Prior to measuring evaporative water loss, we maintained the anurans in plastic containers 0. An open flow system was used to measure the rates of evaporative water loss and the resistance to evaporative water loss.
Flow rates of 23 cm 3 s -1 for the larger chambers and 5 cm 3 s -1 for the smaller ones were generated by a set of air pumps connected to a mass flowmeter SS-3 Subsampler—Sable Systems, Las Vegas, Nevada, USA that allowed the same flux for each chamber to be sent individually. Only records corresponding to periods when the animals stayed in a water conservation posture, identified by visual monitoring and constancy of the water vapor density values, were considered for calculations.
Surface area was estimated using the following formula [ 27 ]: where SA means surface area cm 2 and M means body mass g. Saturated water vapor density at the surface of the animal or the agar model was calculated from the ideal gas law using the surface temperature. The resistance to evaporative water loss calculated for the animal and the agar model correspond, respectively, to the total resistance to evaporative water loss and the resistance to evaporative water loss of the boundary layer.
By subtracting the boundary layer resistance from the total resistance to evaporative water loss, we obtained the skin resistance to evaporative water loss REWL [ 28 ]. Although the animals were weighed every 2 minutes to obtain the estimates of RWU, they remained motionless during the tests, and the curves of body mass gain by time presented R 2 values higher than 0.
Geographical coordinates of occurrence for each species were compiled from the speciesLink Project S1 — S17 Figs [ 29 ]. For each coordinate, mean data from to on eight climatic variables annual mean temperature, maximum temperature of the warmest month, minimum temperature of the coldest month, temperature seasonality, annual precipitation, precipitation of the wettest month, precipitation of the driest month and precipitation seasonality were extracted from Worldclim with 30 arc-seconds resolution [ 30 , 31 ] using DIVA-GIS [ 32 ] version 7.
A composite tree with divergence time estimates for the 17 species of anurans was compiled Fig 1 , mainly based on [ 33 ], which is the most comprehensible current phylogenetic hypothesis for the anurans.
Phylogenetic information that was not available in [ 33 ] was gathered from [ 34 , 35 ], as follows: to include D. Finally, P. The phylogenetic information used to build this composite tree was primarily gathered from molecular studies.
For the few instances in which morphological data were employed [ 34 ], these were probably not related to the physiological variables investigated in the present study.
Consequently, the information used to build this composite tree and the data analyzed in the present study were confidently independent. There were no topological divergences between the phylogenetic proposals used to build our composite tree. The number of species included in the study differed for some physiological measurements.
Composite phylogenetic tree for the 17 anuran species included in the present study, with topology and divergence times based on the literature [ 33 — 35 ]. Descriptive statistics were performed for all physiological and climatic data per species, and data were posteriorly transformed to Log 10 for subsequent analyses. For each species, means of the eight climatic variables extracted from each locality were implemented in principal component analyses PCA , and the scores from the components with eigenvalues greater than 1.
We considered any absolute values higher than 0. Again, given that the number of species included in the study differed for some physiological measurements, two PCAs were conducted: one containing climatic data for the 16 species from which there were data on REWL, and another containing climatic data for the 13 species from which data on RWU and SLPD were available. Phylogenetic regressions were used to investigate the relationship between the physiological variables and body mass [ 36 ], and the residuals of data phylogenetic corrected by size were saved to be implemented in a posteriori analyses.
Phylogenetic regressions [ 37 ] were employed to investigate the relationships between physiological variables and climatic data. Additionally, a phylogenetic ANOVA was implemented using the biome where individuals from the different species were collected for physiological measurements Atlantic Forest and the Cerrado as a categorical factor.
Descriptive statistics and principal component analyses of the climatic variables were performed using the software SPSS for Windows version Phylogenetic trees were built using Mesquite version 2. Procedures for phylogenetic size-correction, phylogenetic regressions and phylogenetic ANOVA were conducted with the software R version 3. The phylogenetic regressions were performed using the function gls, from the package nlme to fit a linear model using generalized least squares.
The comparison between sites of collection in the Atlantic Forest and the Cerrado was performed using the function phylANOVA, from the package phytools, with simulations and Bonferroni correction.
The principal component analyses performed on climatic variables retained two components, which were the same when using a data set of 16 or 13 species Table 4. Component 1 explained Component 2 explained The regression line equations stated in the figure represent the conventional linear regression.
Fulfilled circles represent the mean resistance to evaporative water loss for each species and unfilled circles represent the mean rate of water uptake for each species. It is also possible to observe two distinct clusters of points in the phylogenetic regression analyses between the scores of the first climatic component derived from the geographical points of species occurrence and the fitted values of both SLPD and RWU Fig 3.
These two clouds correspond to species from which individuals were collected in localities from the Atlantic Forest and the Cerrado, respectively. Relations between size adjusted sensitivity of locomotor performance to dehydration A and rates of water uptake B with the PC scores from axis 1. The phylogenetically corrected values for the physiological traits show a positive correlation with the PCA component 1 scores that correspond to a direct association between annual mean temperature, maximum temperature of warmest month, minimum temperature of coldest month and precipitation seasonality, which are inversely associated with temperature seasonality, annual precipitation and precipitation of driest month.
Our interspecific comparative analysis showed that some physiological traits of water balance in anurans, particularly REWL and RWU, show pervasive allometric relations with body mass. Additionally, the analyses showed an association of interspecific variation in RWU and SLPD with climatic characteristics associated with geographical distribution.
These results, based on phylogenetically informed analyses, suggest a pattern of adaptation of anuran water balance to abiotic conditions. Our results suggest that a higher REWL might at least partially compensate for the increased rates of water loss associated with the evolution of smaller body masses in anurans. These results differ from those of previous studies that did not find a relation between interspecific variation in anuran REWL and body mass [ 10 , 40 ].
However, these previous studies included species characterized by very high REWL and relatively low body mass, and these species might, at least in part, mask the allometric function of REWL. A positive allometric association of RWU with body mass has also been previously suggested to exist to some extent in anurans [ 19 — 21 ]. According to these authors, the required time to reach maximum blood cell flux through the pelvic patch increases with body mass.
Otherwise, the magnitude of this flux seems to be related to the environment, given that species from xeric environments show higher flux than species from mesic environments, despite the differences in body mass [ 19 — 21 ].
Our results corroborate the previous positive correlation between RWU and body mass and are based on a phylogenetically controlled analysis that includes a larger number of species. However, large anurans still need absolutely more water to rehydrate.
In this way, our results suggest that a higher hydration rate might be selected to compensate for increased body size. The underlying mechanisms of the body size-related differences in RWU still remain to be investigated, but they might be associated with differences in vascularization [ 18 ] and permeability of the pelvic patch due to the density of aquaporins [ 41 — 43 ].
We also found a clear pattern of association between interspecific variation in RWU and SLPD with climatic variables extracted from the geographical points of occurrence for the different species included in this analysis. In particular, the species with geographical occurrence encompassing areas characterized by higher and more seasonally uniform temperatures, and lower and more seasonally concentrated precipitation, had higher RWU and SLPD.
Moreover, species collected at sites within the domains of the Atlantic Forest and the Cerrado form two dissociated clusters of data distribution in the phylogenetic regression analyses between these physiological variables and the first climatic component derived from the geographical points of occurrence, reinforcing the pattern that emerged from the continuous covariation.
Although these data clearly show the association between the phenotypic variables and the climate of the occurrence points, these data do not allow verification of the contribution of different processes underlying this phenotypic variation genetic adaptation or acclimatization. Phenotypic plasticity might even play a significant role determining the interspecific physiological variation associated with seasonal acclimatization [ 10 , 11 ], given that individuals from different species were collected and measured at different seasons.
The analysis of populations from the same species collected in both biomes, as well as the investigation of the acclimation capacity of these physiological variables, might shed light on these topics. The inclusion of species inhabiting environments characterized by more drastic water restriction, such as arid and semi-arid localities, might also expand the knowledge of patterns of water balance adaptations in anurans.
Several authors have previously reported that terrestrial or arid-dwelling species of anurans show higher hydration rates when compared to semi-aquatic species or to those occurring in mesic environments [ 17 , 20 , 21 ]. These results are consistent with morphological observations showing that species from xeric environments have more vascularized ventral skin [ 18 ].
These joint results suggest a pattern of directional selection of individuals able to hydrate more efficiently and at faster rates once they find water sources in environments where water represents a scarce resource. Again, our results support these previous results and interpretations through a comparative and phylogenetically informed approach.
It is important to highlight that the interspecific variation in RWU reported here was based on measurements from a free water surface, a situation that might not be ecologically relevant for many species. In the field, many species might actually rehydrate more frequently from humid soil, mainly outside of the breeding season [ 44 ].
In this way, RWU from a free water surface might not be directly selected in nature, but it might be functionally associated with differences in efficiency of rehydration from humid substrates. This hypothesis remains to be tested.
Previous comparative studies have found a pattern of negative association between SLPD and the occupation of open and more water-restricted environments [ 6 — 8 ]. These previous results suggest that individuals who are able to maintain behavioral performance at lower states of hydration are under directional selection in water-restricted environments. Our present analysis showed the opposite pattern: species with geographical distribution more tightly associated with mesic environments show lower SLPD than species with geographical distribution encompassing more water-restricted environments.
Although our results contradict previous studies, we believe that this opposite pattern to those described for previous studies might be associated with underlying methodological differences. The present study was conducted with a much higher number of species, split into several phylogenetic lineages, and incorporated phylogenetically corrected analyses.
Furthermore, our study analyzed the association between the physiological traits and climatic data instead of collecting data exclusively on physiology and associating it to namely characterized environments. In this way, we believe that our results are robust and that this pattern might be associated with selection on temporal patterns of activity in these different environments. In environments characterized by lower and more seasonally concentrated precipitation, such as the Cerrado, individuals might be selected to concentrate reproduction and other general activities, such as foraging, to restricted periods with a higher probability of precipitation.
This concentrated pattern of activity might prevent selection from acting on the sensitivity of locomotion to dehydration in the Cerrado. Otherwise, species from environments characterized by higher and seasonally distributed precipitation might maintain continuous activity, with several species showing year-round reproduction or at least foraging activity [ 45 — 49 ].
This sustained activity at periods of lower relative humidity might allow directional selection on SLPD in the Atlantic Forest. This reasoning remains largely speculative, and comparative studies including the duration of reproductive season on different localities are necessary to test hypotheses along these lines. In the present study, we performed tests of SLPD at a single temperature. In this way, we need to consider that species from the Atlantic Forest and Cerrado might show different optimum temperatures where the effects of dehydration are reduced, and the comparative analysis of SLPD at these specific temperatures might change the patterns described here.
Our analysis did not recover an interspecific covariation between REWL and the climatic variables associated with geographical distribution, corroborating results from previous studies that attempted to associate variation in REWL with differences in habitat [ 38 , 50 — 54 ].
These joint results do not corroborate the long-lasting corollary reasoning that high skin permeability would be a direct limitation for the occupation of more water-restricted environments by amphibians and that individuals displaying high REWL and inhabiting these environments would be strongly selected.
It is possible that behavioral adjustments, such as on patterns of time of reproduction and microenvironmental selection during activity might also prevent directional selection on REWL. Furthermore, several studies have emphasized a consistent pattern of anuran interspecific association between REWL and the habit, with arboreal species displaying higher values than terrestrial and semi-aquatic ones [ 9 , 10 , 55 ].
Although we sampled a relatively high number of species for the present investigation, the interspecific variation in habits are highly skewed through the phylogeny, preventing the analysis of the relationship between REWL and habits in this study. In order to protect our water quality in and around our homes it is important to limit sidewalk salts, garden fertilizers and pesticides as much as possible.
Make sure to follow label instructions and application rates. Amphibians are also beneficial as they eat insects, including agricultural pests and serve as food to other wildlife. They have also been an important role in research and medicine. Each day, consider taking small steps in your own house to help the amphibians that call the Garden State home. You can follow any responses to this entry through the RSS 2. Most amphibians have thin skin that is very permeable allowing liquids and gases to pass through it easily.
This is important for two reasons. First, it means that their skin helps them breathe, since oxygen passes easily through it. Second, it means that amphibians lose a lot of water through their skin. This is why most amphibians are found in moist or humid environments, where they can re-load their water reserves. The word amphibian comes from the Greek word amphibios , meaning "a being with a double life.
While dual residence is the rule for most amphibians, some species are strictly aquatic water-dwelling and some are strictly terrestrial land-dwelling. More accurately, amphibians' "double life" refers to two distinct life stages -- a larval stage and an adult stage. Most amphibians lay eggs, which hatch into larvae and undergo an amazing transformation or metamorphosis as they move from larval to adult stages.
For instance, tadpoles the larval stage of frogs have gills and a tail -- features that enable them to live underwater. During metamorphosis, tadpoles lose their gills and develop lungs so they can breathe out of water. At the same time, they begin to grow limbs and lose their tails.
They are important grazers in aquatic systems because they help with nutrient recycling and control algae populations, which help to maintain the health of freshwater ecosystems.
Sometimes tadpoles will eat each other, especially if food resources are low. Some tadpoles eat insect larvae and tiny organisms that are found in the water. Although many species are only active at night, there are some that are active during the day.
Amphibians are usually active at night because they are harder to see and can avoid being eaten. Poisonous amphibians that are brightly colored are often active during the day. Bright colors on an animal will warn predators that they are poisonous, so they do not have to worry about predators. Yes, there are many amphibians that hibernate. Amphibians do not like extreme temperatures. During the cold winter months in non-tropic areas, most amphibians will either hibernate in the mud at the bottom of water or dig down into the ground to hibernate.
Some amphibians stow away in cracks in logs or between rocks during the winter. They slow their metabolism and their heartbeats down and survive off stored body reserves throughout the winter.
There are some frog species that can even survive freezing temperatures by maintaining a high level of glucose in their blood that acts like antifreeze. Some of the frog will actually freeze, like their bladder, but their blood and vital organs do not freeze. The heart can stop beating and the frog can stop breathing, but it when it thaws out, it will still be alive. No, only some species of amphibians are poisonous. Usually they are brightly colored to warn predators of their toxic nature.
Most amphibians secrete chemicals from their skin to make them taste icky to predators or make it difficult to handle them. These secretions can be slippery or can be sticky and irritating to the skin.
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