BREEDING PHENOLOGY AND SPATIO-TEMPORAL DYNAMICS OF POND USE BY THE YELLOW-BELLIED TOAD (BOMBINA VARIEGATA) POPULATION: THE IMPORTANCE OF POND AVAILABILITY AND DURATION

Carry-Over Effects of Desiccation Stress on the Oxidative Status of Fasting Anuran Juveniles

Amphibians are sensitive to deteriorating environmental conditions, especially during transition to a terrestrial environment which is full of uncertainties. Harsh conditions, such as desiccation during earlier stages, affect different larval traits with possible carry-over effects on juvenile and adult life histories. The first consequences of the effects can be seen in juveniles in the challenges to find food and the ability to survive without it in a terrestrial habitat. Body size and the internal energy reserves acquired during the larval phase play an important role in this period. Herein, we tested how different water regimes (low water availability, desiccation and constant high-water availability) during larval development reflect on the oxidative status and ability of yellow belly toad (Bombina variegata) juveniles to endure short-term fasting. The desiccation regime significantly reduced the body size of metamorphs. The same was observed after 2 weeks of fasting, while the feeding treatment reduced differences mostly in the body mass of individuals from different water regimes. This was the result of a greater gain in mass in juveniles pre-exposed to desiccation. Pre-exposure to desiccation also modified the parameters of the antioxidant system (AOS) under feeding conditions, leading to higher values of superoxide dismutase, glutathione reductase and glutathione S-transferase, glutathione and sulfhydryl group concentrations, and lower glutathione peroxidase in comparison to juveniles reared under constant water. The increase in the AOS of juveniles can be considered as a physiological carry-over effect of desiccation, probably as the result of compensatory growth and/or earlier exposure to chronic stress. However, water levels during larval development did not exert significant effects on the oxidative status of juveniles subjected to food unavailability. Fasting juveniles, both control and desiccated, were exposed to oxidative stress, significantly higher lipid peroxide concentrations, lower superoxide dismutase, glutathione peroxidase, glutathione S-transferase, glutathione and sulfhydryl group values in comparison to feeding individuals. The lack of food in juvenile anurans activated the AOS response in the same manner, regardless of body size and stress pre-exposure, suggesting that the generally accepted hypothesis about the influence of metamorphic body size on the fitness of the postmetamorphic stage should be tested further.

Tadpoles of hybridising fire-bellied toads (B. bombina and B. variegata) differ in their susceptibility to predation

The role of adaptive divergence in the formation of new species has been the subject of much recent debate. The most direct evidence comes from traits that can be shown to have diverged under natural selection and that now contribute to reproductive isolation. Here, we investigate differential adaptation of two fire-bellied toads (Anura, Bombinatoridae) to two types of aquatic habitat. Bombina bombina and B. variegata are two anciently diverged taxa that now reproduce in predator-rich ponds and ephemeral aquatic sites, respectively. Nevertheless, they hybridise extensively wherever their distribution ranges adjoin. We show in laboratory experiments that, as expected, B. variegata tadpoles are at relatively greater risk of predation from dragonfly larvae, even when they display a predator-induced phenotype. These tadpoles spent relatively more time swimming and so prompted more attacks from the visually hunting predators. We argue in the discussion that genomic regions linked to high activity in B. variegata should be barred from introgression into the B. bombina gene pool and thus contribute to gene flow barriers that keep the two taxa from merging into one.

Carry-over effects of the larval environment on the post-metamorphic performance of Bombina variegata (Amphibia, Anura)

Metamorphs of the yellow-bellied toad, Bombina variegata, vary widely in size at metamorphosis in the field. We performed a replicated outdoor mesocosm study to simulate the environmental factor combinations in permanent and ephemeral breeding sites and to quantify their effects on tadpole development (duration of the larval period, metamorph size and body condition). Looking for potential carry-over effects of the larval environment, we quantified locomotor performance of all metamorph phenotypes originating from the mesocosms immediately after metamorphosis under controlled conditions. In contrast to the prediction of life-history theory, tadpoles were unable to adjust developmental rate to water availability, but metamorphs originating from the ephemeral pond treatment were smaller and had a lower body condition than those from the permanent pond treatment. Size-dependent carry-over effects included the length of the first jump following tactile stimulation, burst performance (total length of spontaneous jumps) and endurance (total distance covered in 10 forced jumps). A size-independent effect of larval environment was the prolonged locomotor effort to escape (5.7 consecutive jumps following initial stimulus) of metamorphs from the ephemeral pond treatment compared to same-sized ones (3.7 jumps) from the permanent pond treatment. Thus, we demonstrate that carry-over effects of larval environment on metamorph phenotype and behaviour cause a considerable variation in fitness in the early terrestrial stage of B. variegata. Informed conservation management of endangered populations in the northern range should therefore include the provision of small permanent breeding ponds promoting larger and fitter metamorphs.

Designing screening protocols for amphibian disease that account for imperfect and variable capture rates of individuals

The amphibian chytrid fungus, Batrachochytrium dendrobatidis, is one of the main factors in global amphibian decline. Accurate knowledge of its presence and prevalence in an area is needed to trigger conservation actions. However, imperfect capture rates determine the number of individuals caught and tested during field surveys, and contribute to the uncertainty surrounding estimates of prevalence. Screening programs should be planned with the objective of minimizing such uncertainty. We show how this can be achieved by using predictive models that incorporate information about population size and capture rates. Using as a case study an existing screening program for three populations of the yellow-bellied toad (Bombina variegata pachypus) in northern Italy, we sought to quantify the effect of seasonal variation in individual capture rates on the uncertainty surrounding estimates of chytrid prevalence. We obtained estimates of population size and capture rates from mark-recapture data, and found wide seasonal variation in the individual recapture rates. We then incorporated this information in a binomial model to predict the estimates of prevalence that would be obtained by sampling at different times in the season, assuming no infected individuals were found. Sampling during the period of maximum capture probability was predicted to decrease upper 95% credible intervals by a maximum of 36%, compared with least suitable periods, with greater gains when using uninformative priors. We evaluated model predictions by comparing them with the results of screening surveys in 2012. The observed results closely matched the predicted figures for all populations, suggesting that this method can be reliably used to maximize the sampling size of surveillance programs, thus improving their efficiency.

Farmed areas predict the distribution of amphibian ponds in a traditional rural landscape

BACKGROUND

Traditional rural landscapes of Eastern Europe are undergoing major changes due to agricultural intensification, land abandonment, change in agricultural practices and infrastructural development. Small man-made ponds are important yet vulnerable components of rural landscapes. Despite their important role for biodiversity, these ponds tend to be excluded from conservation strategies.

METHODOLOGY/FINDINGS

Our study was conducted in a traditional rural landscape in Eastern Europe. The aim of this study is twofold: (i) to model the distribution of four major man-made pond types and (ii) to present the importance of man-made ponds for the endangered Yellow Bellied Toad (Bombina variegata) and the Common Toad (Bufo bufo). Six environmental variables were used to model pond distribution: Corine landcover, the heterogeneity of the landcover, slope, road distance, distance to closest village and the human population density. Land cover heterogeneity was the most important driver for the distribution of fishponds. Areas used for agriculture with significant areas of natural vegetation were the most important predictors for the distribution of temporary ponds. In addition, areas covered by transitional woodland and scrub were important for the open cattle ponds. Bombina variegata was found predominantly in the temporary ponds (e.g. ponds created by cattle and buffalo, dirt road ponds and concrete ponds created for livestock drinking) and Bufo bufo in fishponds.

CONCLUSIONS/SIGNIFICANCE

Our Maxent models revealed that the highest probability of occurrence for amphibian ponds was in areas used as farmland. The traditional farming practices combined with a low level of infrastructure development produces a large number of amphibian ponds. The challenge is to harmonize economic development and the maintenance of high densities of ponds in these traditional rural landscapes.

Land abandonment may reduce disturbance and affect the breeding sites of an Endangered amphibian in northern Italy

Although human-related disturbance is usually detrimental for biodiversity, in some instances it can simulate natural processes and benefit certain species. Changes in the disturbance regime, both natural and human-driven, can affect species that rely on it. The Apennine yellow-bellied toad Bombina variegata pachypus, an amphibian endemic to peninsular Italy, has declined throughout its range in the last 3 decades. We sought to identify the drivers of the decline in the region of Liguria, at the north-western limit of its distribution. In 2009 and 2010 we surveyed sites where the species occurred until 2005 and related the persistence of breeding activity to the characteristics of sites. Populations had disappeared from 50% of the sites between 2005 and 2009. Current breeding sites have less aquatic and bank vegetation, fewer predators and better insolation. Frequent disturbance events (desiccation and floods) were related to reduced vegetation, which in turn may decrease predator densities and increase insolation. In this region disturbance is provided by natural factors or, in the case of artificial water bodies, by regular maintenance carried out by landowners. The widespread land abandonment in Liguria can disrupt disturbance regimes, interrupting the removal of vegetation, and thus rapidly reduce the suitability of artificial sites. This was confirmed in our study, with most abandoned breeding sites occurring in formerly cultivated areas. Possible short-term conservation actions include creating new ponds, maintaining artificial water bodies and clearing vegetation. However, long-term conservation may be more problematic as the land abandonment process is unlikely to be reversed.

Are there real sexual morphometric differences in yellow-bellied toads (Bombina spp.; Bombinatoridae)?

In this study, we explored the level and pattern of sexual size dimorphism and sexual shape dimorphism in two closely related Bombina species that have low levels of sexual dimorphism in body size and shape. We applied an experimental protocol to explore sexual variations in morphological traits, including a preliminary evaluation of the measurement error. Mean measurement error (MME) and measurement error index (MEI) were estimated on each of the eleven morphometric variables to exclude any possible subjective factor in measuring and to perform, for the first time, an objective functional and statistical evaluation of sexual size differences in the two species. Even if statistically significant, each difference that lies below the level of uncertainty of the measure could not be reliable. Therefore, statistically significant differences in head shape have been rejected, due to an average difference between males and females smaller than the possible MME. We detected significantly longer distal segments of the hind limbs in males, which could account for their use in mating behaviour (e.g. scramble competition, water-wave communication). However, major and more reliable evidences of sexual dimorphism have been found on forelimb measures (MEI > 1), in particular humerus length and amplexus, which are significantly larger in males than in females. These results indicate a mating related sexual dimorphism, when larger and stronger forelimbs can give an advantage during coupling as well as during male-male fighting. The mean measurement error values and formulas provided in this work could be applied to future morphometric studies on Bombina species.