Water frogs (pelophylax) are involved in several hybridogenetic complexes. In each new generation, the non-ridibunda genome is excluded before meiosis and mating with the syntopic parental species restores the diploïdy.

Rana ridibunda

 In France, besides the presence of different Mendelian species such as Rana lessonae, R. ridibunda, and R. perezi, the occurrence of two natural hybrids R. kl esculenta and R. kl grafi was also documented.

 
Hybridogenèse in water frog 
in Lodé 2001 stratégies de reproduction des animaux, Eds Dunod Masson Science.

 Investigations in Southern and Western France produced evidence of new hybridization events between Rana lessonae and R. perezi (some new hybrids tadpoles were discovered), and the existence of new assemblages [R±G, L±P, R±P, P±R±G: (R, ridibunda; G, graf; L, lessonae; P, perezi)]. In respect to hybridogenesis, these assemblages offer opportunities for both primary and secondary hybridizations. Such peculiarities may be explained either by introductions or by relic populations and may influence water frog evolution.

European water frogs are characterized by anthropic introductions and Rana ridibunda may be considered as an invasive species. As such translocations may result in introgression of exotic genes in native populations. Moreover, species poorly differ in their specific mate recognition system, facilitating hybridization events therefore suggesting that postzygotic mechanisms may be prevalent upon prezygotic mechanisms.

The study of Amphibian hybrid zones is of interest in order to specify the rule of such zone in speciation through several aspects (reinforcement, introgression, polyploidy …). Our models are the different fascinating water frog complexes. The water frog complex in western Europe included several species and numerous hybrids resulting from hemiclonal hybridogenetic gametogenesis.

 
Rana perezi

 Two models have been proposed to explain the ubiquity of asexuals: the General-Purpose Genotype (GPG) and the Frozen Niche Variation (FNV) model. According to these models, asexuals differ in their ecological niche width and may occupy narrow specialist niches or ubiquitous niches. In France, we found that hybridogenetic water frogs GPG and FNV hemiclones coexist.

Hybridogenesis induced character convergence in courtship signal with the non-ridibunda species in hybrid zones. In any case, these changes in the courtship signal favoured the particular hybridogenetic process, which constitutes a quasi-parasitism of the non-ridibunda genome.

  PAGANO A., LESBARRERES D., O'HARA R., CRIVELLI A., VEITH M., LODE T. & SCHMELLER D.S. 2008 Geographical and ecological distributions of frog hemiclones suggest occurrence of both “General Purpose Genotype” and “Frozen Niche Variation” clones. Journal of Zoological Systematics and Evolutionary Research, 46:162-168.

OULD-SEHLA Daf, PAGANO Alain & LODÉ T, 2005, Taxonomic diversity and sympatries among water frogs from Southern France: evidence for new assemblages, Amphibia-Reptilia :1-5

PAGANO A., DUBOIS A., LESBARRERES D. & LODÉ T. 2003. Frog alien species : a way for genetic invasion ? C.R. Biologies, 326: 85-92 

PAGANO A, CROCHET PA, GRAF JD, JOLY P &LODÉ T. 2001. Distribution and habitat use of water frog hybrid complexes in France. Global Ecol and Biogeography.10 : 433-441
 
LODÉT. 2001. Character convergence in advertisement call and mate choice in two genetically distinct water frog hybridogenetic lineages (Rana kl esculenta, R. kl grafi). J Zool Syst Evol Res. 39 : 91-96

PAGANO A, LODE T & CROCHET PA. 2001. New contact zone and assemblages among water frog of southern France. J Zool Syst Evol Res. 39 : 63-68

LODÉ T.& PAGANO A. 2000 - Variations in call and morphology in males water frog : taxonomic and evolutionary implications. Compte-Rendus Académie des Sciences Vie/Life Sciences 323 : 995-1001.

PAGANO A., LESBARRERES, D., LODE T. 2004. Ecological restoration in anthropogenic landscapes: dead end road or key for conservation ?. 18th Annual Meeting of the Society for Conservation Biology, New York, USA