Edible Frog

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Edible Frog
Conservation status
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Amphibia
Order: Anura
Family: Ranidae
Genus: Pelophylax
Species: P. lessonae × P. ridibundus
Binomial name
Pelophylax kl. esculentus
(Linnaeus, 1758)
Synonyms

Pelophylax esculentus (Linnaeus, 1758)
Rana esculenta Linnaeus, 1758

Typical gametogenesis in Pelophylax kl. esculentus (in the L-E system). 1 - exclusion of the P. lessonae genome, 2 - duplication (endoreduplication) of the P. ridibundus genome - restoration of diploidy, 3 - meiosis, L and R - P. lessonae and ridibundus genomes. [ 1]
Pelophylax kl. esculentus are a hemiclone here, because they share half of their genome (R haplotype, red arrows). L-E system.

The Edible Frog (Pelophylax kl. esculentus) [ 1][ 1] 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.

Distribution

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.[1]

Hybridogenesis

Pelophylax kl. esculentus is the fertile hybrid of the Pool Frog (Pelophylax lessonae) and the Marsh Frog (Pelophylax ridibundus), hence the addition of the "kl." (for klepton) in the species name.

During the ice ages, 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). [ 1][ 1][ 1][ 1]

Typical hybridization between pool frog (Pelophylax lessonae), marsh frog (Pelophylax ridibundus) and their hybrid - edible frog (Pelophylax kl. esculentus, P. lessonae × P. ridibundus) in a native LE (lessonae-esculentus) hybridogenetic population invaded additionally by P. ridibundus. Predominant matings are P. kl. esculentus females × P. lessonae males and P. ridibundus females × P. lessonae males. P. kl. esculentus × P. kl. esculentus crossings result in inviable P. ridibundus tadpoles and are not shown here. [ 1][ 1][ 1][ 1][ 1] Large circles - adult frogs, small circles - gametes., × - lack of gametes containing genome of one of parental species.

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.[ 1][ 1]

So hybridogenesis is a hemiclonal mode of reproduction — half 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).[ 1]

Typical hybridization between edible frog and marsh frog in R-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. ridibunda 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).[ 1][ 1] P. lessonae and P. ridibundus have distinct habitat requirements and usually don't occur together.[ 1]

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.[ 1]

Adults
(P. kl. esculentus)		 Gametes
LLR → L
LR → LR*, R
LRR → R
Gametes Offspring
L + L → LL P. lessonae
L + LR* → LLR P. kl. esculentus
L + R → LR
LR* + R → LRR
R + R → RR P. ridibundus
Maintenance of pure (all-hybrid) P. kl. esculentus populations, without P. lessonae and ridibundus.[ 1]

L, R - P. lessonae and ridibundus haploid genomes, * females only (eggs), LL, RR - do not survive to sexual maturity.

  • A swimming frog

  • Copulation trial between two males

  • Proof of cannibalism

  • Close-up of the frog head

  • Close-up of the head, other perspective

  • Edible frog on a human arm

References

  1. ↑ "Pelophylax esculentus, Edible Frog". AmphibiaWeb. Retrieved 28 January 2014. 
  2. ↑ Frost, Darrel R. (2006). [http://research.amnh.org/herpetology/amphibia/index.php. "Amphibian Species of the World: an Online Reference. Version 4"]. American Museum of Natural History, New York, USA. Retrieved 17 August 2006. 
  3. ↑ 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.
  4. ↑ Berger, L. (1970). "Some characteristics of the crossess within Rana esculenta complex in postlarval development". Ann. Zool. 27: 374–416. 
  5. ↑ 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. 
  6. ↑ 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. Retrieved 2012-07-24. 
  7. ↑ 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. 
  8. ↑ 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. 
  9. ↑ 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. 
  10. ↑ 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. 
  11. ↑ 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. Retrieved 2012-07-30. 
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