BackgroundRadio-frequency electromagnetic fields (RF EMF) of mobile communication systems are widespread in the living environment, yet their effects on humans are uncertain despite a growing body of literature.ObjectivesWe investigated the influence of a Universal Mobile Telecommunications System (UMTS) base station-like signal on well-being and cognitive performance in subjects with and without self-reported sensitivity to RF EMF.MethodsWe performed a controlled exposure experiment (45 min at an electric field strength of 0, 1, or 10 V/m, incident with a polarization of 45° from the left back side of the subject, weekly intervals) in a randomized, double-blind crossover design. A total of 117 healthy subjects (33 self-reported sensitive, 84 nonsensitive subjects) participated in the study. We assessed well-being, perceived field strength, and cognitive performance with questionnaires and cognitive tasks and conducted statistical analyses using linear mixed models. Organ-specific and brain tissue–specific dosimetry including uncertainty and variation analysis was performed.ResultsIn both groups, well-being and perceived field strength were not associated with actual exposure levels. We observed no consistent condition-induced changes in cognitive performance except for two marginal effects. At 10 V/m we observed a slight effect on speed in one of six tasks in the sensitive subjects and an effect on accuracy in another task in nonsensitive subjects. Both effects disappeared after multiple end point adjustment.ConclusionsIn contrast to a recent Dutch study, we could not confirm a short-term effect of UMTS base station-like exposure on well-being. The reported effects on brain functioning were marginal and may have occurred by chance. Peak spatial absorption in brain tissue was considerably smaller than during use of a mobile phone. No conclusions can be drawn regarding short-term effects of cell phone exposure or the effects of long-term base station-like exposure on human health.

The European waterfrog, Rana esculenta, is a hemiclonal hybrid that must coexist with the parental species Rana lessonae in order to reproduce. It is not clear what allows the two morphologically, genetically, and ecologically similar forms to coexist, but differential success of the hybrid and its sexual host among environments suggests that these frogs may differ in their adaptive abilities, and that ecology plays an important role in determining the relative frequencies of the two related species. The objective of this study was to identify factors that may promote coexistence. We investigated the effect of temperature, food level, and food quality on a variety of life history traits in a laboratory experiment. Our results indicated that tadpoles of the two forms respond differently to temperature. Probability of metamorphosis and survival of R. lessonae were higher at 24ЊC, while the hybrid, R. esculenta, had a better survival rate and a much larger body mass at metamorphosis at 18ЊC. We then tested the results of our laboratory experiment by assessing the distribution of the hybridogen and the parental species in natural populations as a function of temperature, and found that the relative frequency of R. esculenta tadpoles declined with increasing temperature. We use these results to evaluate the applicability of the generalist and frozen niche variation models that had been proposed earlier as explanations for the coexistence of the sexual parental species, R. lessonae, and the hybridogen, R. esculenta.

Earlier studies of habitat-specific subpopulations of mixed clonal and sexual freshwater snails of the species Potamopyrgus antipodarum have revealed clinal variation by depth in several life-history traits, risk of parasite infection, mixed population structure, and the genetic structure of the clonal population. Clinal variation is pronounced in lifehistory traits: snails are larger and start reproduction later in the deeper habitats. The proportion of clonal individuals increases with depth, and many clones are habitat-specific. While these patterns are well documented, it is not known which processes have led to the observed genetic divergence in the clonal population. In this study, we experimentally investigated the contribution of phenotypic plasticity to habitat-specific life-history trait variation using reciprocal transplant experiments with adult and juvenile snails. Assessment of phenotypic plasticity is important because canalized habitat-specific life-history trait variation is one of the alternative explanations for habitat-specific genetic divergence seen in the clonal population. However, if life-history trait variation is largely due to adaptive phenotypic plasticity, canalized optimization of life-history traits is unlikely to explain the divergence observed in the clonal structure. We found significant habitat-induced variation for growth rate, proportion of brooding females, brood size, number of surviving offspring, and juvenile survival, indicating that much of the life-history variation must be considered the result of phenotypic plasticity. Based on these results, it seems that life-history trait divergence is unlikely to explain habitat-specific clonal structure. In contrast, we found genetically based differences in resistance to parasite infections; snails of the deeper Isoetes habitat were more susceptible to infection than snails of the shallow shorebank habitat. To our surprise, we found only a few habitat-by-origin interactions that could directly contribute to the maintenance of the observed habitat-specific clonal structure. One potentially important interaction, however, was that in the deeper Isoetes habitat, reproductive output of snails transplanted from the shallow habitat was lower than that of resident snails. In addition, we also found that survival of clonal snails may be poorer in unfamiliar habitats than that of sexual P. antipodarum, potentially promoting the maintenance of habitatspecific clonal assemblages. Thus, higher parasite resistance of shallow-water snails in both habitats and lower reproductive output of shallow-water snails in the deep habitat are likely to contribute to the maintenance of the habitat-specific clonal structure in P. antipodarum populations, whereas most of the observed variation in life-history traits seems to be due to phenotypic plasticity, which is likely to be adaptive.

Earlier studies of habitat‐specific subpopulations of mixed clonal and sexual freshwater snails of the species Potamopyrgus antipodarum have revealed clinal variation by depth in several life‐history traits, risk of parasite infection, mixed population structure, and the genetic structure of the clonal population. Clinal variation is pronounced in life‐history traits: snails are larger and start reproduction later in the deeper habitats. The proportion of clonal individuals increases with depth, and many clones are habitat‐specific. While these patterns are well documented, it is not known which processes have led to the observed genetic divergence in the clonal population. In this study, we experimentally investigated the contribution of phenotypic plasticity to habitat‐specific life‐history trait variation using reciprocal transplant experiments with adult and juvenile snails. Assessment of phenotypic plasticity is important because canalized habitat‐specific life‐history trait variation is one of the alternative explanations for habitat‐specific genetic divergence seen in the clonal population. However, if life‐history trait variation is largely due to adaptive phenotypic plasticity, canalized optimization of life‐history traits is unlikely to explain the divergence observed in the clonal structure. We found significant habitat‐induced variation for growth rate, proportion of brooding females, brood size, number of surviving offspring, and juvenile survival, indicating that much of the life‐history variation must be considered the result of phenotypic plasticity. Based on these results, it seems that life‐history trait divergence is unlikely to explain habitat‐specific clonal structure. In contrast, we found genetically based differences in resistance to parasite infections; snails of the deeper Isoetes habitat were more susceptible to infection than snails of the shallow shorebank habitat. To our surprise, we found only a few habitat‐by‐origin interactions that could directly contribute to the maintenance of the observed habitat‐specific clonal structure. One potentially important interaction, however, was that in the deeper Isoetes habitat, reproductive output of snails transplanted from the shallow habitat was lower than that of resident snails. In addition, we also found that survival of clonal snails may be poorer in unfamiliar habitats than that of sexual P. antipodarum, potentially promoting the maintenance of habitat‐specific clonal assemblages. Thus, higher parasite resistance of shallow‐water snails in both habitats and lower reproductive output of shallow‐water snails in the deep habitat are likely to contribute to the maintenance of the habitat‐specific clonal structure in P. antipodarum populations, whereas most of the observed variation in life‐history traits seems to be due to phenotypic plasticity, which is likely to be adaptive.

The European waterfrog, Rana esculenta, is a hemiclonal hybrid that must coexist with the parental species Rana lessonae in order to reproduce. It is not clear what allows the two morphologically, genetically, and ecologically similar forms to coexist, but differential success of the hybrid and its sexual host among environments suggests that these frogs may differ in their adaptive abilities, and that ecology plays an important role in determining the relative frequencies of the two related species. The objective of this study was to identify factors that may promote coexistence. We investigated the effect of temperature, food level, and food quality on a variety of life history traits in a laboratory experiment. Our results indicated that tadpoles of the two forms respond differently to temperature. Probability of metamorphosis and survival of R. lessonae were higher at 248C, while the hybrid, R. esculenta, had a better survival rate and a much larger body mass at metamorphosis at 188C. We then tested the results of our laboratory experiment by assessing the distribution of the hybridogen and the parental species in natural populations as a function of temperature, and found that the relative frequency of R. esculenta tadpoles declined with increasing temperature. We use these results to evaluate the applicability of the generalist and frozen niche variation models that had been proposed earlier as explanations for the coexistence of the sexual parental species, R. lessonae, and the hybridogen, R. esculenta. Abstract. The European waterfrog, Rana esculenta, is a hemiclonal hybrid that must coexist with the parental species Rana lessonae in order to reproduce. It is not clear what allows the two morphologically, genetically, and ecologically similar forms to coexist, but differential success of the hybrid and its sexual host among environments suggests that these frogs may differ in their adaptive abilities, and that ecology plays an important role in determining the relative frequencies of the two related species. The objective of this study was to identify factors that may promote coexistence. We investigated the effect of temperature, food level, and food quality on a variety of life history traits in a laboratory experiment. Our results indicated that tadpoles of the two forms respond differently to temperature. Probability of metamorphosis and survival of R. lessonae were higher at 24ЊC, while the hybrid, R. esculenta, had a better survival rate and a much larger body mass at metamorphosis at 18ЊC. We then tested the results of our laboratory experiment by assessing the distribution of the hybridogen and the parental species in natural populations as a function of temperature, and found that the relative frequency of R. esculenta tadpoles declined with increasing temperature. We use these results to evaluate the applicability of the generalist and frozen niche variation models that had been proposed earlier as explanations for the coexistence of the sexual parental species, R. lessonae, and the hy...