Effects of body temperature and hydration state on organismal performance of toads, Bufo americanus

Dehydration followed by restraint sustains high circulating corticosterone and improves immunity in toads

Amphibians are suffering population declines due to a variety of factors such as increased ultraviolet radiation, climate change, habitat loss, pathogens, and pollution, or a combination of these. Such changes are associated with a reduction in the availability of water, exposing these animals to a greater risk of desiccation. In this context, understanding how dehydration can modulate the hypothalamic-pituitary-interrenal axis (HPI) and the immune response is an imperative question to predict how stressors can affect amphibian species. We investigated whether dehydration promotes long-lasting effects on toads' ability to respond to a consecutive stressor (restraint) even if the toads are allowed to rehydrate, as well as its effects on the immune function. We also tested the hypothesis that the toads showing more severe dehydration would exhibit lower responsiveness to restraint challenge, even if the animals were allowed to rehydrate. Individuals of R. ornata were dehydrated mildly and severely. Thereafter, they were submitted to a restraint stress challenge for 1 and 24 h. Our results show that dehydration increased hematocrit and CORT in R. ornata toads. The restraint induced an acute stress response in fully hydrated toads (increased CORT and neutrophil: lymphocyte ratio). Otherwise, restraint in moistened cloth bags allowed full rehydration in previously dehydrated toads and did not induce an additional increase in CORT, but those toads sustained elevated CORT up to 24 h of restraint. Also, these animals showed increased neutrophil: lymphocyte ratio and the phagocytic activity of blood cells, even when they rehydrated during restraint. These results point to a continuous activation of the HPA during dehydration and subsequent restraint, even when they recovered from the dehydration state. Also, acute stressors seem to promote immune cell redistribution and augmentation of immune cellular function in R. ornata toads.

The relationships between toad behaviour, antipredator defences, and spatial and sexual variation in predation pressure

BACKGROUND

Animal behaviour is under strong selection. Selection on behaviour, however, might not act in isolation from other fitness-related traits. Since predators represent outstanding selective forces, animal behaviour could covary with antipredator defences, such that individuals better suited against predators could afford facing the costs of riskier behaviours. Moreover, not all individuals undergo equivalent degrees of predation pressure, which can vary across sexes or habitats. Individuals under lower predation pressure might also exhibit riskier behaviours.

METHODS

In this work, I tested these hypotheses on natterjack toads (Epidalea calamita). Specifically, I gauged activity time, exploratory behaviour and boldness in standard laboratory conditions, and assessed whether they correlated with body size and antipredator strategies, namely sprint speed, parotoid gland area and parotoid gland colour contrast. Additionally, I compared these traits between sexes and individuals from an agrosystem and pine grove, since there is evidence that males and agrosystem individuals are subjected to greater predation pressure.

RESULTS

Sprint speed as well as parotoid gland contrast and size appeared unrelated to the behavioural traits studied. In turn, body mass was negatively related to activity time, boldness and exploration. This trend is consistent with the fact that larger toads could be more detectable to their predators, which are mostly gape unconstrained and could easily consume them. As predicted, females exhibited riskier behaviours. Nonetheless, agrosystem toads did not differ from pine grove toads in the behavioural traits measured, despite being under stronger predation pressure.

Influence of High Temperatures and Heat Wave on Thermal Biology, Locomotor Performance, and Antioxidant System of High-Altitude Frog Nanorana pleskei Endemic to Qinghai-Tibet Plateau

Investigating how highland amphibians respond to changes in ambient temperature may be of great significance for their fate prediction and effective conservation in the background of global warming. Here, using field individuals as the control group, we investigated the influence of high temperatures (20.5 and 25.5°C) and heat wave (15–26.6°C) on the thermal preference, critical thermal limits, locomotor performance, oxidative stress, and antioxidant enzyme activities in high-altitude frog Nanorana pleskei (3,490 m) endemic to the Qinghai-Tibet Plateau (QTP). After 2 weeks of acclimation to high temperatures and heat wave, the thermal preference (Tpref), critical thermal maximum (CTmax), and range of tolerable temperature significantly increased, while the critical thermal minimum (CTmin) was significantly decreased. The total time of jump to exhaustion significantly decreased, and burst swimming speed significantly increased in frogs acclimated in the high temperature and heat wave groups compared with the field group. In the high temperature group, the level of H2O2 and lipid peroxide (malondialdehyde, MDA), as well as the activities of glutathione peroxidase (GPX), glutathione reductase (GR), catalase (CAT), superoxide dismutase (SOD), and total antioxidant capacity (T-AOC) significantly increased in the liver or muscle. However, in the heat wave group, the MDA content significantly decreased in the liver, and antioxidants activities decreased in the liver and muscle except for CAT activities that were significantly increased in the liver. These results indicated that N. pleskei could respond to the oxidative stress caused by high temperatures by enhancing the activity of antioxidant enzymes. The heat wave did not appear to cause oxidative damage in N. pleskei, which may be attributed to the fact that they have successfully adapted to the dramatic temperature fluctuations on the QTP.

Seasonal variations in the intermediate metabolism in South American tree-frog Boana pulchella

Seasonal metabolic changes can be observed in many anurans' species. In subtropical environments with environmental temperatures variations, the temperature is a factor that can influence the extent and intensity of activity in many anuran species. Nonetheless, some species of subtropical frogs may remain active throughout the year. Boana pulchella, a subtropical species, seems to be able to survive low temperatures and remain reproductively active even in the coldest months. Therefore, we hypothesized that B. pulchella presents seasonal changes in the energy metabolism to sustain activity during all year. This study evaluated the main energy substrate levels and metabolism of B. pulchella in plasma, liver and muscle of male individuals collected in winter, spring, summer and fall in the state of Rio Grande do Sul, Brazil. Our results showed that B. pulchella has a higher glycolytic oxidation rate in liver (P = 0.0152) and muscle (P = 0.0003) and higher glycogenesis from glucose in muscle (P = 0.0002) in summer, indicating the main energy substrates in this season is glucose. The higher muscle glycogen (P = 0.0008) and lower plasma glucose in fall (P = 0.0134) may indicate an anticipatory regulation for storing to the most thermally demanding cold period: winter. These results indicated seasonal differences in the main energy substrates, and these metabolic changes among seasons can be part of a metabolic adjustment allowing maintenance of reproductive activity all year in Boana pulchella species.

Feeding alters the preferred body temperature of Cururu toads, Rhinella diptycha (Anura, Bufonidae)

Ectothermic organisms depend primarily on external heat sources and behavioural adjustments to regulate body temperature. Under controlled conditions, in a thermal gradient, body temperature often clusters around a more or less defined range of preferred body temperatures (T_pref). However, T_pref may be modified in response to environmental parameters and/or physiological state. For example, meal ingestion is sometimes followed by a post-prandial thermophilic response leading to a transient increment in T_pref. Although thought to optimize digestive processes, its occurrence, magnitude, and possible determinants remains scarcely documented for anuran amphibians. Herein, we investigated whether the Cururu toad, Rhinella diptycha, exhibits a post-prandial thermophilic response by monitoring the body temperature of fasting and fed toads while they were maintained in a thermal gradient. We found that the toads' T_pref increased by about 13% from day 2 to 4 after feeding, in comparison with the T_pref recorded under fasting. Also, fed animals exhibited a broader range for T_pref at days 2 and 3 post-prandial, which reflects a greater level of locomotor activity compared to fasting individuals. We conclude that R. diptycha is capable to exhibit a post-prandial thermophilic response under the controlled conditions of a thermal gradient. Although this thermoregulatory adjustment is thought to optimize meal digestion yielding important energetic and ecological benefits, its occurrence in anuran amphibians in nature remains uncertain.

Evolution of a high-performance and functionally robust musculoskeletal system in salamanders

The evolution of ballistic tongue projection in plethodontid salamanders-a high-performance and thermally robust musculoskeletal system-is ideal for examining how the components required for extreme performance in animal movement are assembled in evolution. Our comparative data on whole-organism performance measured across a range of temperatures and the musculoskeletal morphology of the tongue apparatus were examined in a phylogenetic framework and combined with data on muscle contractile physiology and neural control. Our analysis reveals that relatively minor evolutionary changes in morphology and neural control have transformed a muscle-powered system with modest performance and high thermal sensitivity into a spring-powered system with extreme performance and functional robustness in the face of evolutionarily conserved muscle contractile physiology. Furthermore, these changes have occurred in parallel in both major clades of this largest family of salamanders. We also find that high-performance tongue projection that exceeds available muscle power and thermal robustness of performance coevolve, both being emergent properties of the same elastic-recoil mechanism. Among the taxa examined, we find muscle-powered and fully fledged elastic systems with enormous performance differences, but no intermediate forms, suggesting that incipient elastic mechanisms do not persist in evolutionary time. A growing body of data from other elastic systems suggests that similar coevolution of traits may be found in other ectothermic animals with high performance, particularly those for which thermoregulation is challenging or ecologically costly.

Toads modulate flight strategy according to distance to refuge

Among antipredator behaviours, escaping and hiding in a refuge are widespread in nature. Frequently, threatened prey flee towards a refuge nearby, if available. Therefore, refuge proximity may affect the fleeing strategy of a prey. In this work, I tested this hypothesis in Epidalea calamita, a cursorial toad that flees by means of intermittent runs. In a linear runway in standardized conditions, toads were recorded while conducting a short-distance (refuge at 70 cm), a medium-distance (refuge at 140 cm, divided in two 70-cm tracks), and a long-distance trial (refuge at 210 cm, divided in three 70-cm tracks), in a random sequence. Video analyses permitted to calculate sprint speed and run rates (number of runs per meter) in each track. Distance to refuge affected toad flight strategy. Toads started flights at a faster speed in the short-distance trials. In the medium- and the long-distance trials, toads accelerated after the first track, seemingly not motivated by refuge proximity. In these trials, run rate was greater in the first tracks. Altogether, these findings suggest that threatened toads respond firstly with slow, intermittent movements, and only shift to less intermittent, faster sprints if the threat persists. However, run rate was lower in the short-distance trial than in the first tracks of the other trials, suggesting straighter (and faster) flight toward the refuge when it is close. The effects of refuge proximity were greater in males, which (jointly with faster sprint speed) could reflect a greater conspicuousness of males to predator resulting in better escape strategies.

Evaluation of the combined temperature and relative humidity preferences of the Colombian terrestrial salamander Bolitoglossa ramosi (Amphibia: Plethodontidae)

Temperature and humidity are critical factors for terrestrial lungless salamanders, as their body temperatures are largely determined by the environmental temperature and require moisture to sustain cutaneous respiration. Herein, we evaluated the preference of Bolitoglossa ramosi Brame and Wake, 1972 between a high temperature and a high relative humidity (RH), the influence of temperature on RH preferences, and the influence of RH on the thermal preferences. This study was performed in a field location in the municipality of Líbano, Tolima, Colombia. There, on different nights, we collected 84 adult B. ramosi and carried out the preference experiments, using aluminum troughs with different thermal and RH gradients. We found that between high temperature and high RH, B. ramosi preferred high RH. However, B. ramosi selected high temperatures when the gradient had a high RH and low temperatures when the gradient had a low RH. These results show that B. ramosi is able to thermoregulate and hydroregulate. Nevertheless, hydroregulation seems to be more important than thermoregulation because B. ramosi always selected the high RH gradients, while their thermal selection relied on the hydric environment.

Temperature and dehydration effects on metabolism, water uptake, and the partitioning between respiratory and cutaneous evaporative water loss in a terrestrial toad

Terrestrial anurans often experience fluctuations in body temperature and hydration state, which are known to influence evaporative water loss through the skin (EWLSkin) and lungs (EWLResp). These effects arises from associated changes in skin permeability, metabolism and lung ventilation. Herein, we determined the rates of EWLSkin and EWLResp in the terrestrial toad, Rhinella schneideri, at different temperatures and hydration states. We measured oxygen uptake rates to verify whether alterations in the partitioning between EWLSkin and EWLResp were associated to metabolic induced changes in pulmonary gas exchange. We also measured the influence of hydration and temperature on water uptake (WU) through the skin. Finally, since estimates of skin resistance to evaporation (Rs) are usually inferred from total evaporative water loss (EWLTotal), under the assumption of negligible EWLResp, we calculate the potential error in accepting this assumption, under different temperature and hydration states. EWLSkin and EWLResp increased with temperature, but this response was greater for EWLResp, which was attributed to the temperature-induced elevation in metabolism and lung ventilation. Dehydration caused a decrease in the relative contribution of EWLSkin to EWLTotal, mirrored by the concurrent increase in the contribution of EWLResp, at all temperatures. Thus, Rs increased with dehydration. WU rates were dictated by dehydration with little influence of temperature. The partitioning between EWLSkin and EWLResp was affected by both temperature and hydration state and, under some set of conditions, considering EWLResp as negligible led to significant errors in the assessment of skin resistance to evaporation.

Trading heat and hops for water: Dehydration effects on locomotor performance, thermal limits, and thermoregulatory behavior of a terrestrial toad

Due to their highly permeable skin and ectothermy, terrestrial amphibians are challenged by compromises between water balance and body temperature regulation. The way in which such compromises are accommodated, under a range of temperatures and dehydration levels, impacts importantly the behavior and ecology of amphibians. Thus, using the terrestrial toad Rhinella schneideri as a model organism, the goals of this study were twofold. First, we determined how the thermal sensitivity of a centrally relevant trait-locomotion-was affected by dehydration. Secondly, we examined the effects of the same levels of dehydration on thermal preference and thermal tolerance. As dehydration becomes more severe, the optimal temperature for locomotor performance was lowered and performance breadth narrower. Similarly, dehydration was accompanied by a decrease in the thermal tolerance range. Such a decrease was caused by both an increase in the critical minimal temperature and a decrease in the thermal maximal temperature, with the latter changing more markedly. In general, our results show that the negative effects of dehydration on behavioral performance and thermal tolerance are, at least partially, counteracted by concurrent adjustments in thermal preference. We discuss some of the potential implications of this observation for the conservation of anuran amphibians.

Not Good, but Not All Bad: Dehydration Effects on Body Fluids, Organ Masses, and Water Flux through the Skin of Rhinella schneideri (Amphibia, Bufonidae)

Because of their permeable skin, terrestrial amphibians are constantly challenged by the potential risk of dehydration. However, some of the physiological consequences associated with dehydration may affect aspects that are themselves relevant to the regulation of water balance. Accordingly, we examined the effects of graded levels of dehydration on the rates of evaporative water loss and water absorption through the skin in the terrestrial Neotropical toad, Rhinella schneideri. Concomitantly, we monitored the effects of dehydration on the mass of visceral organs; hematocrit and hemoglobin content; plasma osmolality; and plasma concentration of urea, sodium, chloride, and potassium. We found that dehydration caused an increase in the concentration of body fluids, as indicated by virtually all the parameters examined. There was a proportional change in the relative masses of visceral organs, except for the liver and kidneys, which exhibited a decrease in their relative masses greater than the whole-body level of dehydration. Changes-or the preservation-of relative organ masses during dehydration may be explained by organ-specific physiological adjustments in response to the functional stress introduced by the dehydration itself. As dehydration progressed, evaporative water loss diminished and water reabsorption increased. In both cases, the increase in body fluid concentration associated with the dehydration provided the osmotic driver for these changes in water flux. Additionally, dehydration-induced alterations on the cutaneous barrier may also have contributed to the decrease in water flux. Dehydration, therefore, while posing a considerable challenge on the water balance regulation of anurans, paradoxically facilitates water conservation and absorption.

Field hydration state varies among tropical frog species with different habitat use

We have previously shown that ecological habit (e.g., arboreal, terrestrial, amphibious) correlates with thermoregulatory behaviors and water balance physiology among species of hylid frogs in northern Australia. We hypothesized that these frogs would be different with respect to their field hydration states because of the challenges associated with the different ecological habits. There are very few data on the hydration levels that frogs maintain in the field, and the existing data are from disparate species and locations and do not relate hydration state to habit or changes in seasonal water availability. We measured the hydration state of 15 species of frogs from tropical northern Australia to determine the influences of ecological habit and season on the hydration state that these frogs maintain. As predicted, frogs were significantly less hydrated in the dry season than they were in the wet season and showed significantly higher variation among individuals, suggesting that maintaining hydration is more challenging in the dry season. In the wet season, terrestrial species were significantly less hydrated than arboreal or amphibious species. During the dry season, amphibious species that sought refuge in cracking mud after the pond dried were significantly less hydrated than terrestrial or arboreal species. These data suggest that hydration behaviors and voluntary tolerance of dehydration vary with habitat use, even within closely related species in the same family or genus. Terrestrial and arboreal species might be expected to be the most vulnerable to changes in water availability, because they are somewhat removed from water sources, but the physiological characteristics of arboreal frogs that result in significant cutaneous resistance to water loss allow them to reduce the effects of their dehydrating microenvironment.

Dehydration hardly slows hopping toads (Rhinella granulosa) from xeric and mesic environments

The locomotor capacity of amphibians depends strongly on temperature and hydration. Understanding the potential interactions between these variables remains an important challenge because temperature and water availability covary strongly in natural environments. We explored the effects of temperature and hydration on the hopping speeds of Rhinella granulosa, a small toad from the semiarid Caatinga and the Atlantic Rain Forest in Brazil. We asked whether thermal and hydric states interact to determine performance and whether toads from the Caatinga differ from their conspecifics from the Atlantic Forest. Both dehydration and cooling impaired hopping speed, but effects were independent of one another. In comparison to performances of other anurans, the performance of R. granulosa was far less sensitive to dehydration. Consequently, dehydrated members of this species may be able to sustain performance through high body temperatures, which agrees with the exceptional heat tolerance of this species. Surprisingly, toads from both the Caatinga and the Atlantic Forest were relatively insensitive to dehydration. This observation suggests that migration or gene flow between toads from the forest and those from a drier region occurred or that toads from a dry region colonized the forest secondarily.

Forest Fragments Surrounded by Sugar Cane Are More Inhospitable to Terrestrial Amphibian Abundance Than Fragments Surrounded by Pasture

In recent years, there has been increasing interest in matrix-type influence on forest fragments. Terrestrial amphibians are good bioindicators for this kind of research because of low vagility and high philopatry. This study compared richness, abundance, and species composition of terrestrial amphibians through pitfall traps in two sets of semideciduous seasonal forest fragments in southeastern Brazil, according to the predominant surrounding matrix (sugar cane and pasture). There were no differences in richness, but fragments surrounded by sugar cane had the lowest abundance of amphibians, whereas fragments surrounded by pastures had greater abundance. The most abundant species,Rhinella ornata, showed no biometric differences between fragment groups but like many other amphibians sampled showed very low numbers of individuals in fragments dominated by sugar cane fields. Our data indicate that the sugar cane matrix negatively influences the community of amphibians present in fragments surrounded by this type of land use.

Habitat split as a cause of local population declines of amphibians with aquatic larvae

Most amphibian species have biphasic life histories and undergo an ontogenetic shift from aquatic to terrestrial habitats. In deforested landscapes, streams and forest fragments are frequently disjunct, jeopardizing the life cycle of forest-associated amphibians with aquatic larvae. We tested the impact of habitat split--defined as human-induced disconnection between habitats used by different life-history stages of a species--on four forest-associated amphibian species in a severely fragmented landscape of the Brazilian Atlantic Forest. We surveyed amphibians in forest fragments with and without streams (referred to as wet and dry fragments, respectively), including the adjacent grass-field matrix. Our comparison of capture rates in dry fragments and nearby streams in the matrix allowed us to evaluate the number of individuals that engaged in high-risk migrations through nonforested habitats. Adult amphibians moved from dry fragments to matrix streams at the beginning of the rainy season, reproduced, and returned at the end of the breeding period. Juveniles of the year moved to dry fragments along with adults. These risky reproductive migrations through nonforested habitats that expose individuals to dehydration, predation, and other hazards may cause population declines in dry fragments. Indeed, capture rates were significantly lower in dry fragments compared with wet fragments. Declining amphibians would strongly benefit from investments in the conservation and restoration of riparian vegetation and corridors linking breeding and nonbreeding areas.

Behavioral response and kinetics of terrestrial atrazine exposure in American toads (Bufo americanus)

Amphibians in terrestrial environments obtain water through a highly vascularized pelvic patch of skin. Chemicals can also be exchanged across this patch. Atrazine (ATZ), a widespread herbicide, continues to be a concern among amphibian ecologists based on potential exposure and toxicity. Few studies have examined its impact on the terrestrial juvenile or adult stages of toads. In the current study, we asked the following questions: (1) Will juvenile American toads (Bufo americanus) avoid soils contaminated with ATZ? (2) Can they absorb ATZ across the pelvic patch? (3) If so, how is it distributed among the organs and eventually eliminated? We conducted a behavioral choice test between control soil and soil dosed with ecologically relevant concentrations of ATZ. In addition, we examined the uptake, distribution, and elimination of water dosed with (14)C-labeled ATZ. Our data demonstrate that toads do not avoid ATZ-laden soils. ATZ crossed the pelvic patch rapidly and reached an apparent equilibrium within 5 h. The majority of the radiolabeled ATZ ended up in the intestines, whereas the greatest concentrations were observed in the gall bladder. Thus, exposure of adult life stages of amphibians through direct uptake of ATZ from soils and runoff water should be considered in risk evaluations.

Thermal relationships and exercise physiology in anuran amphibians: Integration and evolutionary implications

Thermal and water balance are coupled in anurans, and species with particularly permeable skin avoid overheating more effectively than minimizing variance of body temperature. In turn, temperature affects muscle performance in several ways, so documenting the mean and variance of body temperature of active frogs can help explain variation in behavioral performance. The two types of activities studied in most detail, jumping and calling, differ markedly in duration and intensity, and there are distinct differences in the metabolic profile and fiber type of the supporting muscles. Characteristics of jumping and calling also vary significantly among species, and these differences have a number of implications that we discuss in some detail throughout this paper. One question that emerges from this topic is whether anuran species exhibit activity temperatures that match the temperature range over which they perform best. Although this seems the case, thermal preferences are variable and may not necessarily reflect typical activity temperatures. The performance versus temperature curves and the thermal limits for anuran activity reflect the thermal ecology of species more than their systematic position. Anuran thermal physiology, therefore, seems to be phenotypically plastic and susceptible to adaptive evolution. Although generalizations regarding the mechanistic basis of such adjustments are not yet possible, recent attempts have been made to reveal the mechanistic basis of acclimation and acclimatization.

Individual variation affects departure rate from the natal pond in an ephemeral pond-breeding anuran

Frogs exhibit extreme plasticity and individual variation in growth and behavior during metamorphosis, driven by interactions of intrinsic state factors and extrinsic environmental factors. In northern red-legged frogs ( Rana aurora Baird and Girard, 1852), we studied the timing of departure from the natal pond as it relates to date and size of individuals at metamorphosis in the context of environmental uncertainty. To affect body size at metamorphosis, we manipulated food availability during the larval stage for a sample (317) of 1045 uniquely marked individuals and released them at their natal ponds as newly metamorphosed frogs. We recaptured 34% of marked frogs in pitfall traps as they departed and related the timing of their initial terrestrial movements to individual properties using a time-to-event model. Median age at first capture was 4 and 9 days postmetamorphosis at two sites. The rate of departure was positively related to body size and to date of metamorphosis. Departure rate was strongly negatively related to time elapsed since rainfall, and this effect was diminished for smaller and later metamorphosing frogs. Individual variation in metamorphic traits thus affects individuals’ responses to environmental variability, supporting a behavioral link with variation in survival associated with these same metamorphic traits.

Carryover aquatic effects on survival of metamorphic frogs during pond emigration

In organisms with complex life cycles, physiological stressors during early life stages may have fitness-level impacts that are delayed into later stages or habitats. We tested the hypothesis that body size and date of metamorphosis, which are highly responsive to aquatic stressors, influence post-metamorphic survival and movement patterns in the terrestrial phase of an ephemeral pond-breeding frog by examining these traits in two populations of northern red-legged frogs (Rana aurora aurora). To increase variation of body size at metamorphosis, we manipulated food availability for 314 of 1045 uniquely marked tadpoles and estimated the probability that frogs survived and emigrated using concentric rings of drift fencing surrounding ponds and Bayesian capture-recapture modeling. The odds of surviving and emigrating from the ponds to the innermost drift fences, approximately 12 m, increased by factors of 2.20 (95% credibility intervals 1.39-4.23) and 2.54 (0.94-4.91) with each millimeter increase in snout-vent length and decreased by factors of 0.91 (0.85-0.96) and 0.89 (0.80-1.00) with each day's delay in metamorphosis for the two ponds. The odds of surviving and moving to the next ring of fencing, 12 m to approximately 40 m from the ponds, increased by a factor of 1.20 (0.45-4.06) with each millimeter increase in size. Our results demonstrated that body size and timing of metamorphosis relate strongly to the performance of newly metamorphosed frogs during their initial transition into terrestrial habitat. Carryover effects of aquatic stressors that reduce size and delay metamorphosis may have population-level impacts that are not expressed until terrestrial stages. Since changes in both aquatic and terrestrial systems are implicated in many amphibian declines, quantifying both immediate and delayed effects of stressors on demographic rates is critical to sound management.