The occurrence of three green frog taxa [Rana lessonae (L), R. ridibunda (R), and R. esculenta (E)] in Nizhny Novgorod Province was evidenced by DNA flow cytometry analysis. Our data are the first reliable record of the hybrid R. esculenta for the province (the Middle Volga River basin). All hybrids were diploid. Rana lessonae is spread throughout the province, except its extreme north-east. The distribution of Rana ridibunda is wider and covers the northernmost area. Rana esculenta is quite sparse. In the province, all three species, probably, reach the northern limits of their ranges. Six population systems were revealed; both with a single species (R, L, and, probably, E) and with mixed species populations (LE, REL and RL). The geographic trends in occurrences of hybrids and various kinds of population systems in eastern Europe are discussed.
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397In eastern Ukraine, the Rana esculenta complex consists of three species: R. lessonae, R. ridibunda, and hybrid R. esculenta. The first one was rare, whereas two latter frog taxa were very common. Based on DNA flow cytometry, mass occurrence of the triploidy in Rana esculenta has been revealed in 14 localities of Kharkov, Donetsk, and Lugansk Provinces. One hybrid specimen from Kharkov Province was tetraploid. All polyploids were recorded along the middle part of Seversky Donets River (above 450 km). Triploids comprised two groups with different genome composition (LLR and LRR), and were found in three types of population systems (E, R–E, and L–E–R). Geographic distribution of polyploidy in European green frogs is briefly outlined. Different methods of ploidy level identification are discussed. The chromosome count and nuclear DNA cytometry provide the most reliable data.
The purpose of this investigation was to determine the feeding habits of the marsh frog, Rana ridibunda, populations inhabiting Turkish Thrace. Analysis of the stomach contents of 53 (19 ♂♂, 34 ♀♀) adult individuals was performed. The frog diet consisted of a wide variety of arthropods; Diptera (42.62%) and Coleoptera (21.84%) were especially prominent. Aquatic forms did not contribute much to the frog diet. The prey items identified indicate that individuals of this species, like other ranids, are generalist opportunistic predators whose diet is most strongly influenced by prey availability.
The objective of our study was to bring data upon the feeding of Rana lessonae, Rana arvalis from Reci region, Covasna County. We watched at the trophic spectrum of this two Rana species the variation depending on species, sex, habitat and diurnal activity. The feeding of moor frogs is more intense in twilight period. The largest diversity of preys was presented in the stomach contents of Rana lessonae samples captured from the pool. The females both of the two Rana species eat a greatest variety of preys vis a vis the males. Only Rana lessonae captured from the permanent pool present in stomach contents a relatively high number of aquatic preys.
Incompatibilities between parental genomes decrease viability of interspecific hybrids; however, deviations from canonical gametogenesis such as genome endoreplication and elimination can rescue hybrid organisms. To evaluate frequency and regularity of genome elimination and endoreplication during gametogenesis in hybrid animals with different ploidy, we examined genome composition in oocytes of di- and triploid hybrid frogs of the Pelophylax esculentus complex. Obtained results allowed us to suggest that during oogenesis the endoreplication involves all genomes occurring before the selective genome elimination. We accepted the hypothesis that only elimination of one copied genome occurs premeiotically in most of triploid hybrid females. At the same time, we rejected the hypothesis stating that the genome of parental species hybrid frogs co-exist with is always eliminated during oogenesis in diploid hybrids. Diploid hybrid frogs demonstrate an enlarged frequency of deviations in oogenesis comparatively to triploid hybrids. Typical for hybrid frogs deviations in gametogenesis increase variability of produced gametes and provide a mechanism for appearance of different forms of hybrids.
Christoph Vorburger // Ecology Letters, (2001) 4: 628-636
The hemiclonal waterfrog Rana esculenta, a hybrid between R. ridibunda and R. lessonae, eliminates the lessonae genome from the germline and clonally transmits the ridibunda genome (hybridogenesis). Such genomes are prone to accumulate deleterious mutations, which may explain why offspring from matings between hybrids are typically inviable. Here I present ®eld data from a population for which experimental crossings showed that some R. esculenta pairs produce viable R. ridibunda offspring. I demonstrate: (1) that R. ridibunda metamorphs are also produced and survive under natural conditions; (2) that their genotypes are consistent with combinations of clonal ridibunda genomes found in hybrids; and (3) that all R. ridibunda are female. These females possibly recombine the clonal genomes they inherited and, upon mating with syntopic R. lessonae, produce new hemiclones with novel combinations of alleles. Hence, occasional recombination between otherwise clonal ridibunda genomes seems plausible and may provide an escape from the evolutionary dead end they were proposed to be trapped in.
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.
Introduced Rana ridibunda currently replace the native waterfrogs R. lessonae and R. esculenta in several areas of central Europe. The unusual reproductive system in waterfrogs of the Rana esculenta complex suggests that this replacement may be driven by a genetic mechanism: Rana esculenta, a hybrid between R. ridibunda and R. lessonae, eliminates the lessonae genome from the germline and clonally transmits the ridibunda genome (hybridogenesis). Hybrids form mixed populations with R. lessonae (L-E-system) in which they persist by backcrossing with the parental species. Matings between hybrids are unsuccessful, because their ridibunda genomes contain fixed recessive deleterious mutations. When introduced into a L-E-system, R. ridibunda can mate with both native taxa, producing R. ridibunda offspring with R. esculenta,and R. esculenta offspring with R. lessonae (primary hybridizations). If primary hybrids are hybridogenetic, they produce viable R. ridibunda offspring in matings with other hybrids, because their clonal genomes are unlikely to share the deleterious alleles present in the ancient clones. Thus, R. ridibunda will increase in the population at the expense of both native taxa, eventually leaving a pure R. ridibunda population. We provide three lines of evidence for this process from a currently invaded population in Switzerland: (1) Primary hybridizations take place, as roughly 10% of hybrids in the population possess ridibunda genomes derived from the introduced frogs. (2) Hybridogenesis occurs in primary hybrids, although at a low frequency. (3) Many hybrid × hybrid matings in the population indeed produce viable offspring. Hence, the proposed genetic mechanism appears to contribute to the species replacement, although its importance may be limited.
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.
