Leszek Berger

Systematics and Hybridization in European Green Frogs of Rana esculenta Complex

European green frogs include the phenotypically distinct, largely sympatric forms Rana lessonae Camerano 1882, R. esculenta Linnaeus 1758, and R. ridibunda Pallas 1771, the relationships of which is still unsufficiently known. Recent investigations on Polish green frog populations indicate that R. lessonae and R. ridibunda are taxa at species rank, whereas R. esculenta is a hybrid resulting from interspecific crosses between R. lessonae and R. ridibunda. All three forms of green frogs are easily crossable indicating close relationship, and lack of genetic isolation. Ecological isolating mechanisms were probably established during the Pleistocene. In spite of very frequent natural hybridization, very high number of F1 hybrids (= esculanta) in nature, and successful backcrosses especially with lessonae, introgression between lessonae and ridibunda seems not to occur owing to an incompletely understood hereditary mechanism.

Western Palearctic water frogs (Amphibia, Ranidae): Systematics, genetics and population compositions

Recent studies of the western Palearctic water frogs revealed the occurrence of at least 5 types of water frogs (Rana ridibunda, R. lessonae, R. perezi, 1 Italian and 1 Balkan species) as well as 4 types of their hybrids. In addition to the systematics, genetics and population compositions of these frogs, the complex mechanisms that lead to the production of the hybridogenetic hybridRana esculenta are emphasized, and the unsolved problems relating to the control of the hybridogenetic process are discussed.

Progeny of water frog populations in central Poland

The authors discuss progenies of 18 watcr frog populations. Individuals with esculenta phenotype which arc hybridogenetic hybrids between Rana ridibunda and Rana lessonae are the most numerous frogs among the adults and progeny. Esculenta tadpoles began and finished their metamorphosis mostly as first, and in progeny with esculenta phenotype there were more females than males. In pure esculenta population most of progeny belonged to ridibunda phenotype and female sex. The froglets caught in August were larger on an average than those in October or after hibernation.

Spontaneous haploid-triploid mosaicism in the progeny of a Rana kI. esculenta female and Rana lessonae males

A female Rana kl. esculenta was crossed with three different R. lessonae males. Three froglets with unexpected phenotypes appeared. Two of them were chimerae with one side of the body of lessonae, and the other of escutenta phenotype, and one displayed lessonae, instead of the expected esculenta, phenotype. Blood of three individuals was composed of small haploid and large triploid erythrocytes. These results indicate that the froglets were 1n/3n mosaics.

Large eggs and ploidy of green frog populations in Central Europe

Green frogs of Central Europe consist of three taxa: Pelophylax ridibundus, P. lessonae and their natural hybridogenetic hybrid, P. esculentus, which forms as a rule mixed populations with its parental species. We examined 659 095 eggs from P. ridibundus (48 females), P. lessonae (133 females) and P. esculentus (170 females) originating from 39 populations in Austria, Denmark, Germany and Poland. Some females of each taxon laid eggs that fell into discrete size classes (small, medium and large). Large eggs were mostly diploid gametes from which triploids developed. They were found in P. esculentus (25 233 large eggs in 152 spawns), P. lessonae (81 in 10 spawns) andP. ridibundus (7 in 3 spawns). The main purpose of the paper was to demonstrate that the numbers of large eggs were clearly associated with triploid P. esculentus frogs. In pure hybrid (esculentus) populations large eggs comprised between 2.44-40.96% of all ova, while triploid adult frogs constituted between 13.9-73.2% of all individuals, in mixed ridibundus-esculentus populations the large eggs and triploid frogs ranged between 0.85-36.6% and 9.2-56.2%, respectively. However, in mixed lessonae-esculentus populations large eggs comprised only 1.74% of the spawns, whereas triploid frogs represented 2.1% of the adults in the population.