Endocrine Disruption Alters Developmental Energy Allocation and Performance in Rana temporaria

Environmental change exposes wildlife to a wide array of environmental stressors that arise from both anthropogenic and natural sources. Many environmental stressors with the ability to alter endocrine function are known as endocrine disruptors, which may impair the hypothalamus-pituitary-thyroid axis resulting in physiological consequences to wildlife. In this study, we investigated how the alteration of thyroid hormone (TH) levels due to exposure to the environmentally relevant endocrine disruptor sodium perchlorate (SP; inhibitory) and exogenous L-thyroxin (T4; stimulatory) affects metabolic costs and energy allocation during and after metamorphosis in a common amphibian (Rana temporaria). We further tested for possible carry-over effects of endocrine disruption during larval stage on juvenile performance. Energy allocated to development was negatively related to metabolic rate and thus, tadpoles exposed to T4 could allocate 24% less energy to development during metamorphic climax than control animals. Therefore, the energy available for metamorphosis was reduced in tadpoles with increased TH level by exposure to T4. We suggest that differences in metabolic rate caused by altered TH levels during metamorphic climax and energy allocation to maintenance costs might have contributed to a reduced energetic efficiency in tadpoles with high TH levels. Differences in size and energetics persisted beyond the metamorphic boundary and impacted on juvenile performance. Performance differences are mainly related to strong size-effects, as altered TH levels by exposure to T4 and SP significantly affected growth and developmental rate. Nevertheless, we assume that juvenile performance is influenced by a size-independent effect of achieved TH. Energetic efficiency varied between treatments due to differences in size allocation of internal macronutrient stores. Altered TH levels as caused by several environmental stressors lead to persisting effects on metamorphic traits and energetics and, thus, caused carry-over effects on performance of froglets. We demonstrate the mechanisms through which alterations in abiotic and biotic environmental factors can alter phenotypes at metamorphosis and reduce lifetime fitness in these and likely other amphibians.

European common frog Rana temporaria (Anura: Ranidae) larvae show subcellular responses under field-relevant Bacillus thuringiensis var. israelensis (Bti) exposure levels

Bacillus thuringiensis var. israelensis (Bti) is presumed to be an environmental friendly agent for the use in either health-related mosquito control or the reduction of nuisance associated with mosquitoes from seasonal wetlands. Amphibians inhabiting these valuable wetlands may be exposed to Bti products several times during their breeding season. Up until now, information regarding effects on the non-targeted group of amphibians has to be considered rather inconsistent. On this account, we evaluated how three repeated exposures to frequently used Bti formulations (VectoBac^®12AS, VectoBac^®WG) in field-relevant rates affect European common frog (Rana temporaria) larvae. In a laboratory approach, we assessed potential effects with regard to enzymatic biomarkers (glutathione-S-transferase (GST), glutathione reductase (GR), acetylcholine esterase (AChE)), development, body condition and survival until the end of metamorphosis. Although survival and time to metamorphosis were not significantly affected, larval development tended to be shortened in the Bti treated water phase. Furthermore, exposure to Bti induced significant increases of GST (37-550%), GR (5-140%) and AChE (38-137%) irrespectively of the applied formulation, indicating detoxification, antioxidant responses as well as an alteration of neuronal activity. GST activity increased twice as much after two repeatedly executed Bti applications within a time period of 6 days. The examination of several biochemical markers is needed to fully evaluate the ecotoxicological risk of Bti for amphibian populations, especially in the context of worldwide amphibian declines. Nevertheless, following the precautionary principle, it may be advisable to implement certain thresholds for application numbers and intervals in order to ensure environmentally friendly mosquito control programs, especially in areas designated for nature conservation.

The phenotypic variability in Rana temporaria decreases in response to drying habitats

In this study, we evaluated the diversity of skin coloration as a proxy for phenotypic diversity. The European common frog (Rana temporaria) populations from the Southern slope of central Pyrenees lie at the limit of the species distribution in latitude and altitude. We analysed the relationship of skin color typology with different environmental variables and found a large decrease in skin type variety in frogs developing in temporary water bodies when compared to those developing in permanent water bodies. Our results show that our method can be used as a non-invasive way to study phenotypic diversity and suggest that adaptation to an early metamorphosis in a rapidly-drying habitat can have negative effects on adult phenotypic diversity. In light of these results, we argue that access to permanent water bodies is important to prevent loss of diversity in anuran populations and reduce their vulnerability to environmental impacts as well as pathogens.

Differing long term trends for two common amphibian species (Bufo bufo and Rana temporaria) in alpine landscapes of Salzburg, Austria

This study focuses on the population trends of two widespread European anuran species: the common toad (Bufo bufo) and the common frog (Rana temporaria). The basis of this study is data gathered over two decades of amphibian fencing alongside roads in the Austrian state of Salzburg. Different statistical approaches were used to analyse the data. Overall average increase or decrease of each species was estimated by calculating a simple average locality index. In addition the statistical software TRIM was used to verify these trends as well as to categorize the data based on the geographic location of each migration site. The results show differing overall trends for the two species: the common toad being stable and the common frog showing a substantial decline over the last two decades. Further analyses based on geographic categorization reveal the strongest decrease in the alpine range of the species. Drainage and agricultural intensification are still ongoing problems within alpine areas, not only in Salzburg. Particularly in respect to micro-climate and the availability of spawning places these changes appear to have a greater impact on the habitats of the common frog than the common toad. Therefore we consider habitat destruction to be the main potential reason behind this dramatic decline. We also conclude that the substantial loss of biomass of a widespread species such as the common frog must have a severe, and often overlooked, ecological impact.

Physiological mechanisms of adaptive developmental plasticity in Rana temporaria island populations

BACKGROUND

Adaptive plasticity is essential for many species to cope with environmental heterogeneity. In particular, developmental plasticity allows organisms with complex life cycles to adaptively adjust the timing of ontogenetic switch points. Size at and time to metamorphosis are reliable fitness indicators in organisms with complex cycles. The physiological machinery of developmental plasticity commonly involves the activation of alternative neuroendocrine pathways, causing metabolic alterations. Nevertheless, we have still incomplete knowledge about how these mechanisms evolve under environments that select for differences in adaptive plasticity. In this study, we investigate the physiological mechanisms underlying divergent degrees of developmental plasticity across Rana temporaria island populations inhabiting different types of pools in northern Sweden.

METHODS

In a laboratory experiment we estimated developmental plasticity of amphibian larvae from six populations coming from three different island habitats: islands with only permanent pools, islands with only ephemeral pools, and islands with a mixture of both types of pools. We exposed larvae of each population to either constant water level or simulated pool drying, and estimated their physiological responses in terms of corticosterone levels, oxidative stress, and telomere length.

RESULTS

We found that populations from islands with only temporary pools had a higher degree of developmental plasticity than those from the other two types of habitats. All populations increased their corticosterone levels to a similar extent when subjected to simulated pool drying, and therefore variation in secretion of this hormone does not explain the observed differences among populations. However, tadpoles from islands with temporary pools showed lower constitutive activities of catalase and glutathione reductase, and also showed overall shorter telomeres.

CONCLUSIONS

The observed differences are indicative of physiological costs of increased developmental plasticity, suggesting that the potential for plasticity is constrained by its costs. Thus, high levels of responsiveness in the developmental rate of tadpoles have evolved in islands with pools at high but variable risk of desiccation. Moreover, the physiological alterations observed may have important consequences for both short-term odds of survival and long term effects on lifespan.

[Role of hydration in ovulation of common frog oocytes in vitro]

Stimulation of ovulation of the common frog Rana temporaria oocytes with homologous pituitary extract caused an increase in their volume. Factors that are known to inhibit hydration in teleostean oocytes (potassium-free Ringer solution and inhibitor of Na+, K(+)-ATPase--ouabain), as well as use of aquaporin inhibitors (mercuric chloride and methylmethanethiosulphonate) inhibited also homologous pituitary extract-induced volume increase in follicle-enclosed oocytes and let to reduced percentage of ovulated oocytes. Volume of denuded oocytes remained unchanged in the course of maturation when exposed to progesterone or other treatments. The data obtained suggest that stimulation ofoocyte ovulation in the common frog caused an increase in their hydration that in necessary for their ovulation but this did not occur in denuded cells.

[Adaptation of differential sensitivity of auditory neurons to amplitude modulation after a sharp change of signal intensity]

In the common frog Rana temporaria, the neuronal firing evoked by long amplitude-modulated tones was recorded in auditory regions of medulla (dorsal nucleus) and of midbrain (torus semicircularis). We recorded firing rate, synchronization with modulation, and phase of response every 2 or 4 s. After adaptation of neuronal response to the acting stimulus (30-60 s after its onset) the mean level of signal sharply changed (by 20-40 dB), whereas frequency and modulation depth remained constant. Changes of firing density and of degree of its synchronization with modulation period were recorded, as well as the phase of maximum of reaction at the period of modulation. At low modulation depths at the initial site, we observed an adaptation decrease of impulsation density accompanied by an improvement of the response synchronization. A sharp increase (by 20-40 dB) in the mean level led to a rise in the implication density, which could be accompanied either by a continued increase of synchronicity (the more typical effect for the dorsal nucleus) or by a sharp fall of synchronicity with its subsequent slow recovery (the more typical effect for the torus semicircularis). The character of changes in reaction after replacement of intensity could also depend on the signal parameters (the initial level, the jump value, the frequency and depth of modulation). The connection of the revealed physiological effects with psychophysics of perception of small amplitude modulations is discussed.

Effects of a sublethal pesticide exposure on locomotor behavior: a video-tracking analysis in larval amphibians

Organochlorine pesticides such as endosulfan have been shown to have both lethal and sublethal effects on amphibians. In this context, behavioral endpoints have proved their usefulness in evidencing impacts of such chemicals at environmental concentrations that do not necessarily cause mortality. The recent development of video-tracking technologies now offers the possibility of accurately quantifying locomotor behaviors. However, these techniques have not yet been applied to evaluating the toxicity of pesticides in amphibians. We therefore aimed at determining the potential toxicity of endosulfan on endpoints associated with locomotion after short-term environmental endosulfan exposure in Rana temporaria tadpoles and at using these data as warning systems for survival alterations after a longer exposure. To this end, we analyzed video-tracks of 64 tadpoles (two pesticide treatments: 5 and 50 μg L(-1), one control and one solvent-control) with Ethovision XT 7 software. The highest endosulfan concentration had a significant effect on all four behavioral endpoints. Contaminated tadpoles traveled shorter distances, swam less often, at a lower mean speed, and occupied a less peripherical position than control tadpoles. The lowest endosulfan concentration had similar but lower effects, and did not affect mean speed during swimming. Survival was reduced only after a long-term exposure to endosulfan and was associated with short-term behavioral dysfunctions. These results show that endosulfan strongly affects the behavioral repertory of amphibian tadpoles, but in different ways depending on concentration, thus suggesting that the pesticide has complex modes of action. Given the importance of locomotion and space use in tadpole success in their aquatic environment, these results confirm the toxic action of endosulfan. By highlighting effects before mortality markers, video-tracking systems also show their potential as sentinels of sublethal effects of pesticides.

[On filo- and ontogenetic development of dopaminergic regylation of wakefulness-sleep cycle in vertabrates]

The comparative immunohistochemical researches of dofamine containing neurons and fibers are carried uot in telencephalic and diencephalic departments of the brain in different vertebratts (adults rats, rats aged 14 and 30 days and frogs). For analysis of quantitative changes dynamics in thyrozinhydroxylase, D1 and D2 immunoreactive material in sleep-wakefulness cycle the model of sleepdeprivation is used. There are found the facts of morphofunctional correlations in the reactions of dophaminergic system during ontogeny and phylogeny. Besides, the pharmacological effects of dofamine agonist and antagonists on the sleep-wakefulness cycle in young rats and in frogs are shown. So, dopamine and its agonist apomorphine increase in sleep-wakefulness cycle duration of sleep-like state ofcataplexy (homolog of the sleep) in frogs, in 30-day-old rats it increase the share of wakefulness and catalepsy. D1 receptors antagonist (SCH 23390) adminisrated to frogs, caused increase of wakefulness and catatonic type states duration, where as D2 receptors antagonist (apomorphine) increased cataleptic condition. Administration of dopamine antagonist (haloperidol) to 30-day-old rats previously causes the increase of cataleptic state, after which the slow wave sleep state is enhanced. The questions of phylo-, ontogenetic formation of dopaminergic system regulating role in sleep-wakefulness cycle, when transition mainly from neurosecretory diencephalic influences of dophamine to the mainly neurotransmittory functins of telencephalic regions occured, is discussed.

[Effect of barium and ouabain on electrogenesis in various sites of intact and detubulated skeletal muscle fibers of the frog R. temporaria]

In loose patch clamp experiments on intact sartorious muscle fibers of the frog Rana temporaria there were revealed two types of wave forms of the extracellularly recorded action potentials (AP). Responses of the first type (T1AP) consisted of the initial positive phase with subsequent phase of strong negativity. Responses of the second type (T2AP) had an additional positive phase concluding their waveform. In the detubulated fibers, only T1AP were recorded. Application Ba2+ (10 microM) to the muscle led to a significant increase in the amplitude of the third T2AP phase, whereas the T1AP characteristics of both intact and detubulated muscle preparations remained unchanged. After the higher applied Ba2+ concentration (50 microM), in some of the studied intact fibers the late positive signal phase was replaced by the late negative phase. The amplitude of the late negative phase was increased markedly by the high-frequency stimulation. At the combined action of ouabain and Ba2+ there was summation of effects. These results can tentatively be explained by that the locally recorded T1AP and T2AP represent responses of the muscle fiber surface and T-tubular membranes and that caracteristics of the late phase of T2AP are determined by activities of T-tubular potassium channels and of Na, K-ATPase.

[Mechanisms of interactions between glycine- and GABA-mediated responses in spinal cord neurons]

The interactions of GABA- and glycine-mediated responses have been analyzed, the whole cell patch-clamp method being used. The response induced by co-application of glycine and GABA was a lesser one than the sum of responses induced by applying two transmitters separately. The molecular mechanisms underlying this effect have been determined. Due to applications of high concentrations of neurotransmitters it was revealed that GABA could activate glycine receptors in frog spinal motoneurons with relatively high efficiency (EC50 = 1.2 mM). The sequential application of neurotransmitters showed that even a single application of glycine could significantly boost the "run-down" of the GABA-mediated current, suggesting that there was a strong phosphorylation-dependent mechanism of GABAa-receptors inhibition. These mechanisms are likely to take place in frog spinal motoneurons when GABA and glycine are co-released from the same synaptic terminal.

Cumulative effects of road de-icing salt on amphibian behavior

Despite growing evidence of the detrimental effect of chemical substances on organisms, limited research has focused on changes in behavioral patterns, in part due to the difficulties to obtain detailed quantitative data. Recent developments in efficient computer-based video analyses have allowed testing pesticide effects on model species such as the zebrafish. However, these new techniques have not yet been applied to amphibians and directly to conservation issues, i.e., to assess toxicological risks on threatened species. We used video-tracking analyses to test a quantitative effect of an environmental contaminant on the locomotion of amphibian tadpoles (Rana temporaria) by taking into account cumulative effects. Because recent research has demonstrated effects of de-icing salts on survival and community structure, we used sodium chloride in our experimental design (25 replicates, 4 concentrations, 4 times) to test for an effect at the scale of behavior at environmentally relevant concentrations. Analysis of 372 1-h video-tracks (5 samples/s) showed a complex action of salts on behavioral patterns with a dose and cumulative response over time. Although no effects were found on mortality or growth, the highest salt concentrations reduced the speed and movement of tadpoles in comparison with control treatments. The reduced locomotor performance could have detrimental consequences in terms of tadpoles' responses to competition and predation and may be an indicator of the low concentration effect of the contaminant. On one hand, this study demonstrates the usefulness of examining behavior to address conservation issues and understand the complex action of environmental factors and, more particularly, pollutants on organisms. On the other hand, our results highlight the need of new computerized techniques to quantitatively analyze these patterns.

Trait performance correlations across life stages under environmental stress conditions in the common frog, Rana temporaria

If an organism's juvenile and adult life stages inhabit different environments, certain traits may need to be independently adapted to each environment. In many organisms, a move to a different environment during ontogeny is accompanied by metamorphosis. In such organisms phenotypic induction early in ontogeny can affect later phenotypes. In laboratory experiments we first investigated correlations between body morphology and the locomotor performance traits expressed in different life stages of the common frog, Rana temporaria: swimming speed and acceleration in tadpoles; and jump-distance in froglets. We then tested for correlations between these performances across life stages. We also subjected tadpoles to unchanging or decreasing water levels to explore whether decreasing water levels might induce any carry-over effects. Body morphology and performance were correlated in tadpoles; morphology and performance were correlated in froglets: hence body shape and morphology affect performance within each life stage. However, performance was decoupled across life stages, as there was no correlation between performance in tadpoles and performance in froglets. While size did not influence tadpole performance, it was correlated with performance of the metamorphosed froglets. Experiencing decreasing water levels accelerated development time, which resulted in smaller tadpoles and froglets, i.e., a carry-over effect. Interestingly, decreasing water levels positively affected the performance of tadpoles, but negatively affected froglet performance. Our results suggest that performance does not necessarily have to be correlated between life stages. However, froglet performance is size dependent and carried over from the tadpole stage, suggesting that some important size-dependent characters cannot be decoupled via metamorphosis.

Predator-induced changes in metabolism cannot explain the growth/predation risk tradeoff

Defence against predators is usually accompanied by declining rates of growth or development. The classical growth/predation risk tradeoff assumes reduced activity as the cause of these declines. However, in many cases these costs cannot be explained by reduced foraging effort or enhanced allocation to defensive structures under predation risk. Here, we tested for a physiological origin of defence costs by measuring oxygen consumption in tadpoles (Rana temporaria) exposed to predation risk over short and long periods of time. The short term reaction was an increase in oxygen consumption, consistent with the “fight-or-flight” response observed in many organisms. The long term reaction showed the opposite pattern: tadpoles reduced oxygen consumption after three weeks exposure to predators, which would act to reduce the growth cost of predator defence. The results point to an instantaneous and reversible stress response to predation risk. This suggests that the tradeoff between avoiding predators and growing rapidly is not caused by changes in metabolic rate, and must be sought in other behavioural or physiological processes.

[Resident and circulating mast cells in propulsative organs of the frog Rana temporaria]

Mast cells (MCs) of the "blood" and lymph hearts of the adult frog Rana temporaria were investigated at histochemical and ultrastructural levels. Two populations of MCs were revealed in these propulsative organs: population of resident MCs and population of circulating MCs. It has been shown that the resident cardiac MCs have an oval or elongated form and are located between atrial or ventricular myocytes and under endocardial endothelium. The resident cardiac MCs are situated in connective tissue of epicardium, too. Avascular myocardium of the frog ventricle consists of a spongy network of muscle trabeculae. We revealed circulating MCs in intertrabecular spaces and clefts of the spongy myocardium and in the blood of the main central cavity. Circulating MCs are round in shape and contain a large central nucleus enriched with condensed chromatin. They resemble the lymphocytes, but show cytoplasm filled with granules. These granules ultrastructure is much like that of the granules of the cardiac resident MCs. In the lymph heart, oval and somewhat elongated resident MCs are located in the interstitial space among cross-striated muscle fibers and among smooth muscle cells of tubular (afferent and efferent) valves. Sometimes lymphocyte-like circulating MCs are revealed in the cavity of lymph heart. Circulating MCs are also present in the lymphatics located adjacent to the lymph hearts. In certain parts of the lymphatic walls MCs are in close adhesion to the mesothelial cells lining the lymphatic cavity. Our histochemical investigation revealed that both the resident and circulating MCs of the propulsative organs give a strongly positive reaction with alcian blue, but weakly red with safranin and weakly metachromatic with toluidine blue. The presence of population of circulating MCs in the frog suggests that there are differences in biology of MCs between lower and higher vertebrates.

[A comparative analysis of contractile responses induced by acetylcholine and choline in twich and tonic frog skeletal muscle fibres]

A comparative analysis of contractile responses evoked by acetylcholine and external sodium removal in twitch and tonic frog skeletal muscle fibers has been performed. To elucidate the possible differences in the participation of various mechanisms of Ca2+ homeostasis in the regulation of these contractile reactions, selective pharmacological agents: dantrolene, 4-m-chlorocresol, tetrodotoxin, and d-tubocurarine were used. It was found that, although Ca2+ release from sarcoplasmic reticulum is a major source in the acetylcholine contracture for both types of muscle fibers, there are definite differences in the molecular structures of the alpha-isoform and/or the ratio of alpha- and beta-isoforms of ryanodine-sensitive receptor/channels for twitch and tonic fibers. The substitution of Na+ by choline in both twitch and tonic fibers evoked significant long-lasting contractile responses, which were sensitive to the inhibitory action of d-tubocurarine or dantrolene. The application of acetylcholine against the background of choline induced contracture with an amplitude closely related to that in normal solution. These results suggest that choline activates acetylcholine receptor/channel insignificantly, but this type of ionic channels is the main mechanism of its penetration through the surface membrane.

Non-equivalence of growth arrest induced by predation risk or food limitation: context-dependent compensatory growth in anuran tadpoles

1. To gain insight into the evolution of compensatory growth, we studied the growth patterns of anuran (Rana temporaria) larvae following either a period of exogenous growth depression (food restriction) or a period of endogenous depression (exposure to predators). We also investigated the potential deferred costs that larval compensatory growth could impose on post-metamorphic individuals. 2. Food-deprived larvae exhibited full compensatory growth in response to reduced growth rates caused by food limitation, and the growth trajectories of low- and high-rations tadpoles converged before the onset of metamorphosis. 3. According to our predictions, individuals exposed to larval predators did not show growth compensation following predator removal despite undergoing a significant reduction in growth rate associated with low activity levels. 4. Jumping ability of individuals exposed to predators during only 20 days from the commencement of the larval phase was equivalent to that of non-exposed animals, and greater than the jumping capacity of those maintained with predators until the time of metamorphosis. This pattern was consistent with the pattern observed for variation in relative leg length. 5. These results support the suggestion that submaximum and compensatory growth could have evolved to minimize the overall growth/mortality costs in environments with high spatiotemporal variation in predation intensity.

Does habitat fragmentation reduce fitness and adaptability? A case study of the common frog (Rana temporaria)

Studies examining the effects of anthropogenic habitat fragmentation on both neutral and adaptive genetic variability are still scarce. We compared tadpole fitness-related traits (viz. survival probability and body size) among populations of the common frog (Rana temporaria) from fragmented (F) and continuous (C) habitats that differed significantly in population sizes (C > F) and genetic diversity (C > F) in neutral genetic markers. Using data from common garden experiments, we found a significant positive relationship between the mean values of the fitness related traits and the amount of microsatellite variation in a given population. While genetic differentiation in neutral marker loci (F(ST)) tended to be more pronounced in the fragmented than in the continuous habitat, genetic differentiation in quantitative traits (Q(ST)) exceeded that in neutral marker traits in the continuous habitat (i.e. Q(ST) > F(ST)), but not in the fragmented habitat (i.e. Q(ST) approximately F(ST)). These results suggest that the impact of random genetic drift relative to natural selection was higher in the fragmented landscape where populations were small, and had lower genetic diversity and fitness as compared to populations in the more continuous landscape. The findings highlight the potential importance of habitat fragmentation in impairing future adaptive potential of natural populations.

Waterborne amitrole affects the predator-prey relationship between common frog tadpoles (Rana temporaria) and larval spotted salamander (Salamandra salamandra)

Within their aquatic habitats, larval amphibians are often subjected to multiple natural and anthropic stressors. Among these, predation and waterborne pollution represent two types of stressing factor that frequently co-occur. In this connection, the present laboratory study was designed to investigate the effects of amitrole, a commonly used triazole herbicide, on the predator-prey relationship between common frog tadpoles (Rana temporaria) and larval spotted salamander (Salamandra salamandra). Tadpoles were exposed for 3 days to 0, 0.01, 0.1, 1, and 10 mg/L amitrole, either in the absence or in the presence of larval salamanders. Tadpole behavior (refuge use, movements) was monitored every day, and the predation efficiency was assessed at the end of the experiment by counting the number of surviving tadpoles. In the absence of the predator, amitrole-exposed tadpoles (at 0.01, 0.1, and 1 mg/L) increased their refuge use and decreased their rate of movements. In the presence of the predator, amitrole contamination did not affect tadpole behavior, except on the first day, where tadpoles exposed to 10 mg/L were found to be significantly more active than unexposed control tadpoles. Throughout the experiment, control tadpoles were the only group to show significant reductions of activity and visibility in response to the predator's presence. In contrast, tadpoles exposed to 0.01 and 0.1 mg/L amitrole increased their refuge use in response to the predator, whereas their rate of movements remained unaffected. Furthermore, exposures of tadpoles to the two highest amitrole concentrations (1 and 10 mg/L) resulted in the loss of both behavioral responses to the predator's presence. Interestingly, the lack of antipredator behavior in amitrole-exposed tadpoles did not enhance their vulnerability to predation by the larval salamander. Moreover, tadpoles exposed to the two highest herbicide concentrations showed a better survival than unexposed controls, indicating that amitrole contamination also had detrimental effects on the predatory behavior of the larval salamander. These findings emphasize the need to consider the effects of contaminants on both predator and prey before drawing conclusions about the possible consequences of prey behavioral modifications on the predation risk.

FLEXIBLE DEFENSE STRATEGIES: COMPETITION MODIFIES INVESTMENT IN BEHAVIORAL VS. MORPHOLOGICAL DEFENSES

Competition is predicted to affect the expression of inducible defenses, but because costs of behavioral and morphological antipredator defenses differ along resource gradients, its effects on defenses may depend on the traits considered. We tested the predictions from different defense models in tadpoles of the common frog Rana temporaria, which exhibit both types of defenses. In an outdoor experiment, we exposed the tadpoles to nonlethal predators (Aeshna dragonfly larvae) and to a gradient of intraspecific competition. Morphological responses did not follow any of the expected patterns, since investment in defense was not affected by resource level. Instead, tail depth decreased in the absence of predators. Behavioral defenses followed a state-dependent model. Overall, the defense strategy of the tadpoles revealed a shift from morphological and behavioral defenses at low tadpole density to morphological defense only at high density. This difference probably reflects the different efficiency of the defenses. Hiding is an effective means of defense, but it is unsustainable when resources are scarce. Morphological responses become more important with increasing density to compensate for the increase in behavioral risk-taking. Our results indicate that competition can strongly affect reaction norms of inducible defenses and highlight the importance of integrating ecological parameters that affect the cost-benefit balance of phenotypic plasticity.

Sexual dimorphism of extensor carpi radialis muscle size, isometric force, relaxation rate and stamina during the breeding season of the frog Rana temporaria Linnaeus 1758

Mating success of individual male frogs within explosive breeding species can depend on their ability to compete for a mate and to hold onto that mate during amplexus. Such importance of amplexus has resulted in the evolution of sexual dimorphism in the morphology and contractile characteristics of the anuran forelimb muscles used during amplexus. The aims of our study were to use an explosive breeding frog (Rana temporaria) during the breeding season to compare extensor carpi radialis (ECR) muscle length, mass, isometric activation times, relaxation times, absolute force, relative force (stress) and fatigue between male and female frogs. We found that ECR muscle mass and length were greater (tenfold and 1.4-fold, respectively), absolute tetanic muscle force and relative tetanic force (stress) were greater (16-fold and 2.2-fold, respectively) and relaxation times were slower in males than in females. Male ECR muscles incompletely relaxed during fatigue tests and showed less fatigue than female muscles. These sex differences are likely to be beneficial to the male frogs in allowing them to produce relatively high absolute muscle forces for prolonged periods of time to hold onto their mate during amplexus.

[Effect of photostimulation on the wakefulness-sleep cycle in the common frog Rana temporaria]

Effect of daily 30-min photostimulation in the 10 s light: 10 s pause (the total of 5 days) on the time structure of the wakefulness--protosleep cycle (WPC) was studied in the common frog Rana temporaria. Changes were analyzed of EEG wave components in three immobility forms of the type of catalepsy (P-1), catatonia (P-2), and cataplexy (P-3) that form protosleep. The first three photostimulations promoted a gradual increase of the P-1 state to 84.16 +/- 11.6% [the initial value (IV) 22.9 +/- 9.1%] and a decrease of representation of wakefulness to 4.86 +/- 2/1% (IV 13.8 +/- 7.8%), of P-2 to 11.1 +/- 5.3 (IV 53.3 +/- 13.3%), and of P-3 to 2.21 +/- 1.0% (IV 11.1 +/- 5.6%). After 4-5 photostimulations and especially after their complete cessation the percentage of P-1 in the WPC was restored to initial values, whereas the percentage of the frog WPC P-3 considered to be a precursor of the homoiothermal sleep rose to 20 +/- 8.3% after 5 photostimulations and to 38.5 +/- 6.7% the next day. Changes in the frog EEG spectra appeared only after one photostimulation and were characterized by a brief increase of power of alpha-like waves and by inhibition of slow 6-waves. In P-2 the power of the slow delta-waves gradually rose. In P-3 the EEG parameters did not change. In all experimental animals a decrease of the relative thymus and adrenal masses was revealed, which indicates the photostimulation regime used in the work induces stress. The obtained data allow thinking that a certain neurohormonal response to stress has already been formed at the amphibian level and that an important role in this response realization is played by a coordinated interaction of the hypothalamic sleep-regulating system providing protosleep manifestations and of the hypothalamic neurosecretory system triggering the stress-reaction hormonal cascade.

Demographic and genetic estimates of effective population and breeding size in the amphibian Rana temporaria

Genetic methods for estimating effective population size ( Ne) or the effective number of breeders ( Nb) have become popular, but comparisons of these estimates with demographic estimates of Ne and Nb are rare, especially in anurans. We used three genetic (linkage disequilibrium, temporal moments, Bayesian coalescent-based method) and three demographic models, the latter considering number of breeding individuals, sex ratio, reproductive skew, and other demographic data, to estimate Ne and Nb in two subarctic populations (T and P) of the common frog Rana temporaria, subject to long-term capture-recapture studies. Demographic estimates of Ne based on total population size ( Ne ([T])= 44.5-56.9; Ne ([P])= 68.8-93.7) deviated markedly from the genetic estimates obtained using the linkage disequilibrium method ( Ne ([T])= 97.1; Ne ([P])= 13.2). The demographic estimates of Nb, taking into consideration sex ratio and variance in reproductive success ( Nb ([T])= 10.1-39.7; Nb ([P])= 3.9-21.3), were higher than the genetic estimates ( Nb ([T])= 3.7-5.4; Nb ([P])= 3.5-3.9). The main factors affecting the effective size estimates were sex ratio and reproductive skew. The discrepancies between corresponding Ne and Nb estimates highlight the sensitivity of both demographic and genetic estimates on their underlying assumptions. Yet the ratios of effective or breeding effective size to the census population size were similar to those reported earlier for anurans, reinforcing the view that the discrepancy between actual and effective breeding sizes in anuran populations is typically very large.

Investment in defense and cost of predator-induced defense along a resource gradient

An organism's investment in different traits to reduce predation is determined by the fitness benefit of the defense relative to the fitness costs associated with the allocation of time and resources to the defense. Inherent tradeoffs in time and resource allocation should result in differential investment in defense along a resource gradient, but competing models predict different patterns of investment. There are currently insufficient empirical data on changes in investment in defensive traits or their costs along resource gradients to differentiate between the competing allocation models. In this study, I exposed tadpoles to caged predators along a resource gradient in order to estimate investment in defense and costs of defense by assessing predator-induced plasticity. Induced defenses included increased tail depth, reduced feeding, and reduced swimming activity; costs associated with these defenses were reduced developmental rate, reduced growth, and reduced survival. At low resource availability, these costs predominately resulted in reduced survival, while at high resource availability the costs yielded a reduced developmental rate. Defensive traits responded strongly to predation risk, but did not respond to resource availability (with the exception of feeding activity), whereas traits construed as costs of defenses showed the opposite pattern. Therefore, defensive traits were highly sensitive to predation risk, while traits construed as costs of defense were highly sensitive to resource allocation tradeoffs. This difference in sensitivity between the two groups of traits may explain why the correlation between the expression of defensive traits and the expression of the associated defense costs was weak. Furthermore, my results indicate that genetic linkages and mechanistic integration of multiple defensive traits and their associated costs may constrain time and resource allocation in ways that are not addressed in existing models.

Activation and repolarization patterns in the ventricular epicardium under sinus rhythm in frog and rabbit hearts

Our study compared the contributions of activation sequence and local repolarization durations distribution in the organization of epicardial repolarization in animals with fast (rabbit) and slow (frog) myocardial activation under sinus rhythm. Activation times, repolarization times and activation-recovery intervals (ARI) were obtained from ventricular epicardial unipolar electrograms recorded in 13 Chinchilla rabbits (Oryctolagus cuniculus) and 10 frogs (Rana temporaria). In frogs, depolarization travels from the atrioventricular ring radially. ARIs increased progressively from the apex to the middle portion and finally to the base (502+/-75, 557+/-73, 606+/-79 ms, respectively; P<0.01). In rabbits, depolarization spread from two epicardial breakthroughs with the duration of epicardial activation being lower than that in frogs (17+/-3 vs. 44+/-18 ms; P<0.001). ARI durations were 120+/-37, 143+/-45, and 163+/-40 ms in the left ventricular apex, left, and right ventricular bases, respectively (P<0.05). In both species, repolarization sequence was directed from apex to base according to the ARI distribution with dispersion of repolarization being higher than that of activation (P<0.001). Thus, excitation spread sequence and velocity per se do not play a crucial role in the formation of ventricular epicardial repolarization pattern, but the chief factor governing repolarization sequences is the distribution of local repolarization durations.

[Influence of culture medium osmolality on maturation and ovulation of Rana temporaria oocytes stimulated in vitro by the pituitary gland extract or progesterone]

The influence of diluted Ringer solution on ovulation and maturation of common frog oocytes stimulated in vitro by homologous pituitary extract (0.005 pit/ml) or progesterone (1 pg/ml) was studied. During wintering, the dilution of Ringer solution led to a decreased percentage of oocytes ovulated and matured under the influence of both inducers. As the season of reproduction approached, the dependence of oocyte maturation and ovulation on the Ringer solution dilution weakened. Possible causes of different dependence of the ovulation of amphibian and sturgeon oocytes stimulated by gonadotropic hormones or progesterone on the culture medium osmolality is discussed.

Effects of p,p'-DDE on retinoid homeostasis and sex hormones of adult male European common frogs (Rana temporaria)

Reports of declining numbers of species and individuals of amphibians in most parts of the world have caused great concern. Several causative factors have been linked to this amphibian decline, and increased environmental pollution related to pesticide use seems to be one important factor. Persistent organic pollutants may act as endocrine disrupters, and thereby exert adverse effects on development (metamorphosis, growth and sexual differentiation) in amphibians. During periodic events, such as spring snowmelt, amphibians may be exposed to acute high levels of pesticides. 1,1,1-Trichloro-2,2-bis(p-chlorophenyl)ethane (DDT) and its metabolite 1,1-dichloro-2,2-bis(p-chlorophenyl)ethene (p,p'-DDE) is a pesticide that is still found in wetlands and soils. In order to study the effects of p,p'-DDE on susceptible amphibian endocrine systems, adult male European common frogs (Rana temporaria) were exposed to different doses of p,p'-DDE (0, 0.01, 0.1, 1 and 10 mg p,p'-DDE/kg body mass) for 14 d and sex hormone levels (testosterone and 17beta-estradiol) in plasma and retinoid concentrations (retinol and retinyl palmitate) in liver were determined. The results showed a significant variation in the liver retinol concentration at increasing doses of p,p'-DDE, suggesting that p,p'-DDE may interfere in the hepatic metabolism of retinol in adult frogs. Lack of effects on sex hormones may indicate that after arousal from hibernation males are relatively resistant to adverse reproductive effects of p,p'-DDE.

Spikelet currents in frog tectal neurons with different firing patterns in vitro

Neuronal potential-dependent membrane currents are important in shaping the integration of synaptic inputs. Our recordings in voltage-clamp mode indicate that the small fast inward currents (spikelet currents), which were several times smaller than action potential (AP) currents, are a distinguished feature of 33% of neurons from 8 to 6 layers of the frog tectum. Out of all neuronal types described previously, only phasic cells and neurons with 'sag' in response to hyperpolarizing step current injection did not show spikelet currents. These small fast inward currents were sensitive to the intracellular administration of the sodium channel blocker QX-314, but not to the extracellular application of a glutamate receptor antagonist kynurenic acid. This suggests that spikelet currents are mediated by fast voltage-dependent Na(+) channels. Since spikelet currents could also be elicited with synaptic stimulation it is possible that spikelets are generated in dendrites and, thus, are important for fast integration of visual signals in tectal neurons.

Altered hepatic retinol and CYP26 levels in adult European common frogs (Rana temporaria) exposed to p,p'-DDE

The effects of environmental contamination on amphibians are of particular concern because there are reports of declining numbers of species and individuals in most parts of the world during the last 50 years. During the last decade there has been increased focus on the role of persistent organic pollutants as retinoid (vitamin A) disrupters, and their effects on development, growth and sexual differentiation. To study the effects of p,p'-DDE, one of the most persistent metabolites of the pesticide DDT, on retinol homeostasis, we subcutaneously exposed adult male European common frogs (Rana temporaria) to different doses of p,p'-DDE (0, 0.01, 0.1, 1 and 10 mg/kg body mass) and studied the effect of a short term exposure (14 days) on hepatic retinoid levels and CYP26 gene and protein expression. Hepatic retinol concentrations, CYP26 gene and protein levels were analysed using HPLC, quantitative RT-PCR and indirect ELISA, respectively. Our results showed a significant p,p'-DDE dose-specific increase in the hepatic retinol concentration. CYP26 gene and protein expression were reduced in an apparent p,p'-DDE dose-specific manner. The results suggest that p,p'-DDE may interfere with the hepatic metabolism of retinol in adult frogs by decreasing CYP26 expression patterns.

Alien mink predation induces prolonged declines in archipelago amphibians

Amphibians are undergoing enigmatic global declines variously attributed to a complex web of anthropogenic forces. Alien predators pose a fundamental threat to biodiversity generally that is predicted to be most acute in island ecosystems. While amphibian eggs and tadpoles are vulnerable to aquatic predators, the effect of predators on adult, reproducing frogs, which most influence amphibian population processes, is unknown. Here, we report on the responses of amphibian populations in the outer Finnish Archipelago to a long-term, large-scale removal of American mink (Mustela vison Schreb.), an invasive predator linked to recent biodiversity loss across Europe. Removal increased both the densities and distribution of common frogs (Rana temporaria L.) but not those of common toads (Bufo bufo L.), which appear to escape mink predation because of their unpalatable skin. Importantly, the largest benefits of mink removal to frog recovery were slow to appear as frogs apparently have a delayed maturation in these harsh environments, which means we must be cautious about reliance upon short-term results.

Temperature dependence of H+ transport across erythrocyte membrane of Rana temporaria grass frog in media containing Cl- and SO4(2-)

H+ transport across the erythrocyte membrane was studied in Rana temporaria grass frog. The temperature coefficients and activation energy of H+ transport were calculated in media containing Cl- and SO4(2-). Our results show that kinetic characteristics of H+ transport depend on function of band 3 protein in the erythrocyte membrane.

Phosphorylation regulates an inwardly rectifying ATP-sensitive K(+)- conductance in proximal tubule cells of frog kidney

K(+) channels in the renal proximal tubule play an important role in salt reabsorption. Cells of the frog proximal tubule demonstrate an inwardly rectifying, ATP-sensitive K(+) conductance that is inhibited by Ba(2+), G(Ba). In this paper we have investigated the importance of phosphorylation state on the activity of G(Ba) in whole-cell patches. In the absence of ATP, G(Ba) decreased over time; this fall in G(Ba) involved phosphorylation, as rundown was inhibited by alkaline phosphatase and was accelerated by the phosphatase inhibitor F(-)(10 mM: ). Activation of PKC using the phorbol ester PMA accelerated rundown via a mechanism that was dependent on phosphorylation. In contrast, the inactive phorbol ester PDC slowed rundown. Inclusion of the PKC inhibitor PKC-ps in the pipette inhibited rundown. These data indicate that PKC-mediated phosphorylation promotes channel rundown. Rundown was prevented by the inclusion of PIP-2 in the pipette. PIP-2 also abrogated the PMA-mediated increase in rundown, suggesting that regulation of G(Ba) by PIP-2 occurred downstream of PKC-mediated phosphorylation. G-protein activation inhibited G(Ba), with initial currents markedly reduced in the presence of GTPgammas. These properties are consistent with G(Ba) being a member of the ATP-sensitive K(+) channel family.

Quantitative genetics of larval life-history traits in Rana temporaria in different environmental conditions

The degree to which genetic variation in a given trait varies among different populations of the same species and across different environments has seldom been quantified in wild vertebrate species. We investigated the expression of genetic variability and maternal effects in three larval life-history traits of the amphibian Rana temporaria. In a factorial laboratory experiment, five widely separated populations (max. 1600 km) were subjected to two different environmental treatments. Animal model analyses revealed that all traits were heritable (h2≈0·20) in all populations and under most treatment combinations. Although the cross-food treatment genetic correlations were close to unity, heritabilities under a restricted food regime tended to be lower than those under an ad libitum food regime. Likewise, maternal effects (m2≈0·05) were detected in most traits, and they tended to be most pronounced under restricted food conditions. We detected several cross-temperature genetic and maternal effects correlations that were lower than unity, suggesting that genotype–environment interactions and maternal effect–environment interactions are a significant source of phenotypic variation. The results reinforce the perspective that although the expression of genetic and maternal effects may be relatively homogeneous across different populations of the same species, local variation in environmental conditions can lead to significant variation in phenotypic expression of quantitative traits through genotype–environment and maternal effect–environment interactions.

Binaural interaction in the frog dorsal medullary nucleus

We have studied binaural and directional processing in cells in the frog dorsal medullary nucleus (DMN) stimulated with dichotic sound (couplers) and free-field sound. We present evidence that already at this stage of central processing the neural directionality is sharpened, probably by binaural interaction. Binaural interaction in the DMN was usually interpreted as inhibition, mostly driven from the contralateral side and dependent on a certain combination of interaural time differences (ITD) and interaural level differences (ILD). In free-field measurements, the strength and timing of the binaural inputs will depend on sound direction as processed by the auditory fibers. Thus, the directionality of DMN cells is caused by both monaural directional cues generated by acoustical coupling of the eardrums and non-tympanic pathways as well as binaural interaction. Most DMN cells show ovoidal directional characteristics and the directionality is sharpened compared to that of auditory nerve fibers. We suggest that the sharpening is due to the inhibitory interactions.

Common pesticide increases costs of antipredator defenses in Rana temporaria tadpoles

Pesticides represent an important threat for natural populations. While their effects are assessed on short terms acute exposure, some of their harmful consequences may only become apparent when combined with other stressors, notably natural ones, such as predation. Here, we investigated in a laboratory experiment how exposure to a common fungicide (fenpropimorph) would affect the responses to predation in the common frog Rana temporaria. The concentrations of fungicide we used were comparable to those found in nature (0, 2, or 11 microg/L). The higher concentration of fungicide reduced tadpole activity late in the experiment, and only 7% of the tadpoles reached metamorphosis. In the lower concentration, the ability to respond adaptively to predator presence was not affected, but the costs (delayed metamorphosis, smaller relative body size) of this response were increased. Our results highlightthe need to investigate sublethal effects of pesticides on organismal performance if assessment of pesticides real impact is to be obtained.

Habitat specialization and adaptive phenotypic divergence of anuran populations

We tested for adaptive population structure in the frog Rana temporaria by rearing tadpoles from 23 populations in a common garden experiment, with and without larval dragonfly predators. The goal was to compare tadpole phenotypes with the habitats of their source ponds. The choice of traits and habitat variables was guided by prior information about phenotypic function. There were large differences among populations in life history, behaviour, morphological shape, and the predator-induced plasticities in most of these. Body size and behaviour were correlated with predation risk in the source pond, in agreement with adaptive population divergence. Tadpoles from large sunny ponds were morphologically distinct from those inhabiting small woodland ponds, although here an adaptive explanation was unclear. There was no evidence that plasticity evolves in populations exposed to more variable environments. Much among-population variation in phenotype and plasticity was not associated with habitat, perhaps reflecting rapid changes in wetland habitats.

Cytosolic Ca2+ concentration and rate of increase of the cytosolic Ca2+ concentration in the regulation of vascular permeability in Rana in vivo

Vascular permeability is assumed to be regulated by the cytosolic Ca(2+) concentration ([Ca(2+)](c)) of the endothelial cells. When permeability is increased, however, the maximum [Ca(2+)](c) appears to occur after the maximum permeability increase, suggesting that Ca(2+)-dependent mechanisms other than the absolute Ca(2+) concentration may regulate permeability. Here we investigate whether the rate of increase of the [Ca(2+)](c) (d[Ca(2+)](c)/dt) may more closely approximate the time course of the permeability increase. Hydraulic conductivity (L(p)) and endothelial [Ca(2+)](c) were measured in single perfused frog mesenteric microvessels in vivo. The relationships between the time courses of the increased L(p), [Ca(2+)](c) and d[Ca(2+)](c)/dt were examined. L(p) peaked significantly earlier than [Ca(2+)](c) in all drug treatments examined (Ca(2+) store release, store-mediated Ca(2+) influx, and store-independent Ca(2+) influx). When L(p) was increased in a store-dependent manner the time taken for L(p) to peak (3.6 +/- 0.9 min during store release, 1.2 +/- 0.3 min during store-mediated Ca(2+) influx) was significantly less than the time taken for [Ca(2+)](c) to peak (9.2 +/- 2.8 min during store release, 2.1 +/- 0.7 min during store-mediated influx), but very similar to that for the peak d[Ca(2+)](c)/dt to occur (4.3 +/- 2.0 min during store release, 1.1 +/- 0.5 min during Ca(2+) influx). Additionally, when the increase was independent of intracellular Ca(2+) stores, L(p) (0.38 +/- 0.03 min) and d[Ca(2+)](c)/dt (0.30 +/- 0.1 min) both peaked significantly before the [Ca(2+)](c) (1.05 +/- 0.31 min). These data suggest that the regulation of vascular permeability by endothelial cell Ca(2+) may be regulated by the rate of change of the [Ca(2+)](c) rather than the global [Ca(2+)].

Effects of ryanoids on spontaneous and depolarization-evoked calcium release events in frog muscle

The effects of ryanoids on calcium sparks and transients were studied in voltage-clamped cut frog muscle fibers with a laser scanning confocal microscope. For each ryanoid employed, several sequential effects were observed, including: a), transient increases in spontaneous spark frequency; b), conversions of sparks to long-lasting steady glows; and c), occasional interruptions of the glows. The ratio of the amplitude of the glow induced by a ryanoid to that of the precursory spark followed the order: ryanodol > ryanodine > C(10)-O(eq)-glycyl-ryanodine > C(10)-O(eq)-beta-alanyl-ryanodol. This sequence of glow amplitudes parallels that of the subconductances induced by these ryanoids in single-channel studies, suggesting that the glows reflect Ca(2+) fluxes through semiopen calcium release channels. Ryanoids also abolished depolarization-evoked sparks elicited with small pulses, and transformed the calcium release during depolarization to a uniform nonsparking fluorescence signal. The ratio of this signal, averaged spatially, to that of the control followed the order: ryanodol < ryanodine < C(10)-O(eq)-glycyl-ryanodine < C(10)-O(eq)-beta-alanyl-ryanodol, implying an inverse relationship with the amplitudes of ryanoid-induced glows. The observation that depolarization-evoked calcium release can occur after ryanoid suppression of calcium sparks suggests the possibility of a new strategic approach for treating skeletal muscle diseases resulting from leaky calcium release channels.

High degree of population subdivision in a widespread amphibian

In general, amphibians are known to exhibit a higher degree of population subdivision than any other major animal taxa, but large-scale population genetic surveys of widely distributed species are still scarce, especially in the Eurasian continent. Using microsatellite markers and mitochondrial DNA sequences, we investigated the large-scale population genetic structure of the common frog (Rana temporaria)--one of the most widespread amphibians of the Palearctic region. Analyses of cytochrome b sequences revealed evidence for two distinct lineages inhabiting western and eastern parts of Europe. The separation of these lineages c. 700,000 years ago may have been induced by the onset of the Middle Pleistocene continental glaciations. Analyses of the variability of microsatellite loci within each of the clades revealed evidence for evolution of a high degree of population subdivision (FST approximately 0.23) even in northern Fennoscandia, colonized less than 10,000 years ago. The high level of substructuring is puzzling in the face of an apparently high dispersal capacity, as evidenced by the rather rapid recolonization of northern Europe. This suggests that processes other than restricted dispersal capacity need to be explored as explanations for the high degree of population subdivision in amphibians. The colonization of northern Europe has been accompanied by loss of genetic variability as evidenced by decreasing levels of intrapopulational genetic variability in microsatellite loci from south to north across Europe.

Post-mating clutch piracy in an amphibian

Female multiple mating and alternative mating systems can decrease the opportunity for sexual selection. Sperm competition is often the outcome of females mating with multiple males and has been observed in many animals, and alternative reproductive systems are widespread among species with external fertilization and parental care. Multiple paternity without associated complex behaviour related to mating or parental care is also seen in simultaneously spawning amphibians and fishes that release gametes into water. Here we report 'clutch piracy' in a montane population of the common frog Rana temporaria, a reproductive behaviour previously unknown in vertebrates with external fertilization. Males of this species clasp the females and the pair deposits one spherical clutch of eggs. No parental care is provided. 'Pirate' males search for freshly laid clutches, clasp them as they would do a female and fertilize the eggs that were left unfertilized by the 'parental' male. This behaviour does not seem to be size-dependent, and some males mate with a female and perform clutch piracy in the same season. Piracy affected 84% of the clutches and in some cases increased the proportion of eggs fertilized, providing direct fitness benefits both for the pirate males and the females. Sexual selection--probably caused by a strong male-biased sex ratio--occurs in this population, as indicated by size-assortative mating; however, clutch piracy may reduce its impact. This provides a good model to explore how alternative mating strategies can affect the intensity of sexual selection.

Microsatellite marker data suggest sex-biased dispersal in the common frog Rana temporaria

Despite being important models in ecological, evolutionary and conservation biology research, very little is known about the dispersal in anuran amphibians, and juvenile dispersal in particular. Using microsatellite data, we assessed signatures of sex-biased migration in the common frog (Rana temporaria) in Scandinavia. Significant heterozygosity deficiency (FIS) and lower assignment value (mAIc) among females suggest that dispersal in R. temporaria is female biased. Also variance of assignment (vAIc), estimated separately for the two sexes, was consistent with this inference, although the difference was not statistically significant. Possible proximate and ultimate explanations for female-biased dispersal in amphibians are discussed.

Effects of intracellular acidification and varied temperature on force, stiffness, and speed of shortening in frog muscle fibers

This study aimed to establish whether the temperature-dependent effect of acidification on maximum force observed in mammalian muscles also applies to frog muscle. Measurements of force, stiffness, and unloaded velocity of shortening in intact single muscle fibers from the anterior tibialis muscle of Rana temporaria were performed between 0 and 22 degrees C during fused tetani in H(2)CO(3)-CO(2)-buffered Ringer solution with pH adjusted to 7.0 and 6.3, respectively. The force-to-stiffness ratio increased as a rectilinear function of temperature between 0 and 20 degrees C at pH 7.0. Lowering the pH to 6.3 reduced the tetanic force by 13.5 +/- 1.2 and 11.5 +/- 1.4% at 2.8 and 20.5 degrees C, respectively, with only a minor reduction in fiber stiffness. The maximum speed of shortening was decreased by lowered pH by 12.9 +/- 1.5 and 7.8 +/- 1.1% at low and high temperature, respectively. Acidification increased the time to reach 70% of maximum force by 18.0% at approximately 2 degrees C; the same pH change performed at approximately 20 degrees C in the same fibers reduced the rise time by 24.1%. The same increase in the rate of rise of force at high temperature was also found at normal pH after the fibers were fatigued by frequent stimulation. It is concluded that, in frog muscle, the force-depressant effect of acidification does not vary significantly with temperature. By contrast, acidification affects the onset of activation in a manner that is critically dependent on temperature.

Separation of detubulation and vacuolation phenomena in amphibian skeletal muscle

Sartorius muscle fibres from cold-adapted Rana temporaria were exposed to variants of an established detubulation procedure (Koutsis et al. (1995) J Muscle Res Cell Motil 16, 519-528) to test the extent to which detubulation and tubular vacuolation phenomena could be separated using different conditions of osmotic shock. A control procedure was optimised to a 28-min exposure to 400 mM glycerol-Ringer. This was followed by a recovery step involving its replacement by a Ca2+/Mg(2+)-Ringer solution and steady cooling over 30 min from room temperature (approximately 18 degress C) to approximately 10 degress C, followed by the restoration of the normal Ringer solution. This procedure successfully abolished the action potential after-depolarisation component, reflecting a loss of tubular conduction ('detubulation') in 74.3 +/- 5.9% of the fibres studied. Omitting the cooling during the recovery step sharply reduced the incidence of detubulation. So did omitting either the high-[Ca2+] and/or [Mg2+] in the recovery solutions in test procedures, but to significantly different extents (P < 5%). Yet trapping of fluorescent Sulfhorhodamine B dye in 'closed' vacuoles persisted albeit with reduced proportions of fibre volume occupied by vacuoles. Furthermore, the variations in recovery conditions produced similar levels of vacuolation despite smaller vacuole sizes in the cooled fibres (P < 0.05). These findings demonstrate that fibre vacuolation and detubulation are phenomena that are potentially separable through varying the conditions of osmotic shock, with detubulation requiring significantly more stringent conditions than vacuolation.