Predation- and competition-mediated brain plasticity in Rana temporaria tadpoles

An increasing number of studies have demonstrated phenotypic plasticity in brain size and architecture in response to environmental variation. However, our knowledge on how brain architecture is affected by commonplace ecological interactions is rudimentary. For example, while intraspecific competition and risk of predation are known to induce adaptive plastic modifications in morphology and behaviour in a wide variety of organisms, their effects on brain development have not been studied. We studied experimentally the influence of density and predation risk on brain development in common frog (Rana temporaria) tadpoles. Tadpoles grown at low density and under predation risk developed smaller brains than tadpoles at the other treatment combinations. Further, at high densities, tadpoles developed larger optic tecta and smaller medulla oblongata than those grown at low densities. These results demonstrate that ecological interactions - like intraspecific competition and predation risk - can have strong effects on brain development in lower vertebrates.     

Functional differentiation of the tail muscle fibers in Rana temporaria tadpoles

Studies have been made on changes in the electrical properties of muscle membrane and lipid content of two types of myotomal fibers in the tail of tadpoles during metamorphosis. It was shown that during premetamorphosis, peripheral and inner muscle fibers do not differ with respect to their effective resistance, time constant of the membrane and lipid content; the resting membrane potential is higher in the inner fibers. During further development of the tadpoles, differentiation of muscle fibers takes place, and to the beginning of the climax the inner fibers attain lower values of the effective resistance and time constant, as well as lower content of lipids in their sarcoplasm; the difference in the level of resting membrane potential between the peripheral and inner fibers increases. The data obtained suggest that the inner fibers may be referred to as fast ones, whereas the peripheral ones--as slow. These data also reveal specific features in neurotrophic regulation of functional properties of muscle fibers in tadpoles.     

Effect of gutimine derivatives on the metamorphosis of Rana temporaria tadpoles

A one-time addition of gutimine (0.5 g/l), amtizol (0.2 g/l), and unithiol (0.25 g/l) to the medium at early stages of tadpole development was shown to inhibit metamorphosis only upon addition of unithiol. Repeated addition of gutimine, amtizol, and unithiol to the medium leads to reliable delay in metamorphosis. The delay is more pronounced at addition of the compounds to the medium at late stages of tadpole development (beginning at 40 stage). This suggests that the studied compounds may have anti-thyroid activity. All drugs under study induce the skin clearing.     

NAG infection of grass frog (Rana temporaria) tadpoles]

Rana temporaria tadpoles (2250) were contaminated with three types of NAG vibrio cultures. Clinical, bacteriological and morphological examinations showed the larvae to be suffering from an acute infection during the first 2 days after the contamination. Then the vibrios persisted in the tadpole organism for a long time and were excreted in the feces.     

Effects of aluminium and low pH on growth and development in Rana temporaria tadpoles

Summary Rana temporaria tadpoles were raised to metamorphosis at 6 levels of pH (pH 3.6–6.5) and 2 levels of aluminium (800 and 1,600 g l^-1) at pH 4.4. Treatments involved both chronic and acute exposure to depressed pH. Decreasing pH reduced maximum body size and delayed metamorphosis. Growth was depressed and metamorphosis delayed by 800 g l^-1 Al, and several tadpoles died at foreleg emergence. At 1,600 g l^-1 Al, small tadpoles suffered arrested growth and development and eventually died, while larger tadpoles metamorphosed without delay, though at a very small size. There was no mortality among controls. The levels of pH and inorganic monomeric aluminium measured in the experiments were similar to field levels at a site in Scotland, and it is concluded that individual tadpoles will, in certain types of water body, be adversely affected by both acidity and aluminium. The impact of these factors on populations remains to be determined.     

Carry-over effects of embryonic acid conditions on development and growth of Rana temporaria tadpoles

1. Conditions experienced during the early stages of development may have carry‐over effects on performance during later life. The egg laying period and embryonic development of temperate and boreal zone amphibians often coincides with peak acidity resulting from spring snow‐melt, but the effects of acid conditions during embryonic stage on subsequent performance are unknown. 2. We investigated the potential carry‐over effects of acidity during the embryonic stage on performance up to metamorphosis in the common frog (Rana temporaria) tadpoles. There were four combinations of acid (4.5) and neutral (7.5) pH treatments applied to the egg and larval stages in a factorial laboratory experiment. In addition, we studied the difference in embryonic and larval tolerance of acidity between two populations originating from circumneutral (pH 6.6) and acidic conditions (pH 4.8). 3. The effects of acid conditions during the embryonic stage were sublethal, as indicated by delayed development and reduced size. Under acid conditions, tadpoles that had been raised in neutral water as embryos at first grew more slowly than tadpoles raised under acid conditions as embryos. At metamorphosis, no effects of embryonic acidity were detectable indicating that tadpoles were able to compensate fully for the initial reduction in growth. 4. Acid conditions during the larval period had a strongly negative effect on survival, size and age at metamorphosis. The amount of food consumed was lower under acid conditions, suggesting that reduced food consumption was at least partly responsible for the negative effects. 5. Although the two populations differed in the length of larval period, there was no indication of a differential response to the treatments in any of the metamorphic traits studied. 6. These results suggest that, although moderate acid conditions during embryonic development affect growth and development negatively, this influence does not persist after conditions have returned to normal. However, even moderately acid conditions during the larval period may have a strong negative influence on survival and performance of the tadpoles.     

Behavioural responses to predator chemical cues and local variation in antipredator performance in Rana temporaria tadpoles

Antipredator behaviour is an important factor influencing survival probability of prey animals, and it may evolve rapidly as a response to changes in predator regime. I studied antipredator behaviour of common frog ( Rana temporaria ) tadpoles from three populations that differ in predator regimes. In the first experiment, tadpoles obtained from four natural matings in each population were subjected to chemical cues from either European perch ( Perca fluviatilis ) or from larvae of the dragonfly Aeshna juncea . Tadpoles decreased their activity in response to both predators, but the spatial behaviour of tadpoles differed between the two predator treatments. In general, there were no differences in behaviours among the populations, but in three out of four studied behaviours there were differences between parentages within the populations suggesting that these behaviours may be genetically determined. The lack of a significant Predator×Population interaction suggests no differences in plastic antipredator behaviour among the populations, while the lack of significant Predator×Parentage interaction suggests no genetic variance within the populations for plastic antipredator behaviour. In the second experiment, tadpoles from the three populations were exposed to predation by a free-ranging A. juncea . In line with the first experiment, there were no differences in survival rate between the populations. R. temporaria tadpoles seem to rely heavily on plastic antipredator behaviour as their main response to predator chemical cues. There was very little indication of local behavioural differentiation and the possible reasons for the lack of divergence among populations are discussed.     

Induction of micronuclei in tadpoles of Rana temporaria and Xenopus laevis by the pyrethroid Fastac 10 EC.

The mutagenic properties of the pyrethroid Fastac 10 EC were estimated using the micronucleus test in tadpoles of Rana temporaria and Xenopus laevis. The frequency of erythrocytes with micronuclei was examined in blood smears obtained from animals kept for 14 days in water containing 3 different concentrations of Fastac 10 EC. The study was accompanied by a positive control using the known mutagens cyclophosphamide and N-methyl-N-nitrosourea. The results obtained showed that at high concentrations Fastac 10 EC has a clastogenic activity and/or damages the mitotic spindle, as manifested by a significant increase in the frequency of the micronucleated red blood cells. It was also demonstrated that tadpoles of Rana temporaria are more sensitive to the mutagenic effect of the pyrethroid than are those of Xenopus laevis.     

Bottom‐up effects of fungicides on tadpoles of the European common frog (Rana temporaria)

Biodiversity is under pressure worldwide, with amphibians being particularly threatened. Stressors related to human activity, such as chemicals, are contributing to this decline. It remains, however, unclear whether chemicals exhibiting a fungicidal activity could indirectly affect tadpoles that depend on microbially conditioned leaf litter as food source. The indirect effect of fungicides (sum concentration of a fungicide mixture composed of azoxystrobin, carbendazim, cyprodinil, quinoxyfen, and tebuconazole: 100 µg/L) on tadpoles was assessed relative to leaf litter colonized by microbes in absence of fungicides (control) and a worst‐case scenario, that is leached leaf litter without microbial colonization. The quality of leaf litter as food for tadpoles of the European common frog (Rana temporaria) was characterized through neutral lipid fatty acid profiles and microbial sum parameters and verified by sublethal responses in tadpoles (i.e., feeding rate, feces production, growth, and fatty acid composition). Fungicides changed the nutritious quality of leaf litter likely through alterations in leaves’ neutral lipid fatty acid profiles (i.e., changes in some physiologically important highly unsaturated fatty acids reached more than 200%) in combination with a potential adsorption onto leaves during conditioning. These changes were reflected by differences in the development of tadpoles ultimately resulting in an earlier start of metamorphosis. Our data provide a first indication that fungicides potentially affect tadpole development indirectly through bottom‐up effects. This pathway is so far not addressed in fungicide environmental risk assessment and merits further attention.