|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). Instead, each gamete carries a complete (haploid) parental genome. Usually one entire genome of the parental species is excluded prior to meiosis during gametogenesis, such that only one parental genome is represented among gametes and genes from the other parent are not passed on by the hybridogen.
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.
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