Common Toad Bufo Research Articles

The effects of solar UV-B radiation on embryonic mortality and development in three boreal anurans ( Rana temporaria, Rana arvalis and Bufo bufo)

Many species of amphibians have experienced population and range reductions. It has been hypothesized that sensitivity to UV-B may contribute to the population declines of some amphibian species. We performed field experiments to measure the effects of solar UV-B on the hatching success of three Finnish anuran species, the common frog ( Rana temporaria), moor frog ( Rana arvalis) and common toad ( Bufo bufo). Further, the effects of natural UV-B radiation on survival of the tadpoles of the same three species of anurans were tested. A significant percentage of R. temporaria and B. bufo embryos survived when exposed to and protected from solar UV-B and hatching success was not affected by solar radiation. Elimination of solar UV-B significantly increased the hatching success of R. arvalis, but embryonic mortality was high in both treatments. The data indicates that under natural conditions, solar UV-B radiation influences embryo survival in R. arvalis, but has no effect on R. temporaria and B. bufo. Solar UV-B radiation had no effect on R. temporaria and R. arvalis tadpoles, but elimination of UV-B significantly increased survival of B. bufo tadpoles. It seems that ambient UV-radiation levels have no effect on R. temporaria but may affect R. arvalis and B. bufo at different developmental stages.

Environmental correlates of toad abundance and population genetic diversity

Knowledge of factors that affect population demographic and genetic characteristics is of importance to the development of conservation strategies. Using field and remote sensing of microgeographic and landscape-level features of the aquatic and terrestrial environment, we examined the degree to which habitat characteristics were correlated with population demographic and genetic characteristics in the common toad ( Bufo bufo). Measures of genetic diversity and departures from random mating are described for 20 semi-isolated breeding populations of B. bufo from Leicestershire, Great Britain, based on three species-specific single locus variable number of tandem repeat minisatellite loci. Spatial autocorrelation of allele frequencies revealed significant population structuring or lack of independence in allele frequencies over inter-breeding pond intervals of ⩽2 km. Such estimates of “patch size” which are inferred from correlograms, may be useful in defining the extent of effective gene flow and spatial scales over which landscape-level features could plausibly be used to characterize ecological attributes of importance to individuals from specific local breeding populations. Toad presence or absence at amphibian breeding ponds, population size, and population estimates of observed heterozygosity, allelic richness, and Wright's inbreeding coefficient ( F) were individually used as dependent variables in analyses with aquatic and terrestrial habitat characteristics. Inter-population variation in inbreeding coefficients was significantly related to presence of additional ponds near each breeding site. Allelic richness, population size, and toad presence/absence were primarily associated with terrestrial habitat variables, including pond density and vegetative characteristics reflecting surrounding land use (e.g. presence of woodlands, hedgerows, extent of area in livestock [sheep] pasture, and anthropogenic development). In the absence of definitive population demographic data, specific habitat characteristics may offer predictive potential for inferring population characteristics and future viability. However, the choice of ecologically and evolutionarily relevant habitat characteristics should be made with care.

Genetic differentiation of the common toad (Bufo bufo) in the Swiss Alps

AbstractWe analysed the genetic differentiation of tadpoles from 24 Swiss populations of Bufo b. bufo and B. b. spinosus, using horizontal starch gel electrophoresis of eight enzymes coded by ten loci. For comparison, we included ten populations from more distant localities. Populations of Bufo calamita were included as outgroup. A very low level of genetic differentiation was found among populations from the Alpine region, including B. b. bufo populations from the Czech Republic and northern Germany, and B. b. spinosus populations from northern Italy. Genetic differentiation within populations was much higher than differentiation among populations or regions. In contrast, the southern French B. b. spinosus populations were clearly differentiated by allele substitution at three out of ten loci scored. These alleles of the French populations, however, were also found in low frequencies in some populations from western Switzerland and Italy. This is interpreted to result from gene flow. Morphometric data of adult B. bufo (13 populations, 174 adult toads) turned out to be strongly size dependent. However, relative arm length and density of large warts ventral to the parotoids showed differences between the two subspecies.

A sleep inducing factor from common Indian toad ( Bufo melanostictus, Schneider) skin extract

Bufo melanostictus (common Indian toad) acquire different bioactive substances in their skin during their life-time in wide ecological habitat. Earlier investigation from this laboratory revealed that toad ( B. melanostictus) skin extract (TSE) posses different bioactive compounds of different diversity (Das, M., Auddy, B. and Gomes, A., 1996. Pharmacological study of the toad skin extract on experimental animals. Indian J. Pharmacol. 28, 72–76). Among these sleep induction and sleep potentiation indicated the possibility of sleep inducing factor(s) in TSE. One such sleep inducing factor (SIF) was isolated and purified by neutral alumina column chromatography followed by HPLC. Spectroscopy (UV, IR, FAB-MASS) study indicated that the sleep inducing factor was a 880 Dalton conjugated aromatic compound with a hydroxyl and carbonyl functional group. Biological study showed that SIF produced no lethality in male albino mice upto the dose of 8 mg/kg, i.v. Cyproheptadine antagonised SIF induced contraction of isolated smooth muscle indicating histamine/serotonin receptor mediated action of SIF. EEG studies showed that SIF increased sleep and decreased awakening condition of freely moving rats. Biochemical studies showed that SIF produced significant alteration of brain biogenic amine levels, monoamine oxidase (MAO) and tryptophan hydroxylase (TH) activity. This may be the reason of SIF induced sleep, although the SIF induced sleep mechanism needs further detail investigation.

Competitive ability and the coexistence of anuran larvae in freshwater rock‐pools

1 I examined the competitive ability of larval common frogs (Rana temporaria) and common toads (Bufo bufo) in a laboratory experiment by manipulating the number and size of Rana and the number of Bufo. 2 Bufo was the most active tadpole type, whereas small Rana was more active than large Rana. 3 Especially at high food availability, the growth rate of large Rana at metamorphosis was reduced in the presence of small Rana, whereas that of small Rana was not affected by larger conspecifics. 4 Both size classes of Rana were negatively affected by the presence of Bufo. Size at metamorphosis of Bufo was greater when large Rana was present. These results suggest that activity level is important in determining competitive ability. 5 To study competition in the field, tadpoles of Bufo were introduced to small rock-pools that did not support Bufo naturally, but were with or without Rana. 6 In the experimental pools, there were no interspecific effects on the growth rate of either species. However, the growth rate of Bufo was lower in the experimental pools than in pools inhabited naturally. Futher, survival of Bufo was low in small pools. Lower food availability or physical factors associated with small pools, rather than interspecific competition, may be the reason why Bufo avoids breeding in small rock-pools.

Impacts of climate and density on the duration of the tadpole stage of the common toad Bufo bufo

In an ongoing long-term study of a breeding population of common toads Bufo bufo at a pond in southern England, the dates of first spawning have been recorded since 1980, the dates of toadlet emergence since 1984, and the numbers of emergent toadlets estimated since 1988. The dates when spawn was first laid varied considerably between years from the earliest on 2 February 1993 (day 33) to the latest on 19 March 1996 (day 79). The duration of the tadpole stage was negatively correlated with the date of appearance of first spawn and was up to 30 days longer in early spawning years than in late ones. Despite this, toadlets still emerged from the natal pond up to 36 days earlier in early spawning years than in late ones. Significant positive correlations were found between the duration of the tadpole stage and both the proportion of days during the tadpole stage when the minimum ground temperature was at or below 0°C and the proportion of days when 10 mm or more rain fell. Tadpole mortality was positively correlated with the proportion of days during the tadpole stage when the minimum ground temperature was at or below 1.5°C. Evidence was also found to suggest that tadpole mortality was density-dependent, being proportionately higher when initial tadpole numbers were high than when they were low.

Detecting Publication Bias in Meta-analyses: A Case Study of Fluctuating Asymmetry and Sexual Selection.

Those familiar with human nature and the publication process acknowledge that biases due to selective reporting of results are likely widespread in all fields of academic inquiry that depend on tools of statistical inference (e.g., see Begg and Berlin 1988; Iyengar and Greenhouse 1988; and the extensive discussion following each). However, although qualitative and quantitative methods exist for assessing the prevalence of selective reporting, and selective reporting has been studied in the medical and social sciences (Begg 1994, and references therein), the issue has received little attention in recent meta-analyses of ecological and evolutionary patterns. Clearly, “if publication bias is present, and if it operates in the same direction for all studies (as is likely), then [meta-analysis] is likely not only to produce biased summary estimates but also to produce estimates which are apparently precise and accurate leading to conclusions which may not only be wrong but appear convincing” (Begg and Berlin 1988, p. 437). To biologists unacquainted with the formal study of publication patterns, the terms “selective reporting” (statistical significance of an outcome influences its likelihood of being reported or published) and “publication bias” (the inflation of average effect size due to selective reporting) may imply a conscious intent to deceive, but this

Genetic structure of island populations of the anurans rana temporaria and bufo bufo

Amphibians have traditionally been considered to have low dispersal ability and they have become a model for studies on the effects of man-made habitat fragmentation on genetic variation and population differentiation. This study examined the genetic population structure in the common frog (Rana temporaria) and the common toad (Bufo bufo) in an archipelago of the northern Baltic Sea. Heterozygosity was not correlated with distance of the island from the mainland nor, in R. temporaria, with effective population size based on census estimates. Generally, no inbreeding was detected in island populations. The overall differentiation among islands was weak, but the FST values were significantly larger in R. temporaria (FST = 0.068) than in B. bufo (FST = 0.019). Most of the differentiation was a result of differences among groups of islands, differentiation within them playing a minor role. Thus, assuming Wright's island model of migration, gene flow was rather high among closely located islands, but longer distances seemed to form a slight dispersal barrier for R. temporaria. Strong gene flow within the study area was confirmed by lack of isolation by distance. The estimated effective population sizes in R. temporaria were small, the average being 32 breeding females per island. The results indicate that gene flow between island populations across the matrix of open, brackish-water sea is extensive and suggest that the anurans are well able to disperse in this natural metapopulation system.

Amphibian Species Diversity in Kurtuvėnai Regional Park

The main habitat types in Kurtuvėnai Regional Park (KRP) were sampled for amphibians in 1997-1998. Presence or absence of the species was documented using visual encounter surveys, line counting and larval sampling. Overall, 10 species were found. Predominant species in KRP forests and meadows are common toad (Bufo bufo) and grass frog (Rana temporaria), in ponds and lakes – little water frog (Rana lessonae). Only two localities of crested newt (Triturus cristatus) and one of green toad (Bufo viridis) were found in KRP. According to indicators of biological diversity, the diversity of the amphibians observed in KRP is quite high (H = 2.502, λ = 0.209).

The effect of winter temperatures on the timing of breeding activity in the common toad Bufo bufo.

A 19-year study of a common toad population in south Dorset, UK, was carried out between 1980 and 1998. The daily arrival of sexually mature male and female toads at a breeding pond was recorded each year. The timing of the main arrival of toads at the breeding pond was highly correlated with the mean daily temperatures over the 40 days immediately preceding the main arrival. When the temperatures were higher than average, breeding occurred significantly earlier in the year than if they were either average or lower than average. During the study, the toad breeding seasons were early (2-13 February) in 5 years (1989, 1990, 1993, 1995, 1998), late (16-23 March) in 2 years (1986, 1996) and average (25 February-8 March) during the remaining 12 years. Evidence was found suggesting that common toads have a daylength threshold of about 9 h, below which the migration to the breeding pond does not occur. Evidence was also found indicating that common toads in southern England have a threshold temperature for activity of about 6°C and that the onset of breeding activity is highly correlated with the number of days during the 40 days prior to the main arrival at the breeding pond that were at or above this temperature. Predicting the start of the main breeding migration to a pond in any year may be possible by comparing the pattern of the 40-day running mean daily temperatures from 21 December the preceding year with those from previous years when the start of breeding activity is known. Although all five of the earliest recorded toad breeding years occurred during the last 10 years, and were associated with the occurrence of particularly mild winters, a significant trend towards earlier breeding in recent years compared with previous years was not found.

Breeding habitat selection and larval performance of two anurans in freshwater rock‐pools

I studied breeding habitat choice of common toad Bufo bufo and common frog Rana temporaria in 221 freshwater rock‐pools on 15 small islands in the southwestern coast of Finland. I monitored tadpole growth rate in a number of rock‐pools differing in size, competitors and predator regime. Furthermore, I carried out a short‐term field experiment to investigate the effects of different predators on larval survival. Rana bred in pools of virtually all sizes, although the very smallest ones were usually avoided. A logistic regression analysis showed that the amount of aquatic macrophyte vegetation and pool surface area were the most important pool characters for Rana. Bufo preferred the largest pools, and pool surface area was by far the most important habitat variable. Rana avoided pools with the lowest pH. but was more common than expected at pools with pH around 6. In Bufo such an effect was not found, but this may be due to relatively low number of pools occupied by Bufo. In Rana there was a positive correlation between pool area and tadpole body length in early June, but two weeks later this relationship was not significant. In Bufo tadpole body size was not significantly affected by pool area. Presence of predators or presence of the other tadpole species did not affect growth or tadpole body size in either Rana or Bufo. A short‐term experiment in wading pools indicated that both species suffered heavy mortality in the presence of a diving beetle larva. In the presence of predatory fish, mortality of Bufo did not differ from controls, whereas mortality was high among Rana tadpoles. It appears that although predators prey heavily on Rana tadpoles, they do not exclude Rana from larger rock‐pools. However, it is not evident from this study why Bufo avoids smaller pools.

The effect of social interactions on tadpole activity and growth in the British anuran amphibians (Bufo bufo, B. calamita, and Rana temporaria)

AbstractTadpoles of different species of frogs and toads display different tendencies to aggregate. We investigated some of the costs and benefits of aggregating in three British species by examining their behavioural responses to the presence of conspecifics, and by monitoring the performance of tadpoles under different levels of social interaction with other individuals. The common toad (Bufo bufo), an aggregating species, displayed higher levels of activity than the natterjack toad (B. calamita) and common frog (Rana temporaria), two species that form aggregations less frequently. Moreover, out of the three species, only B. bufo increased activity in the presence of conspecifics. In all three species, increased interaction between individuals resulted in increased variation in size. However, average growth rate was affected only in B. bufo, which grew faster when raised in isolation and not interacting with other individuals. Under certain conditions intraspecific competition therefore seems to be more important than social facilitation, but may lead to average size at metamorphosis being larger within the population. The consequences of intraspecific competition within aggregations may therefore be different for individuals and populations.

Loss of genetic diversity and fitness in Common Toad (Bufo bufo) populations isolated by inimical habitat

AbstractMeasures of genetic diversity (including heterozygosity), survival and developmental homeostasis were found to be significantly lower in small, urban populations of the Common Toad (Bufo bufo) than in larger, rural populations of the same region. The autecology and genetic analysis of this relatively sedentary species suggested that the causal mechanism was genetic drift, arising from barriers to migration created by urban development. The pre‐metamorphic survival of larvae cultured in identical conditions increased positively with the mean number of alleles at a locus and the percentage of polymorphic loci. Observed heterozygosity in urban garden and rural populations was correlated inversely with the number of observed physical abnormalities (used as a measure of developmental homeostasis) in the developing tadpoles. Genetic distances between town sites of mean 2.2 km separation were significantly higher than those between rural sites of mean 37 km separation. Genetic data were based on allozyme analysis of 27 loci in 8 urban and 4 rural populations. A subset of these sites (3 urban, 2 rural) were also assessed at 3 minisatellite loci and a positive correlation found between the average number of alleles per locus detected by the two methods. Estimates of Nei's 1972 genetic distance, derived separately from the DNA and protein data, were not, however, correlated. The reduction in genetic diversity and fitness observed in these urban toads provides an example of the effect on population persistence that longer term depletion in numbers and habitat fragmentation can have in the wider environment.

Temperature but not season affects the transplantation immunity of anuran amphibians

The effects of ambient temperature (22 degrees C/10 degrees C) and season (summer/winter) on anuran skin allograft and xenograft rejection was tested in frogs (Rana temporaria and R. esculenta) and toads (Bufo bufo, Bombina variegata, and Bombina bombina). Mean graft survival times were significantly prolonged at the low temperature in a species-specific manner, the edible frog (R. esculenta) being the most sensitive and the common toad (Bufo bufo) relatively resistant. Allografts were more temperature-dependent than xenografts; in the latter case, temperature sensitivity was specific to each donor-host combination. Rejection of second-set grafts in R. esculenta was accelerated both in warmth and in cold, but second-set grafts were less temperature-sensitive than sensitizing ones. Both in summer and in winter, R. esculenta rejected allografts promptly at 22 degrees C but slowly at 10 degrees C. In both seasons, Bombina variegata kept at 22 degrees C rejected allografts in a chronic manner. This indicates that amphibian transplantation immunity depends on the donor-host genetic disparity and ambient temperature but is independent of season.

Lethal and Sublethal Effects of Nitrogen Fertilizer Ammonium Nitrate onCommon Toad (Bufo bufo) Tadpoles

The impact of elevated ammonium nitrate concentrations onthe survival and development of common toad (Bufo bufo) tadpoles wasinvestigated in the laboratory. 1,704 mg/L and 1,637 mg/L nitrate (equivalentto 2,198.7 mg/L and 2,112.3 mg/L ammonium nitrate) were recorded as 96 h and168 h LC50s respectively. These are well above field levels (10-250 mg/L)observed in freshwater in Britain. The exposure of tadpoles to nominalconcentration of 100 mg/L nitrate for 24, 48, and 72 h caused a significantdecrease in their activity but no clear reduction in food consumption ordelay of the development. In subchronic exposures at the nominalconcentrations of 50 and 100 mg/L nitrate, the metamorphosis started earlierand took less time to complete than in the control. However, some of theresults were equivocal, at 50 mg NO3/L the metamorphs weresignificantly larger than the controls, while at 100 mg NO3/Lmetamorphs were not significantly different from the controls. Certaindeformities and unusual swimming patterns were also found in tadpoles exposedto various concentrations of ammonium nitrate.

An Evaluation of Some Marking and Trapping Techniques Currently Used in the Study of Anuran Population Dynamics

An Evaluation of Some Marking and Trapping Techniques Currently Used in the Study of Anuran Population Dynamics

Effective number of breeding adults in Bufo bufo estimated from age-specific variation at minisatellite loci.

Estimates of the effective number of breeding adults were derived for three semi-isolated populations of the common toad Bufo bufo based on temporal (i.e. adult-progeny) variance in allele frequency for three highly polymorphic minisatellite loci. Estimates of spatial variance in allele frequency among populations and of age-specific measures of genetic variability are also described. Each population was characterized by a low effective adult breeding number (Nb) based on a large age-specific variance in minisatellite allele frequency. Estimates of Nb (range 21-46 for population means across three loci) were approximately 55-230-fold lower than estimates of total adult census size. The implications of low effective breeding numbers for long-term maintenance of genetic variability and population viability are discussed relative to the species' reproductive ecology, current land-use practices, and present and historical habitat modification and loss. The utility of indirect measures of population parameters such as Nb and Ne based on time-series data of minisatellite allele frequencies is discussed relative to similar measures estimated from commonly used genetic markers such as protein allozymes.

Different antipredator behaviour in two anuran tadpoles: effects of predator diet

Recent investigations have indicated that animals are able to use chemical cues of predators to assess the magnitude of predation risk. One possible source of such cues is predator diet. Chemical cues may also be important in the development of antipredator behaviour, especially in animals that possess chemical alarm substances. Tadpoles of the common toad (Bufo bufo) are unpalatable to most vertebrate predators and have an alarm substance. Tadpoles of the common frog (Rana temporaria) lack both these characters. We experimentally studied how predator diet, previous experience of predators and body size affect antipredator behaviour in these two tadpole species. Late-instar larvae of the dragonfly Aeshna juncea were used as predators. The dragonfly larvae were fed a diet exclusively of insects, R. temporaria tadpoles or B. bufo tadpoles. R. temporaria tadpoles modified their behaviour according to the perceived predation risk. Depending on predator diet, the tadpoles responded with weak antipredatory behaviour (triggered by insect-fed predators) or strong behaviour (triggered by tadpole-fed predators) with distinct spatial avoidance and lowered activity level. The behaviour of B. bufo in predator diet treatments was indistinguishable from that in the control treatment. This lack of antipredator behaviour is probably related to the effective post-encounter defenses and more intense competitive regime experienced by B. bufo. The behaviour of both tadpole species was dependent on body size, but this was not related to predator treatments. Our results also indicate that antipredator behaviour is largely innate in tadpoles of both species and is not modified by a brief exposure to predators.

Crayfish predation on amphibian eggs and larvae

Abstract We experimentally evaluated the impact of the introduced signal crayfish (Pacifastacus leniusculus) and the native noble crayfish (Astacus astacus) on eggs and larvae of seven species of amphibians, likely to co-occur with crayfish in southern Sweden. In aquarium experiments eggs and tadpoles of all amphibian species were consumed by both crayfish species. The consumption of amphibian eggs by signal crayfish increased with temperature. The noble crayfish consumed more tadpoles than the signal crayfish, but the latter caused more sub-lethal damage to tadpoles. Tadpoles of the common toad (Bufo bufo) were sometimes killed but left uneaten by both crayfish species. In pool experiments, signal crayfish consumed more tadpoles of Hyla arborea in a less complex habitat and significantly reduced survival of Hyla tadpoles and the biomass of aquatic macrophytes.

Cost effective drift fences for toads and newts

Abstract The construction, cost and performance of toad and newt drift fences and associated traps used at three study sites is described. Fence efficiency, in terms of the capture of animals immigrating to breeding sites, was calculated to lie between 39 and 63% of the estimated breeding population for the common toad (Bufo bufo), and between 45 and 61% for the crested newt (Triturus cristatus). Fences were consistently less efficient at intercepting emigrating animals; less than 10% of toads and between 34 and 40% of newts were captured. Cost and performance of the systems are compared with data from the literature.