Bufo Calamita Research Articles

In search of water: orientation behaviour of dehydrated natterjack toads, Bufo calamita

We analysed the water-finding ability of 12 natterjack toads, after mild dehydration, in an experimental environment (octagonal arena) which provided geo- and hydrotactic, magnetic, olfactory and visual cues for orientation. We tested the hypotheses that the water-finding ability is based on pilotage, using gradients of waterborne cues, and that the cues used for water orientation differ between individuals. Random search behaviour of naıve toads released in the arena showed that goal-oriented movements towards the exit leading to water required previous experience of the position of the water source. Thus, the water-finding ability of natterjacks is restricted to familiar areas. Physiological and behavioural responses to training and testing varied considerably between individuals: six toads became oedomatous and learned how to locate water, whereas the remaining six did not. We analysed the orientation behaviour of successfully trained toads in the training arena, when directional cues were removed or provided conflicting information, and present evidence for individuality in the use of orientation cues: three toads relied mainly on geotactic cues and olfactory pilotage, another mainly on visual landmarks and geomagnetic information, and another used all cues available without clear preference. In conclusion, to detect water, dehydrated toads rely on a multisensory orientation system, which is basically the same as that used during breeding migrations and includes several redundancies.

Application of Genetic Bottleneck Testing to the Investigation of Amphibian Declines: a Case Study with Natterjack Toads

Abstract: Declines of amphibians are causing widespread concern and in some cases have been explained by factors such as climate change and the spread of microbial pathogens. A problem remains, however, in the unequivocal demonstration of decline in situations where populations may be undergoing natural fluctuations in abundance. We describe the application of a genetic test for bottlenecks (Cornuet & Luikart 1996) that should distinguish between natural oscillations and true population declines. British natterjack toads ( Bufo calamita ) provide examples of populations that have not declined in recent decades, populations that have declined, and populations in which trends are unclear. Microsatellite allele frequency data from these populations were tested for heterozygote excess and shifts in allele frequency distributions, and inferences from these computations about bottlenecks (i.e., persistently smaller population sizes than the recent means) were compared with demographic information. The genetic test correctly identified bottlenecks and should therefore prove useful in demonstrating whether amphibian declines have occurred where long‐term demographic time series are not available.

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.

Developmental responses to pond desiccation in tadpoles of the British anuran amphibians (Bufo bufo, B. calamita and Rana temporaria)

AbstractTadpole development was compared in three amphibian species (Bufo calamita, B. bufo and Rana temporaria) that suffer different risks of pond desiccation in nature. Using a replicated pond system, development was monitored in desiccating and non‐desiccating ponds, and in vertical‐sided and gently shelving (‘shoreline’) ponds. In desiccating ponds, tadpoles suffered from crowding effects and metamorphosed at a smaller size, but development was not accelerated in response to desiccation in any of the three species. Desiccating ponds had higher maximum temperatures but also lower minimum temperatures, which may explain the lack of any difference in development time between desiccating and non‐desiccating ponds. Although shoreline ponds were slightly warmer than vertical‐sided ponds, development under these conditions was also consistent with a crowding, rather than a temperature, effect. In shoreline ponds, metamorphosis generally took longer, was less synchronized between individuals, and resulted in a smaller size at metamorphosis, compared to development in vertical‐sided ponds. The lack of species‐by‐desiccation interactions indicated that there were no differences between the three species in developmental plasticity. Developmental constraints may place a limit on the degree of plasticity that can evolve in a species such as B. calamita, which breeds only in ephemeral ponds with a variable hydroperiod. Alternatively, low genetic variability within British populations of B. calamita may have constrained the evolution of adaptive plasticity in this species.

Developmental responses to pond desiccation in tadpoles of the British anuran amphibians (Bufo bufo, B. calamita and Rana temporaria)

Tadpole development was compared in three amphibian species (Bufo calamita, B. bufo and Rana temporaria) that suffer different risks of pond desiccation in nature. Using a replicated pond system, development was monitored in desiccating and non-desiccating ponds, and in vertical-sided and gently shelving (‘shoreline’) ponds. In desiccating ponds, tadpoles suffered from crowding effects and metamorphosed at a smaller size, but development was not accelerated in response to desiccation in any of the three species. Desiccating ponds had higher maximum temperatures but also lower minimum temperatures, which may explain the lack of any difference in development time between desiccating and non-desiccating ponds. Although shoreline ponds were slightly warmer than vertical-sided ponds, development under these conditions was also consistent with a crowding, rather than a temperature, effect. In shoreline ponds, metamorphosis generally took longer, was less synchronized between individuals, and resulted in a smaller size at metamorphosis, compared to development in vertical-sided ponds. The lack of species-by-desiccation interactions indicated that there were no differences between the three species in developmental plasticity. Developmental constraints may place a limit on the degree of plasticity that can evolve in a species such as B. calamita, which breeds only in ephemeral ponds with a variable hydroperiod. Alternatively, low genetic variability within British populations of B. calamita may have constrained the evolution of adaptive plasticity in this species.

A microsatellite analysis of natterjack toad, Bufo calamita, metapopulations

Although it is widely recognised that spatial subdivision of populations is common in nature, there is no consensus as to how metapopulation dynamics affect genetic diversity. We investigated the genetic differentiation of natterjack toads, Bufo calamita, in three regions of Britain where habitat continuity indicated the likely occurrence of extensive metapopulations. Our intention was to determine whether genetic analysis supported the existence of metapopulation structures, if so of what type, and to identify barriers to migration between subpopulations. Allele frequencies were determined across eight polymorphic microsatellite loci for a total of 24 toad subpopulations at three separate sites. Genetic differentiation was assessed using five measures of genetic distance, notably FST, RST, Nei's standard distance Ds,Δμ2 and the Cavalli‐Sforza chord distance Dc. B. calamita exhibited small but significant levels of genetic differentiation between subpopulations in all three study areas, and genetic and geographic distance correlations indicated isolation‐by‐distance effects in all three cases. The effects on correlation strengths of compensation for positive (sea, rivers, urban development) and negative (pond clusters) barriers to toad migration between the subpopulations in each area were also determined. Dc, a measure which assumes that differentiation is caused by drift with negligible mutation effect, yielded the most plausible interpretation of metapopulation structures. Overall the patterns of genetic variation suggested the existence of a mixed metapopulation model for this species, with high levels of gene flow compatible with one version of the classical model but often supported by particularly stable subpopulations as in the mainland‐island model.

Microsatellite analysis of natterjack toad Bufo calamita Laurenti populations: consequences of dispersal from a Pleistocene refugium

Abstract Populations of the amphibian Bufo calamita were sampled for genetic analysis in eleven areas distributed across its biogeographical range in Europe. Genetic diversity estimates across eight microsatellite loci showed a decline in polymorphism, numbers of alleles and heterozygosity as a function of distance from the presumed ice-age refugium in Iberia. Trials with a selection of tree-building algorithms indicated that UPGMA of Cavalli-Sforza chord distances ( D c ) generated the tree topology most easily reconciled with other biogeographical information. Genetic distance measures were also calibrated against a postglacial event from which the separation of extant populations could be estimated in real time. D c again outperformed two other measures (Nei's standard distance, D s , and δμ 2 ) in producing realistic correlations with minimal variance. The genetic analysis was consistent with the hypothesis that B. calamita survived in a single refugium (Iberia) during the Pleistocene glaciation and indicated that it spread north and east from there during the last interstadial which commenced about 14 000 years before present (BP). Microsatellites should provide useful tools for biogeographical investigations of other species, especially with respect to patterns of population dispersal.

Microsatellite analysis of natterjack toad Bufo calamita Laurenti populations: consequences of dispersal from a Pleistocene refugium

Populations of the amphibian Bufo calamita were sampled for genetic analysis in eleven areas distributed across its biogeographical range in Europe. Genetic diversity estimates across eight microsatellite loci showed a decline in polymorphism, numbers of alleles and heterozygosity as a function of distance from the presumed ice-age refugium in Iberia. Trials with a selection of tree-building algorithms indicated that UPGMA of Cavalli-Sforza chord distances (Dc) generated the tree topology most easily reconciled with other biogeographical information. Genetic distance measures were also calibrated against a postglacial event from which the separation of extant populations could be estimated in real time. Dcagain outperformed two other measures (Nei's standard distance,Ds , and δμ2) in producing realistic correlations with minimal variance. The genetic analysis was consistent with the hypothesis that B. calamita survived in a single refugium (Iberia) during the Pleistocene glaciation and indicated that it spread north and east from there during the last interstadial which commenced about 14 000 years before present (BP). Microsatellites should provide useful tools for biogeographical investigations of other species, especially with respect to patterns of population dispersal.

Morphological and life history responses to predators in larvae of seven anurans

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.

Terrestrial movements of the natterjack toad Bufo calamita (Amphibia, Anura) in a semi-arid, agricultural landscape

AbstractThe movements of 19 natterjack toads (Bufo calamita) were monitored by telemetry in a semi-arid agricultural landscape in NE Spain. Toads reproduced in two water pools in fields of barley and an ancient clayquarrying zone filled by rainfall. Thirteen toads were followed during the breeding season (weeks 5-17 of 1997) and 11 toads were followed after reproduction (weeks 18 to 46). During the breeding season four toads moved distances of up to 500 m between breeding sites. No significant differences in movement patterns were found between the sexes, but a tendency was observed for males to show higher terrestrial site fidelity than females. Distances moved after the breeding season were substantial. The distance between the furthest positions recorded was from 164 to 1201 m, the maximum distance observed between daily recordings ranged from 125 to 353 m and the maximum overall distances ranged from 567 to 4411 m. No significant differences were observed between males and females or between small and large toads. The movements of these toads in a semi-arid agricultural landscape in Spain are compared with those observed in England and Germany.

The influence of tadpole size on cell-mediated competition between anuran larvae Bufo calamita and Rana temporaria) in the laboratory

AbstractThe faeces of tadpoles frequently contain cells that can inhibit the growth of other individuals. We examined the mechanism of such cell-mediated interference competition in interactions between tadpoles of Rana temporaria and Bufo calamita. When R. temporaria and B. calamita tadpoles were exposed to cell-laden faeces from larger R. temporaria tadpoles, growth was inhibited relative to controls. Tadpoles of B. calamita remained susceptible to the inhibitory effects of the cells for longer during development than those of R. temporaria. In the presence of excess food, cell production by both species was related to stage of development. Tadpoles raised with cell-laden faeces from R. temporaria tadpoles produced more cells/tadpole/hour than those raised without competitor faeces, and smaller tadpoles were more inhibited than larger tadpoles.

A further four polymorphic microsatellite loci in the natterjack toad Bufo calamita

A further four polymorphic microsatellite loci in the natterjack toad Bufo calamita

Effects of Ultraviolet Radiation on Amphibian Embryonic and Larval Development

Effects of ultraviolet radiation on hatching success, larval survival, and induced abnormalities were tested in three threatened (Hyla arborea, Bufo calamita, and Triturus cristatus) and two common (Rana temporaria and Bufo bufo) amphibians of Sweden. In the laboratory, all species were exposed to artificial UV-radiation (intensities corresponding to midsummer conditions in Sweden) or visible light (controls) for ten days, during which hatching occurred. The effects of ambient levels of UV-radiation on hatching success and survival of B. bufo, R. temporaria, and B. calamita were also determined during outdoor conditions when exposed to three different light regimes: Full solar radiation, UV-filtered sunlight (exposed to photo- synthetically active radiation only) or darkness. In the laboratory experiment, neither eggs nor larvae of R. temporaria, B. bufo, B. calamita, and H. arborea were negatively affected by UV-radiation. However, UV-radiation induced darker pigmentation in tadpoles of H. arborea. Only one species, T cristatus, showed reduced hatching frequencies and lower larval survival when exposed to UV-radiation in comparison to visible light. However, since female T cristatus wrap their eggs in macrophyte leaves, embryos are effectively protected against solar radiation. In the outdoor exper- iments, there were no differences between the light treatments for any of the species. Thus, none of these species are likely to be threatened by moderately increased levels of ultraviolet radiation.

Microsatellite heterozygosity, fitness and demography in natterjack toads Bufo calamita

AbstractRelationships between mean individual fitness and genetic heterozygosity remain controversial because multiple studies over many years have yielded inconsistent results. However, molecular measurements of genetic variation have mostly been based on allozyme markers, which may have substantial limitations due to their relative insensitivity and occasionally also to the effects of natural selection. We investigated variation in the number of tandem dinucleotide repeats at eight polymorphic microsatellite loci in 38 natterjack toad, Bufo calamita, populations that varied in census size, degree of isolation and distance from the distributional range edge. We also measured fitness attributes, notably larval survival and growth rates, under standardized conditions using samples from six of these populations. The results indicated that larval growth rates were positively and strongly correlated with expected heterozygosity (He) across the microsatellite loci. He was in turn highest in large populations with minimal isolation, but low near the biogeographical range edge irrespective of population size. Larvae from the smallest and most isolated natterjack population exhibited particularly low fitness and heterozygosity. Our results suggest that microsatellite loci may provide a valuable new approach in studies of links between fitness and heterozygosity.

Microsatellite heterozygosity, fitness and demography in natterjack toads Bufo calamita

Microsatellite heterozygosity, fitness and demography in natterjack toads Bufo calamita

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.

Phylogeography of the natterjack toad Bufo calamita in Britain: genetic differentiation of native and translocated populations

The natterjack toad Bufo calamita is rare in Britain, which is at the northwestern edge of its biogeographical range. We investigated the level of genetic differentiation amongst almost all (34 out of 38) of the surviving British populations of this species, and among six new populations established by translocations during the 1980s. For eight microsatellite loci, allele sizes and frequencies were analysed using samples from each of these populations. The populations clustered into three robustly differentiated groups, each of which corresponded with a geographical region (east/southeast England, Merseyside and Cumbria). The Cumbrian populations showed a further weak geographical substructuring into northern and southern clades. The populations in south Cumbria were genetically more diverse than those in any of the other regions, as judged by the mean numbers of alleles per locus and the mean heterozygosity estimates. The translocated populations clustered close to their founders and, with one exception, did not differ significantly with respect to mean allele numbers, heterozygosity or polymorphism level. However, significant genetic differentiation (as measured by unbiased RST) was found between all but one of the founder‐translocation pairs. The implications of this phylogeographic study for the future conservation of B. calamita in Britain are discussed.

Archive contributions to a molecular phylogeography of the toad Bufo calamita in Britain.

A complete phylogeographic analysis of any species requires sampling throughout its biogeographical range. In the case of the natterjack toad Bufo calamita in Britain, recent local extinctions have left substantial areas of its historical range without extant populations. We therefore obtained tissue samples of archived Bufo calamita from four museums in the United Kingdom. A range of tissues (tongue, liver, skin, lung, and larval tail) was sampled from a total of 33 individual animals. DNA was extracted and eight polymorphic microsatellite loci were scored. One or more loci were amplified successfully from 27 individuals, and sufficient data were obtained from regions with few or no surviving populations to supplement a phylogeographic analysis based on extant populations.

Reaction norms for metamorphic traits in natterjack toads to larval density and pond duration

AbstractThe evolution of environmentally‐induced changes in phenotype or reaction norm implies both the existence at some time of genetic variation within a population for that plasticity measured by the presence of genotype x environment interaction (G x E), and that phenotypic variation affects fitness. Otherwise, the genetic structure of polygenic traits may restrict the evolution of the reaction norm by the lack of independent evolution of a given trait in different environments or by genetic trade‐offs with other traits that affect fitness. In this paper, we analyze the existence of G x E in metamorphic traits to two environmental factors, larval density and pond duration in a factorial experiment with Bufo calamita tadpoles in semi‐natural conditions and in the laboratory.Results showed no plastic temporal response in metamorphosis to pond durability at low larval density. The rank of genotypes did not change across different hydroperiods, implying a high genetic correlation that may constrain the evolution of the reaction norm. At high larval density a significant G x E interaction was found, suggesting the potential for the evolution of the reaction norm. A sibship (#1) attained the presumed “optimal” reaction norm by accelerating developmental rate in short duration ponds and delaying it in longer ponds. This could be translated in fitness by an increment in metamorphic survival and size at metamorphosis in short and long ponds respectively with respect to non‐plastic sibships. However, genetic variability for plasticity suggests that optimal reaction norm for developmental rates may be variable and hard to achieve in the heterogeneous pond environment.Mass at metamorphosis was not plastic across different pond durations but decreased at high larval density. Significant adaptive plasticity for growth rates appeared in environments that differed drastically in level of crowding conditions, both in the field and in the laboratory. The fact that survival of juveniles metamorphosed at high density ponds was a monotonic function of metamorphic size, implies that response to selection may occur in this population of natterjacks and that genetic variability in plasticity may be a reliable mechanism maintaining adaptive genetic variation in growth rates in the highly variable pond environment.

Postmetamorphic dispersal and recruitment of first breeders in a Bufo calamita metapopulation.

The migratory capacity of metamorphs and their later integration into local breeding populations was studied in a Bufo calamita metapopulation inhabiting the northern Rhineland, Germany (1991-1994). A new tagging method allowed unequivocal distinction among metamorphs (n = 1,709), which originated either from the spring-breeding cohort in 1991 and 1992 or from the summer-breeding cohort in 1991. The life history of batch-marked individuals was followed until adulthood, focusing on postmetamorphic dispersal, choice of breeding locality and timing of adult reproduction. Almost all metamorphs left the patches used for breeding within a few weeks after emergence. They were found at about the same density in all favourable microhabitats in a radius of up to 2 km around their native patch. This demonstrates that even small toadlets (6-11 mm snout-to-vent length) migrate distances of several hundred metres within a short time and that they significantly help prevent local extinction in sink populations (rescue effect). Recaptures of reproductive adults originating from tagged metamorphs were limited to males belonging to the 1997 spring and summer cohorts. The absence of recaptured females was probably due to their greater vagility and later sexual maturation. First-breeding males (2 years old) without exception joined the breeding cohort from which they originated: early breeders originated from spawn of the spring cohort, mid-summer breeders from spawn of the summer cohort. This result is in accordance with the hypothesis that the integration of first breeders to a specific breeding cohort is genetically controlled in central European natterjacks. The exchange of individuals between different cohorts in the same patch is considerably less than the migratory exchange between the same breeding cohorts among local populations, as predicted from the allozyme data.