Adaptations of the reed frog Hyperolius viridiflavus (Amphibia, Anura, Hyperoliidae) to its arid environment. VII. The heat budget of Hyperolius viridiflavus nitidulus and the evolution of an optimized body shape

Infrared camouflage in leaf-sitting frogs: a cautionary tale on adaptive convergence

Many cryptic green animals match leaves in invisible near-infrared (NIR) wavelengths. This observation is an enduring puzzle because animals do not see NIR light, so NIR background matching is unlikely to contribute to visual camouflage. Two alternative explanations have been proposed-infrared camouflage (i.e. matching the temperature of the background) and thermoregulation-but neither hypothesis has been experimentally tested. To test these hypotheses, we developed bilayer coatings that mimicked the reflectivity of green leaf-sitting frogs with high NIR (HNIR) or low NIR (LNIR) reflectance. Under a solar simulator in the laboratory, agar model frogs with LNIR reflectance heated up more quickly and reached higher temperatures than those with HNIR reflectance. However, when placed in a tropical rainforest (natural habitat of leaf-sitting frogs), HNIR and LNIR models did not significantly differ in the similarity of surface temperature to the adjacent leaves or in core temperature, thus failing to support the infrared camouflage and thermoregulation hypotheses, respectively. The lack of difference between treatments is probably due to the limited exposure of frogs to direct solar radiation in their natural habitats. We propose an explanation for NIR background matching based on specific mechanisms underlying green coloration and translucence in frogs and caution against assuming adaptive convergence.

Parameterizing mechanistic niche models in biophysical ecology: a review of empirical approaches

Mechanistic niche models are computational tools developed using biophysical principles to address grand challenges in ecology and evolution, such as the mechanisms that shape the fundamental niche and the adaptive significance of traits. Here, we review the empirical basis of mechanistic niche models in biophysical ecology, which are used to answer a broad array of questions in ecology, evolution and global change biology. We describe the experiments and observations that are frequently used to parameterize these models and how these empirical data are then incorporated into mechanistic niche models to predict performance, growth, survival and reproduction. We focus on the physiological, behavioral and morphological traits that are frequently measured and then integrated into these models. We also review the empirical approaches used to incorporate evolutionary processes, phenotypic plasticity and biotic interactions. We discuss the importance of validation experiments and observations in verifying underlying assumptions and complex processes. Despite the reliance of mechanistic niche models on biophysical theory, empirical data have and will continue to play an essential role in their development and implementation.

Body coloration and mechanisms of colour production in Archelosauria: the case of deirocheline turtles

Animal body coloration is a complex trait resulting from the interplay of multiple mechanisms. While many studies address the functions of animal coloration, the mechanisms of colour production still remain unknown in most taxa. Here we compare reflectance spectra, cellular, ultra- and nano-structure of colour-producing elements, and pigment types in two freshwater turtles with contrasting courtship behaviour, Trachemys scripta and Pseudemys concinna. The two species differ in the distribution of pigment cell-types and in pigment diversity. We found xanthophores, melanocytes, abundant iridophores and dermal collagen fibres in stripes of both species. The yellow chin and forelimb stripes of both P. concinna and T. scripta contain xanthophores and iridophores, but the post-orbital regions of the two species differ in cell-type distribution. The yellow post-orbital region of P. concinna contains both xanthophores and iridophores, while T. scripta has only xanthophores in the yellow-red postorbital/zygomatic regions. Moreover, in both species, the xanthophores colouring the yellow-red skin contain carotenoids, pterins and riboflavin, but T. scripta has a higher diversity of pigments than P. concinna. Trachemys s. elegans is sexually dichromatic. Differences in the distribution of pigment cell types across body regions in the two species may be related to visual signalling but do not match predictions based on courtship position. Our results demonstrate that archelosaurs share some colour production mechanisms with amphibians and lepidosaurs (i.e. vertical layering/stacking of different pigment cell types and interplay of carotenoids and pterins), but also employ novel mechanisms (i.e. nano-organization of dermal collagen) shared with mammals.

Thermal equilibrium and temperature differences among body regions in European plethodontid salamanders

Information on species thermal physiology is extremely important to understand species responses to environmental heterogeneity and changes. Thermography is an emerging technology that allows high resolution and accurate measurement of body temperature, but until now it has not been used to study thermal physiology of amphibians in the wild. Hydromantes terrestrial salamanders are strongly depending on ambient temperature for their activity and gas exchanges, but information on their body temperature is extremely limited. In this study we tested if Hydromantes salamanders are thermoconform, we assessed whether there are temperature differences among body regions, and evaluated the time required to reach the thermal equilibrium. During summers of 2014 and 2015 we analysed 56 salamanders (Hydromantes ambrosii and Hydromantes italicus) using infrared thermocamera. We photographed salamanders at the moment in which we found them and 1, 2, 3, 4, 5 and 15min after having kept them in the hands. Body temperature was equal to air temperature; salamanders attained the equilibrium with air temperature in about 8min, the time required to reach equilibrium was longer in individuals with large body size. We detected small temperature differences between body parts, the head being slightly warmer than the body and the tail (mean difference: 0.05°C). These salamanders quickly reach the equilibrium with the environment, thus microhabitat measurement allows obtaining accurate information on their tolerance limits.

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.

Physiological basis for diurnal activity in dispersing juvenile Bufo granulosus in the Caatinga, a Brazilian semi-arid environment

Diurnal activity is characteristic of many toad species, including Bufo granulosus from the Brazilian semi-arid biome called the Caatinga. Because of their patterns of activity, juvenile toads are exposed to hot and dehydrating conditions. Our investigation focuses on temperature and water relationships, and is based on the prediction that anuran diurnal activity in a semi-arid environment must be associated with morphological, physiological and behavioral traits enhancing thermal tolerances, capacity for performance at high temperatures and water balance. To test specific hypothesis related with this prediction, we investigated postmetamorphic B. granulosus and collected data on thermal tolerances and preferences, thermal safety margins, thermal dependence of locomotor behavior, thermal and kinetic properties of citrate synthase (CS), and skin morphophysiology. This information was compared with additional data from adult conspecifics and adult toads from sympatric species or from species from more moderate environments. We found that juvenile B. granulosus exhibit the highest critical maximum temperature reported for toads (44.2 degrees C) and are well suited to move at high temperatures. However, and in contrast with juveniles of other Bufo species, they do not show thermal preferences in a gradient and appear to hydroregulate more than thermoregulate. The CS of adult and juvenile toads shows typical patterns of thermal sensibility, but the thermal stability of this enzyme is much higher in juveniles than in adult Bufo of any other species studied. The inguinal skin exhibits a complex folding pattern and seems highly specialized for capillary water uptake. Diurnal activity in juvenile B. granulosus is possible given high thermal tolerances, keen ability to detect and uptake water, and avoidance behaviors.

Frogs flee from the sound of fire

Fire has an important role in the sensory ecology of many animals. Using acoustic cues to detect approaching fires may give slow-moving animals a head start when fleeing from fires. We report that aestivating juvenile reed frogs (Hyperolius nitidulus) respond to playbacks of the sound of fire by fleeing in the direction of protective cover, where they are safe. This is a novel response to fire not known to occur in other animals. Moreover, we identify the rapid rise-time of the crackling sound of fire as the probable cue used. These results suggest that amphibian hearing not only has evolved through sexual selection, but also must be viewed in a broader context.

Regulation of body water balance in reedfrogs (superspecies Hyperolius viridiflavus and Hyperolius marmoratus: Amphibia, Anura, Hyperoliidae) living in unpredictably varying savannah environments

The regulation of body water balance was examined in the reedfrogs Hyperolius marmoratus taeniatus and Hyperolius viridiflavus ommatostictus. Temperature and stage of post-metamorphic development significantly affected the rate of water uptake. Hydrated reedfrogs prevented hyperhydration by voiding diluted urine when obtaining water. Within 48 hr after rehydration, body fluid osmolality remained at low levels, which may be supportive to counter excessive cutaneous water influx in hydrated frogs. Once evaporative water loss exceeded 10-12% total body mass, reedfrogs became anuric. The rate of water uptake strongly increased with increasing body water deficit. Both the anuric response and the increased rate of water uptake are assumed to strongly enhance the efficacy of using very briefly available water sources during dry-period conditions. Dry-adapted and estivating reedfrogs survived evaporative water losses between 40 and 55% total body mass. Bladder fluid stores contributed substantially to this desiccation tolerance. During a 16-day period of desiccation, H. v. ommatostictus could replace approximately 25% of evaporative water loss from the bladder fluid store. During desiccation, the level of free amino acids selectively increased in the gastrocnemius muscle tissue, which may support cell volume regulation and/or protect cellular structures from osmotic stresses. Even strongly dehydrated reedfrogs rehydrated quickly with no obvious osmoregulatory problem. Rehydration was associated with a higher than expected decrease of free amino acids in the gastrocnemius muscle tissue, a response that may help to protect cells from bursting during fast rehydration.