la Rana esculenta et du Bufo viridis dans le Bassin de la Méditerranée". Comptes Rendus de l'Association Française pour l'Avancement des Sciences. 10: 680–690.
  5. ↑ Camerano, Lorenzo (1884). "Monografia degli anfibi anuri Italiani". Memorie della Reale Accademia delle Scienze di Torino. 2 (in Italian). 35: 187–284.
  6. ↑ Balletto, Emilio; Cherchi, Maria Adelaide; Salvidio, Sebastiano; Lattes, Aldo; Malacrida, Anna; Gasperi, Giuliano; Doria, Giuliano (1986). "Area effect in south western European green frogs (Amphibia, Ranidae)". Bollettino di Zoologia. 53 (1): 97–109. doi:10.1080/11250008609355490. ISSN 0373-4137.
  7. ↑ Berger, Leszek (1966). "Biometrical studies on the population of green frogs from the environs of Poznan". Annales Zoologici. 23: 303–324. S2CID 85846846.
  8. ↑ Dubois, Alain (1992). "Notes sur la classification des Ranidae (Amphibiens, Anoures)". Bulletin mensuel de la Société linnéenne de Lyon (in French). 61 (10): 305–352. doi:10.3406/linly.1992.11011. ISSN 0366-1326.
  9. ↑ Chen, Liqiao; Murphy, Robert W.; Lathrop, Amy; Ngo, Andre; Orlov, Nikolai L.; Ho, Cuc Thu; Somorjai, Ildiko L. M. (2005). "Taxonomic chaos in Asian ranid frogs: an initial phylogenetic resolution". Herpetological Journal. 15 (4): 231–243.
  10. ↑ Frost, Darrel R.; Grant, Taran; Faivovich, JuliáN; Bain, Raoul H.; Haas, Alexander; Haddad, CéLio F.B.; De Sá, Rafael O.; Channing, Alan; Wilkinson, Mark; Donnellan, Stephen C.; Raxworthy, Christopher J.; Campbell, Jonathan A.; Blotto, Boris L.; Moler, Paul; Drewes, Robert C. (2006). "The Amphibian Tree of Life". Bulletin of the American Museum of Natural History. 297: 1–291. doi:10.1206/0003-0090(2006)297[0001:TATOL]2.0.CO;2. ISSN 0003-0090.
  11. ↑ Che, Jing; Pang, Junfeng; Zhao, Hui; Wu, Guan-fu; Zhao, Er-mi; Zhang, Ya-ping (2007). "Phylogeny of Raninae (Anura: Ranidae) inferred from mitochondrial and nuclear sequences". Molecular Phylogenetics and Evolution. 43 (1): 1–13. Bibcode:2007MolPE..43....1C. doi:10.1016/j.ympev.2006.11.032. PMID 17300963.
  12. ↑ Fejérváry, Géza Gyula Imre (1909). Beiträge zur Herpetologie des Rhônetales und seiner Umgebung von Martigny bis Bouveret (in German). Genéve: George & Companie. pp. 20–25. doi:10.5962/bhl.title.12602.
  13. ↑ Karaman, Stanko (1948). "Prilog herpetologiji sjeverne Srbije" (PDF). Prirodoslovna Istrazivanja (in Croatian). 24: 51–74.
  14. ↑ Dubois, Alain; Ohler, Annemarie (1994). "Catalogue of names of frogs in the subgenus Pelophylax (Amphibia, Anura, genus Rana): a few additions and corrections". Zoologica Poloniae. 39 (3): 139–204.
  15. 1 2 3 4 Crochet, Pierre-André; Dubois, Alain (2004). "Recent changes in the taxonomy of European amphibians and reptiles". In Gasc, Jean-Pierre; Cabela, Antonia; Crnobrnja-Isailovic, Jeika; Dolmen, Dag; Grossenbacher, Kurt; Haffner, Patrick; Lescure, Jean; Martens, Harald; Martinez Rica, Juan Pablo; Maurin, Herve; Oliveira, Maria Elisa; Sofianidou, Theodora; Veith, Michael; Annie, Zuiderwijk (eds.). Atlas of amphibians and reptiles in Europe. Collection Patrimoines naturels (Nouv. éd ed.). Paris: Societas Herpetologica Europeae and Museum National Histoire Naturelle. ISBN 978-2-85653-574-5.
  16. 1 2 Canestrelli, Daniele; Nascetti, Giuseppe (2008). "Phylogeography of the pool frog Rana (Pelophylax) lessonae in the Italian peninsula and Sicily: multiple refugia, glacial expansions and nuclear–mitochondrial discordance". Journal of Biogeography. 35 (10): 1923–1936. Bibcode:2008JBiog..35.1923C. doi:10.1111/j.1365-2699.2008.01946.x. ISSN 0305-0270.
  17. 1 2 3 4 Dufresnes, Christophe (10 January 2019). Amphibians of Europe, North Africa and the Middle East: A Photographic Guide. Bloomsbury Publishing. pp. 100–101. ISBN 978-1-4729-4138-1.
  18. ↑ Zeisset, I.; Beebee, T. J. C. (7 May 2001). "Determination of biogeographical range: an application of molecular phylogeography to the European pool frog Rana lessonae". Proceedings of the Royal Society of London. Series B: Biological Sciences. 268 (1470): 933–938. doi:10.1098/rspb.2001.1600. ISSN 0962-8452. PMC 1088690. PMID 11370966.
  19. 1 2 Snell, Charles; Tetteh, John; Evans, Ivor H. (2005). "Phylogeography of the pool frog (Rana lessonae Camerano) in Europe: evidence for native status in Great Britain and for an unusual postglacial colonization route". Biological Journal of the Linnean Society. 85: 41–51. doi:10.1111/j.1095-8312.2005.00471.x.
  20. 1 2 Beebee, Trevor J. C.; Buckley, John; Evans, Ivor; Foster, Jim P.; Gent, Antony H.; Gleed-Owen, Chris P.; Kelly, Geoffrey; Rowe, Graham; Snell, Charles; Wycherley, Julia T.; Zeisset, Inga (2005). "Neglected native or undesirable alien? Resolution of a conservation dilemma concerning the pool frog Rana lessonae". Biodiversity and Conservation. 14 (7): 1607–1626. Bibcode:2005BiCon..14.1607B. doi:10.1007/s10531-004-0532-3.
  21. ↑ Zeisset, Inga; Beebee, Trevor J.C. (2007). "Two clades of north European pool frogs Rana lessonae identified by cytochrome b sequence analysis". The Herpetological Journal. 17: 255–260.
  22. 1 2 Dufresnes, Christophe; Monod-Broca, Benjamin; Bellati, Adriana; Canestrelli, Daniele; Ambu, Johanna; Wielstra, Ben; Dubey, Sylvain; Crochet, Pierre-André; Denoël, Mathieu; Jablonski, Daniel (2024). "Piecing the barcoding puzzle of Palearctic water frogs (Pelophylax) sheds light on amphibian biogeography and global invasions". Global Change Biology. 30 (3) e17180. Bibcode:2024GCBio..30E7180D. doi:10.1111/gcb.17180. hdl:2067/52904. ISSN 1354-1013. PMID 38465701.
  23. 1 2 3 4 5 6 7 Speybroeck, Jeroen; Beukema, Wouter; Bok, Bobby; Voort, Jan Van Der (28 July 2016). Field Guide to the Amphibians and Reptiles of Britain and Europe (PDF). Bloomsbury Publishing. pp. 179–184. ISBN 978-1-4729-2562-6.
  24. ↑ Breka, Katarina; Krizmanić, Imre; Vukov, Tanja; Stamenković, Srdjan (18 May 2020). "A procedure for taxon assessment based on morphological variation in European water frogs (Pelophylax esculentus complex)". Turkish Journal of Zoology. 44 (3): 215–223. doi:10.3906/zoo-1912-29. ISSN 1303-6114.
  25. ↑ "AmphibiaWeb - Pelophylax lessonae". amphibiaweb.org. Retrieved 25 May 2022.
  26. ↑ Holenweg, A. K.; Reyer, H. U. (12 April 2000). "Hibernation behavior of Rana lessonae and R. esculenta in their natural habitat". Oecologia. 123 (1): 41–47. doi:10.1007/s004420050987. ISSN 0029-8549.
  27. ↑ Aliko, Valbona (2013). "Physiological response to freezing in pool frog Pelophylax lessonae (Camerano, 1882)" (PDF). The 1st International Conference on Research and Educatıon–Challenges Toward the Future (ICRAE2013): 1–7.
  28. ↑ Voituron, Yann; Joly, Pierre; Eugène, Michel; Barré, Hervé (2005). "Freezing tolerance of the European water frogs: the good, the bad, and the ugly". American Journal of Physiology-Regulatory, Integrative and Comparative Physiology. 288 (6): R1563–R1570. doi:10.1152/ajpregu.00711.2004. ISSN 0363-6119.
  29. ↑ "UK Biodiversity Action Plan – List of UK BAP Priority Herptile Species" (PDF). data.jncc.gov.uk. 2007. Retrieved 28 November 2025.
  30. ↑ Berger, L. (1970). "Some characteristics of the crossess within Rana esculenta complex in postlarval development". Annales Zoologici. 27: 374–416.
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