Biochemical genic marking, ploidy and sexual structure analysis of green frogs populations of from the Transcarpathians lowland have shown that these places are occupying by the unisex populations consisting exclusively from allodiploid females, including in their own genome an insignificant share of a lake frog genic variety. The phenomenon is discussed in connection with a problem of unisex populations reproduction. The assumption is put forward, that in Transcarpathians hybrid populations hybrids reproduction occurs by parthenogenesis.
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306Strategies for optimal metamorphosis are key adaptations in organisms with complex life cycles, and the components of the larval growth environment causing variation in this trait are well studied empirically and theoretically. However, when relating these findings to a broader evolutionary or ecological context, usually the following assumptions are made: (1) size at metamorphosis positively relates to future fitness, and (2) the larval growth environment affects fitness mainly through its effect on timing of and size at metamorphosis. These assumptions remain poorly tested, because data on postmetamorphic fitness components are still rare. We created variation in timing of and size at metamorphosis by manipulating larval competition, nonlethal presence of predators, pond drying, and onset of larval development, and measured the consequences for subsequent terrestrial survival and growth in 1564 individually marked water frogs (Rana lessonae and R. esculenta), raised in enclosures in their natural environment. Individuals metamorphosing at a large size had an increased chance of survival during the following terrestrial stage (mean linear selection gradient: 0.09), grew faster and were larger at maturity than individuals metamorphosing at smaller sizes. Late metamorphosing individuals had a lower survival rate (mean linear selection gradient: 20.03) and grew more slowly than early metamorphosing ones. We found these patterns to be consistent over the three years of the study and the two species, and the results did not depend on the nature of the larval growth manipulation. Furthermore, individuals did not compensate for a small size at metamorphosis by enhancing their postmetamorphic growth. Thus, we found simple relationships between larval growth and postmetamorphic fitness components, and support for this frequently made assumption. Our results suggest postmetamorphic selection for fast larval growth and provide a quantitative estimate for the water frog example.
Per Sjocren // Biological Journal of the Linnean Sociely (1991), 42: 135-147.
Local extinction along the intrinsic isolation gradient within metapopulations is reviewed with particular reference to a study of the pool frog (Rana lessonae) on the northern periphery of its geographical range. As in the pool frog, many other different taxa show significantly increased extinrtion probabilities with increased interpopulation distance. Present data imply that the relative impact of demographic and genetic factors in such storhastic extinctions depends on the genetic history of thc melapopulation; data also imply that populations fluctuate more greatly in size than predirted from demographic models which have been commonly referred to. By mitigating such fluctuations and inbreeding, and compensating for emigration, immigration undoubtedly 'rescues' local populations from extinction. In this way, and not just in terms of recolonization, connectivity is ronrluded to be a key to metapopulation persistenre. Implications for conservation are also presented.
European water frog hybrids Rana esculenta (R. ridibundarR. lessonae) reproduce hemiclonally, by hybridogenesis : in the germ line they exclude the genome of one parental species and produce haploid gametes with an unrecombined genome of the other parental species. In the widespread L-E population system, both sexes of hybrids (E) coexist with R. lessonae (L). They exclude the lessonae genome and produce ridibunda gametes. In the R-E system, hybrid males coexist with R. ridibunda (R) ; they exclude either their ridibunda or their lessonae genome and produce sperm with a lessonae or with a ridibunda genome or a mixture of both kinds of sperm. We examined 13 male offspring, 12 of which were from crosses between L-E system and R-E system frogs. All were somatically hybrid. With one exception, they excluded the lessonae genome in the germ line and subsequently endoreduplicated the ridibunda genome. Spermatogonial metaphases contained a haploid or a diploid number of ridibunda chromosomes, identified through in situ hybridization to a satellite DNA marker, and by spermatocyte I metaphases containing a haploid number of ridibunda bivalents. The exception, an F1 hybrid between L-E system R. lessonae and R-E system R. ridibunda, was not hybridogenetic, showed no genome exclusion, and evidenced a disturbed gametogenesis resulting from the combination of two heterospecific genomes. None of the hybridogenetic hybrids showed any cell lines excluding the ridibunda genome, the pattern most frequent in hybrids of the system lessonae and R-E system ridibunda genomes seems necessary to induce the R-E system type of hemiclonal gametogenesis. R-E system, unique to that system, and essential for its persistence. A particular combination of R-E
For the last 24 year (1963 - 1986) the author has been working on European water frogs. He has crossed more than 740 pairs of water frogs, and has counted and measured the eggs from over 600 females of all six Europeanspecies and their five hybrids whith live in wild, and other hybrids receved in crossing experiments in laboratory. He has reared over 20 000 metamorphosed froglets of which more than 4000 individuals were devoted for further rearing to study their various features during their ontogenetic development. During this long period he has elaborated numerous rearing and investigative methods whith he has gathered in this paper.
Metamorphosed F1 specimens produced by crosses of three forms of green frogs, viz. Rana lessonae Camerano, R. esculenta Linnaeus and R. ridibunda Pallas, fall into three morphological groups corresponding with them. The indices analysed suggest that only the progeny of lessonae and ridibunda inberit characters of their parents, whereas the offspring of esculenta exhibit, almost exclusivery, characters typical of ridibunda. The group which reveals esculenta characters consist of hybrids obtained by crossing the form lessonae with esculenta or ridibunda. The author concludes that out of the three forms lessonae with esculenta or ridibunda. The author concludes that out of three forms of green frogs, those of lessonae and ridibunda are species and the form esculenta is a hybrid produced, above all, by crossing the two others
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.
In 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.
