Kidney Mass and Relative Medullary Thickness of Rodents in Relation to Habitat, Body Size, and Phylogeny

New insights into morphological adaptation in common mole-rats (Cryptomys hottentotus hottentotus) along an aridity gradient

Morphological adaptation is the change in the form of an organism that benefits the individual in its current habitat. Mole-rats (family Bathyergidae), despite being subterranean, are impacted by both local and broad-scale environmental conditions that occur above ground. Common mole-rats (Cryptomys hottentotus hottentotus) present an ideal mammalian model system for the study of morphological variation in response to ecology, as this species is found along an aridity gradient and thus can be sampled from geographically non-overlapping populations of the same species along an environmental longitudinal cline. Using the mass of five internal organs, ten skeletal measurements and 3D morphometric analyses of skulls, we assessed the morphology of wild non-breeding individuals from five common mole-rat populations in South Africa. We found that the body mass and mean relative mass of the spleen and kidneys in arid populations was larger, and individuals from arid regions possessed shorter legs and larger inter-shoulder widths compared to individuals from mesic regions. Additionally, arid populations demonstrated greater skull depth, and shape change of features such as angular processes of the lower jaw than mesic individuals, indicating that these distinct geographic populations show differences corresponding to the aridity gradient, potentially in response to environmental factors such as the variation in food sources found between different habitats, in addition to different soil compositions found in the different regions. Arid populations potentially require a stronger jaw and neck musculature associated with mastication to chew xeric-adapted plants and to dig through hard soil types, whereas mesic populations excavate through soft, looser soil and may make use of their front limbs to aid the movement of soils when digging. Aridity influences the morphology of this species and could indicate the impact of environmental changes on speciation and mammalian skull morphology.

Effects of the environment on the evolution of the vertebrate urinary tract

Evolution of the vertebrate urinary system occurs in response to numerous selective pressures, which have been incompletely characterized. Developing research into urinary evolution led to the occurrence of clinical applications and insights in paediatric urology, reproductive medicine, urolithiasis and other domains. Each nephron segment and urinary organ has functions that can be contextualized within an evolutionary framework. For example, the structure and function of the glomerulus and proximal tubule are highly conserved, enabling blood cells and proteins to be retained, and facilitating the elimination of oceanic Ca+ and Mg+. Urea emerged as an osmotic mediator during evolution, as cells of large organisms required increased precision in the internal regulation of salinity and solutes. As the first vertebrates moved from water to land, acid-base regulation was shifted from gills to skin and kidneys in amphibians. In reptiles and birds, solute regulation no longer occurred through the skin but through nasal salt glands and post-renally, within the cloaca and the rectum. In placental mammals, nasal salt glands are absent and the rectum and urinary tracts became separate, which limited post-renal urine concentration and led to the necessity of a kidney capable of high urine concentration. Considering the evolutionary and environmental selective pressures that have contributed to renal evolution can help to gain an increased understanding of renal physiology.

Renal adaptation in relation to insectivorous feeding habit in the greater mouse-eared bat, Myotis myotis (Chiroptera: Vespertilionidae)

We examined the histological structure of the kidneys of Myotis myotis to better understand their structural adaptations to dietary habits. M. myotis is an insectivorous bat species that belongs to the family Vespertilionidae. The kidneys of M. myotis are unilobular, bean-shaped, and surrounded by a renal capsule. The two parts are distinguished by a thin cortex and a thicker medulla. Renal corpuscles consist of the glomerulus and Bowman's capsule. The proximal tubule consists of cubic cells with a well-developed brush border, whereas the distal tubule is lined with a simple cubic epithelium without a brush border. The Henle's loop, located in the medullary region, was composed of flat cells. The microvilli of proximal tubule epithelial cells and basal lamina of proximal and distal tubule epithelial cells were periodic acid Schiff (PAS)-positive. The PAS-positive reaction of the microvilli of proximal tubular epithelial cells and basal lamina of proximal and distal tubule epithelial cells is due to the presence of glycogen, which may be used as an energy substrate during absorption. The presence of acidic glycoconjugates in the papilla was demonstrated by Alcian blue (pH 2.5)-PAS staining. According to the result of silver impregnation staining, it was determined that reticular fibers form a dense fibrillary network in the kidney parenchymal tissue. Reticular fibers are responsible for demarcating and supporting the borders of cells by forming a thin network of fibrils beneath the basal lamina of the cells. Structural features in the kidney, such as a thin cortex and thicker medulla, long conical papilla, and division of the thick medulla into inner and outer regions, of M. myotis may be an adaptation to produce concentrated urine, thereby reducing water loss associated with insectivorous feeding habits.

Mobilisation of jerboa kidney gene networks during dehydration and opportunistic rehydration

Desert animals have evolved systems that enable them to thrive under dry conditions. Focusing on the kidney, we have investigated the transcriptomic adaptations that enable a desert rodent, the Lesser Egyptian Jerboa (Jaculus jaculus), to withstand water deprivation and opportunistic rehydration. Analysis of the whole kidney transcriptome showed many differentially expressed genes in the Jerboa kidney, 6.4% of genes following dehydration and an even greater number (36.2%) following rehydration compared to control. Genes correlated with the rehydration condition included many ribosomal protein coding genes suggesting a concerted effort to accelerate protein synthesis when water is made available. We identify an increase in TGF-beta signaling antagonists in dehydration (e.g., GREM2). We also describe expression of multiple aquaporin and solute carrier transporters mapped to specific nephron segments. The desert adapted renal transcriptome presented here is a valuable resource to expand our understanding of osmoregulation beyond that derived from model organisms.

The Inverse Krogh Principle: All Organisms Are Worthy of Study

AbstractKrogh's principle states, "For such a large number of problems there will be some animal of choice, or a few such animals, on which it can be most conveniently studied." The downside of picking a question first and then finding an ideal organism on which to study it is that it will inevitably leave many organisms neglected. Here, we promote the inverse Krogh principle: all organisms are worthy of study. The inverse Krogh principle and the Krogh principle are not opposites. Rather, the inverse Krogh principle emphasizes a different starting point for research: start with a biological unit, such as an organism, clade, or specific organism trait, then seek or create tractable research questions. Even the hardest-to-study species have research questions that can be asked of them: Where does it fall within the tree of life? What resources does it need to survive and reproduce? How does it differ from close relatives? Does it have unique adaptations? The Krogh and inverse Krogh approaches are complementary, and many research programs naturally include both. Other considerations for picking a study species include extreme species, species informative for phylogenetic analyses, and the creation of models when a suitable species does not exist. The inverse Krogh principle also has pitfalls. A scientist that picks the organism first might choose a research question not really suited to the organism, and funding agencies rarely fund organism-centered grant proposals. The inverse Krogh principle does not call for all organisms to receive the same amount of research attention. As knowledge continues to accumulate, some organisms-models-will inevitably have more known about them than others. Rather, it urges a broader search across organismal diversity to find sources of inspiration for research questions and the motivation needed to pursue them.

Shared Patterns of Gene Expression and Protein Evolution Associated with Adaptation to Desert Environments in Rodents

Desert specialization has arisen multiple times across rodents and is often associated with a suite of convergent phenotypes, including modification of the kidneys to mitigate water loss. However, the extent to which phenotypic convergence in desert rodents is mirrored at the molecular level is unknown. Here, we sequenced kidney mRNA and assembled transcriptomes for three pairs of rodent species to search for shared differences in gene expression and amino acid sequence associated with adaptation to deserts. We conducted phylogenetically independent comparisons between a desert specialist and a non-desert relative in three families representing ∼70 million years of evolution. Overall, patterns of gene expression faithfully recapitulated the phylogeny of these six taxa providing a strong evolutionary signal in levels of mRNA abundance. We also found that 8.6% of all genes showed shared patterns of expression divergence between desert and non-desert taxa, much of which likely reflects convergent evolution, and representing more than expected by chance under a model of independent gene evolution. In addition to these shared changes, we observed many species-pair-specific changes in gene expression indicating that instances of adaptation to deserts include a combination of unique and shared changes. Patterns of protein evolution revealed a small number of genes showing evidence of positive selection, the majority of which did not show shared changes in gene expression. Overall, our results suggest that convergent changes in gene regulation play an important role in the complex trait of desert adaptation in rodents.

Increased lipid peroxidation, depleted non-enzymatic antioxidant, and variability in trace elements concentration in serum are correlated with Bangladeshi end-stage renal disease population

INTRODUCTION

End-stage renal disease (ESRD) is an abnormality where the kidneys are not usually working. This case-control study was planned to determine the extent of serum lipid peroxidation, non-enzymatic antioxidant (vitamin c), and trace elements in 50 patients with ESRD as cases and 50 normal healthy individuals as controls.

METHODS

Determination of lipid peroxidation was carried out by ascertaining concentration of malondialdehyde (MDA) and vitamin C in serum using UV spectrophotometry whereas atomic absorption spectroscopy was used for trace elements estimation. The statistical analysis was conducted via the independent t-test samples and Pearson correlation test.

RESULTS

The blood serum study has shown substantially higher MDA values than the control level and lowers vitamin C levels in the patient population (P < .001). A negative correlation was found between the vitamin C in serum with BMI and MDA for both patients (r = -0.017 and r = -0.132, respectively) and the control group (r = -0.014 and r = -0.229, respectively) after Pearson's correlation analysis. Regarding trace elements, significantly (P < .001) lower concentrations of zinc, copper, and manganese were found in the patient group than control subjects. Inter-element-relationship established a strong positive harmonization between these studied elements in both the cases of patients and control subjects.

CONCLUSION

Our results indicate strong associations of the pathogenesis of ESRD with depleted non-enzymatic antioxidant, increased lipid peroxidation, and inconsistency in trace elements concentration in serum, which may provide a prognostic tool for the treatment of this concerning the disease.

Multiomic analysis of the Arabian camel (Camelus dromedarius) kidney reveals a role for cholesterol in water conservation

The Arabian camel (Camelus dromedarius) is the most important livestock animal in arid and semi-arid regions and provides basic necessities to millions of people. In the current context of climate change, there is renewed interest in the mechanisms that enable camelids to survive in arid conditions. Recent investigations described genomic signatures revealing evolutionary adaptations to desert environments. We now present a comprehensive catalogue of the transcriptomes and proteomes of the dromedary kidney and describe how gene expression is modulated as a consequence of chronic dehydration and acute rehydration. Our analyses suggested an enrichment of the cholesterol biosynthetic process and an overrepresentation of categories related to ion transport. Thus, we further validated differentially expressed genes with known roles in water conservation which are affected by changes in cholesterol levels. Our datasets suggest that suppression of cholesterol biosynthesis may facilitate water retention in the kidney by indirectly facilitating the AQP2-mediated water reabsorption.

Gene expression plasticity and desert adaptation in house mice

Understanding how organisms adapt to new environments is a key problem in evolution, yet it remains unclear whether phenotypic plasticity generally facilitates or hinders this process. Here we studied evolved and plastic responses to water-stress in lab-born descendants of wild house mice (Mus musculus domesticus) collected from desert and non-desert environments and measured gene expression and organismal phenotypes under control and water-stressed conditions. After many generations in the lab, desert mice consumed significantly less water than mice from other localities, indicating that this difference has a genetic basis. Under water-stress, desert mice maintained more weight than non-desert mice, and exhibited differences in blood chemistry related to osmoregulatory function. Gene expression in the kidney revealed evolved differences between mice from different environments as well as plastic responses between hydrated and dehydrated mice. Desert mice showed reduced expression plasticity under water-stress compared to non-desert mice. Importantly, non-desert mice under water-stress generally showed shifts toward desert-like expression, consistent with adaptive plasticity. Finally, we identify several co-expression modules linked to phenotypes of interest. These findings provide evidence for local adaptation after a recent invasion and suggest that adaptive plasticity may have facilitated colonization of the desert environment.

The physiological and molecular mechanisms to maintain water and salt homeostasis in response to high salt intake in Mongolian gerbils (Meriones unguiculatus)

Desert rodents are faced with many challenges such as high dietary salt in their natural habitats and they have evolved abilities to conserve water and tolerate salt. However, the physiological and molecular mechanisms involved in water and salt balances in desert rodents are unknown. We hypothesized that desert rodents regulated water and salt balances by altering the expression of AQP2 and α-ENaC in the kidney. Mongolian gerbils (Meriones unguiculatus), a desert species, were acclimated to drinking water with different salt contents: (0, control; 4% NaCl, moderate salt, MS; 8% NaCl, high salt, HS) for 4 weeks. The gerbils drinking salty water had lower body mass, food intake, water intake, metabolic water production and urine volume. The HS gerbils increased the expression of arginine vasopressin (AVP) in the hypothalamus, and also enhanced the expression of AQP2 and cAMP/PKA/CREB signaling pathway in the kidney. In addition, these gerbils reduced serum aldosterone levels and α-ENaC expression in the kidney. Creatinine clearance was lower in the HS group than that in the control group, but serum and urine creatinine levels did not change. These data indicate that desert rodents rely on AVP-dependent upregulation of AQP2 and aldosterone-dependent downregulation of α-ENaC in the kidney to promote water reabsorption and sodium excretion under high salt intake.

Anatomical, histological and biochemical studies of desert rodent Gerbillus tarabuli (Thomas, 1902) kidney

The present work aimed to study the anatomy, histology, cytology and some biochemical parameters (urea, osmolality, haematocrit, serum natrium, serum kalium) of the kidney of Gerbillus tarabuli. The investigated animals (n = 16) were collected from the desert, weighed and transferred alive to the laboratory in separate cages. A blood sample was taken by puncture at the retro-orbital sinus of each animal using a Pasteur-type capillary pipette capillary. They were anaesthetized with urethane injection (25%), after which they were carefully dissected; their organs were taken out and prepared for the histological and cytological studies. Pasteur pipette capillary type the kidney of the Gerbillus tarabuli is subdivided into three regions: Cortex (1193.625±60μm), Outer Medulla (1316.72±73μm), Inner Medulla (2525.08±85 μm). Pasteur pipette capillary type the kidney of the Gerbillus tarabuli is subdivided into three regions: Cortex (1193.625±60μm), Outer Medulla (1316.72±73μm), Inner Medulla (2525.08±85 μm). The concentration of the biochemical parameters of urea (0.41 ± 0.02 g/L), osmolality (300.75 ± 3.33 mOs/kg), haematocrit (34.18 ± 1.3%), serum natrium (141.37 ± 2.31 mmol/L) and serum kalium (7.69 ± 0.39 mmol/L) is in the interval of the norm compared with several studies on desert and semi-desert rodents and also on the Wistar rat. These findings revealed the adaptive morphology and physiological function in the kidney of G. tarabuli to the desert environment.

Anatomical features in the kidney involved in water conservation through urine concentration in dromedaries (Camelus dromedarius)

The aim of this study was to report some of the morphological characteristics of the kidney involved in urine concentration and hence water conservation in the dromedaries. A total of 20 fresh kidneys of 10 apparently healthy camels were used in this study. The architecture of the renal pelvis was revealed by dissection and polyvinyl chloride corrosion casts. Samples were also processed for histology and for enzyme histochemistry. The camel kidney is bean shaped, smooth, multilobar, unipapillary, in which the fusion of renal papillae is complete forming a common renal papilla or crest, which channel urine into a central renal pelvis. It is more or less similar to equine, caprine, ovine and canine kidney. Under certain anatomical requisites the renal pelvis is known to play a role in urine concentration through recycling of urea to increase the medullary osmotic concentration which favors the counter-current mechanism. One of these requisites is an elaborate renal pelvis which is closely associated with the renal medulla. The renal pelvis of the camel has a main crescentic cavity following the long axis and curvature of the kidney. A thick extensive renal crest projects into the cavity of the pelvis. The thick renal crest contains large numbers of long loops of Henle and vasa recta which are important for urine concentration. The renal crest is formed by convergence of the medullary pyramids before it projects into the cavity of the renal pelvis. The crescentic main cavity of the pelvis forms 20-24 three dimensional radiating collateral recesses which contain the medullary pyramids. This close association of the renal pelvis and medulla provide a large surface area for the recycling of urea and hence urine concentration. This large pelvic-medullary interface is lined by simple low cuboidal epithelium which enhances the recycling of urea and water from the pelvic urine into the medulla and directly contributes to urine concentration. The rest of the wall of the renal pelvis and its recesses facing away from the renal crest and medullary pyramids is lined by impermeable transitional epithelium. Another feature is the intense activity of alkaline phosphatase demonstrated in the proximal convoluted tubules which indicates increased membrane transport. It is concluded that the kidney in dromedaries has the anatomical and histochemical requisites for the production of concentrated urine. These requisites enable the kidney to adequately contribute to the ability of the camel to conserve water and withstand the aridity of its habitat.

Diet effect on osmoregulation in the subterranean rodent Ctenomys talarum

Water conservation requires osmoregulatory skills, sometimes limited by the environment and/or physiological and behavioral characteristics acquired along the evolutionary history of the species. Fossoriality had probably emerged as a survival mechanism to face increasing aridity, as suggested for Ctenomys, a genus that radiated to different environments. Ctenomys talarum (tuco-tuco) is an herbivorous subterranean rodent that lives in coastal grasslands inside humid burrows that reduce evaporation. However, their osmoregulatory mechanisms may be challenged by atmospheric variations when foraging aboveground and by the annual variability in dietary water and salt content. Then, it is of great interest to identify how much of this flexibility of C .talarum is attributed to physiological regulation. We analyzed the effect of water and salt content of diet on urinary, plasmatic, fecal and respiratory parameters. Tuco-tucos were not able to maintain their body weight under the offered monodiet, especially under the low hydrated diet, which explains its generalist and opportunistic foraging behavior. C. talarum mainly obtained water through food, whereas water metabolic production was negligible. Evaporative water loss did not vary between diets, but individuals under water restriction showed decreased fecal water loss and urine volume, high urine concentration but stable plasmatic osmolality and ionic concentration values. Under salt stress, urinary parameters remained relatively stable and high plasmatic osmolality was detected. Despite C. talarum produced more diluted urine than rodents from xeric environments, it is able to concentrate it 4 times above than the required at field even under the lowest water availability. This may be a characteristic associated with the evolutionary history of the species, which evolved in an arid context.

Effects of concurrent chloroquine and ethanol administration on the rat kidney morphology

Introduction

The use of antimalarial chloroquine in malaria-endemic regions of Africa is rampant and it is not uncommon to find individuals taken the drug concurrent with alcohol. Effects of anti-malarial drug chloroquine (Chq) and ethanol (Et) combination on kidney volume and function using rat model was investigated.

Methods

32 adult male rats were randomly distributed into four groups of 8 rats each. Group C serve as control and received vehicle only, while Q is Chq treated only, E is Et treated and QE is Et and Chq treated. Chq was administered intraperitoneally at 1mg/100g body weight weekly and 6% Et in drinking water provided ad libitum. Urine volume was collected before the treatment began and after the treatment. After eight weeks, all animals were euthanized; kidneys were harvested and fixed in 10% neutral formalin. The fixed left kidneys were scanned with computed tomography and the scan slices were used to estimate 3-dimensional kidney volume on ImageJ.

Results

Total kidney volume was none significantly increased in Q, E and QE treated compared to control groups (p = 0.5150). Also, microscopic analysis showed increased proximal tubule diameter (p = 0.1426) and epithelial hypertrophy (p = 0.2530) and significant urinary space shrinkage (p = 0.00001). The initial urine volume was not significantly different between the control and treated groups (p = 0.9864) however, following treatment urine volume was significantly reduced in QE rats group (p = 0.0029).

Conclusion

The results suggest chloroquine and ethanol combination as potential cause of kidney injury through structural damage and function derangement.

An association between differential expression and genetic divergence in the Patagonian olive mouse (Abrothrix olivacea)

Recent molecular studies have found striking differences between desert-adapted species and model mammals regarding water conservation. In particular, aquaporin 4, a classical gene involved in water regulation of model species, is absent or not expressed in the kidneys of desert-adapted species. To further understand the molecular response to water availability, we studied the Patagonian olive mouse Abrothrix olivacea, a species with an unusually broad ecological tolerance that exhibits a great urine concentration capability. The species is able to occupy both the arid Patagonian steppe and the Valdivian and Magellanic forests. We sampled 95 olive mouse specimens from four localities (two in the steppe and two in the forests) and analysed both phenotypic variables and transcriptomic data to investigate the response of this species to the contrasting environmental conditions. The relative size of the kidney and the ratio of urine to plasma concentrations were, as expected, negatively correlated with annual rainfall. Expression analyses uncovered nearly 3,000 genes that were differentially expressed between steppe and forest samples and indicated that this species resorts to the "classical" gene pathways for water regulation. Differential expression across biomes also involves genes that involved in immune and detoxification functions. Overall, genes that were differentially expressed showed a slight tendency to be more divergent and to display an excess of intermediate allele frequencies, relative to the remaining loci. Our results indicate that both differential expression in pathways involved in water conservation and geographical allelic variation are important in the occupation of contrasting habitats by the Patagonian olive mouse.

Physiological and biochemical changes associated with acute experimental dehydration in the desert adapted mouse, Peromyscus eremicus

Characterizing traits critical for adaptation to a given environment is an important first step in understanding how phenotypes evolve. How animals adapt to the extreme heat and aridity commonplace to deserts is an exceptionally interesting example of these processes, and has been the focus of study for decades. In contrast to those studies, where experiments are conducted on either wild animals or captive animals held in non-desert conditions, the study described here leverages a unique environmental chamber that replicates desert conditions for captive Peromyscus eremicus (cactus mouse). Here, we establish baseline values for daily water intake and for serum electrolytes, as well as the response of these variables to acute experimental dehydration. In brief, P eremicus daily water intake is very low. Its serum electrolytes are distinct from many previously studied animals, and its response to acute dehydration is profound, though not suggestive of renal impairment, which is atypical of mammals.

Ecological and phylogenetic variability in the spinalis muscle of snakes

Understanding the origin and maintenance of functionally important subordinate traits is a major goal of evolutionary physiologists and ecomorphologists. Within the confines of a limbless body plan, snakes are diverse in terms of body size and ecology, but we know little about the functional traits that underlie this diversity. We used a phylogenetically diverse group of 131 snake species to examine associations between habitat use, sidewinding locomotion and constriction behaviour with the number of body vertebrae spanned by a single segment of the spinalis muscle, with total numbers of body vertebrae used as a covariate in statistical analyses. We compared models with combinations of these predictors to determine which best fit the data among all species and for the advanced snakes only (N = 114). We used both ordinary least-squares models and phylogenetic models in which the residuals were modelled as evolving by the Ornstein-Uhlenbeck process. Snakes with greater numbers of vertebrae tended to have spinalis muscles that spanned more vertebrae. Habitat effects dominated models for analyses of all species and advanced snakes only, with the spinalis length spanning more vertebrae in arboreal species and fewer vertebrae in aquatic and burrowing species. Sidewinding specialists had shorter muscle lengths than nonspecialists. The relationship between prey constriction and spinalis length was less clear. Differences among clades were also strong when considering all species, but not for advanced snakes alone. Overall, these results suggest that muscle morphology may have played a key role in the adaptive radiation of snakes.

Early life experience drives short-term acclimation of metabolic and osmoregulatory traits in the leaf-eared mouse

We studied the putative effect of early life experience on the physiological flexibility of metabolic and osmoregulatory traits in the leaf-eared mouse, Phyllotis darwini, an altricial rodent inhabiting seasonal Mediterranean environments. Adult individuals were collected in central Chile and maintained in breeding pairs. Pups were isolated after weaning and acclimated to different temperatures (cold or warm) and water availability (unrestricted and restricted) until adulthood. Subsequently, individuals were re-acclimated to the opposite treatment. Rodents reared in the warm and subjected to water restriction had lower basal metabolic rate (BMR), total evaporative water loss (TEWL) and body mass (M_b) compared with those developing in the cold treatment; nevertheless, individuals subjected to warm temperatures had greater relative medullary thickness (RMT) and urine concentrating ability (UCA). Cold-reared rodents re-acclimated to warm conditions exhibited physiological flexibility of metabolic traits; however, their osmoregulatory attributes did not vary. Conversely, warm-reared rodents re-acclimated to cold had reduced RMT and UCA, but the metabolic traits of these individuals did not change. These results suggest a trade-off between metabolic performance and renal capabilities that might hinder physiological acclimation. Our results support the hypothesis of ontogenetic dependence of short-term acclimation in osmoregulatory and metabolic traits in P. darwini.

Cranial vault thickness in non-human primates: Allometric and geometric analyses of the vault and its component layers

Extremely thick cranial vaults have been noted as a diagnostic characteristic of Homo erectus since the first fossil of the species was identified, but relatively little work has been done on elucidating its variation within extant non-human primates. Cranial vault thickness (CVT) is not a monolithic trait, and the relationship of its layers to other morphological variables is unknown. Total CVT and the thickness of the cortical and diploë layers individually, as well as the ratio between diploë and total thickness, were calculated from 258 female individuals from 47 species of non-human primate. Measures of CVT were then regressed onto measures of body, brain, vault, facial, and mandibular size as well as vault shape. Total frontal and parietal CVT scales with positive allometry or isometry with measures of size across a combined non-human primate sample, although some variation exists within each infraorder and when diploë thickness alone is compared to measures of size. CVT in this sample correlates weakly with cranial vault shape, but the relationship described here contradicts an earlier hypothesis that long, low vaults should be thicker than higher, globular vaults. This study provides new data on the variation of vault morphology among extant primates that may be used to inform future hypotheses for the cranial vault hypertrophy of H. erectus.

Water deprivation up-regulates urine osmolality and renal aquaporin 2 in Mongolian gerbils (Meriones unguiculatus)

To better understand how desert rodents adapt to water scarcity, we examined urine osmolality, renal distribution and expression of aquaporins (AQPs) in Mongolian gerbils (Meriones unguiculatus) during 7 days of water deprivation (WD). Urine osmolality of the gerbils during WD averaged 7503 mOsm kg(-1). Renal distributions of AQP1, AQP2, and AQP3 were similar to that described in other rodents. After the 7 day WD, renal AQP2 was up-regulated, while resting metabolic rate and total evaporative water loss decreased by 43% and 36%, respectively. Our data demonstrated that Mongolian gerbils showed high urine concentration, renal AQPs expression and body water conservation to cope with limited water availability, which may be critical for their survival during dry seasons in cold deserts.

Differences in physiological traits associated with water balance among rodents, and their relationship to tolerance of habitat fragmentation

Physiological concepts and tools can help us to understand why organisms and populations respond to habitat fragmentation in the way they do, and allow us to determine the mechanisms or individual characteristics underlying this differential sensitivity. Here, we examine food intake, relative medullary thickness and distribution/expression of water channel aquaporin-1 in three species of South American rodents that have been reported to have different levels of tolerance to habitat fragmentation (Akodon montensis, Oligoryzomys nigripes, and Euryoryzomys russatus), using a classic water deprivation experiment to assess their abilities to cope with water shortage. We believe the mechanisms underlying this differential sensitivity are related to the organisms' capacities to maintain water balance, and therefore the species more tolerant to habitat fragmentation (A. montensis and O. nigripes) should have a higher capacity to maintain water balance. We found that A. montensis and O. nigripes were more tolerant to water deprivation than E. russatus, and this difference appears to be unrelated to differences in food ingestion rate. O. nigripes showed the highest values for RMT, followed by A. montensis and E. russatus. However all species showed RMT values that were 2.2% to 14.1% below the lower prediction limit when compared to other rodents through allometric relationships. Water deprivation seems to trigger changes in the distribution of aquaporin-1, mostly for O. nigripes and E. russatus, which may contribute to water balance maintenance. Our data suggest that these intrinsic physiological differences among these species could provide a mechanism for their differential tolerance of habitat fragmentation. J. Exp. Zool. 323A: 731-744, 2015. © 2015 Wiley Periodicals, Inc.

Characterization of the kidney transcriptome of the long-haired mouse Abrothrix hirta (Rodentia, Sigmodontinae) and comparison with that of the olive mouse A. olivacea

To understand how small mammals cope with the challenge of water homeostasis is a matter of interest for ecologists and evolutionary biologists. Here we take a step towards the understanding of the transcriptomic functional response of kidney using as a model the long-haired mouse (Abrothrix hirta) a species that distributes across Patagonian steppes and Austral temperate rainforests in Argentina and Chile. Specifically, we i) characterize the renal transcriptome of A. hirta, and ii) compare it with that-already available-of the co-generic and co-distributed A. olivacea. Renal mRNA transcripts from 16 specimens of A. hirta from natural populations were analyzed. Over 500 million Illumina paired-end reads were assembled de novo under two approaches, an individual assembly for each specimen, and a single in-silico normalized joint assembly including all reads from all specimens. The total number of annotated genes was similar with both strategies: an average of 14,956 in individual assemblies and 14,410 in the joint assembly. Overall, 15,463 distinct genes express in the kidney of A. hirta. Transcriptomes of A. hirta and A. olivacea were similar in terms of gene abundance and composition: 95.6% of the genes of A. hirta were also found in A. olivacea making their functional profiles also similar. However, differences in the transcriptome of these two species were observed in the set of highly expressed genes, in terms of private genes for each species and the functional profiles of highly expressed genes. As part of the novel transcriptome characterization, we provide distinct gene lists with their functional annotation that would constitute the basis for further research on these or any other species of the subfamily Sigmodontinae, which includes about 400 living species distributed from Tierra del Fuego to southern United States.

Cacti supply limited nutrients to a desert rodent community

In the Sonoran Desert, cacti represent a potentially important source of nutrients and water for consumers. Columnar cacti, in particular, produce a large pulse of flowers and succulent fruit during hot summer months. The importance of cactus stems, flowers and fruit to the small mammal community has not been quantified. We exploited natural variation in the carbon isotope (δ(13)C) values of cacti (CAM) versus C3 plants to quantify the relative use of these resources by a diverse desert small mammal community. We also estimated trophic level by measuring nitrogen isotope (δ(15)N) values. We hypothesized that (H1) granivorous heteromyids (kangaroo rats, pocket mice) would exploit the summer pulse of seeds and pulp; (H2) folivorous and omnivorous cactus mice, wood rats, and ground squirrels would exploit cacti stems year-round and seeds when available; and (H3) kangaroo rats and pocket mice would shift from seeds to insects during hot dry months. We found that heteromyids made minimal use of seeds during the period of heavy seed rain. Of the cricetids, only the folivore Neotoma albigula made continuous but highly variable use of cacti resources (annual mean = 32%, range 0-81%), whereas the omnivore Peromyscus eremicus ignored cacti except during the summer, when it exploited seeds and/or fruit pulp (June-July mean = 39%, range 20-64%). We also found little evidence for a shift to greater consumption of insects by heteromyids during the hot dry months. Overall, use of cactus resources by the small mammal community is very limited and highly variable among species.

Natural selection and the genetic basis of osmoregulation in heteromyid rodents as revealed by RNA-seq

One adaptation of ecological and evolutionary interest is the extraordinary ability of desert rodents to retain water during waste production. Much is known regarding the unique kidney physiology of kangaroo rats (Dipodomys spp.) and their ability to retain water during waste production, yet the genetic basis of these physiological adaptations is relatively unknown. Herein, we utilized RNA-seq data to conduct a comparative study to identify osmoregulatory genes expressed in heteromyid rodents. We sequenced kidney tissue from two temperate desert species (Dipodomys spectabilis and Chaetodipus baileyi) from two separate subfamilies of the Heteromyidae and compared these transcriptomes to a tropical mesic species (Heteromys desmarestianus) from a third subfamily. The evolutionary history of these subfamilies provided a robust phylogenetic control that allowed us to separate shared evolutionary history from convergence. Using two methods to detect differential expression (DE), we identified 1890 genes that showed consistent patterns of DE between the arid and mesic species. A three-species reciprocal BLAST analysis revealed 3511 sets of putative orthologues that, upon comparison to known Mus musculus sequences, revealed 323 annotated and full-length genic regions. Selection tests displayed evidence of positive selection (dn/ds > 1) on six genes in the two desert species and remained significant for one of these genes after correction for multiple testing. Thus, our data suggest that both the coding sequence and expression of genes have been shaped by natural selection to provide the genetic architecture for efficient osmoregulation in desert-adapted heteromyid rodents.

Renal intraspecific variation along an aridity gradient detected by new renal indices in a desert herbivorous rodent

Mammals that live in arid and semi-arid environments in South America present physiological mechanisms that enable them to conserve water. Body water is lost through the kidneys, lungs, skin, and intestines. Regarding renal adaptation for water conservation, several indices have been used to estimate the capacity of the kidneys to produce a maximum urine concentration. Most studies were conducted at an inter-specific level, with only few performed at the intraspecific level. In this work, we compare renal function and morphology among five populations of Southern mountain cavy, Microcavia australis, present along an aridity gradient. We hypothesized that individuals from drier zones would present morphological and functional renal modifications that imply a greater capability to conserve body water. These features were studied considering the classical indices (RMT, PMT, PMA, and RMA) and three new indices that consider area measurements; the latter showed to be more adequate to reflect intraspecific differences. Our results suggest that the morphological modifications of kidneys, that is, the greater areas of renal inner medulla, would be related to the aridity gradient where populations of Southern mountain cavy occur.

Phylogenetic analyses: comparing species to infer adaptations and physiological mechanisms

Comparisons among species have been a standard tool in animal physiology to understand how organisms function and adapt to their surrounding environment. During the last two decades, conceptual and methodological advances from different fields, including evolutionary biology and systematics, have revolutionized the way comparative analyses are performed, resulting in the advent of modern phylogenetic statistical methods. This development stems from the realization that conventional analytical methods assume that observations are statistically independent, which is not the case for comparative data because species often resemble each other due to shared ancestry. By taking evolutionary history explicitly into consideration, phylogenetic statistical methods can account for the confounding effects of shared ancestry in interspecific comparisons, improving the reliability of standard approaches such as regressions or correlations in comparative analyses. Importantly, these methods have also enabled researchers to address entirely new evolutionary questions, such as the historical sequence of events that resulted in current patterns of form and function, which can only be studied with a phylogenetic perspective. Here, we provide an overview of phylogenetic approaches and their importance for studying the evolution of physiological processes and mechanisms. We discuss the conceptual framework underlying these methods, and explain when and how phylogenetic information should be employed. We then outline the difficulties and limitations inherent to comparative approaches and discuss potential problems researchers may encounter when designing a comparative study. These issues are illustrated with examples from the literature in which the incorporation of phylogenetic information has been useful, or even crucial, for inferences on how species evolve and adapt to their surrounding environment.

A priori and a posteriori approaches for finding genes of evolutionary interest in non-model species: osmoregulatory genes in the kidney transcriptome of the desert rodent Dipodomys spectabilis (banner-tailed kangaroo rat)

One common goal in evolutionary biology is the identification of genes underlying adaptive traits of evolutionary interest. Recently next-generation sequencing techniques have greatly facilitated such evolutionary studies in species otherwise depauperate of genomic resources. Kangaroo rats (Dipodomys sp.) serve as exemplars of adaptation in that they inhabit extremely arid environments, yet require no drinking water because of ultra-efficient kidney function and osmoregulation. As a basis for identifying water conservation genes in kangaroo rats, we conducted a priori bioinformatics searches in model rodents (Mus musculus and Rattus norvegicus) to identify candidate genes with known or suspected osmoregulatory function. We then obtained 446,758 reads via 454 pyrosequencing to characterize genes expressed in the kidney of banner-tailed kangaroo rats (Dipodomys spectabilis). We also determined candidates a posteriori by identifying genes that were overexpressed in the kidney. The kangaroo rat sequences revealed nine different a priori candidate genes predicted from our Mus and Rattus searches, as well as 32 a posteriori candidate genes that were overexpressed in kidney. Mutations in two of these genes, Slc12a1 and Slc12a3, cause human renal diseases that result in the inability to concentrate urine. These genes are likely key determinants of physiological water conservation in desert rodents.

Gross renal morphology of the numbat (Myrmecobius fasciatus) (Marsupialia:Myrmecobiidae)

There is a strong correlation between the structure of the mammalian kidney and its urinary concentrating ability. We examine here the kidney of an endangered termitivorous marsupial (Myrmecobius fasciatus) and use the measured kidney morphometrics to calculate maximal urinary concentration. The relative medullary area (1.34) of the kidney of M. fasciatus is typical of other dasyuromorph marsupials, as is its predicted maximal urinary concentration of 3617 mOsm kg–1 H2O, despite its historically semiarid/arid distribution. The termitivorous diet of M. fasciatus presumably provides it with sufficient water to limit selection for a high urinary concentrating capacity.

Variation in urine concentrating ability and water balance of the black-tailed tree rat Thallomys nigricauda, along an aridity gradient

Mechanisms behind variation in physiological traits may assist in explaining how certain traits have evolved. The ability of mammals to concentrate urine has been seen as an adaptation to xeric environments. Urine osmolality and relative medullary thickness (RMT) are two indices which indicate urine concentrating powers. In addition, mammals living in xeric regions have lower water turnover rates (WTR) than their mesic counterparts. The RMT, urine concentrating ability (UCA) and WTR of the Black-tailed Tree Rat, Thallomys nigricauda, were investigated at three study sites along an aridity gradient. We investigated the extent to which these traits are influenced by evolutionary adaptation and/or phenotypic flexibility. There was no significant difference in RMT between sites and no difference in osmolalities when site and season were taken into account. In addition, there was no significant effect of site and season on WTR. This suggests that these traits might have a genetic basis, and reflect an evolutionary adaptation. Lack of differences in the renal traits in T. nigricauda across their range may be interpreted as lack of phenotypic flexibility. However, as a consequence of the degree of individual variation in the parameters measured there appears to be phenotypic flexibility with individuals responding to their specific conditions. This has positive implications for the survival of the species in the light of climate change.

Thermoregulatory and Endocrine Responses to Light Pulses in Short‐Day Acclimated Social Voles (Microtus socialis)

In mammals, nocturnal light pulses (NLP) have been demonstrated to affect physiology and behavior. However, the impact of NLP as a stressor has been less broadly examined. The purpose of this study was to examine the effect of NLP (three 15 min 450 lux light pulses) during each scotophase on both thermoregulation and endocrine stress responses under short-day (SD; 8L:16D) acclimation. Voles were acclimated to either SD (SD voles) or SD+NLP (NLP voles). Resistance to cold was estimated by measurements of body temperature (T(b)) during cold exposure (5 degrees C). Daily rhythms of energy expenditure (calculated from oxygen consumption), urine production, and urinary adrenaline and serum cortisol levels were measured. T(b) values of SD voles were generally unaffected by the cold stimulus, whereas in NLP voles, resistance to cold was markedly lowered. While SD- and NLP voles showed similar ultradian characteristics in energy expenditure with a period of 3.5 h, mean energy expenditure levels were lowest for voles exposed to NLP-treatment. In SD voles, but not in NLP voles, urine production rates showed clear time variations and were consistently highest for SD voles, with significant differences during the scotophase. Both mean total urinary adrenaline and serum cortisol levels were significantly elevated in NLP-treated voles compared with the control group. Taken together, the results suggest that NLP negatively affects winter acclimatization of thermoregulatory mechanisms of M. socialis, probably by mimicking summer acclimatization, and consequently the thermoregulatory mechanisms respond inappropriately to ambient conditions. One important finding of this study is that NLP may act as a stressor and correspondingly impose a major threat to the physiological homeostasis of M. socialis, such that over-winter survival might be compromised.

Use of paleontological and molecular data in supertrees for comparative studies: the example of lissamphibian femoral microanatomy

A new method to assemble time-calibrated supertrees is able to incorporate paleontological and molecular dates. This method, along with new branch length transformations, is implemented in the Stratigraphic Tools for Mesquite. It was used here to analyse a dataset on bone microanatomy, body size and habitat of 46 species of lissamphibians through a variety of methods (Felsenstein independent contrasts, variance partition with phylogenetic eigenvector regression, discriminant analyses and simple regressions). Our analyses showed that the new methods can produce adequate standardization for several characters on a tree whose branch lengths can represent evolutionary time. The analyses confirmed previous conclusions about the presence of an ecological signal in bone microanatomical data.

High Rates of Energy Expenditure and Water Flux in Free‐Ranging Point Reyes Mountain BeaversAplodontia rufa phaea

We measured water flux and energy expenditure in free-ranging Point Reyes mountain beavers Aplodontia rufa phaea by using the doubly labeled water method. Previous laboratory investigations have suggested weak urinary concentrating ability, high rates of water flux, and low basal metabolic rates in this species. However, free-ranging measurements from hygric mammals are rare, and it is not known how these features interact in the environment. Rates of water flux (210+/-32 mL d(-1)) and field metabolic rates (1,488+/-486 kJ d(-1)) were 159% and 265%, respectively, of values predicted by allometric equations for similar-sized herbivores. Mountain beavers can likely meet their water needs through metabolic water production and preformed water in food and thus remain in water balance without access to free water. Arginine-vasopressin levels were strongly correlated with rates of water flux and plasma urea : creatinine ratios, suggesting an important role for this hormone in regulating urinary water loss in mountain beavers. High field metabolic rates may result from cool burrow temperatures that are well below lower critical temperatures measured in previous laboratory studies and suggest that thermoregulation costs may strongly influence field energetics and water flux in semifossorial mammals.

Assessment of mercury concentrations in small mammals collected near Las Vegas, Nevada, USA

Mercury concentrations in liver and hair tissue were determined for five species of small mammals captured near Las Vegas, Nevada, USA. These data were then used to evaluate the suitability of using hair as a noninvasive technique for determining body burdens of mercury. A total of 104 small mammals were captured and analyzed; four main species were examined and included: Dipodomys merriami, Chaetodipus penicillatus, Peromyscus eremicus, and Neotoma lepida. Mean mercury concentrations were highest in N. lepida, followed by D. merriami, C. penicillatus, and P. eremicus respectively. Positive associations were found between hair and liver taken from D. merriami (r = 0.647) and C. penicillatus (r = 0.533) indicating that hair may be a suitable indicator of body burdens in these two species.

Relationships between renal morphology and diet in 26 species of new world bats (suborder microchiroptera)

The renal morphology of 24 species of mormoopid and phyllostomid bats feeding on six different diets was examined to test evolutionary changes in several structural traits presumably led by dietary shifts from ancestral insectivorous diets. The kidneys of a fish-eating vespertilionid and an insect-eating emballonurid were also examined but not included in the phylogenetic comparison. The length, width, and breadth of the kidneys were used to calculate relative medullary thickness (RMT). Tissues were processed for stereological analysis, and the volumes of the kidney, nephron components, and vasculature were determined. RMT did not correlate with body mass in either animal-eating or plant-eating phyllostomid and mormoopid bats. The shift from insectivory to frugivory and nectarivory was accompanied by a reduction in RMT, a reduction in the percent of renal medulla, and an increase in the percent of renal cortex. No changes in these traits were observed in bats that shifted to carnivorous, omnivorous or sanguinivorous habits. No changes were observed in renal vasculature, in the percentage of cortical and medullary nephron components or of capillaries surrounding the nephrons in any feeding group. Vespertilionid and emballonurid species had similar values in all traits examined as compared to insectivorous phyllostomids and mormoopids. Our data suggest that diet does not influence a single area of the nephron, but rather the entire nephron such that the relative amounts of renal cortex and medulla are affected.

Allometry, Antilog Transformations, and the Perils of Prediction on the Original Scale

Biologists often use allometric equations that take the form of power functions (e.g., Y = aM(b), where M stands for mass and a and b are empirically fitted constants). Typically, these allometric equations are fitted by taking the antilog of log-log regressions. Predictions from these allometric equations are biased, and the bias my be appreciable. Methods for making predictions that correct for the bias are available, but they have rarely, if ever, been used by ecological and evolutionary physiologists. Just as physiologists would not use an instrument that was not properly calibrated, they should not use allometric equations to make predictions unless they account for the bias of those predictions. We analyzed 20 interspecific and 10 intraspecific data sets. We compared predictions from standard allometric equations with those from several alternative methods. Our analyses suggest that the bias of predictions from interspecific data sets may be substantial. For the intraspecific data sets we analyzed, the bias was likely to be small. Biologists, including ecological and evolutionary physiologists, should exercise care when using allometric equations to make predictions, particularly given that methods to adjust for bias are easily implemented.

The water economy of South American desert rodents: from integrative to molecular physiological ecology

Rodents from arid and semi-arid habitats live under conditions where the spatial and temporal availability of free water is limited, or scarce, thus forcing these rodents to deal with the problem of water conservation. The response of rodents to unproductive desert environments and water deficits has been intensively investigated in many deserts of the world. However, current understanding of the cellular, systemic and organismal physiology of water economy relies heavily on short-term, laboratory-oriented experiments, which usually focus on responses at isolated levels of biological organization. In addition, studies in small South American mammals are scarce. Indeed xeric habitats have existed in South America for a long time and it is intriguing why present day South American desert rodents do not show the wide array of adaptive traits to desert life observed for rodents on other continents. Several authors have pointed out that South American desert rodents lack physiological and energetic specialization for energy and water conservation, hypothesizing that their success is based more on behavioral and ecological strategies. We review phenotypic flexibility and physiological diversity in water flux rate, urine osmolality, and expression of water channels in South American desert-dwelling rodents. As far as we know, this is the first review of integrative studies at cellular, systemic and organismal levels. Our main conclusion is that South American desert rodents possess structural as well as physiological systems for water conservation, which are as remarkable as those found in "classical" rodents inhabiting other desert areas of the world.

Phylogenetic approaches in comparative physiology

Over the past two decades, comparative biological analyses have undergone profound changes with the incorporation of rigorous evolutionary perspectives and phylogenetic information. This change followed in large part from the realization that traditional methods of statistical analysis tacitly assumed independence of all observations, when in fact biological groups such as species are differentially related to each other according to their evolutionary history. New phylogenetically based analytical methods were then rapidly developed, incorporated into ;the comparative method', and applied to many physiological, biochemical, morphological and behavioral investigations. We now review the rationale for including phylogenetic information in comparative studies and briefly discuss three methods for doing this (independent contrasts, generalized least-squares models, and Monte Carlo computer simulations). We discuss when and how to use phylogenetic information in comparative studies and provide several examples in which it has been helpful, or even crucial, to a comparative analysis. We also consider some difficulties with phylogenetically based statistical methods, and of comparative approaches in general, both practical and theoretical. It is our personal opinion that the incorporation of phylogeny information into comparative studies has been highly beneficial, not only because it can improve the reliability of statistical inferences, but also because it continually emphasizes the potential importance of past evolutionary history in determining current form and function.