Pool frog

{{Short description|Species of amphibian}} {{Use dmy dates|date=November 2025}} {{Speciesbox | name = Pool frog | image = Rana lessonae.jpg | status = LC | status_system = IUCN3.1 | status_ref = <ref name=IUCN>{{cite iucn |author=IUCN SSC Amphibian Specialist Group. |year=2022 |title=''Pelophylax lessonae'' |volume=2022 |article-number=e.T58643A177068753 |doi=10.2305/IUCN.UK.2022-1.RLTS.T58643A177068753.en |access-date=16 October 2022}}</ref> | genus = Pelophylax | species = lessonae | authority = (Camerano, 1882) | subdivision_ranks = Subspecies | subdivision = See text | range_map = Pelophylax lessonae dis.png | range_map_caption = Range of the nominate subspecies of the pool frog | synonyms = {{collapsible list |''Rana lessonae'' Camerano, 1882 |''Rana esculenta'' Linnaeus, 1758{{efn|Apparently describing a specimen representing a ''Pelophylax lessonae'' × ''Pelophylax ridibundus'' hybridogen, not a true taxonomic synonym<ref>{{ITIS|taxon=''Rana esculenta'' Linnaeus, 1758|id=665307|access-date=1 August 2024}}</ref>}} |''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 }} | synonyms_ref = <ref>{{ITIS|taxon=''Pelophylax lessonae'' (Camerano, 1882)|id=775190|access-date=1 August 2024}}</ref> }}

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== 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.<ref>{{Cite journal |last=Camerano |first=Lorenzo |date=1882 |title=Recherches sur les variations de la ''Rana esculenta'' et du ''Bufo viridis'' dans le Bassin de la Méditerranée |url=https://www.biodiversitylibrary.org/page/5398044 |journal=Comptes Rendus de l'Association Française pour l'Avancement des Sciences |volume=10 |pages=680–690}}</ref> 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''.<ref>{{Cite journal |last=Camerano |first=Lorenzo |date=1884 |title=Monografia degli anfibi anuri Italiani |url=https://www.biodiversitylibrary.org/page/35941779 |journal=Memorie della Reale accademia delle scienze di Torino |series=2 |language=It |volume=35 |pages=187–284}}</ref> 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.<ref>{{Cite journal |last=Balletto |first=Emilio |last2=Cherchi |first2=Maria Adelaide |last3=Salvidio |first3=Sebastiano |last4=Lattes |first4=Aldo |last5=Malacrida |first5=Anna |last6=Gasperi |first6=Giuliano |last7=Doria |first7=Giuliano |date=1986 |title=Area effect in south western European green frogs (Amphibia, Ranidae) |url=https://www.tandfonline.com/doi/full/10.1080/11250008609355490 |journal=Bollettino di zoologia |language=en |volume=53 |issue=1 |pages=97–109 |doi=10.1080/11250008609355490 |issn=0373-4137}}</ref>

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.<ref>{{Cite journal |last=Berger |first=Leszek |date=1966 |title=Biometrical studies on the population of green frogs from the environs of Poznan |url=https://www.semanticscholar.org/paper/Biometrical-studies-on-the-population-of-green-from-Berger/7c55b4a8afc277b72a406ecf19dadf0c0ee5c188 |journal=Annales Zoologici |volume=23 |pages=303–324 |s2cid=85846846}}</ref> 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''.<ref>{{Cite journal |last=Dubois |first=Alain |date=1992 |title=Notes sur la classification des Ranidae (Amphibiens, Anoures) |url=https://www.researchgate.net/publication/302964694 |journal=Bulletin mensuel de la Société linnéenne de Lyon |language=fr |volume=61 |issue=10 |pages=305–352 |doi=10.3406/linly.1992.11011 |issn=0366-1326}}</ref> 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''.<ref>{{Cite journal |last=Chen |first=Liqiao |last2=Murphy |first2=Robert W. |last3=Lathrop |first3=Amy |last4=Ngo |first4=Andre |last5=Orlov |first5=Nikolai L. |last6=Ho |first6=Cuc Thu |last7=Somorjai |first7=Ildiko L. M. |date=2005 |title=Taxonomic chaos in Asian ranid frogs: an initial phylogenetic resolution |url=https://www.researchgate.net/publication/233621223 |journal=Herpetological Journal |language=en-gb |volume=15 |issue=4 |pages=231–243}}</ref> 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''.<ref>{{Cite journal |last=Frost |first=Darrel R. |last2=Grant |first2=Taran |last3=Faivovich |first3=JuliáN |last4=Bain |first4=Raoul H. |last5=Haas |first5=Alexander |last6=Haddad |first6=CéLio F.B. |last7=De Sá |first7=Rafael O. |last8=Channing |first8=Alan |last9=Wilkinson |first9=Mark |last10=Donnellan |first10=Stephen C. |last11=Raxworthy |first11=Christopher J. |last12=Campbell |first12=Jonathan A. |last13=Blotto |first13=Boris L. |last14=Moler |first14=Paul |last15=Drewes |first15=Robert C. |date=2006 |title=The Amphibian Tree of Life |url=http://www.bioone.org/doi/abs/10.1206/0003-0090%282006%29297%5B0001%3ATATOL%5D2.0.CO%3B2 |journal=Bulletin of the American Museum of Natural History |language=en |volume=297 |pages=1–291 |doi=10.1206/0003-0090(2006)297[0001:TATOL]2.0.CO;2 |issn=0003-0090}}</ref><ref>{{Cite journal |last=Che |first=Jing |last2=Pang |first2=Junfeng |last3=Zhao |first3=Hui |last4=Wu |first4=Guan-fu |last5=Zhao |first5=Er-mi |last6=Zhang |first6=Ya-ping |date=2007 |title=Phylogeny of Raninae (Anura: Ranidae) inferred from mitochondrial and nuclear sequences |url=https://linkinghub.elsevier.com/retrieve/pii/S1055790306004891 |journal=Molecular Phylogenetics and Evolution |language=en |volume=43 |issue=1 |pages=1–13 |doi=10.1016/j.ympev.2006.11.032}}</ref>

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.<ref>{{Cite book |last=Fejérváry |first=Géza Gyula Imre |url=https://www.biodiversitylibrary.org/bibliography/12602 |title=Beiträge zur Herpetologie des Rhônetales und seiner Umgebung von Martigny bis Bouveret |publisher=George & Companie |year=1909 |location=Genéve |pages=20–25 |language=De |doi=10.5962/bhl.title.12602}}</ref> Similary, Yugoslav biologist Stanko Karaman erected a new subspecies of pool frog given the name ''Rana lessonae pannonica'' in 1948 without specifying a type specimen.<ref>{{Cite journal |last=Karaman |first=Stanko |date=1948 |title=Prilog herpetologiji sjeverne Srbije |url=https://www.lacerta.de/AF/Bibliografie/BIB_15516.pdf |journal=Prirodoslovna Istrazivanja |language=Hr |volume=24 |pages=51–74}}</ref> Both of these names were declared as junior synonyms of ''Rana lessonae'' in 1994.<ref>{{Cite journal |last=Dubois |first=Alain |last2=Ohler |first2=Annemarie |date=1994 |title=Catalogue of names of frogs in the subgenus ''Pelophylax'' (Amphibia, Anura, genus ''Rana''): a few additions and corrections |url=https://www.researchgate.net/publication/287389640 |journal=Zoologica Poloniae |volume=39 |issue=3 |pages=139–204}}</ref>

===Subspecies=== 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.<ref name=":0">{{Cite book |title=Atlas of amphibians and reptiles in Europe |publisher=Societas Herpetologica Europeae and Museum National Histoire Naturelle |isbn=978-2-85653-574-5 |editor-last=Gasc |editor-first=Jean-Pierre |edition=Nouv. éd |series=Collection Patrimoines naturels |location=Paris |editor-last2=Cabela |editor-first2=Antonia |editor-last3=Crnobrnja-Isailovic |editor-first3=Jeika |editor-last4=Dolmen |editor-first4=Dag |editor-last5=Grossenbacher |editor-first5=Kurt |editor-last6=Haffner |editor-first6=Patrick |editor-last7=Lescure |editor-first7=Jean |editor-last8=Martens |editor-first8=Harald |editor-last9=Martinez Rica |editor-first9=Juan Pablo|editor-last10=Maurin |editor-first10=Herve |editor-last11=Oliveira |editor-first11=Maria Elisa |editor-last12=Sofianidou |editor-first12=Theodora |editor-last13=Veith |editor-first13=Michael |editor-last14=Annie |editor-first14=Zuiderwijk|last=Crochet|first=Pierre-André|year=2004|last2=Dubois|first2=Alain|chapter=Recent changes in the taxonomy of European amphibians and reptiles|chapter-url=https://www.researchgate.net/publication/313367170}}</ref> A phylogenetic study published in 2008 further supported this.<ref name=":1">{{Cite journal |last=Canestrelli |first=Daniele |last2=Nascetti |first2=Giuseppe |date=2008 |title=Phylogeography of the pool frog ''Rana (Pelophylax) lessonae'' in the Italian peninsula and Sicily: multiple refugia, glacial expansions and nuclear–mitochondrial discordance |url=https://onlinelibrary.wiley.com/doi/10.1111/j.1365-2699.2008.01946.x |journal=Journal of Biogeography |language=en |volume=35 |issue=10 |pages=1923–1936 |doi=10.1111/j.1365-2699.2008.01946.x |issn=0305-0270}}</ref> Under this classification, the pool frog includes the following two named subspecies:

{| class="wikitable collapsible" font="90%" |- style="background: #115a6c" !Subspecies !Trinomial authority !Description !Range |---- |'''Pool frog''' (''P. l. lessonae'') (Nominate subspecies) |(Camerano, 1882) | |Northern Italy and elsewhere in Europe<ref name=":0" /> |- |'''Italian pool frog''' (''P. l. bergeri'') |Günther, in Engelmann, Fritzsche, Günther & Obst, 1986 | |Most of peninsular Italy<ref name=":0" /> |- |}

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''.<ref name=":0" /><ref name=":1" /> 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.<ref>{{Cite journal |last=Dufresnes |first=Christophe |last2=Monod‐Broca |first2=Benjamin |last3=Bellati |first3=Adriana |last4=Canestrelli |first4=Daniele |last5=Ambu |first5=Johanna |last6=Wielstra |first6=Ben |last7=Dubey |first7=Sylvain |last8=Crochet |first8=Pierre‐André |last9=Denoël |first9=Mathieu |last10=Jablonski |first10=Daniel |date=2024 |title=Piecing the barcoding puzzle of Palearctic water frogs (''Pelophylax'') sheds light on amphibian biogeography and global invasions |url=https://onlinelibrary.wiley.com/doi/10.1111/gcb.17180 |journal=Global Change Biology |language=en |volume=30 |issue=3 |doi=10.1111/gcb.17180 |issn=1354-1013}}</ref>

==Description== The pool frog is a small frog which rarely grows to more than {{Convert|8|cm|abbr=on}} long, although females can grow up to {{Convert|9|cm|abbr=on}}. Males are typically around {{Convert|5|cm|abbr=on}} long, while females are around {{Convert|6-6.5|cm|abbr=on}} long. These frogs are brown or green, with dark blotches along their backs, a pair of ridges running from each eye and a cream or yellow stripe down the middle of the frog's back. The vocal sacs on the male are cream or even white.<ref name=froglife>{{Cite web |title=Pool Frog |url=https://www.froglife.org/info-advice/amphibians-and-reptiles/pool-frog/ |access-date=2022-05-25 |website=www.froglife.org}}</ref>

==Distribution== The pool frog is found across most of central Europe from the west coast of northern France to the Western part of Russia. There are also small populations of pool frogs in the United Kingdom, Spain, Sweden and Norway.<ref name=IUCN/> Pool frogs were previously thought to be a non-native species in the UK, but studies have shown that English pool frogs are related to the Swedish and Norwegian populations.<ref name=froglife/>

The pool frog is found in damp areas with dense vegetation, or in calm, slow flowing rivers, ponds, bogs or marshes.<ref name=froglife/>

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.<ref>{{Cite web |title=AmphibiaWeb - Pelophylax lessonae |url=https://amphibiaweb.org/cgi-bin/amphib_query?where-scientific_name=Pelophylax+lessonae |access-date=2022-05-25 |website=amphibiaweb.org}}</ref>

<gallery mode=packed heights=170px> File:James Green & James H. Gardiner - Sciagraphs of British Batrachians and Reptiles - 1897 - Rana Esculenta.jpg|1897 sciagraph (X-ray photograph) of ''P. lessonae'' (then ''Rana Esculenta''), from James Green & James H. Gardiner's "Sciagraphs of British Batrachians and Reptiles" File:Wildgehege Tannenberg 16.07.2008 187.jpg|alt=Wildgehege Tannenberg 16.07.2008|''Pelophylax lessonae'' </gallery>

==Pool frogs in Britain== ''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,<ref>{{cite web |url=https://data.jncc.gov.uk/data/98fb6dab-13ae-470d-884b-7816afce42d4/UKBAP-priority-herptiles.pdf |title=UK Biodiversity Action Plan – List of UK BAP Priority Herptile Species |date=2007 |website=data.jncc.gov.uk |access-date=2025-11-28}}</ref> adding all of the UK's extant, native herpetofauna to this plan; with a notable exception of the Aesculapian snake do 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 pool frog has not always been recognised as a native British species. Part of the reason for this is that specimens are known to have been introduced from southern Europe (though not from Scandinavia). However research has now shown that the potentially native UK pool frogs are closely related to Scandinavian frogs, not to frogs from further south. A native origin is thus most likely.<ref>{{cite journal |last1=Beebee |first1=Trevor J. C. |last2=Buckley |first2=John |last3=Evans |first3=Ivor |last4=Foster |first4=Jim P. |last5=Gent |first5=Antony H. |last6=Gleed-Owen |first6=Chris P. |last7=Kelly |first7=Geoffrey |last8=Rowe |first8=Graham |last9=Snell |first9=Charles |last10=Wycherley |first10=Julia T. |last11=Zeisset |first11=Inga |title=Neglected native or undesirable alien? Resolution of a conservation dilemma concerning the pool frog ''Rana lessonae'' |journal=Biodiversity and Conservation |date=2005 |volume=14 |issue=7 |pages=1607–1626 |doi=10.1007/s10531-004-0532-3|bibcode=2005BiCon..14.1607B }}</ref>

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.

==Two clades==

There are at least two recognised sub-populations of pool frog, the northern and the southern. The southern clade is more widespread whereas the northern clade is endemic to the British Isles, Scandinavia and possibly Estonia.<ref>{{cite journal |url=https://www.thebhs.org/publications/the-herpetological-journal/volume-17-number-4-october-2007/502-06-two-clades-of-north-european-pool-frogs-i-rana-lessonae-i-identified-by-cytochrome-i-b-i-sequence-analysis/file |title=Two clades of north European pool frogs Rana lessonae identified by cytochrome b sequence analysis |journal=Herpetological Journal |date=2007 |access-date=2025-12-16}}</ref>

==Hybridogenesis== {{see also|Hybridogenesis in water frogs}} 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.<ref name="Berger70">{{cite journal | author=Berger, L. | year= 1970| title= Some characteristics of the crossess within ''Rana esculenta'' complex in postlarval development | journal=Annales Zoologici | volume=27 | pages= 374–416 }}</ref>

==Notes== {{notelist}}

==References== {{Reflist}}

==External links== *[https://news.bbc.co.uk/2/hi/uk_news/england/norfolk/4143224.stm BBC News article on the reintroduction] *[https://web.archive.org/web/20051024000408/http://www.herpconstrust.org.uk/animals/pool_frog2.htm Species page at the Herpetological Conservation Trust website] *[https://www.youtube.com/watch?v=Vaw3OpTopcA Movie with sound YouTube]

Category:Pelophylax Category:Amphibians of Europe Category:Amphibians described in 1882 Category:Taxa named by Lorenzo Camerano