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Emerging infectious diseases are major drivers of global and local amphibian biodiversity loss. Therefore, developing effective disinfection methods to manage the impact of diseases in wild and captive "ark" populations are an important goal in amphibian conservation. While chemical disinfectants have been used safely and effectively in larval and adult amphibians infected with pathogenic microbes, their applicability to amphibian egg masses has remained untested. To bridge this gap, we exposed embryos of the common toad (Bufo bufo) and agile frog (Rana dalmatina) experimentally to three widely used disinfectants: voriconazole, chloramphenicol and chlorogen-sesquihydrate. For 3 days we exposed portions of egg masses to these disinfectants at 1×, 2×, 5× and 10× the concentration recommended for the disinfection of tadpoles and adults. Subsequently, we recorded embryonic and larval survival, as well as larval body mass and the incidence of abnormalities 12 days after hatching. Application of voriconazole had species- and concentration-dependent negative impacts on survival and body mass, and caused marked malformations in the viscerocranial structure of B. bufo tadpoles. Exposure to chlorogen-sesquihydrate also resulted in significant mortality in B. bufo embryos and negatively affected body mass of R. dalmatina larvae. Chloramphenicol had little negative effects on embryos or larvae in either species. Based on these results, the application of voriconazole and chlorogen-sesquihydrate cannot be recommended for the disinfection of amphibian eggs, whereas treatment with chloramphenicol appears to be a safe method for eliminating potential pathogens from anuran egg masses and their immediate aquatic environment.

This study explores the cohort patterns in a size versus time plot of individual metamorphs of Rana tadpoles. This meta-study was based on a number of studies where any of three species of Rana tadpoles were raised in tanks under various treatments (variation in source pond, tadpole density, drying regime, hatching date, food level and competitors). A frequent pattern was found where there was an initial decrease in metamorph size as more slowly developing tadpoles metamorphosed. This negative trend sometimes changed to positive as later metamorphs appeared. The later metamorphs were often as large, or even larger, than those first to metamorphose, giving the plot a U-shaped pattern. Also, a number of field studies of two of the Rana species’ were analysed for the same aspect. The U-shaped pattern was much rarer but it did occur. A positive linear slope, rather than a negative one, was also found occasionally. A large number of factors affect the growth and development rates in tadpoles, adaptively and non-adaptively, and thus determine their size at the time of metamorphosis. How these can contribute to the found metamorphosis patterns is discussed.

While the number of studies reporting the presence of individual behavioral consistency (animal personality, behavioral syndrome) has boomed in the recent years, there is still much controversy about the proximate and ultimate mechanisms resulting in the phenomenon. For instance, direct environmental effects during ontogeny (phenotypic plasticity) as the proximate mechanism behind the emergence of consistent individual differences in behavior are usually overlooked compared to environmental effects operating across generations (genetic adaptation). Here, we tested the effects of sociality and perceived predation risk during ontogeny on the strength of behavioral consistency in agile frog (Rana dalmatina) tadpoles in a factorial common garden experiment. Tadpoles reared alone and without predatory cues showed zero repeatability within (i.e., lack of personality) and zero correlation between (i.e., lack of syndrome) activity and risk‐taking. On the other hand, cues from predators alone induced both activity and risk‐taking personalities, while cues from predators and conspecifics together resulted in an activity – risk‐taking behavioral syndrome. Our results show that individual experience has an unequivocal role in the emergence of behavioral consistency. In this particular case, the development of behavioral consistency was most likely the result of genotype × environment interactions, or with other words, individual variation in behavioral plasticity.

Understanding population dynamics is critical for the management of animal populations. Comparatively little is known about the relative importance of endogenous (i.e. density-dependent) and exogenous (i.e. density-independent) factors on the population dynamics of amphibians with complex life cycles. We examined the potential effects of density-dependent and -independent (i.e. climatic) factors on population dynamics by analyzing a 15-yr time series data of the agile frog Rana dalmatina population from Târnava Mare Valley, Romania. We used two statistical models: 1) the partial rate correlation function to identify the feedback structure and the potential time lags in the time series data and 2) a Gompertz state-space model to simultaneously investigate direct and delayed density dependence as well as climatic effects on population growth rate. We found evidence for direct negative density dependence, whereas delayed density dependence and climate did not show a strong influence on population growth rate. Here we demonstrated that direct density dependence rather than delayed density dependence or climate determined the dynamics of our study population. Our results confirm the findings of many experimental studies and suggest that density dependence may buffer amphibian populations against environmental stress. Consequently, it may not be easy to scale up from individual-level effects to population-level effects.

Chlorpyrifos is an organophosphate pesticide among the most widely used in the world, which is suspected to be an endocrine-disrupting compound. To determine the capacity of chlorpyrifos to affect gonadal differentiation in Rana dalmatina, tadpoles were exposed to this pesticide during larval development until completion of metamorphosis at ecologically relevant concentrations (0.025 and 0.05mg/L). No effects of chlorpyrifos exposure on survival, development, or meta morphosis were observed. After a 1 month metamorphosis, the gonadal phenotype was determined by gross morphology and histological examination. Morphological and histological analysis revealed normal ovaries or testes in froglets belonging to control group, whereas testes from several froglets exposed to chlorpyrifos were interspersed with testicular oocytes in histological sections. Chlorpyrifos exposure during the entire larval period did not affect sex ratio, but reduced the percentage of males with histologically normal testes. The findings suggest that chlorpyrifos exposure has significant effects on gonadal differentiation in some animals by inducing an intersex condition and alterations to testicular morphology, and that R. dalmatina is sensitive to endocrine disruption. Thereby, this study provides evidence that the ecologically relevant concentrations of chlorpyrifos, although not adversely affect the survival, development, or metamorphosis, may interfere with sex differentiation and reproductive development of R. dalmatina via endocrinedisrupting mechanisms. J. Exp. Zool. 313A, 2011. & 2011 Wiley-Liss, Inc.

The dear enemy phenomenon in which animals discriminate familiar neighbors from unknown strangers, and respond more aggressively to strangers is well established in various social animals, especially in songbirds and mammals. So far, very few studies of neighbor‐stranger discrimination have been carried out in amphibians and the results have been mixed. Thus, it is unclear whether this phenomenon exists commonly in frogs and toads, and whether it is exhibited by species with large vocal repertoires. We conducted acoustic playback experiments with male concave-eared torrent frogs (Odorrana tormota, a species with an unusually large vocal repertoire) kept in a tank in a quiet room to investigate whether or not they can discriminate strangers from neighbors acoustically. Nine of the 14 males tested showed evoked vocal responses to the calls from strangers, but none to calls from neighbors; vocal response to the calls from strangers was accompanied by aggressive motor activity. These results demonstrate that male O. tormota possess the ability to discriminate neighbors from strangers acoustically. Odorrana tormota therefore joins three ranid species (Rana catesbiana, Rana clamitans, Rana dalmatina, all known to have a comparatively small and stereotyped vocal repertoires) as the only anurans demonstrated to have this ability. Given the difference in signaling complexity between these frog species, the salient acoustic features used for discriminating neighbors and strangers are likely to be quite distinct.

Interspecific reproductive interference can affect fitness-related breeding performance, thus influencing fitness and distribution of populations. Laboratory studies demonstrated the social interference of Rana dalmatina males on R. latastei breeding females: the presence of heterospecific males reduced the percentage of viable embryos in R. latastei eggs. Here, we tested if the negative effects of R. dalmatina males on R. latastei reproductive success occur in field conditions. We compared the percentage of viable embryos of eggs laid in field conditions from populations where R. latastei breeds alone with the percentage of viable embryos of populations where R. latastei cohabits with R. dalmatina. We did not find any significant difference in percentage of viable embryos between R. latastei populations syntopic and allotopic with R. dalmatina, nor a relationship between the relative abundance of heterospecifics and reproductive success. In natural conditions, the presence of heterospecific males does not seem to interfere with the reproductive success of R. latastei. The experimental procedure may influence the interaction among individuals. Therefore, we suggest to validate on natural populations the results of experiments dealing with complex interactions.

A study of the feeding habits and movements of 11 radiotracked polecats Mustela putorius in western France revealed that seasonal predation upon agile frogs, Rana dalmatina, was directly influenced by prey abundance and distribution. Although dietary structure showed the importance of mammalian prey (71.5%), polecats exploited nocturnal, terrestrial anurans in spring (31.6%). The periodic activity of anurans at spawning sites led both to a maximum density in spring and to a patchy distribution. The monthly variations in anuran dietary occurrences were associated with changes in frog availability. The functional response of polecats to frog density was sigmoidal shaped (type 3 response). Frog consumption rate increased more slowly than prey density but frogs were actively removed at higher density. It is therefore suggested that frog populations were moderately affected by the predator and this density dependent effect tends to stabilise anuran populations. Predation upon anurans was also correlated with a prey dispersion index as revealed by a polynomial regression. Polecats concentrated their predation on spawning congregations of the breeding adult frogs. Movements were smallest in spring and polecats changed their track length by increasing the difference between a succession of small movements and of longer journeys towards profitable sites. Changes in movements correlated with the anuran dispersion index and the response was sigmoidal (polynomial regression) revealing an area-restricted search. This response may be regarded as an 'aggregative response' according to the first part of the definition of Begon et al. (1996). Functional and area-restricted search responses to the frog abundance and dispersion constitute an original example of predator-prey coexistence strategies among vertebrates. I suggest that such predation could be favoured by the individualistic habits of the mustelid.

Amphibian larvae often face two major sources of mortality: pond desiccation and predation. Tadpoles of seven anuran species with different preferences for type of breeding habitat, on a hydroperiod scale, were tested for responses to the presence of predators by raising them experimentally in the presence and absence of a separately caged invertebrate predator that was fed on conspecific tadpoles. The species typically breeding in temporary or semi-permanent ponds (Rana temporaria, Rana arvalis, Rana dalmatina and Hyla arborea) - where invertebrate predator populations are predicted to vary considerably spatiotemporally - all showed marked induced increases in tail fin depth in response to predator presence. These species also tended to respond by reduced growth rates. The representative of the most ephemeral habitats, Bufo calamita, did not respond in any of these traits. Its congeneric, Bufo bufo, a toxic inhabitant of permanent ponds and lakes, tended to respond to predator presence by reducing its growth rate, though not by a tail depth increase. I argue that the rather poor swimming performance in Bufo tadpoles may opt for defences other than locomotor ability. The palatable, permanent pond species Pelobates fuscus did not alter either its growth rate or tail morphology. Possible explanations for this result are discussed. (Less)

Ficetola & De Bernardi (2005) test the effects of reproductive interference between Rana latastei and Rana dalmatina on the former’s reproductive success under natural conditions. Their study examines predictions by Hettyey & Pearman (2003), based on natural history observations and experimental results, that reproductive failure may occur because of heterospecific matings when species relative abundance is highly skewed. Ficetola & De Bernardi (2005) measure R. latastei reproductive success, represented by mean embryo viability across clutches raised in the laboratory, using three populations that are syntopic with R. dalmatina and two other populations, where this congener is absent. Ficetola and De Bernardi find no decrease in reproductive success of R. latastei populations in syntopy. They also find no relationship between the relative abundance of heterospecifics and R. latastei reproductive success. Ficetola & De Bernardi (2005) conclude that heterospecific individuals do not interfere with R. latastei reproduction under natural conditions and they emphasize validating experimental results using natural populations. We agree with Ficetola & De Bernardi (2005) that tests of experimental results under natural conditions are needed. Determining an optimal experimental setup is difficult because different setups may yield different results (e.g. Michalak & Rafinski 1999). Further, influential factors in experimental manipulations may be unimportant under natural conditions (e.g. Skelly & Kiesecker 2001). In this sense, the aim of Ficetola & De Bernardi (2005) to test the validity of experimental results using natural populations is admirable. Nonetheless, correlative tests of experimental studies must be designed with statistical rigor and a thorough understanding of the original studies in order to provide valid tests of predictions. Ficetola & De Bernardi (2005) is flawed in this respect. The design in Ficetola & De Bernardi (2005) creates two biases toward accepting the null hypothesis that reproductive interference by R. dalmatina does not affect R. latastei in nature. Firstly, Ficetola & De Bernardi (2005) ignore the result that the relationship between species relative abundance and effectiveness of sexually isolating mechanisms is strongly non-linear (Hettyey & Pearman 2003). Abundance of R. latastei and R. dalmatina in the syntopic study populations of Ficetola and De Bernardi is estimated to be 1:1, 1:2, and 1:5. Hettyey & Pearman (2003) observe no significant decrease in fertilization success in trials, where R. latastei males are not outnumbered by R. dalmatina males by at least 1:5, probably because of the mitigating effect of mate recognition mechanisms. The results and model of Hettyey & Pearman (2003) predict significant decrease in average reproductive success in nature only when one species occurs at very low relative abundance. Decreased reproductive success where R. latastei’s relative abundance is 1:1 and 1:2 is not expected, thus grouping all syntopic populations together biases Ficetola and De Bernardi’s test. Further, absence of a bimodal distribution of embryo viability and no decrease in embryo viability in the one population where R. latastei was outnumbered by 1:5 would suggest that conspecific–heterospecific ratios be

Several experiments were performed to test the toxicity of FIT, a washing-up and general cleaning liquid containing about 10 % sodiumalkanemonosulfonate (industrial name E 30) to spawn and larvae of anura. The LC50 values for spawn were between 1.62 × 10−3 % (Rana dalmatina) and 4.97 × 10−3 % (Rana temporaria). The sensitivity of anuran larvae depends on the concentration and duration of exposure to the detergent as well as on the developmental and differentiation stage of the organisms. The toxicity of FIT is not due solely to the alkanesulfonate it contains, but results from the joint action of the surfactant, polyphosphates and solvents. The results indicate that detergents may be harmful to the amphibian fauna of Central Europe.

The effects of pH and aluminium on embryonic and early larval stages of Swedish brown frogs Rana arvalis, R. temporaria and R. dalmatina were tested in laboratory bioassays. In all three species egg mortality and time needed for embryonic development to hatching increased when pH declined, but no significant effects were found on embryonic development when aluminium level was elevated. In R. arvalis and R. temporaria larval mortality was affected by both pH and aluminium. In both species the frequency of occurrence of larval deformities increased in acid water, and there was a synergistic effect of pH and aluminium. In R. arvalis swimming behaviour was disturbed by high levels of aluminium at pH 5. In all three species the frequency of stressed larvae increased when pH was depressed and aluminium concentration elevated, and there was a synergistic effect when both were combined. The three species differed significantly in egg mortality, time needed for embryonic development, larval mortality, larval deformities and larval stress al low pH and high aluminium levels. R. arvalis showed the highest acid tolerance and R. dalmatina was the most sensitive to low pH.