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1 267Anuran vocalizations are valuable in the determination of species identity and have the potential to discriminate intraspecific variation. We developed novel bioacoustic sampling techniques, based on Fast Fourier Transforms, to increase the precision and sensitivity of male advertisement call analysis and applied the method to European water frogs. This approach robustly separated the three types of north European water frogs (Rana ridibunda, R. lessonae and their viable, fertile hybrid R. esculenta) by their call subunit characteristics. The hybrid frog exhibited a high frequency call component absent from both the parental species. Furthermore, call analysis demonstrated significant intraspecific differences among populations of all three frog types. Call characters of R. ridibunda changed systematically as a function of longitude. This trend may reflect either clinal variation in selection pressures across Europe, or the consequences of drift following postglacial colonization from eastern refugia. High resolution vocalization analysis therefore provides a potentially useful method for investigating intraspecific differentiation and the phylogeographical origins of anuran distributions.
A study of the influence exerted by fluctuations in pH and illumination on larvae of lake frog (Rana ridibunda Pallas) has shown that their growth and development are considerably enhanced under certain variable size and weight, which suggests a positive effect of pH and illumination fluctuations. regimens, with the mortality and variability of tadpole size becoming lower and the duration of the larval stage shorter. First-year individuals raised with the factors studied variying, were larger and showed smaller variation in size and weight, which suggests a positive effect of pH and illumination fluctuations.
Patterns of advertisement call were investigated in two genetically distinct water frog lineages (Rana kl esculenta, Rana. kl grafi), which were identified by starch gel electrophoresis - the aim being to determinate the role of vocalization in the hybridogenetic process. Both hybrids displayed major modifications from the basic structure of the Rana ridibunda call. In Rana kl grafi, the call structure tended to correspond to that of Rana perezi in most of the studied parameters (frequency, duration, number of pulses) whereas the call of Rana kl esculenta tended to resemble that of Rana lessonae. The ascendant hierarchical classi®cation clearly revealed such a convergence toward parental species and accounted for a divergence between hybrids. Changes in call patterns might result from both the expression of the non-ridibunda genome and the sexual selective pressure through female mate choice. Only few non-ridibunda females exhibited a preference for hybrid calls which, however, allowed some hybridogenetic males to obtain successful mates. Thus, hybridogenesis induced character convergence in courtship signal with the non-ridibunda species in hybrid zones. In any case, these changes in the courtship signal favoured the particular hybridogenetic process, which constitutes a quasi-parasitism of the non-ridibunda genome.
Eight morphometric features of water frogs of 14 localities in Turkey, Syria, Jordan and Israel were compared with those of Rana ridibunda in Kazakhstan, Armenia and Greece (Thrace). These study sites include the type localities of R. ridibunda, R. r. caralitana, R. esculenta var. bedriagae and R. levantina. Multivariate comparisons (principal-component analysis, discriminant analysis) based on the log10-transformed variables demonstrate that the data set includes only two taxa that differ significantly in size and shape. By applying a morphospecies criterion, R. ridibunda is represented exclusively by the three reference populations, whereas all other populations (in Turkey, Syria, Jordan and Israel) represent the same species, R. bedriagae.
Temporal characteristics of advertisement calls of water frogs of 10 localities in Turkey, Syria, Israel and Egypt were compared with those of Rana ridibunda in Kazakhstan, Armenia and Greece (Thrace) as reference populations. These study sites include the type localities of R. ridibunda, R. r. caralitana, R. esculenta var. bedriagae und R. levantina. The temperature-dependent as well as the temperature-independent call parameters clearly revealed two species. R. ridibunda is represented by the three reference populations and, in addition, a population in central Turkey. The other populations (in Turkey, Syria, Israel and Egypt) represent R. bedriagae. R. bedriagae is the oldest available name for water frogs of these regions and was given priority over R. r. caralitana and R. levantina.
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.
Strategies 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
