Rates Of Evaporative Water Loss Research Articles

Microclimate preferences correlate with contrasted evaporative water loss in parapatric vipers at their contact zone

Terrestrial ectotherms predominantly use behavioural means to thermoregulate and thereby optimize performances. However, thermoregulation can impart physiological challenges to other critical processes such as water balance by increasing evaporative water loss (EWL). Like thermoregulation, water balance is influenced by both external factors (e.g., microhabitat and environmental constraints) and endogenous traits (e.g., evaporative water loss rates, dehydration tolerance). Although thermoregulation and water balance are tightly linked, the role of water balance is often overlooked when evaluating species climatic adaptation and response to global warming. We studied two congeneric viperid species (the Aspic Viper, Vipera aspis (L., 1758), and the Common Viper, Vipera berus (L., 1758)) with contrasted climatic affinities (south European versus boreal, respectively). These parapatric species are syntopic in narrow contact zones where microhabitat partitioning has been reported. We compared total EWL and cutaneous evaporative water loss (CEWL) of the two species and monitored the thermal and hydric conditions of the microhabitats used in syntopic populations. We found that the boreal V. berus has greater EWL, both total and cutaneous. Accordingly, this species selected more humid microhabitats throughout the year. Humidity appears to be an important determinant of habitat selection, and therefore, V. berus is likely vulnerable to changing precipitation at the southern limit of its distribution.

Ecophysiological Dissimilarities of Two Sympatric Lizards

Abstract: The lizards Podarcis muralis and Iberolacerta horvathi display an overall similarity in morphology and ecology. Although they are widely sympatric in part of their distribution range of Slovenia, areas of altitudinal segregation have been observed. Ecophysiological traits such as preferred body temperatures (Tp) and rates of evaporative water loss (EWL) are some of the factors likely to be subjacent to this pattern. We expect the species that is more abundant in higher altitudes to have lower Tp and higher EWL (due to lower environmental temperatures at higher elevations) than the species that is more abundant in lowlands. We conducted lab experiments to determine whether intra- and interspecific variation in these two physiological traits exists. Contrary to expectations, the means of Tp were similar between the species, but their seasonal dynamics differed, which indicates that thermal accuracy might be more important. Species differed in seasonal (and daily) variation of Tp, rising from spri...

Effects of Water Vapor Density on Cutaneous Resistance to Evaporative Water Loss and Body Temperature in Green Tree Frogs (Hyla cinerea)

Increased cutaneous resistance to evaporative water loss (Rc) in tree frogs results in decreased water loss rate and increased body temperature. We examined sensitivity of Rc to water vapor density (WVD) in Hyla cinerea by exposing individual frogs and agar models to four different WVD environments and measuring cutaneous evaporative water loss rate and body temperature simultaneously using a gravimetric wind tunnel measuring system. We found that water loss rate varied inversely and body temperature directly with WVD but that models were affected to a greater extent than were animals. Mean Rc was significantly different between the highest WVD environment and each of the three drier environments but did not differ among the drier environments, indicating that Rc initially increases and then reaches a plateau in response to decreasing WVD. Rc was equivalent when calculated using either WVD difference or WVD deficit as the driving force for evaporation. We also directly observed secretions from cutaneous glands while measuring body temperature and tested secretions and skin samples for the presence of lipids. We found that irregular transient body temperature depressions observed during wind tunnel trials occur due to evaporative cooling from intermittent skin secretions containing lipids, although we were unable to identify lipid-secreting glands.

Climate influences thermal balance and water use in African and Asian elephants: physiology can predict drivers of elephant distribution

Elephant movement patterns in relation to surface water demonstrate that they are a water-dependent species. Thus, there has been interest in using surface water management to mitigate problems associated with localized elephant overabundance. However, the physiological mechanisms underlying the elephant's water dependence remain unclear. Although thermoregulation is likely an important driver, the relationship between thermoregulation, water use and climate has not been quantified. We measured skin surface temperature of and cutaneous water loss from 13 elephants (seven African, 3768±642 kg; six Asian, 3834±498 kg) and determined the contribution of evaporative cooling to their thermal and water budgets across a range of air temperatures (8-33°C). We also measured respiratory evaporative water loss and resting metabolic heat production on a subset of elephants (N=7). The rate of cutaneous evaporative water loss ranged between 0.31 and 8.9 g min(-1) m(-2) for Asian elephants and 0.26 and 6.5 g min(-1) m(-2) for African elephants. Simulated thermal and water budgets using climate data from Port Elizabeth, South Africa, and Okaukuejo, Namibia, suggested that the 24-h evaporative cooling water debt incurred in warm climates can be more than 4.5 times that incurred in mesic climates. This study confirms elephants are obligate evaporative coolers but suggests that classification of elephants as water dependent is insufficient given the importance of climate in determining the magnitude of this dependence. These data highlight the potential for a physiological modeling approach to predicting the utility of surface water management for specific populations.

Evaporative water loss, spatial distributions, and survival in white-nose-syndrome-affected little brown myotis: a model

Many temperate bat species deal with harsh winter conditions by hibernating. Brief periods of arousal from torpor occur at regular intervals throughout hibernation, although energetically costly. Factors that increase arousal frequency, such as the recently discovered white-nose syndrome (WNS), can thereby greatly decrease survival rates of overwintering bats. Evidence increasingly suggests that evaporative water loss (EWL) may be an important driver of arousal behavior in infected bats. We examined the role that EWL could play in torpor arousals and energy expenditures by developing an individual-based energetics model using EWL as the stimulus for arousal in populations of healthy and WNS-affected little brown myotis (Myotis lucifugus). Our model also examined how EWL could affect spatial distributions of healthy and infected bats within a cave throughout winter. We calculated mean torpor bout duration and survival of populations that inhabited 2 modeled caves typical of both northern and midrange hibernacula. In a northern cave, the mean torpor bout duration was 19.97 days 6 5.49 SD between arousals for healthy bats and 8.60 6 2.11 days for WNS-affected bats, accompanied by survival rates of 0.80 6 0.07 SD (healthy) and 0.04 6 0.02 (infected). In a midrange cave, the mean torpor bout duration was 20.88 6 6.22 days for healthy bats and 8.88 6 2.47 for infected bats, and survival rates were 0.98 6 0.02 (healthy) and 0.55 6 0.05 (infected). When bats clustered, survival rates increased in both healthy and diseased populations; however, slight changes in relative humidity or the rate of EWL from infected skin counteracted these advantages. We show that, by causing an increase in arousal rates, EWL could play an important role in the pathology of WNS. Additionally, populations experiencing shorter southern winters could persist longer than their northern counterparts when faced with WNS, a fact that could be critical in maintaining viable populations for WNS-vulnerable species.

Waking to drink: rates of evaporative water loss determine arousal frequency in hibernating bats

Bats hibernate to cope with low ambient temperatures (T(a)) and low food availability during winter. However, hibernation is frequently interrupted by arousals, when bats increase body temperature (T(b)) and metabolic rate (MR) to normothermic levels. Arousals account for more than 85% of a bat's winter energy expenditure. This has been associated with variation in T(b), T(a) or both, leading to a single testable prediction, i.e. that torpor bout length (TBL) is negatively correlated with T(a) and T(b). T(a) and T(b) were both found to be correlated with TBL, but correlations alone cannot establish a causal link between arousal and T(b) or T(a). Because hydration state has also been implicated in arousals from hibernation, we hypothesized that water loss during hibernation creates the need in bats to arouse to drink. We measured TBL of bats (Pipistrellus kuhlii) at the same T(a) but under different conditions of humidity, and found an inverse relationship between TBL and total evaporative water loss, independent of metabolic rate, which directly supports the hypothesis that hydration state is a cue to arousal in bats.

High metabolic and water-loss rates in caterpillar aggregations: evidence against the resource-conservation hypothesis

Several hypotheses have been proposed for explaining animal aggregation, including energy or water conservation. However, these physiological hypotheses have not been well investigated. Here, we report the effects of aggregation on metabolic ( ) and evaporative water-loss rates ( ) of the gregarious caterpillar Eutricha capensis, by comparing individuals and groups of individuals (N=10-100). Contrary to findings from previous physiological studies, we did not find an advantage to aggregation: unexpectedly, and did not decrease with increasing group size. and generally remained constant or increased in larger groups relative to individuals. The amount of water lost per unit of CO2 exchanged ( : ratio) showed a marked increase in grouped caterpillars, particularly in larger groups. Other benefits of aggregation (e.g. reduced predation or increased growth rates) likely outweigh these potential costs, because individuals of E. capensis aggregate voluntarily despite no obvious energetic or hygric advantage, and other potentially confounding group effects (e.g. increased thermoregulatory advantage or whole-animal activity) are inconsequential. The results of this study provide an important exception to physiological studies reporting enhanced energy or water conservation in animal groups.

Behavioral and physiological correlates of the geographic distributions of amphibious sea kraits (Laticauda spp.)

The physiological costs of living in seawater likely influenced the secondary evolutionary transitions to marine life in tetrapods. However, these costs are alleviated for species that commute between the land and the sea, because terrestrial habitats can provide frequent access to fresh water. Here, we investigate how differences in the ecology and physiology of three sea krait species (Laticauda spp.) interact to determine their environmental tolerances and geographic distributions. These three species vary in their relative use of terrestrial versus marine environments, and they display concomitant adaptations to life on land versus at sea. A species with relatively high dehydration rates in seawater (Laticauda colubrina) occupied oceanic areas with low mean salinities, whereas a species with comparatively high rates of transcutaneous evaporative water loss on land (Laticauda semifasciata) occupied regions with low mean temperatures. A third taxon (Laticauda laticaudata) was intermediate in both of these traits, and yet occupied the broadest geographic range. Our results suggest that the abilities of sea kraits to acquire fresh water on land and tolerate dehydration at sea determine their environmental tolerances and geographic distributions. This finding supports the notion that speciation patterns within sea kraits have been driven by interspecific variation in the degree of reliance upon terrestrial versus marine habitats. Future studies could usefully examine the effects of osmotic challenges on diversification rates in other secondarily marine tetrapod species.

A Phylogenetic Approach to Total Evaporative Water Loss in Mammals

Maintaining appropriate water balance is a constant challenge for terrestrial mammals, and this problem can be exacerbated in desiccating environments. It has been proposed that natural selection has provided desert-dwelling mammals physiological mechanisms to reduce rates of total evaporative water loss. In this study, we evaluated the relationship between total evaporative water loss and body mass in mammals by using a recent phylogenetic hypothesis. We compared total evaporative water loss in 80 species of arid-zone mammals to that in 56 species that inhabit mesic regions, ranging in size from 4 g to 3,500 kg, to test the hypothesis that mammals from arid environments have lower rates of total evaporative water loss than mammals from mesic environments once phylogeny is taken into account. We found that arid species had lower rates of total evaporative water loss than mesic species when using a dichotomous variable to describe habitat (arid or mesic). We also found that total evaporative water loss was negatively correlated with the average maximum and minimum environmental temperature as well as the maximum vapor pressure deficit of the environment. Annual precipitation and the variable Q (a measure of habitat aridity) were positively correlated with total evaporative water loss. These results support the hypothesis that desert-dwelling mammals have lower rates of total evaporative water loss than mesic species after controlling for body mass and evolutionary relatedness regardless of whether categorical or continuous variables are used to describe habitat.

The costs of keeping cool in a warming world: implications of high temperatures for foraging, thermoregulation and body condition of an arid-zone bird.

Recent mass mortalities of bats, birds and even humans highlight the substantial threats that rising global temperatures pose for endotherms. Although less dramatic, sublethal fitness costs of high temperatures may be considerable and result in changing population demographics. Endothermic animals exposed to high environmental temperatures can adjust their behaviour (e.g. reducing activity) or physiology (e.g. elevating rates of evaporative water loss) to maintain body temperatures within tolerable limits. The fitness consequences of these adjustments, in terms of the ability to balance water and energy budgets and therefore maintain body condition, are poorly known. We investigated the effects of daily maximum temperature on foraging and thermoregulatory behaviour as well as maintenance of body condition in a wild, habituated population of Southern Pied Babblers Turdoides bicolor. These birds inhabit a hot, arid area of southern Africa where they commonly experience environmental temperatures exceeding optimal body temperatures. Repeated measurements of individual behaviour and body mass were taken across days varying in maximum air temperature. Contrary to expectations, foraging effort was unaffected by daily maximum temperature. Foraging efficiency, however, was lower on hotter days and this was reflected in a drop in body mass on hotter days. When maximum air temperatures exceeded 35.5°C, individuals no longer gained sufficient weight to counter typical overnight weight loss. This reduction in foraging efficiency is likely driven, in part, by a trade-off with the need to engage in heat-dissipation behaviours. When we controlled for temperature, individuals that actively dissipated heat while continuing to forage experienced a dramatic decrease in their foraging efficiency. This study demonstrates the value of investigations of temperature-dependent behaviour in the context of impacts on body condition, and suggests that increasingly high temperatures will have negative implications for the fitness of these arid-zone birds.

Habitat Selection by Sea Kraits (Laticauda spp.) at Coastal Sites of Orchid Island, Taiwan

Three species of amphibious sea kraits (Laticauda spp.) spend variable time at sea and require fresh water for water balance. Both the rate of cutaneous evaporative water loss and the extent of terrestriality are known to differ among them. Laticauda semifasciata has the greatest rate of water loss and the least extent of terrestriality, whereas L. colubrina exhibits the reverse and L. laticaudata is intermediate. These sea kraits tend to be more abundant at places where there are sources of fresh water, but other factors also influence their distribution. To further clarify the habitat requirements, we investigated the abundance of each species of sea krait at six different habitats and the availability of each type of habitat on Orchid Island, Taiwan. The six habitats were high coral reef without fresh water (HR) and with fresh water (HRF); low coral reef without fresh water (LR) and with fresh water (LRF); sand or gravel coast, which has no coral reef, without fresh water (NR) and with fresh water (NRF). The extent of safety judged from the relative availability of retreat sites, from high to low, was HR, LR, and NR among these habitats. More than 75% of individuals counted for each species were found in HRF. We found no sea kraits in NRF and NR. The most available habitat was LR, but no L. laticaudata or L. semifasciata were found in this habitat. We found 3.3% and 16.7% of L. colubrina in LR and HR, respectively. For L. colubrina, the second abundant habitat was HR, whereas for L. laticaudata and L. semifasciata, the second abundant habitat was LRF. We conclude that both safety (availability of retreat sites) and fresh water are important to the habitat selection of sea kraits. Compared with other species, L. colubrina is characterized by a greater extent of terrestrial habit and possibly greater variety of access to sources of fresh water.

Hydric balance and locomotor performance of an anuran (Rhinella marina) invading the Australian arid zone

Invasive species often encounter environmental conditions well outside those found in their native geographic ranges, and thus provide ideal model systems with which to explore responses to novel abiotic challenges. Within Australia, the invasive cane toad Rhinella marina has colonized areas that are considerably more arid than those found within its native range. Has the colonization of these novel environments been accompanied by shifts in physiology and/or locomotor performance? We measured rates of evaporative water loss, water gain, and effects of desiccation on locomotor performance of cane toads from two invasion fronts: one mesic (the wet‐dry tropics) and one arid (the semi‐desert). The two populations diverged substantially. Contrary to intuition (but consistent with intra‐specific comparisons between other toad populations from mesic vs arid areas), rates of evaporative water loss were lower (not higher) in toads from the mesic population. However, arid‐zone toads gained water more rapidly through their ventral surfaces, and rates of water loss and gain were highly correlated within individual toads from the arid‐zone population. Rates of water exchange in laboratory‐acclimated toads from the semi‐arid zone did not differ from those of free‐ranging conspecifics from the same population, suggesting that divergences between mesic and semi‐arid toads reflect genetic changes that have occurred during the species’ Australian invasion. Mesic and semi‐arid toads showed similar locomotor performance (endurance, distance per hop) when fully hydrated, but locomotor performance declined much more rapidly with desiccation in the mesic toads. Thus, within the short (decades‐long) timespan of the cane toad's Australian invasion, there has been substantial population divergence in the ability to withstand desiccating conditions. If we are to accurately predict the distributions (and hence impacts) of invading organisms, we will need to include adaptation potential in risk assessment schemes.

Cutaneous Resistance to Evaporative Water Loss in the Crab-eating Frog (Fejervarya cancrivora)

Abstract Resistance to cutaneous evaporative water loss has been examined in anuran amphibians that occupy a variety of habitats, except for the ocean. We measured evaporative water loss rate and cutaneous resistance to evaporation in the Crab-eating Frog, Fejervarya cancrivora, a euryhaline species that enters the sea. Studies were conducted on Hoga Island, southeastern Sulawesi, Indonesia. Area-specific evaporative water loss rate was significantly lower in living F. cancrivora than in agar replicas of the frogs and total water loss rate was dependent on body mass. Cutaneous resistance to evaporative water loss was 0.27 sec cm−1, which is the lowest significant resistance known for frogs. Cutaneous resistance may have evolved as a way for F. cancrivora to reduce water loss while on land, thereby offsetting high osmotic losses to seawater before frogs have fully acclimated to higher salinities.

Temperature Fluctuation and Evaporative Loss Rate in an Algae Biofilm Photobioreactor

This study describes the thermal modeling of a novel algal biofilm photobioreactor aimed at cultivating algae for biofuel production. The thermal model is developed to assess the photobioreactor’s thermal profile and evaporative water loss rate for a range of environmental parameters, including ambient air temperature, solar irradiation, relative humidity, and wind speed. First, a week-long simulation of the system has been performed using environmental data for Memphis, TN, on a typical week during the spring, summer, fall, and winter. Then, a sensitivity analysis was performed to assess the effect of each weather parameter on the temperature and evaporative loss rate of the photobioreactor. The range of the daily algae temperature variation was observed to be 12.2 °C, 13.2 °C, 11.7 °C, and 8.2 °C in the spring, summer, fall, and winter, respectively. Furthermore, without active cooling, the characteristic evaporative water loss from the system is approximately 6.0 L/m2 day, 7.3 L/m2 day, 3.4 L/m2 day, and 1.0 L/m2 day in the spring, summer, fall, and winter, respectively.

Desiccation Risk Drives the Spatial Ecology of an Invasive Anuran (Rhinella marina) in the Australian Semi-Desert

Some invasive species flourish in places that impose challenges very different from those faced in their native geographic ranges. Cane toads (Rhinella marina) are native to tropical and subtropical habitats of South and Central America, but have colonised extremely arid regions over the course of their Australian invasion. We radio-tracked 44 adult cane toads at a semi-arid invasion front to investigate how this invasive anuran has managed to expand its geographic range into arid areas that lie outside of its native climatic niche. As predicted from their low physiological control over rates of evaporative water loss, toads selected diurnal shelter sites that were consistently cooler and damper (and thus, conferred lower water loss rates) than nearby random sites. Desiccation risk also had a profound influence on rates of daily movement. Under wet conditions, toads that were far from water moved further between shelter sites than did conspecifics that remained close to water, presumably in an attempt to reach permanent water sources. However, this relationship was reversed under dry conditions, such that only toads that were close to permanent water bodies made substantial daily movements. Toads that were far from water bodies also travelled along straighter paths than did conspecifics that generally remained close to water. Thus, behavioural flexibility—in particular, an ability to exploit spatial and temporal heterogeneity in the availability of moist conditions—has allowed this invasive anuran to successfully colonize arid habitats in Australia. This finding illustrates that risk assessment protocols need to recognise that under some circumstances an introduced species may be able to thrive in conditions far removed from any that it experiences in its native range.

Effects of diet and water supply on energy intake and water loss in a mygalomorph spider in a fluctuating environment of the central Andes

The metabolic and water evaporation strategies in spiders may be part of a set of physiological adaptations to tolerate low or unpredictable food availability, buffering spiders against environmental fluctuations such as those of the high mountains of the central Andes. The aim of this study is to analyze experimentally the variations in metabolic rate and the rate of evaporative water with food and/or water restriction in a high mountain mygalomorph spider population ( Paraphysa sp.). We found that the low metabolism of this spider was not affected by water restriction, but its metabolism was depressed after 3 weeks of food deprivation. The spider did not show seasonal metabolic changes but it presented seasonal changes in the rate of evaporative water loss at high temperatures. Females with egg sacs reduced their metabolic rate and evaporative water at high temperatures. These findings constitute a set of possible adaptations to a highly fluctuating Mediterranean environment, which is completely covered with snow for many months and then progresses rapidly to a very dry climate with high temperatures.

Evaporative Water Loss Is a Plausible Explanation for Mortality of Bats from White-Nose Syndrome

White-nose syndrome (WNS) has caused alarming declines of North American bat populations in the 5 years since its discovery. Affected bats appear to starve during hibernation, possibly because of disruption of normal cycles of torpor and arousal. The importance of hydration state and evaporative water loss (EWL) for influencing the duration of torpor bouts in hibernating mammals recently led to "the dehydration hypothesis," that cutaneous infection of the wing membranes of bats with the fungus Geomyces destructans causes dehydration which in turn, increases arousal frequency during hibernation. This hypothesis predicts that uninfected individuals of species most susceptible to WNS, like little brown bats (Myotis lucifugus), exhibit high rates of EWL compared to less susceptible species. We tested the feasibility of this prediction using data from the literature and new data quantifying EWL in Natterer's bats (Myotis nattereri), a species that is, like other European bats, sympatric with G. destructans but does not appear to suffer significant mortality from WNS. We found that little brown bats exhibited significantly higher rates of normothermic EWL than did other bat species for which comparable EWL data are available. We also found that Natterer's bats exhibited significantly lower rates of EWL, in both wet and dry air, compared with values predicted for little brown bats exposed to identical relative humidity (RH). We used a population model to show that the increase in EWL required to cause the pattern of mortality observed for WNS-affected little brown bats was small, equivalent to a solitary bat hibernating exposed to RH of ∼95%, or clusters hibernating in ∼87% RH, as opposed to typical near-saturation conditions. Both of these results suggest the dehydration hypothesis is plausible and worth pursuing as a possible explanation for mortality of bats from WNS.

House sparrows (Passer domesticus) increase protein catabolism in response to water restriction

Birds primarily rely on fat for energy during fasting and to fuel energetically demanding activities. Proteins are catabolized supplemental to fat, the function of which in birds remains poorly understood. It has been proposed that birds may increase the catabolism of body protein under dehydrating conditions as a means to maintain water balance, because catabolism of wet protein yields more total metabolic and bound water (0.155·H(2)O(-1)·kJ(-1)) than wet lipids (0.029 g·H(2)O(-1)·kJ(-1)). On the other hand, protein sparing should be important to maintain function of muscles and organs. We used quantitative magnetic resonance body composition analysis and hygrometry to investigate the effect of water restriction on fat and lean mass catabolism during short-term fasting at rest and in response to a metabolic challenge (4-h shivering) in house sparrows (Passer domesticus). Water loss at rest and during shivering was compared with water gains from the catabolism of tissue. At rest, water-restricted birds had significantly greater lean mass loss, higher plasma uric acid concentration, and plasma osmolality than control birds. Endogenous water gains from lean mass catabolism offset losses over the resting period. Water restriction had no effect on lean mass catabolism during shivering, as water gains from fat oxidation appeared sufficient to maintain water balance. These data provide direct evidence supporting the hypothesis that water stress can increase protein catabolism at rest, possibly as a metabolic strategy to offset high rates of evaporative water loss.

The Relative Importance of Respiratory Water Loss in Scorpions Is Correlated with Species Habitat Type and Activity Pattern

Scorpions exhibit some of the lowest recorded water loss rates compared with those of other terrestrial arthropods of similar body size. Evaporative water loss (EWL) includes cuticular transpiration and respiratory water loss (RWL) from gas exchange surfaces, that is, book lung lamellae. Estimated fractions of cuticular and respiratory losses currently available from the literature show considerable variation, at least partly as a result of differences in methodology. This study reports RWL rates and their relative importance in scorpions from two families (Buthidae and Scorpionidae), including both xeric and mesic species (or subspecies). Two of the included Buthidae were surface-dwelling species, and another inhabits empty burrows of other terrestrial arthropods. This experimental design enabled correlating RWL importance with scorpion phylogeny, habitat type, and/or homing behavior. Buthidae species exhibited significantly lower EWL rates compared with those of Scorpionidae, whereas effects of habitat type and homing behavior were not significant. Resting RWL rates were not significantly affected by scorpion phylogeny, but rates for the xeric species (totaling ~10% of EWL rates at 30°C) were significantly lower compared with those of mesic species. These lower RWL values were correlated with significantly lower H(2)O/CO(2) emission rates in xeric species. The experimental setup and ~24-h duration of each individual recording allowed estimating the effect of interspecific variation in activity on RWL proportions. The high respiratory losses in active hydrated Scorpio maurus fuscus, totaling 30% of EWL, suggest that behavioral discretion in this species is a more likely mechanism for body water conservation under stressful conditions when compared with the responses of other studied species.

Cutaneous Resistance to Evaporative Water Loss in Brazilian Rhinella (Anura: Bufonidae) from Contrasting Environments

In anurans, cutaneous resistance (RS) to evaporative water loss (EWL) correlates with ecological features and is influenced by taxonomic position. For example, bufonids are regarded as exhibiting a permeable skin that seems typical for terrestrial anurans. However, this assumption is supported by information on only four bufonid species; therefore, the enormous ecological diversity of the family remains poorly investigated. To assess whether variation in RS within related bufonids correlates with environmental aridity, we measured area-specific rates of EWL of two Brazilian populations of Rhinella granulosa (previously Bufo granulosus), one from the Atlantic Forest and other from the semi-arid Caatinga, and compared both with the forest species R. ornata. Rhinella granulosa from the Atlantic Forest had higher cutaneous resistance than conspecifics from Caatinga and R. ornata. Rhinella ornata presented the lowest cutaneous resistance values. However, RS were very close to zero in all three populations. We conclude that enhanced RS is not part of the suite of traits allowing R. granulosa to exploit the Caatinga, and that variation in RS within bufonids may relate to traits other than water conservation. Some information on microhabitat occupation and ventral skin morphology supports the idea that exceptional abilities for detecting and taking up water may be the key factors enhancing the survival of R. granulosa, and possibly other bufonids, in xeric environments.