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We assessed changes in fundamental climate‐niche space for lizard and snake species in western North America under modeled climate scenarios to inform natural resource managers of possible shifts in species distributions. We generated eight distribution models for each of 130 snake and lizard species in western North America under six time‐by‐climate scenarios. We combined the highest‐performing models per species into a single ensemble model for each scenario. Maps were generated from the ensemble models to depict climate‐niche space for each species and scenario. Patterns of species richness based on climate suitability and niche shifts were calculated from the projections at the scale of the entire study area and individual states and provinces, from Canada to Mexico. Squamate species' climate‐niche space for the recent‐time climate scenario and published known ranges were highly correlated (r = 0.81). Overall, reptile climate‐niche space was projected to move northward in the future. Sixty‐eight percent of species were projected to expand their current climate‐niche space rather than to shift, contract, or remain stable. Only 8.5% of species were projected to lose climate‐niche space in the future, and these species primarily occurred in Mexico and the southwestern U.S. We found few species were projected to lose all suitable climate‐niche space at the state or province level, although species were often predicted to occupy novel areas, such as at higher elevations. Most squamate species were projected to increase their climate‐niche space in future climate scenarios. As climate niches move northward, species are predicted to cross administrative borders, resulting in novel conservation issues for local landowners and natural resource agencies. However, information on species dispersal abilities, landscape connectivity, biophysical tolerances, and habitat suitability is needed to contextualize predictions relative to realized future niche expansions. [ABSTRACT FROM AUTHOR]

ABSTRACT We assessed changes in fundamental climate‐niche space for lizard and snake species in western North America under modeled climate scenarios to inform natural resource managers of possible shifts in species distributions. We generated eight distribution models for each of 130 snake and lizard species in western North America under six time‐by‐climate scenarios. We combined the highest‐performing models per species into a single ensemble model for each scenario. Maps were generated from the ensemble models to depict climate‐niche space for each species and scenario. Patterns of species richness based on climate suitability and niche shifts were calculated from the projections at the scale of the entire study area and individual states and provinces, from Canada to Mexico. Squamate species' climate‐niche space for the recent‐time climate scenario and published known ranges were highly correlated (r = 0.81). Overall, reptile climate‐niche space was projected to move northward in the future. Sixty‐eight percent of species were projected to expand their current climate‐niche space rather than to shift, contract, or remain stable. Only 8.5% of species were projected to lose climate‐niche space in the future, and these species primarily occurred in Mexico and the southwestern U.S. We found few species were projected to lose all suitable climate‐niche space at the state or province level, although species were often predicted to occupy novel areas, such as at higher elevations. Most squamate species were projected to increase their climate‐niche space in future climate scenarios. As climate niches move northward, species are predicted to cross administrative borders, resulting in novel conservation issues for local landowners and natural resource agencies. However, information on species dispersal abilities, landscape connectivity, biophysical tolerances, and habitat suitability is needed to contextualize predictions relative to realized future niche expansions.

Abstract Vertebrate brains show extensive variation in relative size. The expensive brain hypothesis argues that one important source of this variation is linked to a species’ ability to generate the energy required to sustain the brain, especially during periods of unavoidable food scarcity. Here we ask whether this hypothesis, tested so far in endothermic vertebrates, also applies to ectotherms, where ambient temperature is an additional major aspect of energy balance. Phylogenetic comparative analyses of reptiles and amphibians support the hypothesis. First, relative brain size increases with higher body temperature in those species active during the day that can gain free energy by basking. Second, relative brain size is smaller among nocturnal species, which generally face less favorable energy budgets, especially when maintaining high body temperature. However, we do not find an effect of seasonal variation in ambient temperature or food on brain size, unlike in endotherms. We conclude that the factors affecting energy balance in ectotherms and endotherms are overlapping but not identical. We therefore discuss the idea that when body temperatures are seasonally very low, cognitive benefits may be thwarted and selection on larger brain size may be rare. Indeed, mammalian hibernators may show similarities to ectotherms.

Diving as a lifestyle has evolved on multiple occasions when air-breathing terrestrial animals invaded the aquatic realm, and diving performance shapes the ecology and behaviour of all air-breathing aquatic taxa, from small insects to great whales. Using the largest dataset yet assembled, we show that maximum dive duration increases predictably with body mass in both ectotherms and endotherms. Compared to endotherms, ectotherms can remain submerged for longer, but the mass scaling relationship for dive duration is much steeper in endotherms than in ectotherms. These differences in diving allometry can be fully explained by inherent differences between the two groups in their metabolic rate and how metabolism scales with body mass and temperature. Therefore, we suggest that similar constraints on oxygen storage and usage have shaped the evolutionary ecology of diving in all air-breathing animals, irrespective of their evolutionary history and metabolic mode. The steeper scaling relationship between body mass and dive duration in endotherms not only helps explain why the largest extant vertebrate divers are endothermic rather than ectothermic, but also fits well with the emerging consensus that large extinct tetrapod divers (e.g. plesiosaurs, ichthyosaurs and mosasaurs) were endothermic.

Transposable elements (TEs) are sequences that replicate and move throughout genomes, and they can be silenced through methylation of cytosines at CpG dinucleotides. TE abundance contributes to genome size, but TE silencing variation across genomes of different sizes remains underexplored. Salamanders include most of the largest C‐values – 9 to 120 Gb. We measured CpG methylation levels in salamanders with genomes ranging from 2N = ∼58 Gb to 4N = ∼116 Gb. We compared these levels to results from endo‐ and ectothermic vertebrates with more typical genomes. Salamander methylation levels are approximately 90%, higher than all endotherms. However, salamander methylation does not differ from other ectotherms, despite an approximately 100‐fold difference in nuclear DNA content. Because methylation affects the nucleotide compositional landscape through 5‐methylcytosine deamination to thymine, we quantified salamander CpG dinucleotide levels and compared them to other vertebrates. Salamanders and other ectotherms have comparable CpG levels, and ectotherm levels are higher than endotherms. These data show no shift in global methylation at the base of salamanders, despite a dramatic increase in TE load and genome size. This result is reconcilable with previous studies that considered endothermy and ectothermy, which may be more important drivers of methylation in vertebrates than genome size. [ABSTRACT FROM AUTHOR]

Abstract Amniote vertebrates share a suite of extra-embryonic membranes that distinguish them from anamniotes. Other than that, however, their reproductive characteristics could not be more different. They differ in basic ectothermic vs endothermic physiology, in that two clades evolved powered flight, and one clade evolved a protective shell. In terms of reproductive strategies, some produce eggs and others give birth to live young, at various degrees of development. Crucially, endotherms provide lengthy parental care, including thermal and food provisioning—whereas ectotherms seldom do. These differences could be expected to manifest themselves in major differences between clades in quantitative reproductive traits. We review the reproductive characteristics, and the distributions of brood sizes, breeding frequencies, offspring sizes and their derivatives (yearly fecundity and biomass production rates) of the four major amniote clades (mammals, birds, turtles and squamates), and several major subclades (birds: Palaeognathae, Galloanserae, Neoaves; mammals: Metatheria and Eutheria). While there are differences between these clades in some of these traits, they generally show similar ranges, distribution shapes and central tendencies across birds, placental mammals and squamates. Marsupials and turtles, however, differ in having smaller offspring, a strategy which subsequently influences other traits.

Models of foraging behaviour typically assume that prey do not adapt to temporal variation in predation risk, such as by avoiding foraging at certain times of the day. When this behavioural plasticity is considered—such as in predator–prey games—the role of abiotic factors is usually ignored.An abiotic factor that exerts strong influence on the physiology and behaviour of many animals is ambient temperature, although it is often ignored from game models as it is implicitly assumed that both predators and prey are homothermic. However, poikilotherms' performance may be reduced in cold conditions due to reduced muscle function, limiting the prey‐capture ability of predators and the predator‐avoidance and foraging abilities of prey.Here, we use a game‐theoretic predator–prey model in which diel temperature changes influence foraging gains and costs to predict the evolutionarily stable diel activity of predators.Our model predicts the range of patterns observed in nature, including nocturnal, diurnal, crepuscular and a previously unexplained post‐sunset crepuscular pattern observed in some sharks. In general, smaller predators are predicted to be more diurnal than larger ones. The safety of prey when not foraging is critical, explaining why predators in coral reef systems (with safe refuges) may often have different foraging patterns to pelagic predators.We make a range of testable predictions that will enable the further evaluation of this theoretical framework for understanding diel foraging patterns in poikilotherms. [ABSTRACT FROM AUTHOR]

Insect jumping and other explosive animal movements often make use of elastic‐recoil mechanisms to enhance performance. These mechanisms circumvent the intrinsic rate limitations on muscle shortening, allowing for greater power production as well as thermal robustness of the associated movements. Here we examine the performance and temperature effects on jumping in the house cricket, Acheta domesticus, using high‐speed imaging and inverse dynamics analysis. We find that adult house crickets jumped with greater performance than would be possible using direct muscle shortening, generating a peak power of over 2000 W/kg of muscle mass and maintaining high performance across the entire tested range of body temperatures (12–32°C). Performance declined at the lowest temperature (12°C), yet jump power still exceeds available muscle power. These results reveal that Acheta domesticus makes use of an elastic‐recoil mechanism that enhances both the performance and thermal robustness of jumping. Research Highlights: House crickets' jumping performance exceeds available muscle power output across a range of body temperatures.House crickets make use of an elastic‐recoil mechanism that enhances both the performance and thermal robustness of jumping. [ABSTRACT FROM AUTHOR]

Abstract Within a population of apex predators, differences among individuals can influence both their ecological impact and their vulnerability to threatening processes. Our field studies on a large monitor lizard (Varanus panoptes) in the Australian wet–dry tropics show that diets shift seasonally and depend upon a lizard’s sex and body size. Individuals that had previously been recorded to consume frogs were most at risk following biological invasion by toxic cane toads (Rhinella marina), as were individuals with broad diets during the wet season. As a result, mortality of those individual predators likely reduced predation pressure on other taxa (invertebrates and reptiles) that were frequently consumed by the same lizards that ate frogs, but with less benefit for taxa (e.g., rodents) that were consumed by non‐anuran‐eating individuals within the predator population. In particular, individuals killed by cane toads often had consumed agamid lizards, a group whose abundance has been reported to increase due to toad‐induced mortality of V. panoptes. To understand the vulnerability of apex predators, or the ecological consequences of their extirpation, we need to incorporate the role of variation among individuals in critical ecological traits.

Within a population of apex predators, differences among individuals can influence both their ecological impact and their vulnerability to threatening processes. Our field studies on a large monitor lizard (Varanus panoptes) in the Australian wet–dry tropics show that diets shift seasonally and depend upon a lizard's sex and body size. Individuals that had previously been recorded to consume frogs were most at risk following biological invasion by toxic cane toads (Rhinella marina), as were individuals with broad diets during the wet season. As a result, mortality of those individual predators likely reduced predation pressure on other taxa (invertebrates and reptiles) that were frequently consumed by the same lizards that ate frogs, but with less benefit for taxa (e.g., rodents) that were consumed by non‐anuran‐eating individuals within the predator population. In particular, individuals killed by cane toads often had consumed agamid lizards, a group whose abundance has been reported to increase due to toad‐induced mortality of V. panoptes. To understand the vulnerability of apex predators, or the ecological consequences of their extirpation, we need to incorporate the role of variation among individuals in critical ecological traits. [ABSTRACT FROM AUTHOR]

Most Notosuchia were active terrestrial predators. A few were semi-aquatic, or were insectivorous, omnivorous or herbivorous. A question relative to their thermometabolism remains to be answered: were Notosuchia warm-blooded? Here we use quantitative bone palaeohistology to answer this question. Two variables were used as proxies to infer thermometabolism: resting metabolic rate and red blood cell dimensions. Resting metabolic rate was inferred using relative primary osteon area and osteocyte size, shape and density. Blood cell dimensions were inferred using harmonic mean canal diameter and minimum canal diameter. All inferences were performed using phylogenetic eigenvector maps. Both sets of analyses suggest that the seven species of Notosuchia sampled in this study were ectotherms. Given that extant Neosuchia (their sister group) are also ectotherms, and that archosaurs were primitively endotherms, parsimony suggests that endothermy may have been lost at the node Metasuchia (Notosuchia–Neosuchia) by the Early Jurassic. Semi-aquatic taxa such as Pepesuchus may have had thermoregulatory strategies similar to those of recent crocodylians, whereas the terrestrial taxa (Araripesuchus , Armadillosuchus , Iberosuchus , Mariliasuchus , Stratiotosuchus) may have been thermoregulators similar to active predatory varanids. Thermal inertia may have contributed to maintaining a stable temperature in large notosuchians such as Baurusuchus. [ABSTRACT FROM AUTHOR]

What is the most humane way to kill amphibians and small reptiles that are used in research? Historically, such animals were often killed by cooling followed by freezing, but this method was outlawed by ethics committees because of concerns that ice-crystals may form in peripheral tissues while the animal is still conscious, putatively causing intense pain. This argument relies on assumptions about the capacity of such animals to feel pain, the thermal thresholds for tissue freezing, the temperature-dependence of nerve-impulse transmission and brain activity, and the magnitude of thermal differentials within the bodies of rapidly-cooling animals. A review of published studies casts doubt on those assumptions, and our laboratory experiments on cane toads (Rhinella marina) show that brain activity declines smoothly during freezing, with no indication of pain perception. Thus, cooling followed by freezing can offer a humane method of killing cane toads, and may be widely applicable to other ectotherms (especially, small species that are rarely active at low body temperatures). More generally, many animal-ethics regulations have little empirical basis, and research on this topic is urgently required in order to reduce animal suffering.

Rising temperatures accompanying global climate change are expected to affect mountain lizards. Therefore, basic information on how these ectotherms deal with their thermal environment is important for further management. We conducted a field study to evaluate how body temperature of the small-sized mountain lizard Eurolophosaurus nanuzae relates to the thermal environment. After capture, the body temperature of the lizards was measured immediately, quickly followed by the substrate and air temperatures, wind intensity, and solar radiation at the capture locations. Linear relationships showed that the body temperature of individuals was positively related to rocky substrate temperatures but negatively related to wind speed. However, air temperature and solar radiation were unrelated to body temperature. Although the substrate is an important heat source for E. nanuzae , in an open environment it can reach temperatures up to 10 °C above the maximum body temperatures of lizards, and can thus be a low-quality thermal substrate. However, individuals seemed to use wind as a cooling source to counterbalance the risks of overheating from high substrate temperatures. As the montane environment that E. nanuzae inhabits seems to have hotter temperatures than those preferred by the species, lizards should benefit from the cooling winds to keep their body temperature at appropriate levels. Different to previous studies that evaluated wind effects on body temperatures of lizards, our results showed that winds seemed to promote thermoregulation for E. nanuzae . [ABSTRACT FROM AUTHOR]

In fish, regional endothermy (i.e., the capacity to significantly elevate tissue temperatures above ambient via vascular heat exchangers) in the red swimming muscles (RM) has evolved only in a few marine groups (e.g., sharks: Lamnidae, Alopiidae, and teleosts Scombridae). Within these taxa, several species have also been shown to share similar physiological adaptations to enhance oxygen delivery to the working tissues. Although the hemoglobin (Hb) of most fish has a decreased affinity for oxygen with an increase in temperature, some regionally endothermic teleosts (e.g., tunas) have evolved Hbs that have a very low or even an increased affinity for oxygen with an increase in temperature. For sharks, however, blood oxygen affinities remain largely unknown. We examined the effects of temperature on the blood oxygen affinity in two pelagic species (the regionally endothermic shortfin mako shark and the ectothermic blue shark) at 15, 20, and 25 °C, and two coastal ectothermic species (the leopard shark and brown smooth-hound shark) at 10, 15, and 20 °C. Relative to the effects of temperature on the blood oxygen affinity of ectothermic sharks (e.g., blue shark), shortfin mako shark blood was less affected by an increase in temperature, a scenario similar to that documented in some of the tunas. In the shortfin mako shark, this may act to prevent premature oxygen dissociation from Hb as the blood is warmed during its passage through vascular heat exchangers. Even though the shortfin mako shark and blue shark occupy a similar niche, the effects of temperature on blood oxygen affinity in the latter more closely resembled that of the blood in the two coastal shark species examined in this study. The only exception was a small, reverse temperature effect (an increase in blood oxygen affinity with temperature) observed during the warming of the leopard shark blood under simulated arterial conditions, a finding that is likely related to the estuarine ecology of this species. Taken together, we found species-specific differences in how temperature affects blood oxygen affinity in sharks, with some similarities between the regionally endothermic sharks and several regionally endothermic teleost fishes. [ABSTRACT FROM AUTHOR]

Crocodilians grow slowly and have low metabolic rates similar to other living reptiles, but palaeohistology indicates that they evolved from an ancestor with higher growth rates. 1,2,3,4,5 It remains unclear when slow growth appeared in the clade due to the sparse data on key divergences among early Mesozoic members of their stem lineage. We present new osteohistological data from a broad sample of early crocodylomorphs, evaluated in a phylogenetic context alongside other pseudosuchians. We find that the transition to slow-growing bone types during mid-late ontogeny occurred around the origin of Crocodylomorpha during the Late Triassic. Earlier-diverging pseudosuchians had high maximum growth rates, as indicated by the presence of woven bone during middle and (sometimes) late ontogeny. 6,7,8,9 Large-bodied pseudosuchians in particular exhibit some of the fastest-growing bone types, giving evidence for prolonged, rapid growth. By contrast, early-branching crocodylomorphs, including a new large-bodied taxon, had slow maximum rates of bone deposition, as evidenced by the presence of predominantly parallel-fibered or lamellar bone tissue during middle-late ontogeny. Late Triassic crocodylomorphs show skeletal anatomy consistent with "active" terrestrial habits, 10,11,12 and their slow growth rates reject hypotheses linking this transition with sedentary, semiaquatic lifestyles or sprawling posture. Faster-growing pseudosuchian lineages go extinct in the Triassic, whereas slow-growing crocodylomorphs do not. This contrasts with the Jurassic radiation of fast-growing dinosaurs on the bird-stem lineage, 13 suggesting that the End-Triassic mass extinction initiated a divergent distribution of growth strategies that persist in present-day archosaurs. • A new giant basal crocodylomorph ancestor shows slow growth rates • Small, active, terrestrial early crocodylomorphs grew like living crocodilians • Only slow-growing crocodylomorphs survived the End-Triassic mass extinction • This differs from the fast-growing dinosaurs that lived alongside them Living crocodilians grow slowly, contrasting with their ancestors, who grew rapidly. Botha et al. constrain the origin of this transition to the Late Triassic. Thus, crocodylomorphs already differed from their concurrent relatives (including dinosaurs), prior to the End-Triassic extinction, with only slow-growing crocodylomorphs surviving the event. [ABSTRACT FROM AUTHOR]

Recently we demonstrated that the capacity of isolated muscle mitochondria to produce reactive oxygen species, measured as H2O2 efflux, is temperature-sensitive in isolated muscle mitochondria of ectothermic fish and the rat, a representative endothermic mammal. However, at physiological temperatures (15° and 37°C for the fish and rat, respectively), the fraction of total mitochondrial electron flux that generated H2O2, the fractional electron leak (FEL), was far lower in the rat than in fish. Those results suggested that the elevated body temperatures associated with endothermy may lead to a compensatory decrease in mitochondrial ROS production relative to respiratory capacity. To test this hypothesis we compare slow twitch (red) muscle mitochondria from the endothermic Pacific bluefin tuna (Thunnus orientalis) with mitochondria from three ectothermic fishes [rainbow trout (Oncorhynchus mykiss), common carp (Cyprinus carpio), and the lake sturgeon (Acipenser fulvescens)] and the rat. At a common assay temperature (25°C) rates of mitochondrial respiration and H2O2 efflux were similar in tuna and the other fishes. The thermal sensitivity of fish mitochondria was similar irrespective of ectothermy or endothermy. Comparing tuna to the rat at a common temperature, respiration rates were similar, or lower depending on mitochondrial substrates. FEL was not different across fish species at a common assay temperature (25°C) but was markedly higher in fishes than in rat. Overall, endothermy and warming of Pacific Bluefin tuna red muscle may increase the potential for ROS production by muscle mitochondria but the evolution of endothermy in this species is not necessarily associated with a compensatory reduction of ROS production relative to the respiratory capacity of mitochondria.

Regulation of thoracic muscle temperature has been investigated in a number of dragonfly species but is poorly known in the large and diverse family, Gomphidae. Moreover, temperatures of other body regions have been recorded in very few ectothermic insects. In addition, correlations among multiple components of thermoregulatory behavior have rarely been examined quantitatively. Here I examine thermoregulation in Arigomphus villosipes, a medium-sized gomphid common at the shores of lakes and ponds in the northeastern USA. Measurements of the temperatures of the thorax (Tth), head (Th) and abdomen (Tab), using standard "grab and jab"techniques, indicate that both Tth and Th are relatively independent of air temperature (Ta). It is not clear whether Tth and Th are independently regulated, although some data suggest that they might be. Arigomphus villosipes can warm its thoracic musculature endothermically to maintain high Tth during cool Ta in conditions of low solar radiation intensity. However, regulation is principally behavioral, involving variation in body and wing postures and perhaps in perch substrate choice. Certain of these behaviors are closely associated to form suites of behavior that together are adapted to enhance or inhibit heating, while others are constrained by trade-offs with other functional demands. The former have a significant demonstrable effect on Tth. These combinations of behaviors results in a well-developed capacity for thermoregulation, allowing the insects to expand their activity periods and choice of perches, and probably improving male performance during competitive chases of females prior to mating. [ABSTRACT FROM AUTHOR]

Endothermy and its evolution are still an unresolved issue. Here, we present a model which transforms an ectothermic amniote (ancestor) into a derived amniote (descendant) showing many characteristics seen in extant endothermic birds and mammals. Consistent with the fossil record within the ancestral lineages of birds and mammals, the model assumes that mutations in genes which get active during ontogeny and affect body growth resulted in a reduced asymptotic body size and an early growth stop of the descendant. We show that such a postulated early growth stop in the descendant simultaneously increases the growth rate and metabolic rate, and also changes six life history traits (offspring mass, annual clutch/litter mass, number of offspring per year, age and mass at which sexual maturity is reached, age at which the individual is fully grown) of the descendant compared to a similar-sized ancestor. All these changes coincide with known differences between recent ectothermic and endothermic amniotes. We also elaborate many other differences and similarities in biological characteristics supporting the early growth stop. An early stop in growth during ontogeny thus could have played a key role in the evolution of endothermy within the reptilia and therapsids. It generated variability in characteristics of ancestral ectotherms, which was subject to natural selection in the past and resulted in many adaptations linked to endothermy in today's birds and mammals. [ABSTRACT FROM AUTHOR]

Bergmann's rule originally described a positive relationship between body size and latitude in warm-blooded animals. Larger animals, with a smaller surface/volume ratio, are better enabled to conserve heat in cooler climates (thermoregulatory hypothesis). Studies on endothermic vertebrates have provided support for Bergmann's rule, whereas studies on ectotherms have yielded conflicting results. If the thermoregulatory hypothesis is correct, negative relationships between body size and temperature should occur in temporal in addition to geographical gradients. To explore this possibility, we analysed seasonal activity patterns in a bee fauna comprising 245 species. In agreement with our hypothesis of a different relationship for large (endothermic) and small (ectothermic) species, we found that species larger than 27.81 mg (dry weight) followed Bergmann's rule, whereas species below this threshold did not. Our results represent a temporal extension of Bergmann's rule and indicate that body size and thermal physiology play an important role in structuring community phenology. [ABSTRACT FROM AUTHOR]

It is widely believed that enzymatic activities in ectothermic organisms adapt to environmental temperatures. However, to date, no study has thoroughly compared multiple thermodynamic enzymatic characteristics across species living in dramatically different environments. To start to address this gap, we compared the characteristics of lactate dehydrogenase (LDH) purified from the muscles from slime flounder Microstomus achne white muscle and bovine skeletal muscle (bM4) and heart. The Km and Vmax for pyruvate reduction were about three times higher for M. achne LDH than bM4. Surprisingly, maximum LDH activity was observed at ∼30 °C and ∼50 °C for M. achne and bovine LDHs, respectively, suggesting that the maximum enzymatic activity of LDH is set at a temperature ∼20 °C higher than environmental or body temperature across species. Although Km and Vmax values of these LDHs increased with temperature, the Vmax/Km ratio for M. achne LDH and bM4 was independent. Differential scanning calorimetry and enthalpy change measurements confirmed that M. achne and bovine muscle-specific LDHs shared similar properties. Based on the present findings and previous reports, we hypothesize that the function and thermodynamic properties of muscle LDH are highly conserved between a teleost adapted to cold, M. achne, and bovine. [ABSTRACT FROM AUTHOR]

Information on the foraging behaviour of sea snakes has the potential to clarify adaptive pathways involved in the evolutionary invasion of marine habitats by terrestrial vertebrates. However, logistical obstacles have precluded studies in this field. To obtain preliminary data of diving behaviour, we surgically implanted temperature-depth loggers into two sympatric, amphibious, benthic foraging sea krait species from New Caledonia. Based on logger recovery from three snakes (1 L aticauda laticaudata and 2 L . saintgironsi), we obtained data on a total of 1850 dives carried out over eight foraging trips and 39.6 days at sea. Almost 99% of dives were <30 m deep. Average dive depth was 10.7 ± 7.0 m, but snakes dived as deep as 82.6 m. Maximum dive duration was ≥123.7 min. At sea, snakes dived continuously, with over 90% of surface recovery periods lasting less than 3 min in L. saintgironsi ( n = 1). Periods at the surface (between successive dives) were longer at night than by day, plausibly reflecting more intense hunting activity by the snake. Locomotor speed, as measured by the rate of vertical descent or ascent during diving, was low (0.15 m s−1). In combination with other data on these species, we estimate that metabolic expenditure was about 10 times greater while the snakes were at sea than on land; and their overall field metabolic rate (70-145 kJ kg−1 day−1) was an order of magnitude less than has been reported for diving endotherms. Despite low sample sizes, our study shows that implanted data loggers can provide novel insights into sea snake biology. Our data emphasize the behavioural and ecological consequences of ectothermy for secondary marine vertebrates. In particular, they illustrate how ectothermy allows species to thrive on rates of energy intake vastly lower than are required for their endothermic competitors. [ABSTRACT FROM AUTHOR]

Tortoises that live in regions where food plants grow in winter may have to cope with relatively low environmental temperatures to obtain resources. The speckled tortoise, Homopus signatus, inhabits an arid winter rainfall range where it is active in winter and spring at environmental temperatures well below its preferred body temperature. Although H. signatus is a threatened species, we have no information how it deals with low environmental temperatures. Therefore, we made continuous recordings of behaviour in nine female H. signatus on 29 days in the early spring. The group of females as a whole showed activity (i.e., behaviours other than hiding) throughout the day in a unimodal pattern. However, individual tortoises were active only for approximately 4.5 h per day and spent as much as 73% of their active time basking, mostly under the protective cover of shrubs. In addition, a negative relationship between the percentage of active time spent in sun and environmental temperature indicated that H. signatus used active behaviours other than basking to absorb heat, particularly on cold days. Tortoises completed all active behaviours other than basking in 1.2 h per day, including a mere 24 min of feeding, probably facilitated by the abundant availability of food plants in the early spring. We predict that a reduced availability of food plants for H. signatus might lead to increased active time and possibly increased predation pressure, or to a decreased proportion of active time spent basking and reduced body temperatures. [ABSTRACT FROM AUTHOR]

Satellite cells (SCs), stem cells in skeletal muscle, are mitotically quiescent in adult mammals until activated for growth or regeneration. In mouse muscle, SCs are activated by nitric oxide (NO), hepatocyte growth factor (HGF) and the mechanically induced NO-HGF signaling cascade. Here, the SC population on fibers from the adult, ectothermic zebrafish and SC responsiveness to activating stimuli were assessed using the model system of isolated fibers cultured at 27 and 21°C. SCs were identified by immunostaining for the HGF receptor, c-met, and activation was determined using bromodeoxyuridine uptake in culture or in vivo. In dose-response studies, SC activation was increased by treatment with the NO-donor drug isosorbide dinitrate (1 mmol l-1) or HGF (10 ng ml-1) to maximum activation at lower concentrations of both than in previous studies of mouse fibers. HGF-induced activation was blocked by anti-c-met antibody, and reduced by culture at 21°C. The effect of cyclical stretch (3 h at 4 cycles per minute) increased activation and was blocked by nitric oxide synthase inhibition and reduced by culture at 21°C. The number of c-met+ SCs per fiber increased rapidly (by 3 h) after stretching. The character of signaling in SC activation on zebrafish fibers, in particular temperature-dependent responses to HGF and stretch, gives new insights into the influence of ectothermy on regulation of muscle growth in teleosts and suggests the use of the single-fiber model system to explore the basis of fiber hyperplasia and the conservation of regulatory pathways between species. [ABSTRACT FROM AUTHOR]

Satellite cells (SC), stem cells in skeletal muscle, are mitotically quiescent in adult mammals until activated for growth or regeneration. In mouse muscle, SC are activated by nitric oxide (NO), hepatocyte growth factor (HGF) and the mechanically induced NO-HGF signaling cascade. Here, the SC population on fibers from the adult, ectothermic zebrafish and SC responsiveness to activating stimuli were assessed using the model system of isolated fibers cultured at 27°C and 21°C. SC were identified by immunostaining for the HGF receptor, c-met, and activation was determined using bromodeoxyuridine uptake in culture or in vivo. In dose-response studies, SC activation was increased by treatment with the NO-donor drug isosorbide dinitrate (1mM) or HGF (10 ng/mL) to maximum activation at lower and higher concentrations, respectively, than in previous studies of mouse fibers. HGF-induced activation was blocked by anti-c-met antibody, and reduced by culture at 21°C. The effect of cyclical stretch (3 hr at 4 cycles per min) increased activation and was blocked by NOS inhibition and reduced by culture at 21°C. The number of c-met+ SC/fiber increased rapidly (by 3 hr) after stretching. The character of signaling in SC activation on zebrafish fibers, in particular temperature-dependent responses to HGF and stretch gives new insights into the influence of ectothermy on regulation of muscle growth in teleosts and suggests use of the single-fiber model system to explore the basis of fiber hyperplasia and the conservation of regulatory pathways between species. [ABSTRACT FROM AUTHOR]

Population dynamics of terrestrial vertebrates are affected by climatic fluctuations, notably in ectotherms. An understanding of the interaction between physiology and demographic processes is necessary to predict the impacts of climate change. Reptiles are particularly sensitive to temperature, but only a few studies have explored the relationship between thermoregulatory strategy and demography in these animals. Using 12 years of mark-recapture data on two sympatric colubrid snakes ( Hierophis viridiflavus and Zamenis longissimus), we tested whether demographic parameters are influenced by contrasted thermoregulatory strategies. The thermophilic and conspicuous species ( H. viridiflavus) grew faster than the thermoconforming and secretive species ( Z. longissimus), and this difference was most pronounced in open habitats, suggesting that the metabolic benefits associated with high thermal preferences depend on environmental factors at small spatial scales. Survival varied annually in both species, but was not lower in H. viridiflavus despite a higher degree of exposure. In Z. longissimus, survival was negatively affected by low temperatures during the active season, possibly underlying an exposure trade-off. [ABSTRACT FROM AUTHOR]

The lack of shelter can perturb behaviors, increase stress level and thus alter physiological performance (e.g. digestive, immune or reproductive functions). Although intuitive, such potential impacts of lack of shelter remain poorly documented. We manipulated shelter availability and environmental and physiological variables (i.e. access to a heat source, predator attack, feeding status) in a viviparous snake, and assessed sun-basking behavior, digestive performance (i.e. digestive transit time, crude estimate of assimilation, regurgitation rate) and plasma corticosterone levels (a proxy of stress level). Shelter deprivation provoked a strong increase in sun-basking behavior and thus elevated body temperature, even in unfed individuals for which energy savings would have been otherwise beneficial. The lack of heat was detrimental to digestive performance; simulated predator attacks worsened the situation and entailed a further deterioration of digestion. The combination of the lack of shelter with cool ambient temperatures markedly elevated basal corticosterone level and was associated with low digestive performance. This hormonal effect was absent when only one negative factor was involved, suggesting a threshold response. Overall, our results revealed important non-linear cascading impacts of shelter availability on stress-hormone levels, behaviors and physiological performance. These results infer that shelter availability is important for laboratory studies, captive husbandry and possibly conservation plans. [ABSTRACT FROM AUTHOR]

Abstract: Herbivorous tortoises in arid, winter-rainfall regions need to forage in seasons that provide relatively little heat for their ectothermic metabolism. To help understand how tortoises exploit resources in winter-rainfall areas, I recorded ambient, soil, and body temperatures for Homopus signatus in four spring seasons, and in one summer, autumn, and winter. The spring thermal environment enabled H. signatus to maintain body temperatures that were high compared to other small tortoise species. Mature females had higher spring body temperatures than males and immature individuals, probably because mature females were developing eggs. In summer, autumn, and winter, body temperatures differed between males and females, relating to sexually different activities and retreat uses. The relatively high body temperatures of H. signatus in winter and spring, along with a non-isometric relationship between body temperature and soil temperature, suggest that tortoises thermoregulated and may need considerable time to gain heat. Additional studies should compare body temperatures of H. signatus to operative temperatures, and determine the vulnerability of the taxon to human interferences that affect behavioural time budgets and body temperatures. [Copyright &y& Elsevier]

The size of the mainland Nova Scotia moose (Alces alces) population has declined pre-cipitously over the last several decades and their current distribution is discontinuous. In recognition of the state of its moose population, Nova Scotia declared moose as 'endangered' under Nova Scotia's Endangered Species Act in 2003. A variety of factors have been attributed to the decline, and the goal of this project was to determine whether thennoregulatory stress may be impacting the viability of the moose population. Location and temperature information were collected from GPS-collared moose to test predictions related to whether moose behaviour changes in response to high temperatures. Overall, our results suggest that moose exhibit behaviours (i.e., ectothermy) that are consistent with thermoregu-latory stress, but the actual impacts of this, if any, on population productivity requires further study. The greatest response occurred in the summer during both day and night, when moose moved to areas of lower ambient temperature. Further, overall movements were significantly reduced during periods of high temperatures. [ABSTRACT FROM AUTHOR]

The article provides information on a study which examined the breeding biology of free ranging Python molurus molurus during May-August 2008 in Keoladeo National Park (KNP) in Bharatpur, India. Python burrows in KNP, identified through body marks, shed skins, or direct sightings of snakes, were monitored at fortnightly intervals. Two nesting sites, 6.25 kilometers apart from each other, were identified and the eggs were not visible until July 14, 2008. In both nests, hatching success of P. molurus was 95 percent, while throughout the incubation period, Python molurus maintained their body temperature within a narrow range of 31.3-33.9 degrees Celsius.

Various conceptual or qualitative models have been proposed to explain the evolution of homeothermic endothermy from heterothermic ectothermy. Assessment of the feasibility of these models may benefit from quantitative analyses of hypotheses deriving from them. In this study, a quantitative approach was applied to a recent conceptual model which proposed a stepwise progression from ectothermy to endothermy in a medium sized vertebrate "evolving" in a warm, mesic thermal environment. By assuming that selection acted to maximise time available for activit>c this study showed that endogenous heat, whether from activity or shivering thermogenesis, increased time within nominal preferred body temperatures only if low values of thermal conductance associated with insulation were already in place. Further, this study demonstrated that benefits were enhanced if the insulation was by-passable and associated with a wide range of thermal conductance. Because aerobic scope was incorporated as a constraint to thermogenic capacit~c increases in standard metabolic rate were relatively ineffective until they were substantial and, at one stage, plesiomorphic daily torpor emerged, at least in the circumstances modelled, Also emerging from the modelling were the thermal neutral zone and basal metabolic rate characteristic of homeothermic endotherms. Additionally, benefits from rudimentary turbinal scrolls were quantified for this modelled, hypothetical animal in this particular environment. This initial exploratory study demonstrated how quantifying aspects of proposed models for the evolution of endothermy can provide insight into their feasibility. In so doing, this quantitative modelling highlighted avenues for further enquiry and demonstrated one tool for addressing debate about the evolution of endothermy. [ABSTRACT FROM AUTHOR]

Seasonal movements between foraging, breeding, and overwintering sites occur in a wide variety of reptile species. Terrestrial snakes, lizards, and turtles migrate short distances (<20 km) between seasonal habitats, whereas fully aquatic marine turtles migrate hundreds to thousands of kilometers between foraging and breeding areas. The purpose of this article is to summarize aspects of migratory physiology and behavior in reptiles, particularly with regards to energetics and sensory mechanisms for navigation and orientation. We discuss the influence of aerobic scope, endurance, and cost of transport on migratory capacity, the effects of temperature and circulating hormones on activity and behavior, and mechanisms of detecting and transducing environmental cues to successfully navigate and orient toward a goal during migration. Topics worthy of further research are highlighted in the text, and we conclude with a discussion of how information on migration patterns of reptiles may be used to manage and conserve threatened populations. [ABSTRACT FROM AUTHOR]

Nonrecombining Y chromosomes are expected to degenerate through the progressive accumulation of deleterious mutations. In lower vertebrates, however, most species display homomorphic sex chromosomes. To address this, paradox I propose a role for sex reversal, which occasionally occurs in ectotherms due to the general dependence of physiological processes on temperature. Because sex-specific recombination patterns depend on phenotypic, rather than genotypic sex, homomorphic X and Y chromosomes are expected to recombine in sex-reversed females. These rare events should generate bursts of new Y haplotypes, which will be quickly sorted out by natural or sexual selection. By counteracting Muller's ratchet, this regular purge should prevent the evolutionary decay of Y chromosomes. I review empirical data supporting this suggestion, and propose further investigations for testing it. [ABSTRACT FROM AUTHOR]

Some dinosaurs reached masses that were ≈8 times those of the largest, ecologically equivalent terrestrial mammals. The factors most responsible for setting the maximal body size of vertebrates are resource quality and quantity, as modified by the mobility of the consumer, and the vertebrate's rate of energy expenditure. If the food intake of the largest herbivorous mammals defines the maximal rate at which plant resources can be consumed in terrestrial environments and if that limit applied to dinosaurs, then the large size of sauropods occurred because they expended energy in the field at rates extrapolated from those of varanid lizards, which are ≈22% of the rates in mammals and 3.6 times the rates of other lizards of equal size. Of 2 species having the same energy income, the species that uses the most energy for mass-independent maintenance of necessity has a smaller size. The larger mass found in some marine mammals reflects a greater resource abundance in marine environments. The presumptively low energy expenditures of dinosaurs potentially permitted Mesozoic communities to support dinosaur biomasses that were up to 5 times those found in mammalian herbivores in Africa today. The maximal size of predatory theropods was ≈8 tons, which if it reflected the maximal capacity to consume vertebrates in terrestrial environments, corresponds in predatory mammals to a maximal mass less than a ton, which is what is observed. Some coelurosaurs may have evolved endothermy in association with the evolution of feathered insulation and a small mass. [ABSTRACT FROM AUTHOR]

Information on behavioural and physiological processes of newborn reptiles is often difficult to obtain under natural conditions, especially in lizards and snakes. Consequently, we lack information on a wide range of biological phenomena (e.g. thermoregulation, digestion, circadian activity rhythms) in neonates of these taxa. Here, we report novel behaviour in newborn sibling sidewinder rattlesnakes Crotalus cerastes, a desert-inhabiting species of south-western North America. At the entrances of their natal burrows, neonates formed aggregations (‘balls’) during daylight hours, which involved frequent movements of individuals within these balls. Through the study of two radio-telemetered females and their litters ( n=20 offspring), we obtained temperature data from the mothers, centre of the snake balls, and from multiple sites in the immediate environment for 10 days post-birth, the period that is coincident with maternal attendance and the first cycle of ecdysis. The core temperatures of the snake balls showed significant stability over the extreme thermal ranges of the environment. Although other functions are possible, such as those related to water conservation and antipredator defence, we suggest that frequent movements of individuals within the balls involved selection of a thermal optimum to enhance ecdysis. Based on other studies of aggregation in animals, dynamic aggregative behaviour in newborn sibling C. cerastes implicates self-assembly and suggests that individuals benefit from behavioural interactions with their siblings. One plausible scenario for the evolution of this type of dynamic aggregation involves thermal selection among sibling neonates for optimal basking sites within natal refugia in extreme environments such as desert landscapes. Moreover, it is possibly limited to species of vipers (and other snakes) that are viviparous and where maternal care is present up to the time of shedding in neonates. [ABSTRACT FROM AUTHOR]

Body mass positively influences diving capacities in air-breathing vertebrates and has been identified as a key determinant for the evolution of diving. Our review on the relationship between body mass and dive duration (a major parameter of dive performances) encompassed for the first time a wide diversity of air-breathing vertebrates. We included a substantial number of nonavian and nonmammalian diving species belonging to various independent lineages (sea snakes, iguana, turtles and crocodiles). Our analyses suggest that the widely accepted size dependency of dive duration applies with significantly less force in ectotherms compared with endotherms; notably we failed to detect any effect of body mass in ectotherms. We hypothesize that the absence of tight physiological links between body mass and respiratory demands documented in ectotherms blurred our ability to detect the expected correlation. Further exploration of the evolution of diving physiology may well necessitate adopting novel perspectives to encompass both ectothermic and endothermic modes. [ABSTRACT FROM AUTHOR]