|Species:||P. lessonae × P. ridibundus|
|Pelophylax kl. esculentus
Pelophylax esculentus (Linnaeus, 1758)
The edible frog (Pelophylax kl. esculentus)  is a name for a common European frog, also known as the common water frog or green frog (however, this latter term is also used for the North American species Rana clamitans). It is used for food, particularly in France for the delicacy frog legs. Females are between 5 to 9 cm long, males between 6 to 11 cm.
P. esculentus is endemic to Europe. It naturally occurs from the northern half of France to western Russia, and from Estonia and Denmark to Bulgaria and northern Italy. It is introduced in Spain and the United Kingdom. The natural range is nearly identical to that of P. lessonae.
During the ice ages,[clarification needed] the population of the common ancestor of both species was split into two. These populations diverged, but remained genetically close enough to be able to create fertile hybrids. However, when edible frogs mate with each other, their offspring are often malformed, so there are no pure populations of edible frogs.
The hybrid populations are propagated predominantly by female edible frogs mating with males of one of the parental species (P. kl. esculentus × P. lessonae or rarely × P. ridibundus). 
Hybridogenesis implies that gametes of hybrids don't contain mixed parental genomes, as normally occurs by independent chromosome segregation and crossover in meiosis (see also second Mendel's law, recombination), but intact one of them or two. Usually because one entire genome of the parental species is excluded prior to meiosis during gametogenesis.
So hybridogenesis is a clonal mode of reproduction — of a hybrid genome is transmitted intact clonally from generation to generation (R genome in the L-E system) — not recombined with a parental species genome (L here), while the other half (L) is transmitted sexually — obtained each generation by sexual reproduction with a parental species (P. lessonae in the L-E system).
In the most widespread, so called L-E (lessonae-esculentus) hybridogenetic population system, frogs P. kl. esculentus exclude the P. lessonae genome and make exclusively clonal P. ridibundus gametes (see image above). In other words edible frogs produce gametes of marsh frogs! There are however other systems known, of which the R-E (ridibundus-esculentus) system is best known. In this case frogs P. kl. esculentus predominantly (but not exclusively) produce P. lessonae gametes.
In the L-E system P. kl. esculentus must mate with P. lessonae to produce new hybrids, in the R-E system with P. ridibundus (see image on the left). P. lessonae and P. ridibundus have distinct habitat requirements and usually don't occur together.
Moreover P. kl. esculentus frogs can be not only diploid hybrids (LR), but in some areas also triploid (LLR and LRR) and even tetraploid (LLRR). Triploid hybrids enable P. kl. esculentus populations to persist without the parental species (P. lessonae and P. ridibundus); however, there are still gaps in the knowledge of how this system works.
|Maintenance of pure (all-hybrid) P. kl. esculentus populations, without P. lessonae and ridibundus.
- Tunner H. G., Heppich-Tunner S. (1991). "Genome exclusion and two strategies of chromosome duplication in oogenesis of a hybrid frog. Short Communications.". Naturwissenschaften 78 (1): 32–34. doi:10.1007/BF01134041. Retrieved 2012-07-28.
- Frost, Darrel R. (2006). "Amphibian Species of the World: an Online Reference. Version 4". American Museum of Natural History, New York, USA. Retrieved 17 August 2006.
- Frost, Grant, Faivovich, Bain, Haas, Haddad, de Sá, Channing, Wilkinson, Donnellan, Raxworthy, Campbell, Blotto, Moler, Drewes, Nussbaum, Lynch, Green, and Wheeler 2006. The amphibian tree of life. Bulletin of the American Museum of Natural History. Number 297. New York. Issued March 15, 2006.
- "Pelophylax esculentus, Edible Frog". AmphibiaWeb. Retrieved 28 January 2014.
- Berger, L. (1970). "Some characteristics of the crossess within Rana esculenta complex in postlarval development". Ann. Zool. 27: 374–416.
- C Spolsky andT Uzzell (1986). "Evolutionary history of the hybridogenetic hybrid frog Rana esculenta as deduced from mtDNA analyses.". Mol Biol Evol 3 (1): 44–56. Retrieved 2012-07-24.
- Gaby Abt Tietje and Heinz-Ulrich Reyer (2004). "Larval Development and Recruitment of Juveniles in a Natural Population of Rana lessonae and Rana esculenta". Copeia 3: 638–646. doi:10.1643/ce-03-273r1. Retrieved 2012-07-24.
- Christiansen D. G. (2009). "Gamete types, sex determination and stable equilibria of all-hybrid populations of diploid and triploid edible frogs (Pelophylax esculentus) Rana esculenta as deduced from mtDNA analyses.". BMC Evolutionary Biology 9 (135). doi:10.1186/1471-2148-9-135. Retrieved 2012-07-25.
- Ragghianti M, Bucci S, Marracci S, Casola C, Mancino G, Hotz H, Guex GD, Plötner J, Uzzell T. (February 2007). "Gametogenesis of intergroup hybrids of hemiclonal frogs.". Genet Res. 89 (1): 39–45. doi:10.1017/S0016672307008610. Retrieved 2012-07-25.
- Simon J.-C., Delmotte F., Rispe C., Crease T. (2003). "Phylogenetic relationships between parthenogens and their sexual relatives: the possible routes to parthenogenesis in animals.". Biological Journal of the Linnean Society 79: 151–163. doi:10.1046/j.1095-8312.2003.00175.x. Retrieved 2012-07-30.
- Holenweg Peter A. K. (December 2001). "Dispersal rates and distances in adult water frogs, Rana lessonae, R. ridibunda and their hybridogenetic associate R. esculenta.". Herpetologica (Herpetologists' League) 57 (4): 449–460. Retrieved 2012-07-26.
|Wikimedia Commons has media related to Rana esculenta.|