Linking physiology and climate to infer species distributions in Australian skinks.

Climate has a key impact on animal physiology, which in turn can have a profound influence on geographic distributions. Yet, the mechanisms linking climate, physiology and distribution are not fully resolved. Using an integrative framework, we tested the predictions of the climatic variability hypothesis (CVH), which states that species with broader distributions have broader physiological tolerance than range-restricted species, in a group of Lampropholis skinks (8 species, 196 individuals) along a latitudinal gradient in eastern Australia. We investigated several physiological aspects including metabolism, water balance, thermal physiology, thermoregulatory behaviour and ecological performance. Additionally, to test whether organismal information (e.g. behaviour and physiology) can enhance distribution models, hence providing evidence that physiology and climate interact to shape range sizes, we tested whether species distribution models incorporating physiology better predict the range sizes than models using solely climatic layers. In agreement with the CVH, our results confirm that widespread species can tolerate and perform better at broader temperature ranges than range-restricted species. We also found differences in field body temperatures, but not thermal preference, between widespread and range-restricted species. However, metabolism and water balance did not correlate with range size. Biophysical modelling revealed that the incorporation of physiological and behavioural data improves predictions of Lampropholis distributions compared with models based solely on macroclimatic inputs, but mainly for range-restricted species. By integrating several aspects of the physiology and niche modelling of a group of ectothermic animals, our study provides evidence that physiology correlates with species distributions. Physiological responses to climate are central in establishing geographic ranges of skinks, and the incorporation of processes occurring at local scales (e.g. behaviour) can improve species distribution models.

Acclimation of thermal physiology to new basking regimes in a widespread Australian skink.

Changes in thermal environments are a challenge for many ectotherms, as they would have to acclimate their physiology to new thermal environments to maintain high-levels of performance. Time spent basking is key for many ectothermic animals to keep their body temperature within optimal thermal ranges. However, little is known about the impact of changes in basking time on the thermal physiology of ectothermic animals. We investigated how different basking regimes (low intensity vs high intensity) affected key thermal physiological traits of a widespread Australian skink (Lampropholis delicata). We quantified thermal performance curves and thermal preferences of skinks subjected to low and high intensity basking regimes over a 12-week period. We found that skinks acclimated their thermal performance breadth in both basking regimes, with the skinks from the low-intensity basking regime showing narrower performance breadths. Although maximum velocity and optimum temperatures increased after the acclimation period, these traits did not differ between basking regimes. Similarly, no variation was detected for thermal preference. These results provide insight into mechanisms that allow these skinks to successfully overcome environmental constraints in the field. Acclimation of thermal performance curves seems to be key for widespread species to colonise new environments, and can buffer ectothermic animals in novel climatic scenarios.

Comparison of vertebrate skin structure at class level: A review.

The skin is a barrier between the internal and external environment of an organism. Depending on the species, it participates in multiple functions. The skin is the organ that holds the body together, covers and protects it, and provides communication with its environment. It is also the body's primary line of defense, especially for anamniotes. All vertebrates have multilayered skin composed of three main layers: the epidermis, the dermis, and the hypodermis. The vital mission of the integument in aquatic vertebrates is mucus secretion. Cornification began in apmhibians, improved in reptilians, and endured in avian and mammalian epidermis. The feather, the most ostentatious and functional structure of avian skin, evolved in the Mesozoic period. After the extinction of the dinosaurs, birds continued to diversify, followed by the enlargement, expansion, and diversification of mammals, which brings us to the most complicated skin organization of mammals with differing glands, cells, physiological pathways, and the evolution of hair. Throughout these radical changes, some features were preserved among classes such as basic dermal structure, pigment cell types, basic coloration genetics, and similar sensory features, which enable us to track the evolutionary path. The structural and physiological properties of the skin in all classes of vertebrates are presented. The purpose of this review is to go all the way back to the agnathans and follow the path step by step up to mammals to provide a comparative large and updated survey about vertebrate skin in terms of morphology, physiology, genetics, ecology, and immunology.

How do the physiological traits of a lizard change during its invasion of an oceanic island?

Physiology is crucial for the survival of invasive species in new environments. Yet, new climatic conditions and the limited genetic variation found within many invasive populations may influence physiological responses to new environmental conditions. Here, we studied the case of the delicate skinks (Lampropholis delicata) invading Lord Howe Island (LHI), Australia. On LHI, the climate is different from the mainland source of the skinks, and independent introduction events generated invasive populations with distinct genetic backgrounds. To understand how climate and genetic background may shape physiological responses along biological invasions, we compared the physiological traits of a source and two invasive (single-haplotype and multi-haplotype) populations of the delicate skink. For each population, we quantified physiological traits related to metabolism, sprint speed, and thermal physiology. We found that, for most physiological traits analysed, population history did not influence the ecophysiology of delicate skinks. However, invasive populations showed higher maximum speed than the source population, which indicates that locomotor performance might be a trait under selection during biological invasions. As well, the invasive population with a single haplotype was less cold-tolerant than the multi-haplotype and source populations. Our results suggest that limited genetic variability and climate may influence physiological responses of invasive organisms in novel environments. Incorporating the interplay between genetic and physiological responses into models predicting species invasions can result in more accurate understanding of the potential habitats those species can occupy.

Seasonal variation in the thermal biology of a terrestrial toad, Rhinella icterica (Bufonidae), from the Brazilian Atlantic Forest.

As ectotherms, amphibians may exhibit changes in their thermal biology associated with spatial and temporal environmental contingencies. However, our knowledge on how amphibian´s thermal biology responds to seasonal changes in the environment is restricted to a few species, mostly from temperate regions, in a marked contrast with the high species diversity found in the Neotropics. We investigated whether or not the seasonal variation in climatic parameters from a high-montane ombrophilous forest in the Brazilian Atlantic Forest could lead to concurrent adjustments in the thermal biology of the terrestrial toad Rhinella icterica. We measured active body temperature (Tb) in the field, and preferred body temperature (Tpref) and thermal tolerance (critical thermal minimum, CTmin, and maximum, CTmax) in the laboratory, for toads collected at two distinct seasons: warm/wet and cold/dry. We also measured operative environmental temperatures (Te) using agar toad models coupled with dataloggers distributed in different microhabitats in the field to estimate accuracy (db) and effectiveness (E) of thermoregulation of the toads for both seasons. Toads had higher Tpref in the warm/wet season compared to the cold/dry season, even though no seasonal change occurred in field Tb's. In the warm/wet season, toads decreased the accuracy of thermoregulation and avoided thermally favorable microhabitats, while in the cold/dry season they increased the accuracy of thermoregulation and exhibited high degree of thermoconformity. This result may encompass thermoregulatory adjustments to seasonal changes in Te's, but may also reflect seasonal differences in compromises between Tb regulation and other ecologically relevant activities (reproduction, foraging). Toads did not exhibit changes in CTmin or CTmax, which indicates a low risk of exposure to extreme temperatures in this particular habitat, at both seasons, possibly combined with a low flexibility of this trait. Overall, our study shows seasonal acclimatization in some aspects of the thermal biology of the toad, R. icterica.

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.