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. Received: 16 July 1998 / Accepted: 14 September 1998     

Breeding pond fidelity in the common toad, Bufo bufo

Two independent studies of adult common toad, Bufo bufo , movements between different spawning ponds/populations both within and between years were made in England and Sweden during the spring breeding periods of1987–1990. The results of the two studies were subsequently combined since they were found to be complementary. In addition, in England during 1984 and 1985, large numbers of 'toadlets' were marked so that they could be identified if recaptured as breeding adults.
The degree of relocation between ponds was negatively correlated to the distance between ponds. The proportion of both males and females that moved between ponds within a particular year was significantly less than the proportion relocating between years. In any year, between 79% and 96% of adults that survived to breed the following year, returned to the original pond. Similarly, of the toadlets marked during1984–85, 81% of the males that subsequently returned as breeding adults were captured in their pond of origin.
Isolation, in relation to both population dynamics and population genetics, is defined and its implications for the management of common toad populatins discussed.     

Changes in the Oscillatory Electric Potential on the Olfactory Epithelium and in Reproductive Hormone Levels during the Breeding Season in the Toad (Bufo japonicus)

A slow transient electric potential change (electro-olfactogram, EOG) can be recorded through an Ag-AgCl electrode placed on the olfactory epithelium in response to stimulation with an air stream to the tissue in toads (Bufo japonicus). During the breeding season, oscillatory potential changes (OSC) superimpose on the EOG. In the present study the OSC amplitude was found to be highly correlated with the migratory behavior. Since toads track the route to and from the breeding pond using olfactory cues along the migration route, the enhanced OSC should be responsible for the breeding migration.A significant positive correlation was found between plasma gonadotropin levels and the OSC amplitude in males captured during the breeding migration. There was no significant relationship between plasma gonadotropin levels and the OSC amplitude in female toads during the breeding season, but there was a significant correlation between plasma progesterone levels and the OSC amplitude. In males, hypophysectomy just before the breeding season decreased the OSC amplitude. And testis weight was also positively correlated with the OSC amplitude in January. These results suggest that the appearance of the OSC is related to the timing of the activation of the reproductive system. However, treatment of toads with hCG (human chorionic gonadotropin), testosterone, estradiol or progesterone in the non-breeding season did not induce a significant change in the OSC amplitude. Other factor or factors may be required in activation of the olfactory system of the toad in a non-reproductive stage together with the hormones of the gonadal axis.     

Interspecific spawning between Common frogs (Rana temporaria) and Common toads (Bufo bufo)

The interaction between Common frogs (Rana temporaria) and Common toads (Bufo bufo) during the breeding season was studied at a small pond on Portland, Dorset. Although the frogs started and finished spawning earlier than the toads there was a period during which interspecific spawning between female toads and male frogs took place. This appears to have resulted from reduced male toad activity caused by the cold breeding season given that spatial, temporal and behavioural species separation did not occur.     

Non-random mating by size in American toads, Bufo americanus

Male American toads, Bufo americanus, captured in amplexus at least once during the season were significantly longer than males captured only singly in the same breeding population in all three cases studied. Absence of any correlation between the body lengths of the members of amplexing pairs argues against selection for optimal relative size. Males successful at breeding were those that (1) were larger, (2) were at the pond more nights, and (3) spent more time calling than unsuccessful males. Residency, per se, did not enhance breeding success, however, as on any given day successful males were equally likely to come from recaptured males previously present at the pond and unmarked males presumed new to the pond. Amount of movement about the pond did not vary with breeding success; all males tended to remain in one area on any given night and to change areas between nights. A very low displacement rate (about 7%) of males in amplexus argues against primacy of this form of male-male competition in producing differential mating by size. Rather it appears that some combination of other forms of intrasexual competition and female choice caused the mating pattern seen.     

The relationship between body length, age and sexual maturity in the common toad, Bufo bufo

An investigation of the relationship between the onset of sexual maturity, age and body size in common toads Bufo bufo was started in 1984 at a pond in southern England. During the toad breeding seasons of 1984 and 1985, 7259 common toad'metamorphs'were captured and permanently marked so that if captured as adults their true age would be known. Although a very small proportion of males and females reached sexual maturity at ages of two and four years respectively, most did so much later and asynchronously. The body size of toads breeding for the first time was relatively constant for each sex and not correlated with age. The rational behind our understanding of the mechanism of female choice is discussed in the light of these results.     

Mating patterns of Minshan's toad (Bufo minshanicus) from three populations along an altitudinal gradient

The large-male mating advantage and size-assortative mating are two different size-based patterns, which deviate from random mating in toads. These two pairing patterns may arise due to female choice, male-male competition, male choice, or a combination of these. This study investigated the mating system of Minshan's toad (Bufo minshanicus) from three populations along an altitudinal gradient during two breeding reasons in the northeastern Tibetan plateau. Our study shows that males found in amplexus with females were larger on average than non-amplectant males in two sites with higher operational sex ratios. Similarly, in those sites, males and females found in amplexus maintained an optimal size ratio. These data suggest that male-male competition leads to size-assortative mating in the lack of mate choice (female and male mate choice) by Minshan's toad, as larger males performed higher frequencies for taking-over other low quality ones with amplectant females.     

The successful elimination of Cane toads, <Emphasis Type="Italic">Bufo marinus</Emphasis>, from an island with breeding habitat off Bermuda

The 6.5 Ha Nonsuch island nature reserve in Castle harbour, Bermuda, under restoration as a “Living museum” of Bermuda’s pre-colonial terrestrial flora and fauna since 1962, was unexpectedly compromised by the colonization of a manmade freshwater pond by the invasive Cane toad Bufo marinus, which managed to cross a 175 m seawater barrier isolating the island. The toad was considered to pose a threat to the endemic Skink, for which Nonsuch is a key sanctuary, and to the burrow nesting Bermuda petrel or Cahow, which was about to be translocated to that larger island in order to establish a colony safe from the global warming threat of sealevel rise. A non-lethal method of removing the toads was devised through installation of a toad barrier around the freshwater pond, constructed of robust high density polyethylene (HDPE). Toads outside the barrier were no longer able to breed and were captured and removed by night searches over a five year period as they piled up against it. Removal of the breeding population inside the barrier was only possible by capturing all individuals resulting from each spawning before they could reach breeding age. This also took 5 years despite the small size (0.06 Ha) of the pond. A total of 1,244 toads were removed to Bermuda’s mainland. As breeding age is attained in 2 years the collection total for the first 2 years provided an approximation of the population density on the island before removal began (~80 per Ha). Although the immigration rate to Nonsuch is estimated to be less than one per year, this still requires maintaining the barrier as a permanent fixture. As future immigrants can be fairly quickly intercepted, the toad is now essentially extaxic on Nonsuch. This is the first published report of a successful eradication of the species from an island with breeding habitat.     

The effects of density,rainfall and environmental temperature on body condition and fecundity in the common toad,Bufo bufo

The body length and body weight of all adult common toads (Bufo bufo) breeding at a pond in south Dorset were measured between 1983 and 1993. Each toad was placed into one of four categories depending on its sex and whether it was either a first time breeder or an animal that had previously bred. The body condition of each male and female toad for each year was compared with the average body condition of all the male and female toads captured over the 11 years of the study so that between-year differences in condition could be detected. Changes in body condition were compared with changes in body condition were compared with changes in toad density, rainfall and climatic temperature during the previous summer (March–September), during hibernation (October–February) and during the month preceding the start of spawning. During the study there was a decline in the body condition of all toad categories and these changes were significantly correlated with changes in toad density and climatic temperature. Toads were also more likely to enter hibernation in poor condition following a hot dry summer than after either cool wet or hot wet summers. Body condition explained 41% of the size-specific variation in fecundity.     

Modeling spatial distribution of amphibian populations: a GIS approach based on habitat matrix permeability

Predictions of occurrence of two amphibian species, the common toad and the alpine newt, were made using information on land use surrounding breeding ponds. A geographical information system (GIS) was used to compile a landuse map, from which permeability estimates (friction) were derived. Potential migration zones based on friction and maximum migration distance were then modeled. Contacts between several migration zones suggest the potential for migration between ponds by adult individuals. The ability of the migration zones to enhance predictions of species occurrence was tested using generalized additive models (GAMs), and several landscape variables were selected as determinants of amphibian presence. The area of a migration zone and the number of ponds within that zone were positively related to both toad and newt presence, suggesting the importance of buffer habitats around each pond in amphibian conservation. Toad presence declined with cultivated field area and newt presence declined with vineyard area, suggesting the negative effect of agricultural activity on amphibians. The friction-based modeling approach improved the prediction of toad presence when compared to a more classical analysis of habitat composition within a circular zone centered on the focal pond. Prediction of newt presence was, however, less accurate than prediction of toad presence. Despite its exploratory nature and the subjectivity of permeability estimates, this study shows the usefulness of GIS in the functional analysis of a landscape, with potential applications in biological conservation. It also highlights the need for improving our knowledge of habitat use by animals.     

Patterns of synchrony in natterjack toad breeding activity and reproductive success at local and regional scales

Empirical studies of the spatiotemporal dynamics of populations are required to better understand natural fluctuations in abundance and reproductive success, and to better target conservation and monitoring programmes. In particular, spatial synchrony in amphibian populations remains little studied. We used data from a comprehensive three year study of natterjack toad Bufo calamita populations breeding at 36 ponds to assess whether there was spatial synchrony in the toad breeding activity (start and length of breeding season, total number of egg strings) and reproductive success (premetamorphic survival and production of metamorphs). We defined a novel approach to assess the importance of short‐term synchrony at both local and regional scales. The approach employs similarity indices and quantifies the interaction between the temporal and spatial components of populations using mixed effects models. There was no synchrony in the toad breeding activity and reproductive success at the local scale, suggesting that populations function as individual clusters independent of each other. Regional synchrony was apparent in the commencement and duration of the breeding season and in the number of egg strings laid (indicative of female population size). Regional synchrony in both rainfall and temperature are likely to explain the patterns observed (e.g. Moran effect). There was no evidence supporting regional synchrony in reproductive success, most likely due to spatial variability in the environmental conditions at the breeding ponds, and to differences in local population fitness (e.g. fecundity). The small scale asynchronous dynamics and regional synchronous dynamics in the number of breeding females indicate that it is best to monitor several populations within a subset of regions. Importantly, variations in the toad breeding activity and reproductive success are not synchronous, and it is thus important to consider them both when assessing the conservation status of pond‐breeding amphibians.     

Life stage specific variation in the occupancy of ponds by Litoria aurea,a threatened amphibian

Breeding aggregations are a reproductive strategy to increase mate finding opportunity. However, because aggregations skew the distribution of mature animals through conspecific attraction, rather than resource availability, the distribution of breeding sites may be reduced, so that not all suitable breeding sites are used. To examine the relationship between landscape and reproductive strategies of a threatened frog, Litoria aurea, we studied its distribution at Sydney Olympic Park over two breeding seasons. We aimed to: (i) determine the distribution and predictors of breeding ponds; and (ii) assess the significance of dispersal in the juvenile age‐class. We found that the distribution of the calling males was highly skewed and occurred in large, well‐connected ponds. Despite this, breeding ponds were not aggregated; pond size was the single factor explaining the distribution of breeding ponds. Juvenile frogs dispersed from breeding ponds and were not associated with a specific pond characteristic. Less breeding occurred in the second season during which fewer ponds were used for breeding including many different ponds from the previous year. These changes suggest that breeding effort and breeding pond choice are dynamic and therefore knowledge of the factors that drive breeding events will be a powerful tool in managing species, particularly in light of changing climatic regimes.     

Spawn site selection and colony size of the frog (Rana temporaria) and the toad (Bufo bufo)

Information has been collected from various sources on spawn site selection and colony size of the frog ( Rana temporaria ) and the toad ( Bufo bufo ). Details are tabulated for 764 frog breeding sites in Britain and in the Republic of Ireland and for 139 toad sites in Britain (the toad does not occur in Ireland). Both species tend to breed in whatever types of site are most available. In Britain the garden pond has steadily increased in importance for both species since 1950. Frogs usually spawned in shallow water, 266 reports out of a total of 588 (45%) referring to water up to six inches (15 cm) deep. Toads tended to spawn in deeper water, 48 reports out of 82 (59%) mentioning water 7–18 inches (18–46 cm) in depth. Median depths were: frog, seven inches (18 cm); toad 13 inches (33 cm). Information on colony size was assimilated for 574 frog colonies and 86 toad colonies. Colonies in gardens were smaller than those in other types of site. Relatively fewer large frog colonies (≡100 animals) were found to occur in London than elsewhere in Britain, and British colonies were generally larger than those in Ireland. Colonies of 100 or more individuals were recorded relatively more frequently for toads than for frogs. By combining information on choice of site and colony size, rough estimates can be derived of the percentage of frogs and toads breeding in gardens and other types of site. For instance, in the London area in the 1960s perhaps 20–25% of the frogs bred in gardens and private grounds. The ecological significance of these observations is discussed.     

大凉螈繁殖生态

大凉螈是我国特有的珍稀有尾两栖动物,其种群数量目前呈现明显下降趋势,然而涉及该物种保护的繁殖生态学研究仍十分匮乏。通过融合围栏陷阱及标志重捕的样方调查法,对大凉螈石棉栗子坪种群繁殖个体和变态登陆幼体的迁徙、繁殖群体种群大小、繁殖场内雌雄有效性比变化等进行了研究。运用Jolly-Seber法估测了繁殖种群大小,运用单因素方差分析或Kruskal-Wallis秩和检验比较了不同时期进入繁殖场的雄性大凉螈头体长及体重,运用t检验或者Wilcoxon秩和检验比较了雌雄性间形态上的差异,运用t检验、t′检验或Wilcoxon秩和检验比较了野外抱对雄性与非抱对雄性间的体征差别,运用Pearson相关分析探讨了雌性产卵量与其身体形态的关系,同时观察了卵的孵化情况。研究结果表明:大凉螈的繁殖季为每年的4月下旬到7月下旬,幼体最早于8月上旬变态登陆。估测调查地繁殖场内雄性大凉螈繁殖种群大小约为391尾,雄螈较雌螈更早进入繁殖场且在场内停留时间更长,体重较轻的雄螈较晚迁入繁殖场。有效性比明显偏雄(雌/雄:0.03—0.10)。雌雄间具明显性二型性,雌性个体的头体长、体重及肥满度均大于雄性,而雄性的尾高和尾长占全长的比例则大于雌性。对比自然抱对雄性和非抱对雄性个体发现,抱对个体在头体长、体重和尾高等体征方面显著大于非抱对个体,暗示这些形态特征可能在雄性竞争配偶的过程中起到关键作用。雌螈在室内条件下平均产卵数为176枚,产卵历时2—4 d,产卵量与雌性肥满度正相关,卵的平均孵化期为15.7 d,孵出幼体平均全长为9.74 mm。     

Mapping the Relative Probability of Common Toad Occurrence in Terrestrial Lowland Farm Habitat in the United Kingdom

Introduction

The common toad (Bufo bufo) is of increasing conservation concern in the United Kingdom (UK) due to dramatic population declines occurring in the past century. Many of these population declines coincided with reductions in both terrestrial and aquatic habitat availability and quality and have been primarily attributed to the effect of agricultural land conversion (of natural and semi-natural habitats to arable and pasture fields) and pond drainage. However, there is little evidence available to link habitat availability with common toad population declines, especially when examined at a broad landscape scale. Assessing such patterns of population declines at the landscape scale, for instance, require an understanding of how this species uses terrestrial habitat.

Methods

We intensively studied the terrestrial resource selection of a large population of common toads in Oxfordshire, England, UK. Adult common toads were fitted with passive integrated transponder (PIT) tags to allow detection in the terrestrial environment using a portable PIT antenna once toads left the pond and before going into hibernation (April/May-October 2012 and 2013). We developed a population-level resource selection function (RSF) to assess the relative probability of toad occurrence in the terrestrial environment by collecting location data for 90 recaptured toads.

Results

The predicted relative probability of toad occurrence for this population was greatest in wooded habitat near to water bodies; relative probability of occurrence declined dramatically > 50 m from these habitats. Toads also tended to select habitat near to their breeding pond and toad occurrence was negatively related to urban environments.     

Seasonal changes in the migratory behaviour of the toad Bufo bufo: direction and magnitude of movements

Summary The migratory behaviour of the toad Bufo bufo was studied from February 1985 to April 1986 in the submontane region of Bavaria, West Germany. Toads were fitted with a mechanical tracking device to record individual paths of migration. Three aspects of migratory behaviour were quantified: orientation in relation to the breeding site, straightness of path, and locomotory activity. The annual activity period began with migration from the hibernation sites to the breeding pond in April. The paths went straight towards the breeding pond independent of the distance (70–420 m). During the period of oviposition the preference for the breeding site direction vanished and toads moved away from the breeding pond, but in less straight paths than before. In summer migratory activity decreased considerably and was restricted to small areas, the home ranges, at distances of 55–1600 m from the natal breeding pond. The straightness of path was rather low, because toads often returned to their starting points. During rainy nights toads occasionally left their home ranges for extensive excursions. In autumn most toads again migrated towards the breeding pond, but paths were significantly less straight and direct than in spring. However, toads stopped before reaching the breeding pond and hibernated in holes or under the leaf layer. The mortality rate of tracked toads was about 45%. The relative influence of 17 environmental variables on locomotory activity was evaluated by principal component analysis and stepwise multiple regression. Temperature at night and rainfall variables accounted for significant amounts of variance, whereas temperature by day, air humidity, and atmospheric pressure showed no correlation. Activity decreased if temperature approached 0° C or after long periods without rainfall. Within a certain range of tolerance, however, the locomotory activity of the toads was widely independent of environmental factors, indicating that endogeneous factors are more important sources of variation in the migratory behaviour of these toads than commonly assumed.     

To breed or not to breed: past reproductive status and environmental cues drive current breeding decisions in a long-lived amphibian

Iteroparity is an adaptive response to uncertainty in reproductive success. However, spreading reproductive success over multiple reproduction events during a lifetime is constrained by adult mortality and the stochasticity associated with interactions between external factors and physiological states. The acquisition of information about environmental conditions during the growth of progeny and sufficient resources during the non-reproductive period are key factors for breeding success. Consequently, we hypothesized that long-lived animals may skip a breeding opportunity when information about unfavourable environmental conditions is available. In addition, nutritional constraints could prevent an animal from replenishing its reserves sufficiently to invest in the current breeding period. We investigated these questions using capture–recapture data from a 5-year study on a large population of yellow-bellied toads in a forest in north-eastern France. We took advantage of various advances in multi-state capture–recapture models (e.g. unobservable states and mixture models) to test our hypotheses. Our results show that the combined effects of rainfall deficit and the breeding/non-breeding state of individuals during the past breeding season affect breeding probability during the following breeding opportunity. We also found that females breed less frequently than males, suggesting that the overall energy cost of reproduction differs between genders. Finally, the results indicate that toad survival appears to be negatively influenced by rainfall deficits. We discuss the yellow-bellied toad’s reproductive behaviour in term of bet-hedging strategy and life history trait evolution.     

Female polyandry and size‐assortative mating in isolated local populations of the Japanese common toad Bufo japonicus

In anurans, female polyandry under male harassment is distributed across taxa because of external aquatic fertilization. According to the sexual selection theory, male–male competition for access to females is affected by the operational sex ratio (OSR) and population density. The Japanese common toad, Bufo japonicus, is widespread in mainland Japan, and like the European common toad, B. bufo, it engages in explosive breeding. In this study, we observed the breeding behaviour of B. japonicus in isolated local populations for over four years in two breeding ponds with different population sizes and densities: large‐low (L‐pond) and small‐high (S‐pond). We analysed the relative polyandry ratio in egg clutches laid by females and estimated the size‐assortative mating pattern to be an indicator of male–male competition in the two ponds. Both ponds tended to exhibit a size‐assortative mating pattern; however, the frequency of polyandry was different in the two ponds (L‐pond = 20% and S‐pond = 90%). Our results showed that polyandry could occur without multiple amplexus with a high population density, i.e. eggs were often fertilized by free‐swimming sperm in the small shallow pond. We propose that high female polyandry ratios without continuous male harassment are generated because of a male‐biased OSR and a high population density in the small pond. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 113 , 236–242.     

HABITAT DURATION,LENGTH OF LARVAL PERIOD,AND THE EVOLUTION OF A COMPLEX LIFE CYCLE OF A SALAMANDER,AMBYSTOMA TEXANUM

In many organisms, genotypic selection may be a less effective means of adapting to unpredictable environments than is selection for phenotypic plasticity. To determine whether genotypic selection is important in the evolution of complex life cycles of amphibians that breed in seasonally ephemeral habitats, we examined whether mortality risk from habitat drying in natural populations of small-mouthed salamanders (Ambystoma texanum) corresponded to length of larval period when larvae from the same populations were grown in a common laboratory environment. Comparisons were made at two levels of organization within the species: 1) among geographic races that are under strongly divergent selection regimes associated with the use of pond and stream habitats and 2) among populations within races that use the same types of breeding habitats. Morphological evidence indicates that stream-breeding A. texanum evolved from pond-breeding populations that recently colonized streams. Larvae in streams incur heavy mortality from stream drying, so the upper bound on length of larval period is currently set by the seasonal duration of breeding sites. We hypothesized that selection would reduce length of larval period of pond-breeders that colonize streams if their larval periods are inherently longer than those of stream-breeders. The results of laboratory experiments support this hypothesis. When grown individually in a common environment, larvae from stream populations had significantly shorter larval periods than larvae from pond populations. Within races, however, length of larval period did not correlate significantly with seasonal duration of breeding sites. When males of both races were crossed to a single pond female, offspring of stream males had significantly shorter larval periods than offspring of pond males. Collectively, these data suggest that differences in complex life cycles among pond and stream-breeders are due to genotypic selection related to mortality from habitat drying. Stream larvae in the common-environment experiment were significantly smaller at metamorphosis than pond larvae. Yet, the evolution of metamorphic size cannot be explained readily by direct selection: there are no intuitively obvious advantages of being relatively small at metamorphosis in streams. A positive phenotypic correlation was observed between size at metamorphosis and length of larval period in most laboratory populations. A positive additive genetic correlation between these traits was demonstrated recently in another amphibian. Thus, we suspect that metamorphic size of stream-breeders evolved indirectly as a consequence of selection to shorten length of larval period.     

Unequal catchability of male Bufo bufo within breeding populations

For 9 years, three breeding populations of the common toad Bufo bufo were censused during the breeding season. The hypothesis that catchability is equal for breeding males in each population and breeding period was tested. By comparing the lengths of all males captured with those recaptured in the same breeding period, it was shown that large males had a higher catchability than small ones. The ultimate cause of this unequal catchability remains unclear, but several causes can be rejected. Population parameters based on capture and capture – recapture data are highly influenced by this unequal catchability.