Hybridogenesis in water frogs

in the Danube delta

The fertile hybrids of European water frogs (genus Pelophylax) reproduce by hybridogenesis (hemiclonally). This means that during gametogenesis, they discard the genome of one of the parental species and produce gametes of the other parental species (containing a genome not recombined with the genome of the first parental species).[1][2][3][4] The first parental genome is restored by fertilization of these gametes with gametes from the first species (sexual host).[5][1][4] In all-hybrid populations of the edible frog Pelophylax kl. esculentus, however, triploid hybrids provide this missing genome.[3][6][2]

Because half of the genome is transmitted to the next generation clonally (not excluded unrecombined intact genome), and only the other half sexually (recombined genome of the sexual host), the hybridogenesis is a hemiclonal mode of reproduction.[7][8][4]

For example, the edible frog Pelophylax kl. esculentus (mostly RL genome), which is a hybridogenetic hybrid of the marsh frog P. ridibundus (RR) and the pool frog P. lessonae (LL), usually excludes the lessonae genome (L) and generates gametes of the P. ridibundus (R). In other words, edible frogs produce gametes of marsh frogs.[2][3][4]

The hybrid populations are propagated, however, not by the above primary hybridisations, but predominantly by backcrosses with one of the parental species they coexist (live in sympatry[9][10]) with (see below in the middle). [11][2][3][12][9][4]

Example crosses between pool frog (Pelophylax lessonae), marsh frog (P. ridibundus) and their hybrid - edible frog (P. kl. esculentus). The first example is the primary hybridization-generating cross.[2] The second one is an example of hybridogenesis and occurs in the most widespread hybridogenetic L–E system,[11][2][3][4][9][12][8] the third example occurs in the R–E system, is less frequent in nature [2][4], but is considered as possible e.g., if an L-E system is invaded by P. ridibundus [8]. P. kl. esculentus × P. kl. esculentus crossings result in inviable P. ridibundus tadpoles and are not shown here.[2][3] Large circles - adult frogs, small circles - gametes, × - lack of gametes containing genome of one of the parental species.

Since the hybridogenetic hybrids require another taxon as sexual host to reproduce, usually one of the parental species, they are called kleptons[13][14][5] (with "kl." in scientific names[15]).

Edible frog Pelophylax kl. esculentus

There are three known hybridogenetic hybrids of the European water frogs:

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  12. ^ a b Cite error: The named reference TietjeReyer04 was invoked but never defined (see the help page).
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