The hemiclonal waterfrog Rana esculenta (RL genotype), a bisexual hybrid between R. ridibunda (RR) and R. lessonae (LL), eliminates the L genome from its germline and clonally transmits the R genome (hybridogenesis). Matings between hybrids produce R. ridibunda offspring, but they generally die at an early larval stage. Mortality may be due to fixed recessive deleterious mutations in the clonally inherited R genomes that were either acquired through the advance of Muller’s ratchet or else frozen in these genomes at hemiclone formation. From this hypothesis results a straightforward prediction: Matings between different hemiclones, that is, between R. esculenta possessing different R genomes of independent origin, should produce viable R. ridibunda offspring because it is unlikely that different clonal lineages have become fixed for the same mutations. I tested this prediction by comparing survival and larval performance of tadpoles from within- and between-population crossings using R. esculenta from Seseglio (Se) in southern, Alpnach (Al) in central, and Elliker Auen (El) in northern Switzerland, respectively. Se is isolated from the other populations by the Alps. Enzyme electrophoresis revealed that parents from Se belonged to a single hemiclone that was different from all hemiclones found north of the Alps. Parents from Al also belonged to one hemiclone, but parents from El belonged to three hemiclones, one of which was indistinguishable from the one in Al. Rana esculenta from Se produced inviable tadpoles when crossed with other hybrids of their own population, but when crossed with R. esculenta from Al and El, tadpoles successfully completed metamorphosis, supporting the hypothesis I tested. Within-population crosses from Al were also inviable, but some within-population crosses from El, where three hemiclones were present, produced viable offspring. Only part of the crosses between Al and El were viable, but there was no consistent relationship between hemiclone combination and tadpole survival.When backcrossed with the parental species R. ridibunda, hybrids from all source populations produced viable offspring. Performance of these tadpoles with a sexual and a clonal genome was comparable to that of normal, sexually produced R. ridibunda tadpoles. Thus, in the heterozygous state, the deleterious mutations on the clonal R genomes did not appear to reduce tadpole fitness.

The pool frog, Rana lessonae, has historically been considered an introduction into Britain, with Italy the most likely source. Recently, the possibility of native status for a Norfolk pool frog population was raised. We used random amplified DNA (RAPD) analyses to clarify the status issue. Nine arbitrarily designed primers detected 160 polymorphisms in 174 pool frogs from 11 European locations. Polymorphism levels varied widely, being lowest in the northern populations and highest in the south. As with many isolated populations, the peninsular and insular populations of Sweden, Norway and Britain showed relatively little polymorphism. Principal component and cluster analysis showed clear geographical groupings. The Norfolk, Norwegian and Swedish individuals formed a closely related group a northern clade, substantiating native status for the Norfolk population, which, interestingly, had idiosyncratic features suggestive of a distinctive evolutionary history. Phylograms constructed from RAPD data were consistent with an unexpected postglacial colonization route, in which the northern clade derived from migration out of Italy, via Hungary and Poland, though cryptic glacial refugia in Eastern Europe are an alternative explanation. Our RAPD analyses concur with a parallel microsatellite investigation. Both genetic studies and bioacoustic and archaeozoological findings support native status for Norfolk pool frogs and have prompted a programme for re-establishing the northern clade in England.

We tested for environmental factors that may lead to balancing selection and to the maintenance of a genetic polymorphism at the enzyme locus lactate dehydrogenase B (LDH-B) in the pool frog, Rana lessonae. We raised tadpoles individually in a factorial experiment in which we manipulated temperature, food level, and food quality. The only statistically significant difference among LDH-B genotypes was in growth rate, with the heterozygote performing best. Although the difference was not significant, heterozygotes also tended to perform best for size at metamorphosis. However, heterozygotes did not perform best in terms of other traits (age at metamorphosis and rates of survival and metamorphosis), where differences among LDH-B genotypes were also not significant. The size of the effect of LDH-B genotype depended on the environment, which suggests that the locus may be selectively neutral in some environments. There were no genotype–environment interactions in the sense that reaction norms along environmental gradients did not cross. When we raised tadpoles in groups,  e/e homozygotes had a significantly higher body mass and developed at the significantly highest rate. In addition, there may be a trade-off between larval and adult performance: adult frogs show a different ranking in performance of LDH-B genotypes than tadpoles do. These results suggest that this genetic polymorphism is maintained through heterozygote advantage, possibly in conjunction with antagonistic pleiotropy.

Based on material collected in 2001 – 2002, The diet of  R. ridibunda in  Mordovia included 200 different species. Arthropoda (Insecta, Arachnida) were common. Among vertebrates, the consumption of tailless amphibians and fish indicate well-developed cannibalism in this species. Mammals were also a part of the diet.

По материалам, собранным в 2001 – 2002  гг.,  в  пище  озерной  лягушки  встречаются  около 200  различных  видов животных,  среди  которых  преобладают  бесхвостые  земноводные,  что  указывает на  довольно  сильный  развитый  каннибализм.  В  диету  также  входят  различные виды рыб и млекопитающих.

Water frogs are involved in several hybridogenetic complexes. However, investigations in Southern and Western France produced evidence of new hybridization events between R. 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, grafi; 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.